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Effects of a mediterranean diet on the gut microbiota and microbial metabolites: A systematic review of randomized controlled trials and observational studies.
Kimble, R, Gouinguenet, P, Ashor, A, Stewart, C, Deighton, K, Matu, J, Griffiths, A, Malcomson, FC, Joel, A, Houghton, D, et al
Critical reviews in food science and nutrition. 2023;(27):8698-8719
Abstract
Consumption of the Mediterranean dietary pattern (MedDiet) is associated with reduced risk of numerous non-communicable diseases. Modulation of the composition and metabolism of the gut microbiota represents a potential mechanism through which the MedDiet elicits these effects. We conducted a systematic literature search (Prospero registration: CRD42020168977) using PubMed, The Cochrane Library, MEDLINE, SPORTDiscuss, Scopus and CINAHL databases for randomized controlled trials (RCTs) and observational studies exploring the impact of a MedDiet on gut microbiota composition (i.e., relative abundance of bacteria or diversity metrics) and metabolites (e.g., short chain fatty acids). Seventeen RCTs and 17 observational studies were eligible for inclusion in this review. Risk of bias across the studies was mixed but mainly identified as low and unclear. Overall, RCTs and observational studies provided no clear evidence of a consistent effect of a MedDiet on composition or metabolism of the gut microbiota. These findings may be related to the diverse methods across studies (e.g., MedDiet classification and analytical techniques), cohort characteristics, and variable quality of studies. Further, well-designed studies are warranted to advance understanding of the potential effects of the MedDiet using more detailed examination of microbiota and microbial metabolites with reference to emerging characteristics of a healthy gut microbiome.
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The Effects of Exercise on Indirect Markers of Gut Damage and Permeability: A Systematic Review and Meta-analysis.
Chantler, S, Griffiths, A, Matu, J, Davison, G, Jones, B, Deighton, K
Sports medicine (Auckland, N.Z.). 2021;51(1):113-124
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Plain language summary
Gut permeability and intestinal cell damage are often observed in various gastrointestinal and metabolic conditions. Based on recent findings, exercise appears to cause damage to intestinal cells, leading to an increase in gut permeability. The aim of this review was to determine the effect of an acute bout of exercise on gut damage and permeability and explore the plausible mechanisms underlying these effects. This review analysed 34 studies that evaluated biomarkers of gut permeability and cell damage in response to exercise compared to resting controls. These findings revealed a significant impact of exercise on gut damage and permeability, and the markers were exacerbated when exercise was performed in hot conditions. The duration of exercise did not have any impact on cell damage or permeability. Based on these results, the authors conclude a single bout of exercise increases gut damage and permeability and they encourage further investigation into nutritional strategies to prevent adverse effects during the post-exercise period. Future research should consider the efficacy nutritional interventions to minimize these negative effects to optimise athletic health and performance.
Abstract
AIM: Exercise appears to cause damage to the endothelial lining of the human gastrointestinal tract and elicit a significant increase in gut permeability. OBJECTIVE The aim of this review was to determine the effect of an acute bout of exercise on gut damage and permeability outcomes in healthy populations using a meta-analysis. METHODS PubMed, The Cochrane Library as well as MEDLINE, SPORTDiscus and CINHAL, via EBSCOhost were searched through February 2019. Studies were selected that evaluated urinary (ratio of disaccharide/monosaccharide excretion) or plasma markers [intestinal Fatty Acid Binding Protein (i-FABP)] of gut permeability and gut cell damage in response to a single bout of exercise. RESULTS A total of 34 studies were included. A random-effects meta-analysis was performed, and showed a large and moderate effect size for markers of gut damage (i-FABP) (ES 0.81; 95% CI 0.63-0.98; n = 26; p < 0.001) and gut permeability (Disaccharide Sugar/Monosaccharide Sugar) (ES 0.70; 95% CI 0.29-1.11; n = 17; p < 0.001), respectively. Exercise performed in hot conditions (> 23 °C) further increased markers of gut damage compared with thermoneutral conditions [ES 1.06 (95% CI 0.88-1.23) vs. 0.66 (95% CI 0.43-0.89); p < 0.001]. Exercise duration did not have any significant effect on gut damage or permeability outcomes. CONCLUSIONS These findings demonstrate that a single bout of exercise increases gut damage and gut permeability in healthy participants, with gut damage being exacerbated in hot environments. Further investigation into nutritional strategies to minimise gut damage and permeability after exercise is required. PROSPERO database number (CRD42018086339).
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Effects of a Mediterranean diet on blood pressure: a systematic review and meta-analysis of randomized controlled trials and observational studies.
Cowell, OR, Mistry, N, Deighton, K, Matu, J, Griffiths, A, Minihane, AM, Mathers, JC, Shannon, OM, Siervo, M
Journal of hypertension. 2021;(4):729-739
Abstract
OBJECTIVE To conduct a systematic review and meta-analysis investigating effects of MedDiet on blood pressure in randomized controlled trials (RCTs) and associations of MedDiet with risk of hypertension in observational studies. METHODS PubMed, The Cochrane Library and EBSCOhost were searched from inception until January 2020 for studies that met the following criteria: participants aged at least 18 years, RCTs investigating effects of a MedDiet versus control on BP, observational studies exploring associations between MedDiet adherence and risk of hypertension. Random-effects meta-analyses were conducted. Meta-regression and subgroup analyses were performed for RCTs to identify potential effect moderators. RESULTS Nineteen RCTs reporting data on 4137 participants and 16 observational studies reporting data on 59 001 participants were included in the meta-analysis. MedDiet interventions reduced SBP and DBP by a mean -1.4 mmHg (95% CI: -2.40 to -0.39 mmHg, P = 0.007, I2 = 53.5%, Q = 44.7, τ2 = 1.65, df = 19) and -1.5 mmHg (95% CI: -2.74 to -0.32 mmHg, P = 0.013, I2 = 71.5%, Q = 51.6, τ2 = 4.72, df = 19) versus control, respectively. Meta-regression revealed that longer study duration and higher baseline SBP was associated with a greater decrease in BP, in response to a MedDiet (P < 0.05). In observational studies, odds of developing hypertension were 13% lower with higher versus lower MedDiet adherence (95% CI: 0.78--0.98, P = 0.017, I2 = 69.6%, Q = 41.1, τ2 = 0.03, df = 17). CONCLUSION Data suggest that MedDiet is an effective dietary strategy to aid BP control, which may contribute towards the lower risk of CVD reported with this dietary pattern. This study was registered with PROSPERO CRD42019125073.
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Body composition differences by age and playing standard in male rugby union and rugby league: A systematic review and meta-analysis.
Geeson-Brown, T, Jones, B, Till, K, Chantler, S, Deighton, K
Journal of sports sciences. 2020;(19):2161-2176
Abstract
This systematic review and meta-analysis aimed to determine differences in body compositionn between playing standard and age in male rugby union and rugby league athletes. The MOOSE (Meta-analysis of Observational Studies in Epidemiology) guidelines for design, implementation, and reporting were followed. Studies were required to be in male rugby union or league and have body composition as the primary or secondary outcome. Data was required to be presented separately for positional groups and body composition presented as whole-body. A systematic search was performed in PubMed, Cochrane Library, MEDLINE, SPORTDiscus, and CINHAHL via EBSCOhost. 57 studies were included for meta-analysis. Results highlighted significantly higher fat-free mass in senior elite than senior sub-elite or junior elite athletes for all RU and RL forwards. Small and non-significant differences were found in fat mass between rugby union playing standards and age categories. Rugby league senior elite forwards had less fat mass than junior elite forwards. Practitioners should prioritise training and nutritional strategies that maximise fat-free mass development, especially in junior elite cohorts.
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How well do activity monitors estimate energy expenditure? A systematic review and meta-analysis of the validity of current technologies.
O'Driscoll, R, Turicchi, J, Beaulieu, K, Scott, S, Matu, J, Deighton, K, Finlayson, G, Stubbs, J
British journal of sports medicine. 2020;(6):332-340
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Abstract
OBJECTIVE To determine the accuracy of wrist and arm-worn activity monitors' estimates of energy expenditure (EE). DATA SOURCES SportDISCUS (EBSCOHost), PubMed, MEDLINE (Ovid), PsycINFO (EBSCOHost), Embase (Ovid) and CINAHL (EBSCOHost). DESIGN A random effects meta-analysis was performed to evaluate the difference in EE estimates between activity monitors and criterion measurements. Moderator analyses were conducted to determine the benefit of additional sensors and to compare the accuracy of devices used for research purposes with commercially available devices. ELIGIBILITY CRITERIA We included studies validating EE estimates from wrist-worn or arm-worn activity monitors against criterion measures (indirect calorimetry, room calorimeters and doubly labelled water) in healthy adult populations. RESULTS 60 studies (104 effect sizes) were included in the meta-analysis. Devices showed variable accuracy depending on activity type. Large and significant heterogeneity was observed for many devices (I2 >75%). Combining heart rate or heat sensing technology with accelerometry decreased the error in most activity types. Research-grade devices were statistically more accurate for comparisons of total EE but less accurate than commercial devices during ambulatory activity and sedentary tasks. CONCLUSIONS EE estimates from wrist and arm-worn devices differ in accuracy depending on activity type. Addition of physiological sensors improves estimates of EE, and research-grade devices are superior for total EE. These data highlight the need to improve estimates of EE from wearable devices, and one way this can be achieved is with the addition of heart rate to accelerometry. PROSPEROREGISTRATION NUMBER CRD42018085016.
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Differences in circulating appetite-related hormone concentrations between younger and older adults: a systematic review and meta-analysis.
Johnson, KO, Shannon, OM, Matu, J, Holliday, A, Ispoglou, T, Deighton, K
Aging clinical and experimental research. 2020;(7):1233-1244
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Abstract
Ageing is associated with reduced appetite and energy intakes. However, the mechanisms underlying this phenomenon are not fully understood. This systematic review and meta-analysis quantified differences in circulating concentrations of appetite-related hormones between healthy older and younger adults. Six databases were searched through 12th June 2018 for studies that compared appetite-related hormone concentrations between older and younger adults. Data were pooled using random-effects meta-analysis and are presented as standardised mean difference (Hedges' g) with 95% confidence intervals (95% CI). Thirty-five studies were included involving 710 older adults (mean ± SD; age: 73 ± 5 years) and 713 younger adults (age: 28 ± 7 years). Compared with younger adults, older adults exhibited higher fasted and postprandial concentrations of the anorectic hormones cholecystokinin (Fasted: SMD 0.41 (95% CI 0.24, 0.57); p < 0.001. Postprandial: SMD 0.41 (0.20, 0.62); p < 0.001), leptin [Fasted: SMD 1.23 (0.15, 2.30); p = 0.025. Postprandial: SMD 0.62 (0.23, 1.01); p = 0.002] and insulin [Fasted: SMD 0.24 (- 0.02, 0.50); p = 0.073. Postprandial: SMD 0.16 (0.01, 0.32); p = 0.043]. Higher postprandial concentrations of peptide-YY were also observed in older adults compared with younger adults [SMD 0.31 (- 0.03, 0.65); p = 0.075]. Compared with younger adults, older adults had lower energy intakes [SMD - 0.98 (- 1.74, - 0.22); p = 0.011], and lower hunger perceptions in the fasted [SMD - 1.00 (- 1.54, - 0.46); p < 0.001] and postprandial states [SMD - 0.31, (- 0.64, 0.02); p = 0.064]. Higher circulating concentrations of insulin, leptin, cholecystokinin and peptide-YY accord with reduced appetite and energy intakes in healthy older adults. Interventions to reduce circulating levels of these hormones may be beneficial for combatting the anorexia of ageing.
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Appetite and energy intake responses to breakfast consumption and carbohydrate supplementation in hypoxia.
Griffiths, A, Deighton, K, Shannon, OM, Boos, C, Rowe, J, Matu, J, King, R, O'Hara, JP
Appetite. 2020;:104564
Abstract
PURPOSE The purpose of experiment one was to determine the appetite, acylated ghrelin and energy intake response to breakfast consumption and omission in hypoxia and normoxia. Experiment two aimed to determine the appetite, acylated ghrelin and energy intake response to carbohydrate supplementation after both breakfast consumption and omission in hypoxia. METHODS In experiment one, twelve participants rested and exercised once after breakfast consumption and once after omission in normobaric hypoxia (4300 m: FiO2 ~11.7%) and normoxia. In experiment two, eleven participants rested and exercised in normobaric hypoxia (4300 m: FiO2 ~11.7%), twice after consuming a high carbohydrate breakfast and twice after breakfast omission. Participants consumed both a carbohydrate (1.2g·min-1 glucose) and a placebo beverage after breakfast consumption and omission. Measures of appetite perceptions and acylated ghrelin were taken at regular intervals throughout both experiments and an ad-libitum meal was provided post-exercise to quantify energy intake. RESULTS Breakfast consumption had no significant effect on post exercise energy intake or acylated ghrelin concentrations, despite reductions in appetite perceptions. As such, breakfast consumption increased total trial energy intake compared with breakfast omission in hypoxia (7136 ± 2047 kJ vs. 5412 ± 1652 kJ; p = 0.02) and normoxia (9276 ± 3058 vs. 6654 ± 2091 kJ; p < 0.01). Carbohydrate supplementation had no effect on appetite perceptions or acylated ghrelin concentrations after breakfast consumption or omission. As such, carbohydrate supplementation increased total energy intake after breakfast consumption (10222 ± 2831 kJ vs. 7695 ± 1970 kJ p < 0.01) and omission (8058 ± 2574 kJ vs. 6174 ± 2222 kJ p = 0.02). CONCLUSION Both breakfast consumption and carbohydrate supplementation provide beneficial dietary interventions for increasing energy intake in hypoxic conditions.
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Response: Commentary on the effects of hypoxia on energy substrate use during exercise.
Griffiths, A, Shannon, O, Matu, J, King, R, Deighton, K, O'Hara, JP
Journal of the International Society of Sports Nutrition. 2019;(1):61
Abstract
BACKGROUND A recent commentary has been published on our meta-analysis, which investigated substrate oxidation during exercise matched for relative intensities in hypoxia compared with normoxia. Within this commentary, the authors proposed that exercise matched for absolute intensities in hypoxia compared with normoxia, should have been included within the analysis, as this model provides a more suitable experimental design when considering nutritional interventions in hypoxia. MAIN BODY Within this response, we provide a rationale for the use of exercise matched for relative intensities in hypoxia compared with normoxia. Specifically, we argue that this model provides a physiological stimulus replicable of real world situations, by reducing the absolute workload undertaken in hypoxia. Further, the use of exercise matched for relative intensities isolates the metabolic response to hypoxia, rather than the increased relative exercise intensity experienced in hypoxia when utilising exercise matched for absolute intensities. In addition, we also report previously unpublished data analysed at the time of the original meta-analysis, assessing substrate oxidation during exercise matched for absolute intensities in hypoxia compared with normoxia. CONCLUSION An increased reliance on carbohydrate oxidation was observed during exercise matched for absolute intensities in hypoxia compared with normoxia. These data now provide a comparable dataset for the use of researchers and practitioners alike in the design of nutritional interventions for relevant populations.
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A single day of mixed-macronutrient overfeeding does not elicit compensatory appetite or energy intake responses but exaggerates postprandial lipaemia during the next day in healthy young men.
Deighton, K, King, AJ, Matu, J, Shannon, OM, Whiteman, O, Long, A, Huby, MD, Sekula, M, Holliday, A
The British journal of nutrition. 2019;(8):945-954
Abstract
Discrete episodes of overconsumption may induce a positive energy balance and impair metabolic control. However, the effects of an ecologically relevant, single day of balanced macronutrient overfeeding are unknown. Twelve healthy men (of age 22 (sd 2) years, BMI 26·1 (sd 4·2) kg/m2) completed two 28 h, single-blind experimental trials. In a counterbalanced repeated measures design, participants either consumed their calculated daily energy requirements (energy balance trial (EB): 10 755 (sd 593) kJ) or were overfed by 50 % (overfeed trial (OF): 16 132 (sd 889) kJ) under laboratory supervision. Participants returned to the laboratory the next day, after an overnight fast, to complete a mixed-meal tolerance test (MTT). Appetite was not different between trials during day 1 (P>0·211) or during the MTT in the fasted or postprandial state (P>0·507). Accordingly, plasma acylated ghrelin, total glucagon-like peptide-1 and total peptide YY concentrations did not differ between trials during the MTT (all P>0·335). Ad libitum energy intake, assessed upon completion of the MTT, did not differ between trials (EB 6081 (sd 2260) kJ; OF 6182 (sd 1960) kJ; P=0·781). Plasma glucose and insulin concentrations were not different between trials (P>0·715). Fasted NEFA concentrations were lower in OF compared with EB (P=0·005), and TAG concentrations increased to a greater extent on OF than on EB during the MTT (P=0·009). The absence of compensatory changes in appetite-related variables after 1 d of mixed macronutrient overfeeding highlights the limited physiological response to defend against excess energy intake. This supports the concept that repeated discrete episodes of overconsumption may promote weight gain, while elevations in postprandial lipaemia may increase CVD risk.
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The effects of environmental hypoxia on substrate utilisation during exercise: a meta-analysis.
Griffiths, A, Shannon, OM, Matu, J, King, R, Deighton, K, O'Hara, JP
Journal of the International Society of Sports Nutrition. 2019;(1):10
Abstract
BACKGROUND A better understanding of hypoxia-induced changes in substrate utilisation can facilitate the development of nutritional strategies for mountaineers, military personnel and athletes during exposure to altitude. However, reported metabolic responses are currently divergent. As such, this systematic review and meta-analysis aims to determine the changes in substrate utilisation during exercise in hypoxia compared with normoxia and identify study characteristics responsible for the heterogeneity in findings. METHODS A total of six databases (PubMed, the Cochrane Library, MEDLINE, SPORTDiscus, PsychINFO, and CINAHL via EBSCOhost) were searched for published original studies, conference proceedings, abstracts, dissertations and theses. Studies were included if they evaluated respiratory exchange ratio (RER) and/or carbohydrate or fat oxidation during steady state exercise matched for relative intensities in normoxia and hypoxia (normobaric or hypobaric). A random-effects meta-analysis was performed on outcome variables. Meta-regression analysis was performed to investigate potential sources of heterogeneity. RESULTS In total, 18 studies were included in the meta-analysis. There was no significant change in RER during exercise matched for relative exercise intensities in hypoxia, compared with normoxia (mean difference: 0.01, 95% CI: -0.02 to 0.05; n = 31, p = 0.45). Meta-regression analysis suggests that consumption of a pre-exercise meal (p < 0.01) and a higher exercise intensity (p = 0.04) when exposed to hypoxia may increase carbohydrate oxidation compared with normoxia. CONCLUSIONS Exposure to hypoxia did not induce a consistent change in the relative contribution of carbohydrate or fat to the total energy yield during exercise matched for relative intensities, compared with normoxia. The direction of these responses appears to be mediated by the consumption of a pre-exercise meal and exercise intensity.