-
1.
Predictive metabolites for incident myocardial infarction: a two-step meta-analysis of individual patient data from six cohorts comprising 7897 individuals from the COnsortium of METabolomics Studies.
Nogal, A, Alkis, T, Lee, Y, Kifer, D, Hu, J, Murphy, RA, Huang, Z, Wang-Sattler, R, Kastenmüler, G, Linkohr, B, et al
Cardiovascular research. 2023;119(17):2743-2754
-
-
-
-
Free full text
-
Plain language summary
Heart disease is a major cause of death worldwide. Individuals at risk are usually identified by the presence of diseases such as obesity and diabetes, and lifestyle factors such as smoking. However, there is a new understanding that when the body converts food into energy it creates by-products which might play an important role in the development of heart disease. Better understanding of these may be able to aid the identification of individuals at risk. This analysis of 7897 participants from 6 different cohort studies aimed to determine biomarkers associated with a heart attack. The results showed there were 56 metabolites associated with heart attack, some of which were associated with an increased occurrence and some a decreased occurrence. Most of the identified metabolites were lipids. Metabolites involved in bile acid production and amino acids were also identified. It was concluded that these metabolites may act as an indicator for individuals who are at risk of heart attack, however further research is needed. This study could be used by healthcare professionals to understand that the science behind the use of metabolites to indicate risk for heart attack is developing but still in its infancy.
Expert Review
Conflicts of interest:
None
Take Home Message:
- There are certain lipids and amino acids that are associated with the incidence of MI, but the use of these to identify people at risk of MI is still in its infancy
- Current proven strategies to identify those at risk should take precedence over the measurement, identification and use of metabolites. However, this area of research is of current interest.
Evidence Category:
-
X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
Introduction
Individuals at risk of cardiovascular disease are usually identified by the presence of comorbidities (e.g. obesity and diabetes), and lifestyle factors (e.g. smoking). However, there is a new understanding that certain metabolites may be associated with myocardial infarction (MI) and a better understanding of these may be able to aid the identification of individuals at risk. This meta-analysis aimed to determine metabolites associated with a MI.
Methods
- This meta-analysis of 6 cohort studies from the USA and Europe involved 7897 participants
- The primary outcome was the metabolites associated with incident MI
- The secondary outcome was the metabolites associated with prevalent MI
- A total of 1442 metabolites were measured.
Results
- There were 1373 MI cases from the studies
- The results showed that there were 56 metabolites associated with MI, 42 had a direct association and 14 had an inverse relationship
- Most of the identified metabolites were lipids (n=21) and amino acids (n=17)
- Of the lipids, 3-methyladipate and 1-palmitoyl-2-linoleoyl-glycerol (16:0/18:2) were associated with a higher risk of MI (HR estimates ranged from 1.28; 95% confidence interval (CI) = 1.13–1.44, P < 0.001 to 1.21; 95% CI = 1.08–1.35, P = <0.005 respectively)
- Of the amino acids, 4-hydroxyphenylacetate and cystathionine had the largest increase in risk (HR estimates 1.24; 95% CI = 1.11–1.38, P = <0.01 and 1.2; 95% CI = 1.07–1.35, P = <0.01 respectively)
- When the meta-analysis was stratified by race, it showed that out of the 56 metabolites identified, the majority were associated with white individuals (n=41), whereas only 18 were associated with black individuals. Of these, 3 were specific to individuals with an African ancestry.
Conclusion
- It was concluded that certain metabolites and their associated pathways may help to identify individuals at risk for MI before disease onset and lead to better prevention
Clinical practice applications:
- Research into metabolite association with increased risk of MI is still in its infancy and has little merit until we understand the mechanisms involved and the direction of causation
- It does however give an idea of the tools that may be developed in the future that will aid identification and help to develop prevention strategies
- The metabolites associated with MI may be racially specific and further understanding is needed on this. Hence the data should be interpreted with caution.
Considerations for future research:
- Whilst associations are indicative of relationships, they do not identify causation. Future research should focus on the pathways which may link the metabolites with MI
- Identifying these pathways will also help to develop prevention strategies pertinent to specific nutrients
- A better understanding of how metabolites may be racially distinct is also required.
Abstract
AIMS: Myocardial infarction (MI) is a major cause of death and disability worldwide. Most metabolomics studies investigating metabolites predicting MI are limited by the participant number and/or the demographic diversity. We sought to identify biomarkers of incident MI in the COnsortium of METabolomics Studies. METHODS AND RESULTS We included 7897 individuals aged on average 66 years from six intercontinental cohorts with blood metabolomic profiling (n = 1428 metabolites, of which 168 were present in at least three cohorts with over 80% prevalence) and MI information (1373 cases). We performed a two-stage individual patient data meta-analysis. We first assessed the associations between circulating metabolites and incident MI for each cohort adjusting for traditional risk factors and then performed a fixed effect inverse variance meta-analysis to pull the results together. Finally, we conducted a pathway enrichment analysis to identify potential pathways linked to MI. On meta-analysis, 56 metabolites including 21 lipids and 17 amino acids were associated with incident MI after adjusting for multiple testing (false discovery rate < 0.05), and 10 were novel. The largest increased risk was observed for the carbohydrate mannitol/sorbitol {hazard ratio [HR] [95% confidence interval (CI)] = 1.40 [1.26-1.56], P < 0.001}, whereas the largest decrease in risk was found for glutamine [HR (95% CI) = 0.74 (0.67-0.82), P < 0.001]. Moreover, the identified metabolites were significantly enriched (corrected P < 0.05) in pathways previously linked with cardiovascular diseases, including aminoacyl-tRNA biosynthesis. CONCLUSIONS In the most comprehensive metabolomic study of incident MI to date, 10 novel metabolites were associated with MI. Metabolite profiles might help to identify high-risk individuals before disease onset. Further research is needed to fully understand the mechanisms of action and elaborate pathway findings.
-
2.
Effects of an educational intervention on frailty status, physical function, physical activity, sleep patterns, and nutritional status of older adults with frailty or pre-frailty: the FRAGSALUD study.
Casals, C, Ávila-Cabeza-de-Vaca, L, González-Mariscal, A, Marín-Galindo, A, Costilla, M, Ponce-Gonzalez, JG, Vázquez-Sánchez, MÁ, Corral-Pérez, J
Frontiers in public health. 2023;11:1267666
-
-
-
-
Free full text
Plain language summary
Frailty and pre-frailty are associated with an increased risk of premature mortality. Factors involved in the development of frailty include physical activity, sleep and nutrition. The aim of this 6-month randomised controlled trial was to evaluate the effects of an educational programme on frailty, physical function, physical activity, sleep and nutritional status. 166 community-dwelling individuals aged 65 years or over with frailty or pre-frailty were randomised to either receive a health education programme consisting of 4 group sessions in the first month which included guidelines for physical activity, nutrition and cognitive training as well as the promotion of psychological and social wellbeing and 6 follow-up calls over 6 months or their usual healthcare (control). Compared to the control group, the intervention group had significant reductions in frailty score, exhaustion and fatigue score, increase in gait speed and improvements in various physical function tests. The intervention group also showed significant improvements in mini nutritional assessment compared to the control group although this was not associated with significant changes in anthropometric parameters. There was a significant increase in awakenings in the control group whilst this parameter did not change in the intervention group, whilst there were no changes in other sleep parameters. The authors concluded that the simplicity, affordability and effectiveness of the health education programme may contribute to healthy ageing.
Expert Review
Conflicts of interest:
None
Take Home Message:
To improve frailty and physical functioning, a comprehensive programme may be effective, which includes:
- Nutrition
- Physical exercise
- Cognitive training
- Promotion of social and psychological wellbeing.
Evidence Category:
-
X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
Introduction
- Frailty and pre-frailty increase the risk of premature mortality but are reversible
- The aim of this study was to evaluate the effects of a health education programme on frailty status in frail or pre-frail older persons.
Methods
- Randomised controlled trial
- Participants: 166 community-dwelling individuals aged 65 years or over with frailty or pre-frailty living in Spain were enrolled, 163 completed the study (80 in intervention and 83 in control group)
- Four weekly group sessions which included guidelines for physical activity, nutrition and cognitive training as well as the promotion of psychological and social wellbeing and 6 follow-up calls over 6 months versus usual healthcare (control).
Results
- Baseline demographics: The educational group consisted of more women (p=0.001), had a younger average age (p=0.019), lower height (p=0.001) and a higher average education level (p=0.013) compared to the control group.
Effects on intervention group:
- Reductions in frailty score (p<0.05 vs baseline and change vs change in control group), with 30% of participants in the intervention group no longer being classified as frail or pre-frail in contrast to none in the control group
- Reductions in fatigue and exhaustion score (p<0.05 vs baseline and change vs change in control group)
- Increase in gait speed and improvements in various physical function tests (all p<0.05 vs baseline and change vs change in control group)
- Improvements in mini nutritional assessment (p<0.001 vs baseline and change vs change in control group)
- Improvement in sleep behaviour demonstrated by an increase in awakenings in the control group (p<0.05 vs baseline and change vs change in intervention group) whilst this parameter did not change in the intervention group.
No effects (vs control) on:
- Anthropometric parameters/unintended weight loss
- Other sleep parameters
- Physical activity expenditure and physical activity score
- Hand grip strength.
Conclusion
This affordable and simple health education programme is effective in reducing frailty in elderly and may contribute to healthy ageing.
Clinical practice applications:
- A comprehensive programme, encompassing not only nutrition, but also exercise, cognitive training and a focus on social and psychological wellbeing may be most effective in improving frailty and physical functioning
- Nutrition intervention, alongside other lifestyle interventions, may have benefits for nutritional status in older adults, even if this is not reflected in a change in anthropometric parameters, such as weight.
Considerations for future research:
- Studies with longer-term follow-up would help evaluate whether/for how long the benefits are sustained.
Abstract
INTRODUCTION The prevalence of frailty is increasing worldwide, emphasizing the importance of prioritizing healthy ageing. To address this, cost-effective and minimally supervised interventions are being sought. This study aimed to assess the impact of an educational program on frailty status, physical function, physical activity, sleep patterns, and nutritional status in community-dwelling older adults with at least 1 Fried's frailty criteria. METHODS A 6-month multicentre randomized controlled trial was conducted from March 2022 to February 2023 in 14 health centres located in Cadiz and Malaga, Spain. The educational intervention consisted of 4 group sessions and 6 follow-up phone calls spread over 6 months. The program focused on educating participants about frailty and its impact on health, providing guidelines for physical activity, healthy dietary habits, cognitive training, psychological well-being and social activities. A total of 163 participants, divided into control (n = 80) and educational groups (n = 83) were assessed before and after the intervention. RESULTS The results showed a significant group-time interaction in the physical function evaluated with a large effect on Short Physical Performance Battery score (η2p = 0.179, -0.1 [-1.2-1.0] points for control group vs. 1.0 [0.0-3.0] points for educational group, p < 0.001), and an effect on the 4-meter gait test ((η2p = 0.122, 0.5 [0.1-0.0] s for control group vs. -0.4 [-0.5- -0.3] s for educational group, p < 0.001), and the 5-repetition sit-to-stand test (η2p = 0.136, 1.0 [0.0-1.2] s for control group vs. -4.3 [-7.0- -2.3] for educational group, p < 0.001). Additionally, the use of accelerometers to assess physical activity, inactivity, and sleep patterns revealed a significant small effect in the number of awakenings at night ((η2p = 0.040, 1.1 [-0.5-3.4] awakenings for control group vs. 0.0 [-2.2-0.0] awakenings for educational group, p = 0.009). The findings also highlighted a significant medium effect regarding malnutrition risk, which was assessed using the Mini-Nutritional Assessment score (η2p = 0.088, -0.7 [-2.3-1.5] points for control group vs. 1.5 [-0.5-3.0] points for educational group, p < 0.001). DISCUSSION Thus, the 6-month educational program effectively improved physical function, sleep patterns, and nutritional status compared to usual healthcare attendance in community-dwelling older adults with frailty or pre-frailty. These findings underscore the potential of minimally supervised interventions in promoting a healthy lifestyle in this vulnerable population.
-
3.
Impact of probiotics on muscle mass, muscle strength and lean mass: a systematic review and meta-analysis of randomized controlled trials.
Prokopidis, K, Giannos, P, Kirwan, R, Ispoglou, T, Galli, F, Witard, OC, Triantafyllidis, KK, Kechagias, KS, Morwani-Mangnani, J, Ticinesi, A, et al
Journal of cachexia, sarcopenia and muscle. 2023;14(1):30-44
-
-
-
-
Free full text
-
Plain language summary
Sarcopenia is a progressive skeletal muscle disorder involving accelerated loss of muscle mass, strength and function. It generally occurs in older age groups but can also be seen in younger people. Multiple factors contribute to the development of the condition. Besides nutritional management strategies, probiotics have recently caught the interest of researchers. As probiotics promote metabolic building activity, aid digestion and absorption and reduce muscle breakdown by favourably managing inflammation, they present great potential for the management of sarcopenia. This systematic review and meta-analysis explored the impact of probiotic supplementation on muscle mass, total lean mass and muscle strength in human adults. The review included 24 studies, with probiotics mainly from the Bifidobacteria or Lactobacilli family. The analysis concluded that probiotic supplementation improved muscle mass in comparison to placebos. It also significantly increased overall muscle strength in 6 randomized controlled trials, which was most obvious in age groups of 50 and above. However, no changes were seen concerning total lean mass. It appeared that longer studies, of >12 weeks or more, showed better outcomes in this review. Furthermore, Bifidobacteria species seemed to exhibit more favourable effects, and the authors also noted the beneficial results were more significant in Asian populations. Further research is needed to understand more about the underlying mechanism, best probiotics strains and the specifics of different demographic groups. This article yields a concise overview of sarcopenia, the nutritional aspects of the disease and how probiotics may be beneficial in disease management, strengthened with data from the review.
Expert Review
Conflicts of interest:
None
Take Home Message:
- This was a well-conducted meta-analysis based on its methodological approach that demonstrated that Lactobacillus and Bifidobacterium probiotic supplementation may contribute to improved muscle mass in younger adults and improved muscle strength in older adults.
- Bifidobacterium probiotic supplementation was associated with enhanced muscle mass in younger adults, a potential focus for those considering probiotic supplements.
- The duration of probiotic therapy matters, with longer-term (12 weeks or more) supplementation showing improvements in muscle mass and strength..
Evidence Category:
-
X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
Introduction
This systematic review and meta-analysis evaluated the effect of probiotics on muscle mass, total lean mass and muscle strength in both young and older adults.
Methods
- The search encompassed PubMed, Scopus, Web of Science, and Cochrane Library databases, from inception up to June 2022; studies included spanned a period from 2013 to June 2022.
- The study adhered to Preferred Reporting Items for Systematic Reviews (PRISMA) guidelines and included the Risk-of-Bias tool to assess study quality.
- The study focused on changes in muscle mass, total lean mass, and muscle strength.
- Inclusion criteria: randomised controlled trials (RCTs) with adult participants (>18 years); interventions involving any probiotics, and a control group receiving either no treatment or a placebo.
Results
- 24 RCTs were included (709 participants), with studies conducted in Europe, USA, and Asia. Intervention durations: ranged from 3 weeks to 12 months.
- Participants included overweight, untrained healthy and resistance-trained individuals, and those with specific conditions like metabolic syndrome and frailty.
- Body composition assessments were conducted using bioelectrical impedance (BIA) and/or dual-energy X-ray absorptiometry (DXA).
- Probiotic strains employed in the included studies varied, with Lactobacillus the most common, followed by Bifidobacterium; some combined both. 5 of 24 studies also used additional strains.
- Dosages: ranged from 2 × 10^9 to 11.2 × 10^10 colony-forming units (CFU).
- 4 out of 24 studies used fermented food products like cheese and noodles as sources of probiotics.
- 22 RCTs measured muscle mass and total lean mass; 6 RCTs measured global muscle strength.
- Probiotic supplementation (≥12 weeks) moderately increased muscle mass, with a standardised mean difference (SMD) of 0.42. This significant effect (95% CI: 0.10–0.74, P=0.009) was observed only in younger Asian adults (<50 years) after Bifidobacterium supplementation, based on a meta-analysis of 10 studies.
- Probiotic supplementation (≥12 weeks) significantly increased global muscle strength in older adults (>50 years; SMD: 0.69, 95% CI: 0.33–1.06, P = 0.0002).
- Probiotic supplementation showed no significant impact on lean mass (SMD: -0.03, 95% CI: 0.19 – 0.13, P = 0.69).
Conclusion
Probiotic supplementation, especially Lactobacillus and Bifidobacterium may have a positive impact on muscle mass and global strength
Clinical practice applications:
- Consumption of probiotics, mainly Lactobacillus and Bifidobacterium may contribute to improved muscle strength in older individuals (>50y).
- Consumption of Bifidobacterium strains was associated with improved muscle mass in younger individuals (<50y) in Asian countries, in a low number of studies (k=2).
- Bifidobacterium breve B-3 was associated with an improvement in muscle mass in older overweight individuals, although a causal relationship was not established.
- Probiotics may enhance muscle mass or strength by enhancing protein digestion and amino acid absorption for muscle synthesis and function.
- Considering an individual’s goals, a practitioner could consider probiotic supplementation as a complementary intervention when aiming to enhance muscle mass or strength .
Considerations for future research:
- Future research could focus on pinpointing which specific probiotic strains are most effective for muscle strength or muscle mass to tailor more precise interventions.
- Most studies did not exceed 12 weeks, highlighting the need for long-term research on probiotics sustained muscle impact.
- Future research could investigate the effects of probiotics across diverse demographic groups including different ages, sexes, and ethnic backgrounds to understand the impact in different populations.
- Delving deeper into the mechanisms by which probiotics influence muscle health could lead to targeted probiotic therapies that address specific physiological pathways.
- Finally, future research could explore how probiotics can be combined with other interventions, such as exercise or nutritional modifications, to synergistically improve muscle health and function.
Abstract
Probiotics have shown potential to counteract sarcopenia, although the extent to which they can influence domains of sarcopenia such as muscle mass and strength in humans is unclear. The aim of this systematic review and meta-analysis was to explore the impact of probiotic supplementation on muscle mass, total lean mass and muscle strength in human adults. A literature search of randomized controlled trials (RCTs) was conducted through PubMed, Scopus, Web of Science and Cochrane Library from inception until June 2022. Eligible RCTs compared the effect of probiotic supplementation versus placebo on muscle and total lean mass and global muscle strength (composite score of all muscle strength outcomes) in adults (>18 years). To evaluate the differences between groups, a meta-analysis was conducted using the random effects inverse-variance model by utilizing standardized mean differences. Twenty-four studies were included in the systematic review and meta-analysis exploring the effects of probiotics on muscle mass, total lean mass and global muscle strength. Our main analysis (k = 10) revealed that muscle mass was improved following probiotics compared with placebo (SMD: 0.42, 95% CI: 0.10-0.74, I2 = 57%, P = 0.009), although no changes were revealed in relation to total lean mass (k = 12; SMD: -0.03, 95% CI: -0.19 - 0.13, I2 = 0%, P = 0.69). Interestingly, a significant increase in global muscle strength was also observed among six RCTs (SMD: 0.69, 95% CI: 0.33-1.06, I2 = 64%, P = 0.0002). Probiotic supplementation enhances both muscle mass and global muscle strength; however, no beneficial effects were observed in total lean mass. Investigating the physiological mechanisms underpinning different ageing groups and elucidating appropriate probiotic strains for optimal gains in muscle mass and strength are warranted.
-
4.
Effects of exercise training programmes on fasting gastrointestinal appetite hormones in adults with overweight and obesity: A systematic review and meta-analysis.
Almesbehi, T, Harris, L, McGarty, A, Alqallaf, S, Westrop, S, Edwards, CA, Dorling, JL, Malkova, D
Appetite. 2023;182:106424
-
-
-
-
Free full text
Plain language summary
Appetite is controlled by several hormones including those of the gastrointestinal (GI) system. There has been controversy over whether exercise can affect these hormones resulting in altered food intake and this systematic review and meta-analysis aimed to address this. The results showed that 9 studies have been performed aimed at the effect of 16 different exercise interventions on appetite hormones of the GI system. Exercise had no effect on total ghrelin, acetylated ghrelin and peptide YY, however body mass index and body mass were significantly reduced in individuals with obesity or who are overweight. It was concluded that any increased appetite or energy intake during exercise interventions is unlikely related to GI appetite hormones. This study could be used by healthcare professionals to understand that although exercise may not affect food intake it can still aid weight loss in individuals who are overweight or obese.
Expert Review
Conflicts of interest:
None
Take Home Message:
- This systematic review and meta-analysis found that exercise training programmes in individuals living with overweight and obesity have no impact on fasting concentrations of total and acylated ghrelin, PYY, GLP-1 and CCK.
- This finding suggests that any increase in appetite and energy intake typical of exercise training, would be related to different factors and not from changes in fasting concentrations of gastrointestinal appetite hormones.
Evidence Category:
-
X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
Background
Overweight and obesity prevalence is increasing globally. Exercise is advocated as an effective preventive and treatment for obesity. However, exercise may affect appetite regulation, and understanding how this functions in people with overweight and obesity is of interest. Notably, the evidence regarding the effects of exercise training on gastrointestinal hormones such as ghrelin, has not been extensively synthesised.
Aim
- The aim of this systematic review and meta-analysis was therefore to synthesise the literature describing the effect of exercise programmes of >4 weeks’ duration from randomised controlled trials (RCT) on the fasting and gastrointestinal appetite hormones of adults living with overweight and obesity.
- The review followed PRISMA reporting guidelines and standard systematic review and meta analysis methodology.
Results
- After screening 13,204 records, nine studies with a total of 707 participants (259 men and 448 women) were identified that fit the pre-defined inclusion criteria and were included in the review.
- Overall, after exercise interventions in comparison to control, there was a reduction in body mass (effect size (d)= −0.22, 95% CI −0.42 to −0.03, p = 0.03; 7 studies) and BMI (d= −0.31, 95% CI −0.50 to −0.12, p = 0.001; 8 studies).
- Exercise had no impact on total fasting ghrelin (d = 1.06; 95% CI -0.38 to 2.5; p=0.15; 4 interventions) or fasting acylated ghrelin concentration (d = 0.08; 95% CI -0.31 to 0.47; p=0.68; 7 interventions).
- Fasting anorexigenic peptide YY did not differ between exercise and control (d = −0.16, 95% CI: −0.62 to 0.31, P = 0.51; 7 interventions).
- Two studies assessed the effects of exercise training on GLP-1 and meta-analyses were not possible. In one study, fasting GLP-1 was higher in the intervention group (p=0.04) though the other study found no difference (P>0.05). Only one study looked at fasting plasma cholecystokinin (CCK), which found no change between exercise and control interventions (p>0.5).
- When looking at the correlation between body mass and appetite hormone changes, weight loss (p<0.05) and BMI reduction (p<0.05) occurring with exercise was positively associated with an increase in total plasma ghrelin (p<0.05); increased ghrelin was associated to reductions in body weight and BMI (both p<0.0001). Further, one study reported a positive correlation of body mass loss and BMI reduction with a reduction in acylated ghrelin (p=0.003 and 0.009, respectively) and negatively with an increase in plasma PYY concentration (p=0.003 and 0.03, respectively).
Clinical practice applications:
This systematic review suggested that any compensatory increase in energy intake due to exercise training is unlikely to be related to fasting gastrointestinal appetite hormone changes. Therefore, nutritional therapists should bear this in mind when consulting with clients and find personalised lifestyle strategies to help people manage their caloric consumption in relation to exercise training.
Considerations for future research:
- The relation between changes in body mass or BMI and fasting appetite hormones could not be fully explored due to the small number of studies included in this review. Moreover, the results of this review should be interpreted with caution because most studies were underpowered with a high risk of bias, and there was considerable heterogeneity within some meta-analyses. The effect of exercise training on gastrointestinal satiety hormones including ghrelin, PYY, and CCK therefore require further investigation in individuals living with overweight and obesity, in order to reach more substantial conclusions.
- Exercise enhances the coupling between energy intake and energy expenditure after food consumption, where controlled studies are needed to test how postprandial concentrations of gastrointestinal hormones are influenced by exercise training in individuals with overweight and obesity.
Abstract
A systematic review and meta-analysis was performed to determine the effect of exercise training on fasting gastrointestinal appetite hormones in adults living with overweight and obesity. For eligibility, only randomised controlled trials (duration ≥ four weeks) examining the effect of exercise training interventions were considered. This review was registered in the International Prospective Register of Systematic Reviews (CRD42020218976). The searches were performed on five databases: MEDLINE, EMBASE, Cochrane Library, Web of Science, and Scopus. The initial search identified 13204 records. Nine studies, which include sixteen exercise interventions, met the criteria for inclusion. Meta-analysis was calculated as the standardised mean difference (Cohen's d). Exercise training had no effect on fasting concentrations of total ghrelin (d: 1.06, 95% CI -0.38 to 2.50, P = 0.15), acylated ghrelin (d: 0.08, 95% CI: -0.31 to 0.47, P = 0.68) and peptide YY (PYY) (d = -0.16, 95% CI: -0.62 to 0.31, P = 0.51) compared to the control group. Analysis of body mass index (BMI) (d: -0.31, 95% CI: -0.50 to -0.12, P < 0.01) and body mass (d: -0.22, 95% CI: -0.42 to -0.03, P = 0.03) found a significant reduction after exercise compared to controls. Overall, exercise interventions did not modify fasting concentrations of total ghrelin, acylated ghrelin, and PYY in individuals with overweight or obesity, although they reduced body mass and BMI. Thus, any upregulation of appetite and energy intake in individuals with overweight and obesity participating in exercise programmes is unlikely to be related to fasting concentrations of gastrointestinal appetite hormones.
-
5.
Influence of water-based exercise on energy intake, appetite, and appetite-related hormones in adults: A systematic review and meta-analysis.
Grigg, MJ, Thake, CD, Allgrove, JE, King, JA, Thackray, AE, Stensel, DJ, Owen, A, Broom, DR
Appetite. 2023;180:106375
-
-
-
-
Free full text
Plain language summary
Exercise is an effective way to improve mental and physical health and can influence weight management due to the energy expenditure. Energy balance is influenced by day-to-day variations in energy intake and expenditure. The aim of this study was to address whether water-based exercise influences energy intake, appetite, and appetite related hormones differently to land based exercise in adults. This study is a systematic review and meta-analysis of nine studies which include randomised crossover ( 7 trials), semi-random (1 trial) (water-trial was required prior to iso-energetically matched water trial) and independent group (1 trial) (used in the 12-week study) designs. Results show that post-exercise energy intake is higher after water-based exercise versus a resting control. However, there wasn’t any difference in energy intake when water-based exercise was compared with land-based exercise. Furthermore, when different water temperatures were analysed, post-exercise energy intake was higher in cold water versus neutral water. Additionally, cycling and swimming did not alter fasting plasma concentrations of appetite regulating hormones (ghrelin and leptin), insulin or total peptide YY [gut hormone] but contributed to body mass loss. Authors conclude that if body mass management is a person’s primary focus, it is important to be mindful of the tendency to eat more in the subsequent hours after water-based exercise, as energy intake may be increased when compared to a no exercise control.
Expert Review
Conflicts of interest:
None
Take Home Message:
- The only type of exercise reporting an increase in energy intake was in water-based activities, where the temperature was between 18-20• C. However, this was only when explored in comparison to a resting control. No difference was reported in energy intake when water-based exercise was compared with land-based exercise.
- Any form of exercise, whether land or water-based should be considered where appropriate to reduce the risks of sedentary behaviour.
Evidence Category:
-
X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
Introduction:
Exercise is effective for weight-management alongside other physical and mental health benefits. Changes in appetite-regulating hormones may affect energy balance, e.g. some exercise may suppress appetite, known as exercise-induced anorexia. This review evaluated differences in energy intake, appetite and appetite-related hormones in land-based versus water-based exercise.
Methods:
The meta-analysis followed PRISMA guidelines and was registered on PROSPERO. Literature searching resulted in eight studies published between 1991 and 2021, which met the inclusion criteria (water v control), 5 studies (water v land) and 2 studies (water at different temperatures). Risk of Bias was assessed using Cochrane’s Risk of Bias for randomised trials.
Results:
Data were analysed in RevMan 5.4.1 using fixed effects, generic inverse variance method on energy intake. High heterogeneity prevented analysis on appetite and appetite-related hormones. Standard deviation was inputted based on estimated values for missing data. Heterogeneity was calculated using the I2 index. Sensitivity analyses were conducted. Statistical significance was set at p<0.05 and analyses based on two-tailed Z tests.
All participants had a healthy BMI, were aged 19-39 and ranged from well-trained to non-exercisers. A single bout of water-based exercise increased ad-libitum energy intake compared to a non-exercise control (mean difference [95% CI]: 330 [118, 542] kJ, P = 0.002) but no difference was identified between water and land-based exercise (78 [-176, 334] kJ, P = 0.55). Cold water exercise (18–20 •C) increased energy intake more than neutral water (27–33 •C) temperature (719 [222, 1215] kJ; P < 0.005). One 12-week study reported cycling and swimming did not alter fasting plasma concentrations of total ghrelin, insulin, leptin or total PYY but contributed to body mass loss 87.3 (5.2) to 85.9 (5.0) kg and 88.9 (4.9) to 86.4 (4.5) kg (P < 0.05) respectively.
Conclusion:
Despite limitations, this review may provide preliminary evidence on energy intake and appetite for water-based activities. If weight management is a primary focus, then water temperature needs to be considered, particularly if sub 20•C .
Clinical practice applications:
Although this study suggests cold water exercise may cause an increase in energy intake, 95% confidence intervals for individual studies are very large so results should be interpreted cautiously. Those preferring exercise in cold water, should be encouraged, providing they are mindful of the tendency to eat more post-exercise.
It is not possible to draw any robust conclusions about the ratings of hunger in response to different types of exercise due to limited data. However, according to the review, five studies demonstrated that hunger was suppressed more than control prior at the start of water-based exercise, and during and immediately after exercise.
Considerations for future research:
Most participants were of healthy weight and physically active, however since appetite signals may be dysregulated in obesity, including all weight categories and different activity levels may generate a more comprehensive overview.
Further research recommendations include:
- Measuring the effects of water- based activities on appetite, appetite related hormones and energy intake at different time points following exercise in order to provide recommendations for effective weight management strategies and in a range of different temperatures.
- Using a ‘no exercise’ water immersion control. Evidence suggests that immersion in cold water alone may increase energy expenditure
- Evaluating the effect of a water-based activity, such as swimming performed in a ‘fasted’ and ‘non-fasted’ state to investigate the impact on appetite, appetite related hormones and energy intake.
Abstract
Single bouts of land-based exercise suppress appetite and do not typically alter energy intake in the short-term, whereas it has been suggested that water-based exercise may evoke orexigenic effects. The primary aim was to systematically review the available literature investigating the influence of water-based exercise on energy intake in adults (PROSPERO ID number CRD42022314349). PubMed, Medline, Sport-Discus, Academic Search Complete, CINAHL and Public Health Database were searched for peer-reviewed articles published in English from 1900 to May 2022. Included studies implemented a water-based exercise intervention versus a control or comparator. Risk of bias was assessed using the revised Cochrane 'Risk of bias tool for randomised trials' (RoB 2.0). We identified eight acute (same day) exercise studies which met the inclusion criteria. Meta-analysis was performed using a fixed effects generic inverse variance method on energy intake (8 studies (water versus control), 5 studies (water versus land) and 2 studies (water at two different temperatures)). Appetite and appetite-related hormones are also examined but high heterogeneity did not allow a meta-analysis of these outcome measures. We identified one chronic exercise training study which met the inclusion criteria with findings discussed narratively. Meta-analysis revealed that a single bout of exercise in water increased ad-libitum energy intake compared to a non-exercise control (mean difference [95% CI]: 330 [118, 542] kJ, P = 0.002). No difference in ad libitum energy intake was identified between water and land-based exercise (78 [-176, 334] kJ, P = 0.55). Exercising in cold water (18-20 °C) increased energy intake to a greater extent than neutral water (27-33 °C) temperature (719 [222, 1215] kJ; P < 0.005). The one eligible 12-week study did not assess whether water-based exercise influenced energy intake but did find that cycling and swimming did not alter fasting plasma concentrations of total ghrelin, insulin, leptin or total PYY but contributed to body mass loss 87.3 (5.2) to 85.9 (5.0) kg and 88.9 (4.9) to 86.4 (4.5) kg (P < 0.05) respectively. To conclude, if body mass management is a person's primary focus, they should be mindful of the tendency to eat more in the hours after a water-based exercise session, particularly when the water temperature is cold (18-20 °C).
-
6.
Effectiveness of Exercise Training on Male Factor Infertility: A Systematic Review and Network Meta-analysis.
Hajizadeh Maleki, B, Tartibian, B, Chehrazi, M
Sports health. 2022;14(4):508-517
-
-
-
-
Free full text
-
Plain language summary
Male factor infertility is characterised by the existence of suboptimal sperm parameters in the male partner of childbearing age and is presently defined as the inability to conceive a child with frequent and unprotected sexual intercourse in the fertile phase of the menstrual cycles for a year or longer. The main aim of this study was to evaluate the effectiveness of 1 or more of the selected types of exercise interventions (moderate-intensity continuous training (MICT), resistance training (RT), combined aerobic and resistance training (CET), high-intensity continuous training (HICT), and high-intensity interval training (HIIT)) in the prevention and treatment of male factor infertility. This study is a systematic review and meta-analysis of seven randomised controlled trials representing 18 groups (11 exercise, 7 non-intervention control [NON-EX]) and 2641 participants and/or patients (1429 exercise, 1212 NON-EX). Results show that in the setting of couples with male factor infertility, when compared with the NON-EX group, selected types of exercise interventions improved the relative risk of pregnancy rate in the following order: CET > MICT > RT > HICT > HIIT. The top-ranking interventions for live birth rate were for MICT, RT, HIIT, CET, and HICT. In addition, the interventions with the highest probability of being the best approach out of all available options in improving semen quality parameters were for CET, MICT, HICT, RT, and HIIT. Authors conclude that when clinicians are formulating clinical recommendations for preventing and treating male factor infertility, the findings of this study should be considered.
Expert Review
Conflicts of interest:
None
Take Home Message:
- For couples with male factor infertility, this review recommends moderate intensity-aerobic exercise in combination with strength training to be the intervention with the highest probability of being the best approach for reproductive health benefits.
- A conservative interpretation of the findings is required because they were based on single studies.
Evidence Category:
-
X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
Introduction
The World Health Organisation estimates that infertility affects 10% to 15% of couples in industrialised countries. Approximately 50% of all infertility cases are attributed to male-related factors, in particular, poor semen quality (called male factor infertility). The aim of this study was to evaluate the effectiveness of exercise training on male factor infertility and seminal markers of inflammation.
Methods
This is the first study to undertake a systematic review with network meta-analysis of 7 RCTs to evaluate the effectiveness of 1 or more types of exercise interventions on male factor infertility and seminal markers of inflammation, as well as to provide clinicians with a ranking of treatments to inform them of the treatment effects of exercise training and physical activity.
The forms of exercise include: moderate-intensity continuous training (MICT), resistance training (RT), combined aerobic and resistance training (CET), high-intensity continuous training (HICT), and high-intensity interval training (HIIT).
7 RCTs representing 18 groups (11 exercise (supervised, not home-based), 7 non-intervention control [NON-EX]) and 2641 participants and/or patients (1429 exercise, 1212 NON-EX). All the RCTs were conducted in Iran involving healthy adult participants and/or infertile patients (with doctor-diagnosed male factor infertility). The intervention period was ≥10 weeks with a follow-up period.
None of the studies reported changes in either patients’ dietary intakes or normal daily physical activities and lifestyles during the intervention period.
Results
Compared with a non-intervention control group, the top ranking interventions:
For pregnancy rate:
Combined aerobic and resistance training (CET) (p= 0.89 relative risk [RR] = 27.81), moderate-intensity continuous training (MICT) (p=0.87, RR = 26.67), resistance training (RT) (p=0.61,RR = 12.54), high intensity continuous training (HICT) (p=0.34, RR = 5.55), and high-intensity interval training (HIIT) (p=0.28, RR = 4.63).
For live birth rate:
MICT (p=0.82, RR = 10.05), RT (p=0.70, RR = 4.92), HIIT (p=0.66, RR = 4.38)), CET (p=0.45, RR = 2.20), and HICT (p=0.30, RR = 1.55)
The following parameters/markers rank the 5 exercise strategies in order of effectiveness:
- Semen quality parameters were significantly improved after the following types of exercise interventions as compared with the non-intervention group [NON-EX]: CET > MICT > HICT > RT > HIIT
- The following training strategies were significantly better at improving seminal markers of oxidative stress: CET > MICT > HIIT > HICT > RT
- The following training strategies were significantly better at improving seminal markers of inflammation: CET > MICT > HIIT > RT > HICT
- The following training strategies were significantly better at improving measures of body composition and VO2 max: CET > HICT > MICT > HIIT > RT
- There was insufficient evidence of a difference for the selected types of exercise interventions versus NON-EX group for pregnancy and live birth rates in healthy participants.
Conclusion
Combined aerobic and resistance training (CET) was found to be the intervention with the highest probability of being the best approach for improving the male factor infertility.
Clinical practice applications:
- In light of these findings, it is reasonable to propose that infertile men and at-risk populations take part in the top-ranking interventions identified in this analysis.
- For substantial reproductive health benefits, one should consider doing all of the selected types of exercise interventions (CET, MICT, RT, HICT, and HIIT); however, moderate intensity-aerobic exercise and strength training in combination would generally be more favourable to lend clinically significant improvements.
- To add to this, exercise can offer a myriad of other health benefits, is a possibly safe activity and a cost-effective treatment strategy for male factor infertility.
Considerations for future research:
- There was only a small number of relevant trials available for comparison suggesting the need for additional study in this field.
- Further trials are needed to analyse the dose-response impacts of exercise modalities on male reproductive function.
- The results propose several domains for development in the reporting of RCTs addressing the impacts of interventional exercise studies on male reproductive function.
- Heterogeneity of some findings and discrepancy across the included studies was significant. For example, variations in the characteristics of training programs. Future analyses should aim to continue to address this.
- There is a concern that this study may not relate to already active patients with male factor infertility which future studies should address.
Abstract
CONTEXT Mounting evidence from the literature suggests that different types of training interventions can be successful at improving several aspects of male reproductive function in both fertile and infertile populations. OBJECTIVE The aim of this study was to evaluate the effectiveness of exercise training on male factor infertility and seminal markers of inflammation. DATA SOURCES We searched PubMed, CISCOM, Springer, Elsevier Science, Cochrane Central Register of Controlled Trials, Scopus, PEDro, Ovid (Medline, EMBASE, PsycINFO), Sport Discus, Orbis, CINAHL, Web of Science, ProQuest, and the ClinicalTrials.gov registry for randomized controlled trials (RCTs) that analyzed the impacts of selected types of exercise interventions on markers of male reproductive function and reproductive performance. STUDY SELECTION A total of 336 records were identified, of which we included 7 trials reporting on 2641 fertile and infertile men in the systematic review and network meta-analysis. LEVEL OF EVIDENCE Level 1 (because this is a systematic review of RCTs). DATA EXTRACTION The data included the study design, participant characteristics, inclusion and exclusion, intervention characteristics, outcome measures, and the main results of the study. RESULTS The results of network meta-analysis showed that, compared with a nonintervention control group, the top-ranking interventions for pregnancy rate were for combined aerobic and resistance training (CET) (relative risk [RR] = 27.81), moderate-intensity continuous training (MICT) (RR = 26.67), resistance training (RT) (RR = 12.54), high-intensity continuous training (HICT) (RR = 5.55), and high-intensity interval training (HIIT) (RR = 4.63). While the top-ranking interventions for live birth rate were for MICT (RR = 10.05), RT (RR = 4.92), HIIT (RR = 4.38), CET (RR = 2.20), and HICT (RR = 1.55). Also, with the following order of effectiveness, 5 training strategies were significantly better at improving semen quality parameters (CET > MICT > HICT > RT > HIIT), seminal markers of oxidative stress (CET > MICT > HIIT > HICT > RT), seminal markers of inflammation (CET > MICT > HIIT > RT > HICT), as well as measures of body composition and VO2max (CET > HICT > MICT > HIIT > RT). CONCLUSION The review recommends that the intervention with the highest probability of being the best approach out of all available options for improving the male factor infertility was for CET.
-
7.
Impact of Probiotics on the Performance of Endurance Athletes: A Systematic Review.
Díaz-Jiménez, J, Sánchez-Sánchez, E, Ordoñez, FJ, Rosety, I, Díaz, AJ, Rosety-Rodriguez, M, Rosety, MÁ, Brenes, F
International journal of environmental research and public health. 2021;18(21)
-
-
-
-
Free full text
Plain language summary
The relationship between the gut microbiome and exercise has recently been explored to ascertain potential methods of improving athletic performance. Athletes have begun utilising probiotics to improve performance, support the immune system and reduce gastrointestinal problems, however no systematic review has been done to assess the efficacy behind these notions. The aim of this study is to review the use of probiotics in endurance athletes and assess both the direct and indirect associative factors. This review included nine studies and found improvements in athletic performance, oxidative stress markers, immune support, and incidence of upper respiratory tract infections with probiotic use. While there is little scientific evidence on the causative relationship between probiotics and performance, the authors conclude probiotics can enhance athletic performance by ameliorating the indirect consequences of oxidative stress and infection.
Expert Review
Conflicts of interest:
None
Take Home Message:
- Endurance athletes may take probiotic supplements to support immune or GI health or for other reasons
- Currently there is little evidence that probiotics directly or specifically enhance athletic performance
- Probiotic supplementation potentially impacts on immune health particularly during intensive training and may facilitate muscle recovery or maintain performance
- Whilst probiotics may reduced GI symptom frequency and severity, further research is clearly warranted
Evidence Category:
-
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
X
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
- There is current interest in the potential therapeutic benefits of probiotic strategies to support training and in-race performance for endurance athletes.
- Probiotic supplements are typically used by endurance athletes to limit or prevent upper respiratory tract infections (URTIs), reduce oxidative stress, support the immune system and modulate gastrointestinal function.
- Based on a limited number of articles sourced in this review (n=26), only 9 met the underlying quality and inclusion criteria. This highlights an important need for further research to be undertaken in this area.
- The review highlighted that different preparations, number of bacterial colony-forming units (CFUs), species type, timecourse and study objectives makes it difficult to determine fundamental conclusions on the efficacy of probiotics.
- That said, papers reviewed indicated the potential for a 55% increase in anti-inflammatory cytokines, reduced prevalence of URTIs, reduced Epstein-Barr and cytomegalovirus citrate antibodies, and improved recovery times.
- Probiotic supplementation likely enhances microbiota diversity and may indirectly support increased training load, and performance maintenance through immune defence. However, there were no indications that endurance performance was specifically enhanced.
Clinical practice applications:
- Most of the papers reviewed used formulae containing either Lactobacillus spp. (e.g. Plantarum, Acidophilus, Casei Shirota) or Bifidobacterium spp. (e.g. animalis subsp., bifidum, lactis, longum subsp.) or combinations. There was little mention of prebiotic or symbiotic strategies.
- Any impact of probiotics on exercise performance is likely to relate to both immune modulation and/or mechanisms leading to reduced muscle damage.
- Surprisingly, there was only partial mention of the use of probiotics for GI support and several notable papers were not included in the review. That said, the authors did note that with increased prevalence of exercise-induced gastrointestinal symptoms with endurance sport due to acute GI hypoperfusion and localised ischemia, acute probiotic strategies have resulted in reduced GI symptom frequency and severity in athletes.
- Importantly no adverse events following probiotic supplementation in endurance athletes were reported.
Considerations for future research:
- Clearly further research is warranted in terms of probiotic strain specific benefits both in training and in-race event effectiveness.
- The authors reported that there were no studies found on the effect of probiotics on hormonal or nervous systems in endurance athletes.
- Further research is needed to consider the impact of acute versus chronic probiotic use on intestinal metabolites, especially considering recent interactions between specific bacterial strains and short-chain fatty acid production being associated with performance (see: https://www.nutrition-evidence.com/article/31235964?term=31235964.
Abstract
BACKGROUND Probiotic supplements contain different strains of living microorganisms that promote the health of the host. These dietary supplements are increasingly being used by athletes to improve different aspects such as athletic performance, upper respiratory tract infections (URTIs), the immune system, oxidative stress, gastrointestinal (GI) problems, etc. This study aimed to identify the current evidence on the management of probiotics in endurance athletes and their relationship with sports performance. METHODS A systematic review of the last five years was carried out in PubMed, Scopus, Web of science, Sportdiscus and Embase databases. RESULTS Nine articles met the quality criteria. Of these, three reported direct benefits on sports performance. The remaining six articles found improvements in the reduction of oxidative stress, increased immune response and decreased incidence of URTIs. There is little scientific evidence on the direct relationship between the administration of probiotics in endurance athletes and sports performance. CONCLUSIONS Benefits were found that probiotics could indirectly influence sports performance by improving other parameters such as the immune system, response to URTIs and decreased oxidative stress, as well as the monitoring of scheduled workouts.
-
8.
Effect of dietary nitrate on human muscle power: a systematic review and individual participant data meta-analysis.
Coggan, AR, Baranauskas, MN, Hinrichs, RJ, Liu, Z, Carter, SJ
Journal of the International Society of Sports Nutrition. 2021;18(1):66
-
-
-
-
Free full text
Plain language summary
Previous reviews have concluded that dietary nitrate (NO3−) improves maximal neuromuscular power in humans, but these were based on a limited number of studies. This is the first systematic review and meta-analysis evaluating the effects of dietary NO3− supplementation on muscular power in humans. The study also aims to quantify the size of this beneficial effect. 19 studies with a total of 268 participants were included. Most of these used concentrated beetroot juice as the source of NO3− given as an acute dose (short term high level). A positive effect of dietary NO3− on muscle power was observed in all 19 studies. Analyses were done on sub groups - age, sex and the amount of muscle mass engaged in the activity. Dietary NO3− intake significantly increases maximal muscle power in humans. The magnitude of this effect has practical and clinical importance; not just for athletes but also for patient groups. This effect is independent of subject age, sex, or the amount of muscle mass engaged in the activity but may be greater with acute vs. repeated dosing. Further research is needed to determine factors such as the optimal supplementation regimen and target population.
Expert Review
Conflicts of interest:
None
Take Home Message:
- This meta-analysis lends quantitative support to previous narrative reviews that nitrate supplementation can enhance maximal power output.
- These findings are highly relevant to team and strength sport athletes, who may not otherwise be supplementing with nitrates.
- These findings are also highly relevant for older populations, where risk of falls and fractures are high and can lead to significant adverse effects on health and quality of life.
Evidence Category:
-
X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
-
B: Systematic reviews including RCTs of limited number
-
C: Non-randomized trials, observational studies, narrative reviews
-
D: Case-reports, evidence-based clinical findings
-
E: Opinion piece, other
Summary Review:
- In 2007, researchers uncovered the ingestion of dietary nitrates reduced the oxygen cost of submaximal exercise, and since, over 100 studies have examined the effects of nitrates on endurance performance.
- With regards to the impact of nitrates on maximal force output, only trivial results had been previously found.
- This review study found that while nitrates do not impact force development, they do demonstrate primary effect on the speed of muscle contraction (i.e. muscular power is the product of force x speed).
- The reviews primary finding was that nitrate intake can significantly enhance muscular power, regardless of subject age or sex.
Clinical practice applications:
- These new findings highlight the ability of dietary nitrates to improve neuromuscular power production is highly relevant for team sport athletes, due to the explosive nature of these sports with constant accelerations and decelerations during training and competition.
- In the general population, falls and fractures amongst older adults significantly reduces quality of life and costs the healthcare system hundreds of millions of pounds to treat.
- Improved contractile properties of muscle, most notably speed of contraction, may offer protection to older adults as well as the benefit of additional nitric oxide (NO) to support vascular health as well.
- The typical intake of dietary nitrates in the general population is about 31-185mg/day in Europe and 40-100mg/day in North America. Most studies use doses between 300-600mg of dietary nitrates. Increasing dietary or supplemental intake is key to achieving the neuromuscular effect.
Considerations for future research:
- The results of the present meta-analysis clearly demonstrate that dietary nitrates increases muscle power in humans, but the mechanism responsible for this effect is still unclear.
- There are notable differences between rodent and human metabolism of dietary nitrates, therefore the biochemical mechanism by which nitrate intake improves human muscle power requires additional study.
Abstract
BACKGROUND Previous narrative reviews have concluded that dietary nitrate (NO3-) improves maximal neuromuscular power in humans. This conclusion, however, was based on a limited number of studies, and no attempt has been made to quantify the exact magnitude of this beneficial effect. Such information would help ensure adequate statistical power in future studies and could help place the effects of dietary NO3- on various aspects of exercise performance (i.e., endurance vs. strength vs. power) in better context. We therefore undertook a systematic review and individual participant data meta-analysis to quantify the effects of NO3- supplementation on human muscle power. METHODS The literature was searched using a strategy developed by a health sciences librarian. Data sources included Medline Ovid, Embase, SPORTDiscus, Scopus, Clinicaltrials.gov , and Google Scholar. Studies were included if they used a randomized, double-blind, placebo-controlled, crossover experimental design to measure the effects of dietary NO3- on maximal power during exercise in the non-fatigued state and the within-subject correlation could be determined from data in the published manuscript or obtained from the authors. RESULTS Nineteen studies of a total of 268 participants (218 men, 50 women) met the criteria for inclusion. The overall effect size (ES; Hedge's g) calculated using a fixed effects model was 0.42 (95% confidence interval (CI) 0.29, 0.56; p = 6.310 × 10- 11). There was limited heterogeneity between studies (i.e., I2 = 22.79%, H2 = 1.30, p = 0.3460). The ES estimated using a random effects model was therefore similar (i.e., 0.45, 95% CI 0.30, 0.61; p = 1.064 × 10- 9). Sub-group analyses revealed no significant differences due to subject age, sex, or test modality (i.e., small vs. large muscle mass exercise). However, the ES in studies using an acute dose (i.e., 0.54, 95% CI 0.37, 0.71; p = 6.774 × 10- 12) was greater (p = 0.0211) than in studies using a multiple dose regimen (i.e., 0.22, 95% CI 0.01, 0.43; p = 0.003630). CONCLUSIONS Acute or chronic dietary NO3- intake significantly increases maximal muscle power in humans. The magnitude of this effect-on average, ~ 5%-is likely to be of considerable practical and clinical importance.