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The Influence of n-3PUFA Supplementation on Muscle Strength, Mass, and Function: A Systematic Review and Meta-Analysis.
Santo André, HC, Esteves, GP, Barreto, GHC, Longhini, F, Dolan, E, Benatti, FB
Advances in nutrition (Bethesda, Md.). 2023;14(1):115-127
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Omega 3 polyunsaturated fatty acids (n-3PUFA) are long-chain polyunsaturated fatty acids essential to human health. They play a role in cell membrane integrity, immune and inflammation regulation, cognition and neuromuscular function. As the human body cannot make these fatty acids, they need to be obtained through diet or supplementation. Regarding skeletal muscle, recent research showed that n-3PUFAs may increase the uptake of amino acids by increasing the membrane fluidity in the muscle, and by activating pathways that inhibit protein breakdown. This led to the hypothesis that n-3PUFAs may enhance muscle mass gain and strength. This systematic review sought to gather all available evidence about the impact of n-3PUFA supplementation on muscle mass, strength, and function in healthy young and older adults. The review included 14 studies with a total of 1443 participants. The authors found that n-3PUFA supplementation had no significant effect on muscle mass or muscle function in healthy young and older adults, however, a very small but significant positive effect was noted regarding muscle strength. In the discussion section, the authors explain the challenges of their review and how these findings integrate with the current understanding and other research findings. They concluded more research is needed to get a better insight into the effects of n-3PUFA on muscle function and the variants.
Abstract
The effects of omega 3 polyunsaturated fatty acids (n-3PUFA) supplementation on skeletal muscle are currently unclear. The purpose of this systematic review was to synthesize all available evidence regarding the influence of n-3PUFA supplementation on muscle mass, strength, and function in healthy young and older adults. Four databases were searched (Medline, Embase, Cochrane CENTRAL, and SportDiscus). Predefined eligibility criteria were determined according to Population, Intervention, Comparator, Outcomes, and Study Design. Only peer-reviewed studies were included. The Cochrane RoB2 Tool and the NutriGrade approach were used to access risk of bias and certainty in evidence. Effect sizes were calculated using pre-post scores and analyzed using a three-level, random-effects meta-analysis. When sufficient studies were available, subanalyses were performed in the muscle mass, strength, and function outcomes according to participant's age (<60 or ≥60 years), supplementation dosage (<2 or ≥2 g/day), and training intervention ("resistance training" vs. "none or other"). Overall, 14 individual studies were included, total 1443 participants (913 females; 520 males) and 52 outcomes measures. Studies had high overall risk of bias and consideration of all NutriGrade elements resulted in a certainty assessment of moderate meta-evidence for all outcomes. n-3PUFA supplementation had no significant effect on muscle mass (standard mean difference [SMD] = 0.07 [95% CI: -0.02, 0.17], P = 0.11) and muscle function (SMD = 0.03 [95% CI: -0.09, 0.15], P = 0.58), but it showed a very small albeit significant positive effect on muscle strength (SMD = 0.12 [95% CI: 0.006, 0.24], P = 0.04) in participants when compared with placebo. Subgroup analyses showed that age, supplementation dose, or cosupplementation alongside resistance training did not influence these responses. In conclusion, our analyses indicated that n-3PUFA supplementation may lead to very small increases in muscle strength but did not impact muscle mass and function in healthy young and older adults. To our knowledge, this is the first review and meta-analysis investigating whether n-3PUFA supplementation can lead to increases in muscle strength, mass, and function in healthy adults. Registered protocol: doi.org/10.17605/OSF.IO/2FWQT.
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High-protein diets and testosterone.
Whittaker, J
Nutrition and health. 2023;29(2):185-191
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High protein diets have been shown to have several benefits such as weight loss and the promotion of feeling fuller for longer following food. A recent study has however shown that testosterone levels are decreased in men who follow a high protein diet. This study aimed to summarise the data on high protein diets and testosterone. The results showed that diets with more than 3.4g/kg/day protein decreased total testosterone levels possibly due to the body adjusting its biochemistry to ensure that the excess protein in the diet is metabolised. Furthermore, inflammation in response to an increased amount of protein may suppress testosterone production. It was concluded that increased protein intake of more than 3.4g/kg/day drives the decrease in total testosterone in the body of men regardless of what happens to the level of carbohydrate and fat in the body. This study could be used by healthcare professionals to understand that high protein diets may decrease testosterone levels in men.
Abstract
A recent meta-analysis found low-carbohydrate, high-protein diets (> 3.4 g/kg of bodyweight/day) (g/kg/day) decreased men's total testosterone (∼5.23 nmol/L) [Whittaker and Harris (2022) Low-carbohydrate diets and men's cortisol and testosterone: systematic review and meta-analysis. Nutrition and Health. DOI: 10.1177/02601060221083079]. This finding has generated substantial discussion, however, it has often lacked clarity and context, with the term 'high-protein' being used unqualified. Firstly, diets < 3.4 g/kg/day are not associated with a consistent decrease in testosterone. Secondly, the average protein intake is ∼1.3 g/kg/day, conventional 'high-protein' diets are ∼1.8-3 g/kg/day and the vast majority of athletes are < 3.4 g/kg/day; meaning very few individuals will ever surpass 3.4 g/kg/day. To avoid such confusion in the future, the following definitions are proposed: very high (> 3.4 g/kg/day), high (1.9-3.4 g/kg/day), moderate (1.25-1.9 g/kg/day) and low (<1.25 g/kg/day). Using these, very high-protein diets (> 3.4 g/kg/day) appear to decrease testosterone, however high- and moderate-protein diets (1.25-3.4 g/kg/day) do not.
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Influence of methyl donor nutrients as epigenetic regulators in colorectal cancer: A systematic review of observational studies.
Chávez-Hidalgo, LP, Martín-Fernández-de-Labastida, S, M de Pancorbo, M, Arroyo-Izaga, M
World journal of gastroenterology. 2023;29(7):1219-1234
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Colorectal cancer (CRC) is the third most frequent type of cancer and yet has the second highest mortality rate in cancer patients worldwide. Hence there is an urgency to understand more about dietary and lifestyle factors that can help to prevent this type of cancer. It is known that folate has a preventive function in CRC, possibly due to its role in DNA methylation. Methylation is the addition of methyl groups to DNA, which influences gene expression and regulation. This systematic review investigated how folate and other dietary methyl groups and methyl influencers such as B vitamins and alcohol influence the development of CRC, whilst also considering various genetic variants in methyl-metabolising enzymes (polymorphisms). The analysis included a total of 19 case-control and cohort studies and highlighted that potential interactions between methyl donor nutrients, genetic variants, and alcohol influence CRC risk. For most, high levels of folate intake were considered a protective factor, while high alcohol consumption proved to be a risk factor. Yet these interactions appear to be complex, with gender, genetic variations and folate status appearing to contribute to variable and, in some cases, contradictory outcomes. The authors suggested in their findings that Vitamin B6, Vitamin B3 (Niacin), and alcohol may affect CRC by influencing its risk by acting on both the genetic code itself and the epigenetic factors that control gene activity. Further research is needed to better understand the complexity of these mechanisms, and to help clarify the influence of methyl group donors as epigenetic regulators of gene activity in CRC development.
Abstract
BACKGROUND Dietary methyl donors might influence DNA methylation during carcinogenesis of colorectal cancer (CRC). However, whether the influence of methyl donor intake is modified by polymorphisms in such epigenetic regulators is still unclear. AIM: To improve the current understanding of the molecular basis of CRC. METHODS A literature search in the Medline database, Reference Citation Analysis (https:// www.referencecitationanalysis.com/), and manual reference screening were performed to identify observational studies published from inception to May 2022. RESULTS A total of fourteen case-control studies and five cohort studies were identified. These studies included information on dietary methyl donors, dietary components that potentially modulate the bioavailability of methyl groups, genetic variants of methyl metabolizing enzymes, and/or markers of CpG island methylator phenotype and/or microsatellite instability, and their possible interactions on CRC risk. CONCLUSION Several studies have suggested interactions between methylenetetrahydrofolate reductase polymorphisms, methyl donor nutrients (such as folate) and alcohol on CRC risk. Moreover, vitamin B6, niacin, and alcohol may affect CRC risk through not only genetic but also epigenetic regulation. Identification of specific mechanisms in these interactions associated with CRC may assist in developing targeted prevention strategies for individuals at the highest risk of developing CRC.
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Life expectancy can increase by up to 10 years following sustained shifts towards healthier diets in the United Kingdom.
Fadnes, LT, Celis-Morales, C, Økland, JM, Parra-Soto, S, Livingstone, KM, Ho, FK, Pell, JP, Balakrishna, R, Javadi Arjmand, E, Johansson, KA, et al
Nature food. 2023;4(11):961-965
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The mortality rate is rising in the United Kingdom (UK) due to the poor quality dietary patterns among the general population. Public Health England and the UK government recommend the population eat a healthy balanced diet based on the Eatwell Guide. Adherence to the Eatwell Guide dietary pattern could reduce the mortality rate among the general population in the UK. This research estimated the benefits of sustainably changing the unhealthy dietary pattern to the Eatwell Guide or longevity-associated dietary pattern on life expectancy in the UK. Longevity-associated dietary pattern is based on a moderate consumption of whole grains, fruit, fish and white meat; a substantial consumption of dairy, vegetables, nuts and legumes; a comparatively low consumption of eggs, red meat and sugar-sweetened beverages; and a low consumption of refined grains and processed meat. The unhealthy dietary pattern included limited amounts of whole grains, vegetables, fruits, nuts, legumes, fish, milk and dairy, and white meat and high consumption of processed meat, eggs, refined grains and sugar-sweetened beverages. This peer-reviewed review used prospective population-based cohort data from the UK Biobank. In UK adults aged 40 years, the change from an unhealthy dietary pattern to the Eatwell guide added 8.9 years in males and 8.6 years in females to their life expectancy. Furthermore, sustained adherence to the Eatwell guide increased life expectancy up to 10.8 years in males and 10.4 years in females. Further robust studies are required to evaluate the correlation between life expectancy and different food groups due to the limitations of the current research. However, healthcare professionals can use the results of this research to develop health policies and to understand the beneficial effect of following the Eatwell Guide or longevity dietary pattern in increasing life expectancy in middle-aged men and women in the UK.
Abstract
Adherence to healthy dietary patterns can prevent the development of non-communicable diseases and affect life expectancy. Here, using a prospective population-based cohort data from the UK Biobank, we show that sustained dietary change from unhealthy dietary patterns to the Eatwell Guide dietary recommendations is associated with 8.9 and 8.6 years gain in life expectancy for 40-year-old males and females, respectively. In the same population, sustained dietary change from unhealthy to longevity-associated dietary patterns is associated with 10.8 and 10.4 years gain in life expectancy in males and females, respectively. The largest gains are obtained from consuming more whole grains, nuts and fruits and less sugar-sweetened beverages and processed meats. Understanding the contribution of sustained dietary changes to life expectancy can provide guidance for the development of health policies.
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Effect of Serum Lipid Profile on the Risk of Breast Cancer: Systematic Review and Meta-Analysis of 1,628,871 Women.
Nouri, M, Mohsenpour, MA, Katsiki, N, Ghobadi, S, Jafari, A, Faghih, S, Banach, M, Mazidi, M
Journal of clinical medicine. 2022;11(15)
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Elevated fats in the blood have been associated with an increased risk for breast cancer. However, exact relationships between which fats is still unclear. This systematic review and meta-analysis of 26 studies with 36,590 women aimed to investigate the relationship between fat in the blood and breast cancer risk. The results showed that high levels of high-density lipoprotein (HDL) in the blood decreased a woman’s risk of developing breast cancer, however other fats in the blood such as triglycerides, cholesterol and low-density lipoprotein had no relationship with breast cancer risk. It was concluded that low levels of HDL in the blood are related to an increased risk for breast cancer. This study could be used by healthcare professionals to understand that it is important to recommend exercise, which is a way of increasing HDL’s, in women who are at risk of breast cancer development.
Abstract
Dyslipidemia has been linked to breast cancer incidence. The aim of the present meta-analysis was to further investigate the relationship between the serum lipid profile and breast cancer risk. Databases such as PubMed, EMBASE, and Web of Sciences were searched up to the end of January 2021 using certain MeSH and non-MeSH keywords and combinations to extract related published articles. Twenty-six prospective studies involving 1,628,871 women, of whom 36,590 were diagnosed with breast cancer during the follow-up period met the inclusion criteria. A negative and significant association was found between the HDL-C level and the risk of breast cancer (relative risk (RR): 0.85, 95% CI: 0.72-0.99, I2: 67.6%, p = 0.04). In contrast, TG (RR: 1.02, 95% CI: 0.91-1.13, I2: 54.2%, p = 0.79), total cholesterol (TC) (RR: 0.98, 95% CI: 0.90-1.06, I2: 67.2%, p = 0.57), apolipoprotein A (ApoA) (RR: 0.96, 95% CI: 0.70-1.30, I2: 83.5%, p = 0.78) and LDL-C (RR: 0.93, 95% CI: 0.79-1.09, I2: 0%, p = 0.386) were not associated with breast cancer development. In studies adjusting for hormone use and physical activity, breast cancer risk was positively correlated with TC (RR: 1.05, 95% CI: 1.01-1.10). Similarly, TG was significantly related to breast cancer development after adjustment for baseline lipids (RR: 0.92, 95% CI: 0.85-0.99) and race (any races mentioned in each study) (RR: 1.80, 95% CI: 1.22-2.65). In the present meta-analysis, HDL-C was inversely related to breast cancer risk. Overall, data on the links between lipids and breast cancer are conflicting. However, there is increasing evidence that low HDL-C is related to an increased risk for this type of malignancy.
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The effects of conjugated linoleic acid supplementation on lipid profile in adults: A systematic review and dose-response meta-analysis.
Asbaghi, O, Ashtary-Larky, D, Naseri, K, Saadati, S, Zamani, M, Rezaei Kelishadi, M, Nadery, M, Doaei, S, Haghighat, N
Frontiers in nutrition. 2022;9:953012
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Elevated fats circulating in the blood has been shown to be a predictor for heart disease. Conjugated linoleic acid (CLA) is a type of fat that is found in the milk and meat of animals such as cows, sheep and goats. Although classed as a fat, when taken in a supplemental form, some studies have shown it to decrease circulating fats whereas others have shown no beneficial effects. This systematic review and meta-analysis of 56 randomised control trials aimed to explore the effects of CLA on circulating blood profiles. The results showed that CLA increased levels of cholesterols, which may contribute to heart disease, but also increased cholesterol which may help to prevent heart disease. It was concluded that CLA supplementation has little effect on fats in the blood. This study could be used by healthcare professionals to understand that there may be little utility in recommending a supplemental CLA for the management of heart disease.
Abstract
BACKGROUND The findings of trials investigating the effect of conjugated linoleic acid (CLA) administration on lipid profile are controversial. This meta-analysis of randomized controlled trials (RCTs) was performed to explore the effects of CLA supplementation on lipid profile. METHODS Two authors independently searched electronic databases including PubMed, Web of Science, and Scopus until March 2022, in order to find relevant RCTs. The random effects model was used to evaluate the mean and standard deviation. RESULTS In total, 56 RCTs with 73 effect sizes met the inclusion criteria and were eligible for the meta-analysis. CLA supplementation significantly alter triglycerides (TG) (WMD: 1.76; 95% CI: -1.65, 5.19), total cholesterols (TC) (WMD: 0.86; 95% CI: -0.42, 2.26), low-density lipoprotein cholesterols (LDL-C) (WMD: 0.49; 95% CI: -0.75, 2.74), apolipoprotein A (WMD: -3.15; 95% CI: -16.12, 9.81), and apolipoprotein B (WMD: -0.73; 95% CI: -9.87, 8.41) concentrations. However, CLA supplementation significantly increased the density lipoprotein cholesterol (HDL-C) (WMD: -0.40; 95% CI: -0.72, -0.07) concentrations. CONCLUSION CLA supplementation significantly improved HDL-C concentrations, however, increased concentrations of TG, TC, LDL-C, apolipoprotein A, and apolipoprotein B. SYSTEMATIC REVIEW REGISTRATION https://www.crd.york.ac.uk/prospero/#recordDetails, identifier: CRD42022331100.
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Western Dietary Pattern Antioxidant Intakes and Oxidative Stress: Importance During the SARS-CoV-2/COVID-19 Pandemic.
Trujillo-Mayol, I, Guerra-Valle, M, Casas-Forero, N, Sobral, MMC, Viegas, O, Alarcón-Enos, J, Ferreira, IM, Pinho, O
Advances in nutrition (Bethesda, Md.). 2021;12(3):670-681
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The Atlantic diet (AD), Mediterranean diet (MD) and diets which follow the American dietary guidelines (AmD) all supply enough nutrients for the body to stay healthy. However, during periods of viral pandemics, such as the Covid-19 pandemic, these diets may be inadequate for optimal resistance to infection. Furthermore, nutrient requirements may alter with age, stress, and health. This review paper aimed to discuss the three different diets and their suitability depending on age and physical and mental state. Supplementation during a pandemic was also discussed. When the body contracts viruses such as Covid-19, reactive oxygen species can accumulate resulting in oxidative stress which can damage the cells. Nutrients in the diet, which act as antioxidants may be of benefit, in this instance, however traditional balanced diets such as the AD, MD and AmD may be inadequate. In tandem with a balanced diet, supplementation may improve health. Zinc, vitamin A, selenium, vitamin D, vitamin C, and iron have been shown in research to improve the body’s response to viruses. It was concluded that the Covid-19 pandemic has caused severe infections, which can result in oxidative stress, increasing vulnerability to viral infections. Supplementing certain nutrients may be of benefit especially in vulnerable individuals. This study could be used by healthcare professionals to understand that a balanced diet is essential during viral pandemics, and it may be necessary to consider supplementation for high-risk individuals.
Abstract
The importance of balanced dietary habits, which include appropriate amounts of antioxidants to maintain the immune system, has become increasingly relevant during the current SARS-CoV-2/COVID-19 pandemic, because viral infections are characterized by high oxidative stress. Furthermore, the measures taken by governments to control the pandemic have led to increased anxiety, stress, and depression, which affect physical and mental health, all of which are influenced by nutritional status, diet, and lifestyle. The Mediterranean diet (MD), Atlantic diet (AD), and the Dietary Guidelines for Americans all provide the essential vitamins, minerals, and phenolic compounds needed to activate enzymatic and nonenzymatic antioxidant responses. However, viral pandemics such as the current COVID-19 crisis entail high oxidative damage caused by both the infection and the resultant social stresses within populations, which increases the probability and severity of infection. Balanced dietary patterns such as the MD and the AD are characterized by the consumption of fruit, vegetables, legumes, olive oil, and whole grains with low intakes of processed foods and red meat. For a healthy lifestyle in young adults, the MD in particular provides the required amount of antioxidants per day for vitamins D (0.3-3.8 μg), E (17.0 mg), C (137.2-269.8 mg), A (1273.3 μg), B-12 (1.5-2.0 μg), and folate (455.1-561.3 μg), the minerals Se (120.0 μg), Zn (11.0 mg), Fe (15.0-18.8 mg), and Mn (5.2-12.5 mg), and polyphenols (1171.00 mg) needed to maintain an active immune response. However, all of these diets are deficient in the recommended amount of vitamin D (20 μg/d). Therefore, vulnerable populations such as elders and obese individuals could benefit from antioxidant supplementation to improve their antioxidant response. Although evidence remains scarce, there is some indication that a healthy diet, along with supplemental antioxidant intake, is beneficial to COVID-19 patients.
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Plant-Based Foods and Their Bioactive Compounds on Fatty Liver Disease: Effects, Mechanisms, and Clinical Application.
Li, HY, Gan, RY, Shang, A, Mao, QQ, Sun, QC, Wu, DT, Geng, F, He, XQ, Li, HB
Oxidative medicine and cellular longevity. 2021;2021:6621644
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Fatty liver disease is the accumulation of fats and inflammation associated with poor dietary patterns. Plant-based foods have been recommended to manage this disease and this review aimed to highlight the most recent data on the mechanisms for this. Beyond their obvious capabilities of being low in fat, plant-based foods may contain naturally occurring compounds that can help alleviate fatty liver disease through improved inflammation, improved gut microbiota and cellular changes. In support of this, clinical benefits on fatty liver outcomes have been reported in the research. There may be safety issues with isolating certain natural compounds from plant-based foods, which requires more research, however plant-based foods is a promising therapy for fatty liver disease.
Abstract
Fatty liver disease (FLD), including nonalcoholic fatty liver disease (NAFLD) and alcoholic fatty liver disease (AFLD), is a serious chronic metabolic disease that affects a wide range of people. Lipid accumulation accompanied by oxidative stress and inflammation in the liver is the most important pathogenesis of FLD. The plant-based, high-fiber, and low-fat diet has been recommended to manage FLD for a long time. This review discusses the current state of the art into the effects, mechanisms, and clinical application of plant-based foods in NAFLD and AFLD, with highlighting related molecular mechanisms. Epidemiological evidence revealed that the consumption of several plant-based foods was beneficial to alleviating FLD. Further experimental studies found out that fruits, spices, teas, coffee, and other plants, as well as their bioactive compounds, such as resveratrol, anthocyanin, curcumin, and tea polyphenols, could alleviate FLD by ameliorating hepatic steatosis, oxidative stress, inflammation, gut dysbiosis, and apoptosis, as well as regulating autophagy and ethanol metabolism. More importantly, clinical trials confirmed the beneficial effects of plant-based foods on patients with fatty liver. However, several issues need to be further studied especially the safety and effective doses of plant-based foods and their bioactive compounds. Overall, certain plant-based foods are promising natural sources of bioactive compounds to prevent and alleviate fatty liver disease.
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An updated systematic review and meta-analysis on adherence to mediterranean diet and risk of cancer.
Morze, J, Danielewicz, A, Przybyłowicz, K, Zeng, H, Hoffmann, G, Schwingshackl, L
European journal of nutrition. 2021;60(3):1561-1586
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The development of cancer is associated with a number of risk factors, including smoking, obesity, sedentary lifestyles, alcohol consumption, infections, pollution, and dietary imbalances. Based on previous research, optimal consumption of fruits, vegetables, and whole grains, along with reduced consumption of red and processed meat, reduces cancer risk. According to this systematic review and meta-analysis, adherence to the Mediterranean diet is associated with lower cancer mortality and site-specific cancer development. A Mediterranean diet includes fruits, vegetables, nuts, legumes, fish, whole grains, extra virgin olive oil, and low amounts of red meat, processed meat, egg, and dairy, along with moderate amounts of red wine. According to this systematic review and meta-analysis, adherence to the Mediterranean diet reduces the risk of cancer mortality and the risk of developing cancers specific to the site, such as colorectal cancer, bladder cancer, gastric cancer, and lung cancer. Among the components of the Mediterranean diet, fruits, vegetables, and whole grains have been shown to reduce cancer risk. Bioactive substances found in Mediterranean diet components require additional robust studies to evaluate their benefits. A healthcare professional can use the results of this study to make clinical decisions and recommend therapeutic interventions to cancer patients.
Abstract
PURPOSE The aim of current systematic review was to update the body of evidence on associations between adherence to the Mediterranean diet (MedDiet) and risk of cancer mortality, site-specific cancer in the general population; all-cause, and cancer mortality as well as cancer reoccurrence among cancer survivors. METHODS A literature search for randomized controlled trials (RCTs), case-control and cohort studies published up to April 2020 was performed using PubMed and Scopus. Study-specific risk estimates for the highest versus lowest adherence to the MedDiet category were pooled using random-effects meta-analyses. Certainty of evidence from cohort studies and RCTs was evaluated using the NutriGrade scoring system. RESULTS The updated search revealed 44 studies not identified in the previous review. Altogether, 117 studies including 3,202,496 participants were enclosed for meta-analysis. The highest adherence to MedDiet was inversely associated with cancer mortality (RRcohort: 0.87, 95% CI 0.82, 0.92; N = 18 studies), all-cause mortality among cancer survivors (RRcohort: 0.75, 95% CI 0.66, 0.86; N = 8), breast (RRobservational: 0.94, 95% CI 0.90, 0.97; N = 23), colorectal (RRobservational: 0.83, 95% CI 0.76, 0.90; N = 17), head and neck (RRobservational: 0.56, 95% CI 0.44, 0.72; N = 9), respiratory (RRcohort: 0.84, 95% CI 0.76, 0.94; N = 5), gastric (RRobservational: 0.70, 95% CI 0.61, 0.80; N = 7), bladder (RRobservational: 0.87, 95% CI 0.76, 0.98; N = 4), and liver cancer (RRobservational: 0.64, 95% CI 0.54, 0.75; N = 4). Adhering to MedDiet did not modify risk of blood, esophageal, pancreatic and prostate cancer risk. CONCLUSION In conclusion, our results suggest that highest adherence to the MedDiet was related to lower risk of cancer mortality in the general population, and all-cause mortality among cancer survivors as well as colorectal, head and neck, respiratory, gastric, liver and bladder cancer risks. Moderate certainty of evidence from cohort studies suggest an inverse association for cancer mortality and colorectal cancer, but most of the comparisons were rated as low or very low certainty of evidence.
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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
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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:
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X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
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B: Systematic reviews including RCTs of limited number
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C: Non-randomized trials, observational studies, narrative reviews
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D: Case-reports, evidence-based clinical findings
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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.