Higher protein intake during resistance training does not potentiate strength, but modulates gut microbiota, in middle-aged adults: a randomized control trial

Influence of dietary protein and fiber intake interactions on the human gut microbiota composition and function: a systematic review and network meta-analysis of randomized controlled trials

Quantity and source of dietary protein intakes impact the gut microbiota differently. However, these effects have not been systematically studied. This review aimed to investigate these effects whilst controlling for fiber intake. Seven databases were searched, with 50 and 15 randomized controlled trials selected for the systematic review and network meta-analysis respectively. Most gut microbiota-related outcomes showed no significant differences between different protein and fiber intake combinations. Compared to Normal Protein, High Fiber intakes, High Protein, Low Fiber (HPLF) intakes showed greater fecal valerate (SMD = 0.79, 95% CrI: 0.35, 1.24) and plasma trimethylamine N-oxide (TMAO) (SMD = 2.90, 95% CrI: 0.16, 5.65) levels. HPLF intakes also showed greater fecal propionate (SMD = 0.49, 95% CrI: 0.02, 1.07) and valerate (SMD = 0.79, 95% CrI: 0.31, 1.28) levels compared to High Protein, High Fiber intakes. Greater plasma TMAO levels were observed with greater animal protein intakes. Overall, protein quantity and source do not generally alter the gut microbiota composition, although protein quantity can influence microbiota function via modulations in proteolytic fermentation. Both protein and fiber intake should be considered when assessing the impact of dietary protein on the gut microbiota. This trial was registered at PROSPERO (CRD42023391270).

Do high-protein diets have the potential to reduce gut barrier function in a sex-dependent manner?

PURPOSE

Impaired gut barrier function is associated with systemic inflammation and many chronic diseases. Undigested dietary proteins are fermented in the colon by the gut microbiota which produces nitrogenous metabolites shown to reduce barrier function in vitro. With growing evidence of sex-based differences in gut microbiotas, we determined whether there were sex by dietary protein interactions which could differentially impact barrier function via microbiota modification.

METHODS

Fermentation systems were inoculated with faeces from healthy males (n = 5) and females (n = 5) and supplemented with 0.9 g of non-hydrolysed proteins sourced from whey, fish, milk, soya, egg, pea, or mycoprotein. Microbial populations were quantified using fluorescence in situ hybridisation with flow cytometry. Metabolite concentrations were analysed using gas chromatography, solid phase microextraction coupled with gas chromatography-mass spectrometry and ELISA.

RESULTS

Increased protein availability resulted in increased proteolytic Bacteroides spp (p < 0.01) and Clostridium coccoides (p < 0.01), along with increased phenol (p < 0.01), p-cresol (p < 0.01), indole (p = 0.018) and ammonia (p < 0.01), varying by protein type. Counts of Clostridium cluster IX (p = 0.03) and concentration of p-cresol (p = 0.025) increased in males, while females produced more ammonia (p = 0.02), irrespective of protein type. Further, we observed significant sex-protein interactions affecting bacterial populations and metabolites (p < 0.005).

CONCLUSIONS

Our findings suggest that protein fermentation by the gut microbiota in vitro is influenced by both protein source and the donor's sex. Should these results be confirmed through human studies, they could have major implications for developing dietary recommendations tailored by sex to prevent chronic illnesses.

Becoming a World Champion Powerlifter at 71 Years of Age: It Is Never Too Late to Start Exercising

This case study assessed body composition, muscle strength, cardiorespiratory fitness, and metabolic health of the present female world champion powerlifter in the 70+ age category who started resistance exercise training at 63 years of age with no prior experience with structured exercise training. Measures of body composition (magnetic resonance imaging, computed tomography, and dual-energy X-ray absorptiometry scanning, leg volume); strength (one-repetition maximum leg press and extension, maximum voluntary contraction, and handgrip strength); physical function (short physical performance battery); cardiorespiratory fitness (peak oxygen consumption); and metabolic health (oral glucose tolerance test) were assessed. In addition, a muscle biopsy was collected to assess muscle fiber type distribution and cross-sectional area (CSA). Where possible, data were compared with previously (un)published sex- and age-matched data using z scores. Skeletal muscle mass index was calculated by dividing limb muscle mass by height squared. Data from the control groups are expressed as mean ± 95% confidence interval. Our participant (age: 71 years; body mass: 64.5 kg; body mass index: 27.6 kg/m2) reported a good bone mineral density of 1.09 g/cm2 (T score between -1 and +1) and very low values of abdominal and organ body fat (i.e., between 20% and 70% lower compared with a reference group of postmenopausal women). In addition, she showed a 33% greater skeletal muscle mass index when compared with healthy, older female control subjects (7.9 vs. 5.9 [5.7-6.2] kg/m2; n = 61) as well as 37% greater muscle quadriceps CSA (63.8 vs. 46.6 [44.5-48.7] cm2; n = 48) and 46% greater Type II muscle fiber CSA (4,536 vs. 3,097 [2,707-3,488] μm2; n = 19). Absolute leg press muscle strength was 36% greater (190 vs. 140 [132-147] kg; n = 30) and handgrip strength was 33% greater (33 vs. 25 [23-26] kg; n = 48) when compared with healthy, age-matched controls. In conclusion, even for resistance exercise naïve individuals, starting exercise at an advanced age can lead to improvements in body composition and muscle strength allowing older adults to reduce the risk for developing metabolic syndrome, live independently, and even compete at a world class level.

Summatory Effects of Anaerobic Exercise and a 'Westernized Athletic Diet' on Gut Dysbiosis and Chronic Low-Grade Metabolic Acidosis

Anaerobic exercise decreases systemic pH and increases metabolic acidosis in athletes, altering the acid-base homeostasis. In addition, nutritional recommendations advising athletes to intake higher amounts of proteins and simple carbohydrates (including from sport functional supplements) could be detrimental to restoring acid-base balance. Here, this specific nutrition could be classified as an acidic diet and defined as 'Westernized athletic nutrition'. The maintenance of a chronic physiological state of low-grade metabolic acidosis produces detrimental effects on systemic health, physical performance, and inflammation. Therefore, nutrition must be capable of compensating for systemic acidosis from anaerobic exercise. The healthy gut microbiota can contribute to improving health and physical performance in athletes and, specifically, decrease the systemic acidic load through the conversion of lactate from systemic circulation to short-chain fatty acids in the proximal colon. On the contrary, microbial dysbiosis results in negative consequences for host health and physical performance because it results in a greater accumulation of systemic lactate, hydrogen ions, carbon dioxide, bacterial endotoxins, bioamines, and immunogenic compounds that are transported through the epithelia into the blood circulation. In conclusion, the systemic metabolic acidosis resulting from anaerobic exercise can be aggravated through an acidic diet, promoting chronic, low-grade metabolic acidosis in athletes. The individuality of athletic training and nutrition must take into consideration the acid-base homeostasis to modulate microbiota and adaptive physiological responses.

Short-term resistance training combined with cheese supplementation can optimize body parameters and intestinal microbiota in healthy adults

Background

Resistance training (RT) and protein supplementation have beneficial effects on the human body. However, it is unknown if RT's health-promoting benefits are enhanced by food-borne protein, such as cheese supplements. This study investigated at how the body composition, lipid profile, muscle strength and intestinal microbiota changed following four weeks of RT combined with cheese supplementation.

Methods

Thirty-five male and untrained adults were divided into 4 groups [control group (CON), low-dose group (LG), medium-dose group (MG), and high-dose group (HG)] and underwent a 4-week RT (3 times/week) in combination with cheese supplementation. Participants received 108 g (LG), 216 g (MG), or 324 g (HG) of cheese on the day of RT, and each serving (108 g) of cheese contained 6.7 g of food-borne protein. The RT program was a whole-body program with movements such as chest presses, leg presses, seated rowing, knee extensions and triceps pushdown. The exercise consisted of 3 sets of 8-12 repetitions at 70%RM, with a 120-s break in between. Body parameters (body composition, lipid profile and muscle strength) were assessed at baseline and after the 4 weeks of the intervention. The feces sample was taken every weekend. A two-way (group × time) mixed-design ANOVA was used to examine the body parameters. Independent one-way ANOVA was used to analyze the differences between groups in baseline characteristics and different values of each parameter.

Results

HDL-C level was higher in MG than in LG. In comparison to LG, MG had lower levels of total cholesterol, low-density lipoprotein cholesterol, body weight, body mass index, body fat mass and body fat percentage. However, there was no difference in muscle strength between in the four groups. The abundance of Actinobacteria was higher in LG and Erysipelotrichaceae was lower in MG and HG.

Conclusion

The findings suggest that cheese could be a readily available food-borne protein supplement to enhance the beneficial effects of RT on health. It may improve body composition and lipid profile by altering the proportion of intestinal microbiota. During the 4-week RT intervention, 13.4 g of foodborne protein in the form of cheese 3 times per week was the ideal dosage.

Comparative Efficacy of Different Protein Supplements on Muscle Mass, Strength, and Physical Indices of Sarcopenia among Community-Dwelling, Hospitalized or Institutionalized Older Adults Undergoing Resistance Training: A Network Meta-Analysis of Randomized Controlled Trials

Aging-related sarcopenia exerts harmful impacts on muscle mass, strength, and physical mobility. Protein supplementation has been demonstrated to augment efficacy of resistance training (RT) in elderly. This study compared the relative effects of different protein supplements on muscle mass, strength, and mobility outcomes in middle-aged and older individuals undergoing RT. A comprehensive search of online databases was performed to identify randomized controlled trials (RCTs) examining the efficacy of protein supplement plus RT in untrained community-dwelling adults, hospitalized, or institutionalized residents who suffered acute or chronic health conditions. Network meta-analysis (NMA) was performed using a frequentist method for all analyses. Treatment effects for main outcomes were expressed as standard mean difference (SMD) with 95% confidence interval (CI). We used the surface-under-the cumulative-ranking (SUCRA) scores to rank probabilities of effect estimation among all identified treatments. Meta-regression analyses were performed to identify any relevant moderator of the treatment efficacy and results were expressed as β with 95% credible interval (CrI). We finally included 78 RCTs (5272 participants) for analyses. Among the six protein sources identified in this NMA, namely whey, milk, casein, meat, soy, and peanut, whey supplement yielded the most effective treatments augmenting efficacy of RT on muscle mass (SMD = 1.29, 95% CI: 0.96, 1.62; SUCRA = 0.86), handgrip strength (SMD = 1.46, 95% CI: 0.92, 2.00; SUCRA = 0.85), and walking speed (SMD = 0.73, 95% CI: 0.39, 1.07; SUCRA = 0.84). Participant's health condition, sex, and supplementation dose were significant factors moderating the treatment efficacy on muscle mass (β = 0.74; 95% CrI: 0.22, 1.25), handgrip strength (β = -1.72; 95% CrI: -2.68, -0.77), and leg strength (β = 0.76; 95% CrI: 0.06, 1.47), respectively. Our findings suggest whey protein yields the optimal supplements to counter sarcopenia in older individuals undergoing RT.

The effects of 6 wk of resistance training on the gut microbiome and cardiometabolic health in young adults with overweight and obesity

Obesity is a known risk factor for the development of insulin resistance and other cardiometabolic disorders. Recently, the gut microbiome has been associated with obesity and subsequent health complications. Exercise has been regularly utilized as a therapeutic intervention to treat obesity and its associated comorbidities. This study examined the effects of a 6-wk resistance training exercise program (RT) on the diversity, composition, and metabolic pathways of the gut microbiome. Sedentary young adults (age 18-35 yr) with overweight and obesity (BMI 25-45 kg/m2) were recruited to participate in this randomized controlled trial. Participants were randomized to RT (n = 16), a 6-wk resistance training program (3 days/wk), or control (CT) (n = 16), a nonexercising control. Main outcomes of the study included gut microbiome measures (taxa abundances, diversity, and predicted function) and cardiometabolic outcomes [blood pressure (BP) and glucoregulation]. Increased abundances of Roseburia, a short-chain fatty acid (SCFA) producer were observed over 6 wk (W6) with RT compared with CT (group × week, P < 0.05, q < 0.25). RT also induced marginal alterations in predicted microbial metabolic and cell motility pathways compared with CT (group × week, P < 0.05, q < 0.25). However, RT did not significantly impact overall microbial diversity. Furthermore, RT resulted in higher quantitative insulin-sensitivity check index (QUICKI) and lower diastolic BP at W6 compared with CT [baseline (BL)-adjusted P < 0.05]. RT had mixed effects on the gut microbiome. Although RT increased abundances of Roseburia and induced minor changes in microbial pathways, it is important to consider these changes in the context of the overall stability observed in the microbiome composition.NEW & NOTEWORTHY Resistance training induces mixed changes in the gut microbiome, including an increase in the abundances of the Roseburia genus and minor alterations in microbial pathways. However, it is vital to interpret these changes in light of the broader context, where we observe stability in the overall microbiome composition. This stability may be attributed to the microbiome's resilience, demonstrating its capacity to withstand short-term physiological stressors.

The Relationship between the Source of Dietary Animal Fats and Proteins and the Gut Microbiota Condition and Obesity in Humans

The relationship between gut microbiota and obesity is well documented in humans and animal models. Dietary factors can change the intestinal microbiota composition and influence obesity development. However, knowledge of how diet, metabolism, and intestinal microbiota interact and modulate energy metabolism and obesity development is still limited. Epidemiological studies show a link between consuming dietary proteins and fats from specific sources and obesity. Animal studies confirm that proteins and fats of different origins differ in their ability to prevent or induce obesity. Protein sources, such as meat, dairy products, vegetables, pulses, and seafood, vary in their amino acid composition. In addition, the type and level of other factors, such as fatty acids or persistent organic pollutants, vary depending on the source of dietary protein. All these factors can modulate the intestinal microbiota composition and, thus, may influence obesity development. This review summarizes selected evidence of how proteins and fats of different origins affect energy efficiency, obesity development, and intestinal microbiota, linking protein and fat-dependent changes in the intestinal microbiota with obesity.

Identification of three bacterial species associated with increased appendicular lean mass: the HUNT study

Appendicular lean mass (ALM) associates with mobility and bone mineral density (BMD). While associations between gut microbiota composition and ALM have been reported, previous studies rely on relatively small sample sizes. Here, we determine the associations between prevalent gut microbes and ALM in large discovery and replication cohorts with information on relevant confounders within the population-based Norwegian HUNT cohort (n = 5196, including women and men). We show that the presence of three bacterial species - Coprococcus comes, Dorea longicatena, and Eubacterium ventriosum - are reproducibly associated with higher ALM. When combined into an anabolic species count, participants with all three anabolic species have 0.80 kg higher ALM than those without any. In an exploratory analysis, the anabolic species count is positively associated with femoral neck and total hip BMD. We conclude that the anabolic species count may be used as a marker of ALM and BMD. The therapeutic potential of these anabolic species to prevent sarcopenia and osteoporosis needs to be determined.

Sex-based comparisons of muscle cellular adaptations after 10 weeks of progressive resistance training in middle-aged adults

Resistance training combined with adequate protein intake supports skeletal muscle strength and hypertrophy. These adaptations are supported by the action of muscle stem cells (MuSCs), which are regulated, in part, by fibro-adipogenic progenitors (FAPs) and circulating factors delivered through capillaries. It is unclear if middle-aged males and females have similar adaptations to resistance training at the cellular level. To address this gap, 27 (13 males, 14 females) middle-aged (40-64 yr) adults participated in 10 wk of whole body resistance training with dietary counseling. Muscle biopsies were collected from the vastus lateralis pre- and posttraining. Type II fiber cross-sectional area increased similarly with training in both sexes (P = 0.014). MuSC content was not altered with training; however, training increased PDGFRα⁺/CD90⁺ FAP content (P < 0.0001) and reduced PDGFRα⁺/CD90^- FAP content (P = 0.044), independent of sex. The number of CD31⁺ capillaries per fiber also increased similarly in both sexes (P < 0.05). These results suggest that muscle fiber hypertrophy, stem/progenitor cell, and capillary adaptations are similar between middle-aged males and females in response to whole body resistance training.NEW & NOTEWORTHY We demonstrate that resistance training-induced increases in fiber hypertrophy, FAP content, and capillarization are similar between middle-aged males and females.

Intestinal microbiome in normal ageing, frailty and cognition decline

PURPOSE OF REVIEW

The intestinal microbiome modulates the risk of several age-related chronic diseases and syndromes, including frailty and neurodegenerative diseases. Herein we provided an update on the influence of gut microbiota on physical and cognitive performance in older age and suggest microbiota-targeted interventions for healthy ageing.

RECENT FINDINGS

Low uniqueness index of the gut microbiome and high representation of Bacteroides are independently associated with mortality in older individuals, while the centenarian microbiome is characterized by high abundance of Lactobacilli and Bifidobacteria . Frailty syndrome, sarcopenia and cognitive decline are associated with reduced faecal microbiota biodiversity, reduced abundance of bacteria able to synthetize short-chain fatty acids (SCFA), including Faecalibacterium prausnitzii , and reduced faecal butyrate levels. Dietary intervention, especially involving Mediterranean diet, and exercise training seem to be associated with improved biodiversity of the microbiota, increased capacity of SCFA synthesis and, probably, protection against the onset of frailty and cognitive decline.

SUMMARY

The gut microbiota biodiversity and composition may reflect the different ageing trajectory, but further research is needed to understand potential independent and combined effects of environmental and lifestyle factors in older adults, especially from a clinical point of view.

Gut microbiota and meat quality

Sustainable meat production is important to providing safe and quality protein sources for humans worldwide. Intensive artificial selection and high energy input into the diet of many commercial animals for the last decade has significantly increased the daily gain of body weight and shortened the raising period, but unexpectedly decreased the meat quality. The gastrointestinal tract of animals harbors a diverse and complex microbial community that plays a vital role in the digestion and absorption of nutrients, immune system development, pathogen exclusion, and meat quality. Fatty acid composition and oxidative stress in adipose and muscle tissue influences meat quality in livestock and poultry. Recent studies showed that nutraceuticals are receiving increased attention, which could alter the intestinal microbiota and regulate the fat deposition and immunity of hosts to improve their meat quality. Understanding the microbiota composition, the functions of key bacteria, and the host-microbiota interaction is crucial for the development of knowledge-based strategies to improve both animal meat quality and host health. This paper reviews the microorganisms that affect the meat quality of livestock and poultry. A greater understanding of microbial changes that accompany beneficial dietary changes will lead to novel strategies to improve livestock and poultry meat product quality.

Muscle strength after resistance training correlates to mediators of muscle mass and mitochondrial respiration in middle-aged adults

Skeletal muscle aging is a multi-dimensional pathology of atrophy, reduced strength, and oxidative damage. While some molecular targets may mediate both hypertrophic and oxidative adaptations in muscle, their responsiveness in humans and relationship with functional outcomes like strength remain unclear. Promising therapeutic targets to combat muscle aging like apelin, vitamin D receptor (VDR), and spermine oxidase (SMOX) have been investigated in preclinical models but the adaptive response in humans is not well defined. In an exploratory investigation, we examined how strength gains with resistance training relate to regulators of both muscle mass and oxidative function in middle-aged adults. Forty-one middle-aged adults (18M, 23F; 50±7y; 27.8±3.7kg/m²; mean±SD) participated in a 10-week resistance training intervention. Muscle biopsies and plasma were sampled at baseline and post-intervention. High-resolution fluo-respirometry was performed on a subset of muscle tissue. Apelin signaling (plasma apelin, P=0.002; Apln mRNA, P<0.001; apelin receptor mRNA Aplnr, P=0.001) increased with resistance training. Muscle Vdr mRNA (P=0.007) and Smox mRNA (P=0.027) were also upregulated after the intervention. Mitochondrial respiratory capacity increased (V_max, oxidative phosphorylation, and uncoupled electron transport system, P<0.050), yet there were no changes in ADP sensitivity (K_m P=0.579), hydrogen peroxide emission (P=0.469), nor transcriptional signals for mitochondrial biogenesis (nuclear respiratory factor 2, Gapba P=0.766) and mitofusion (mitochondrial dynamin like GTPase, Opa1 P=0.072). Muscular strength with resistance training positively correlated to Apln, Aplnr, Vdr, and Smox transcriptional adaptations, as well as mitochondrial respiratory capacity (unadjusted P<0.050, r=0.400-0.781). Further research is required to understand the interrelationships of these targets with aged muscle phenotype.

Cathepsin B and Muscular Strength are Independently Associated with Cognitive Control

Although muscular strength has been linked to greater cognitive function across different cognitive domains, the mechanism(s) through which this occurs remain(s) poorly understood. Indeed, while an emerging body of literature suggests peripheral myokines released from muscular contractions may play a role in this relationship, additional research is needed to understand this link. Accordingly, this study sought to compare the influences of a particular myokine, Cathepsin B (CTSB), and muscular strength on hippocampal-dependent relational memory and cognitive control in 40 adults (age = 50.0±7.3 yrs). Overnight fasted venous blood draws were taken to assess plasma CTSB and muscular strength was assessed as maximal isokinetic strength testing using a Biodex dynamometer. Cognitive performance was assessed using a Spatial Reconstruction Task to assess relational memory and a modified Flanker task to assess cognitive control. Neuroelectric function for cognitive control was assessed using event-related potentials (ERPs) recorded during the Flanker task. Initial bivariate correlational analyses revealed that neither sex, age, lean body mass, or muscular strength was associated with CTSB. However, CTSB was inversely associated with reaction time and fractional peak latency of the P3 component of the Flanker task. Muscular strength was also inversely associated with reaction time and positively associated with relational memory performance. However, the influence of muscular strength on relational memory did not persist following adjustment for covariates. Greater circulating CTSB was selectively associated with greater cognitive control as well as faster information processing speed. These findings are the first to link circulating CTSB to both cognitive control and neuroelectric function. Future intervention studies are needed to examine the effects of changes in muscular strength, circulating myokines, and different domains of cognitive function.

Resistance and Endurance Exercise Training Induce Differential Changes in Gut Microbiota Composition in Murine Models

Background: The effect of resistance training on gut microbiota composition has not been explored, despite the evidence about endurance exercise. The aim of this study was to compare the effect of resistance and endurance training on gut microbiota composition in mice.

Methods: Cecal samples were collected from 26 C57BL/6N mice, divided into three groups: sedentary (CTL), endurance training on a treadmill (END), and resistance training on a vertical ladder (RES). After 2 weeks of adaption, mice were trained for 4 weeks, 5 days/week. Maximal endurance and resistance capacity test were performed before and after training. Genomic DNA was extracted and 16S Ribosomal RNA sequenced for metagenomics analysis. The percentages for each phylum, class, order, family, or genus/species were obtained using an open-source bioinformatics pipeline.

Results: END showed higher diversity and evenness. Significant differences among groups in microbiota composition were only observed at genera and species level. END showed a significantly higher relative abundance of Desulfovibrio and Desulfovibrio sp., while Clostridium and C. cocleatum where higher for RES. Trained mice showed significantly lower relative abundance of Ruminococcus gnavus and higher of the genus Parabacteroides compared to CTL. We explored the relationship between relative taxa abundance and maximal endurance and resistance capacities after the training period. Lachnospiraceae and Lactobacillaceae families were negatively associated with endurance performance, while several taxa, including Prevotellaceae family, Prevotella genus, and Akkermansia muciniphila, were positively correlated. About resistance performance, Desulfovibrio sp. was negatively correlated, while Alistipes showed a positive correlation.

Conclusion: Resistance and endurance training differentially modify gut microbiota composition in mice, under a high-controlled environment. Interestingly, taxa associated with anti- and proinflammatory responses presented the same pattern after both models of exercise. Furthermore, the abundance of several taxa was differently related to maximal endurance or resistance performance, most of them did not respond to training.

Fueling Gut Microbes: A Review of the Interaction between Diet, Exercise, and the Gut Microbiota in Athletes

The athlete's goal is to optimize their performance. Towards this end, nutrition has been used to improve the health of athletes' brains, bones, muscles, and cardiovascular system. However, recent research suggests that the gut and its resident microbiota may also play a role in athlete health and performance. Therefore, athletes should consider dietary strategies in the context of their potential effects on the gut microbiota, including the impact of sports-centric dietary strategies (e.g., protein supplements, carbohydrate loading) on the gut microbiota as well as the effects of gut-centric dietary strategies (e.g., probiotics, prebiotics) on performance. This review provides an overview of the interaction between diet, exercise, and the gut microbiota, focusing on dietary strategies that may impact both the gut microbiota and athletic performance. Current evidence suggests that the gut microbiota could, in theory, contribute to the effects of dietary intake on athletic performance by influencing microbial metabolite production, gastrointestinal physiology, and immune modulation. Common dietary strategies such as high protein and simple carbohydrate intake, low fiber intake, and food avoidance may adversely impact the gut microbiota and, in turn, performance. Conversely, intake of adequate dietary fiber, a variety of protein sources, and emphasis on unsaturated fats, especially omega-3 (ɷ-3) fatty acids, in addition to consumption of prebiotics, probiotics, and synbiotics, have shown promising results in optimizing athlete health and performance. Ultimately, while this is an emerging and promising area of research, more studies are needed that incorporate, control, and manipulate all 3 of these elements (i.e., diet, exercise, and gut microbiome) to provide recommendations for athletes on how to "fuel their microbes."

Gut Microbiota, Microbial Metabolites and Human Physical Performance

Trillions of microbes inhabiting the gut modulate the metabolism of the host. Cross-sectional studies have reported associations between physical performance and the gut microbiota (GM). Physical activity seems to increase GM diversity and the abundance of certain health-beneficial microbes. We reviewed the evidence from longitudinal studies on the connection between physically active lifestyle or long-term exercise interventions and the GM. We made literature searches using databases of Web of Science and PubMed Medline to collect human studies showing or not the associations between the GM and exercise. Many controversies exist in the studies. However, the longitudinal studies show that frequently, medium-intensity endurance exercise has yielded most beneficial effects on the GM, but the results vary depending on the study population and exercise protocol. In addition, the literature shows that certain microbes own the potency to increase physical activity and performance. Generally, a physically active lifestyle and exercise associate with a “healthy” GM. However, in previously sedentary subjects, the exercise-induced improvements in the GM seem to disappear unless the active lifestyle is continued. Unfortunately, several studies are not controlled for the diet. Thus, in the future, more longitudinal studies on the GM and physical performance are needed, with detailed dietary information.

Intestinal dysfunction in chronic disease

PURPOSE OF REVIEW

This review will discuss recent studies showing that patients with chronic wasting diseases suffer from a variety of small intestinal impairments which might negatively impact the colonic microbiota and overall well-being. New insights will be addressed as well as novel approaches to assess intestinal function.

RECENT FINDINGS

Small intestinal dysfunction can enhance the amount and alter the composition of undigested food reaching the colon. As a result of reduced protein digestion and absorption, a large amount of undigested protein might reach the colon promoting the presence of pathogenic colonic bacteria and a switch from bacterial fiber fermentation to protein fermentation. While microbial metabolites of fiber fermentation, such as short-chain fatty acids (SCFA), are mainly considered beneficial for overall health, metabolites of protein fermentation, i.e. ammonia, branched SCFAs, hydrogen sulfide, polyamines, phenols, and indoles, can exert beneficial or deleterious effects on overall health. Substantial advances have been made in the assessment of small intestinal dysfunction in chronic diseases, but studies investigating the connection to colonic microbial metabolism are needed. A promising new stable isotope approach can enable the measurement of metabolite production by the colonic microbiota.

SUMMARY

Several studies have been conducted to assess intestinal function in chronic diseases. Impairments in intestinal barrier function, sugar absorption, protein digestion, and absorption, as well as small intestinal bacterial overgrowth were observed and possibly might negatively impact colonic bacterial metabolism. We suggest that improving these perturbations will improve overall patient health.

Early resistance training-mediated stimulation of daily muscle protein synthetic responses to higher habitual protein intake in middle-aged adults

KEY POINTS

The ingestion of protein potentiates the stimulation of myofibrillar protein synthesis rates after an acute bout of resistance exercise. Protein supplementation (eating above the protein Recommended Dietary Allowance) during resistance training has been shown to maximize lean mass and strength gains in healthy young and older adults. Here, contractile, oxidative, and structural protein synthesis were assessed in skeletal muscle in response to a moderate or higher protein diet during the early adaptive phase of resistance training in middle-aged adults. The stimulation of myofibrillar, mitochondrial or collagen protein synthesis rates during 0-3 weeks of resistance training is not further enhanced by a higher protein diet. These results show that moderate protein diets are sufficient to support the skeletal muscle adaptive response during the early phase of a resistance training programme.

ABSTRACT

Protein ingestion augments muscle protein synthesis (MPS) rates acutely after resistance exercise and can offset age-related loss in muscle mass. Skeletal muscle contains a variety of protein pools, such as myofibrillar (contractile), mitochondrial (substrate oxidation), and collagen (structural support) proteins, and the sensitivity to nutrition and exercise seems to be dependent on the major protein fraction studied. However, it is unknown how free-living conditions with high dietary protein density and habitual resistance exercise mediates muscle protein subfraction synthesis. Therefore, we investigated the effect of moderate (MOD: 1.06 ± 0.22 g kg^-1  day^-1 ) or high (HIGH: 1.55 ± 0.25 g kg^-1  day^-1 ) protein intake on daily MPS rates within the myofibrillar (MyoPS), mitochondrial (MitoPS) and collagen (CPS) protein fractions in middle-aged men and women (n = 20, 47 ± 1 years, BMI 28 ± 1 kg m^-2 ) during the early phase (0-3 weeks) of a dietary counselling-controlled resistance training programme. Participants were loaded with deuterated water, followed by daily maintenance doses throughout the intervention. Muscle biopsies were collected at baseline and after weeks 1, 2 and 3. MyoPS in the HIGH condition remained constant (P = 1.000), but MOD decreased over time (P = 0.023). MitoPS decreased after 0-3 weeks when compared to 0-1 week (P = 0.010) with no effects of protein intake (P = 0.827). A similar decline with no difference between groups (P = 0.323) was also observed for CPS (P = 0.007). Our results demonstrated that additional protein intake above moderate amounts does not potentiate the stimulation of longer-term MPS responses during the early stage of resistance training adaptations in middle-aged adults.