Dietary protein and the intestinal microbiota: An understudied relationship

Increased dietary protein stimulates amino acid catabolism via the gut microbiota and secondary bile acid production

Excess amino acids from a protein-rich diet are mainly catabolized in the liver. However, it is still unclear to what extent the gut microbiota may be involved in the mechanisms governing this catabolism. Therefore, the aim of this study was to investigate whether consumption of different dietary protein concentrations induces changes in the taxonomy of the gut microbiota, which may contribute to the regulation of hepatic amino acid catabolism. Consumption of a high-protein diet caused overexpression of HIF-1α in the colon and increase in mitochondrial activity, creating a more anaerobic environment that was associated with changes in the taxonomy of the gut microbiota promoting an increase in the synthesis of secondary bile acids, increased secretion of pancreatic glucagon. This effect was demonstrated in pancreatic islets, where secondary bile acids stimulated the expression of the PC2 enzyme that promotes glucagon formation. The increase in circulating glucagon was associated with an induction of the expression of hepatic amino acid-degrading enzymes, an effect attenuated by antibiotics. Thus, high protein intake in mice and humans induced the increase of different species in the gut microbiota with the capacity to produce secondary bile acids leading to an increase in secondary bile acids and glucagon levels, promoting amino acid catabolism.

Beneficial impact of MTGase-modified fish gelatin on collagen supplementation in rats: Insights from serum metabolomics and gut microbiota

Sustained release technology facilitates precise regulation of active ingredient delivery, attenuating enzymatic degradation while optimizing bioavailability in malabsorptive conditions. Microbial transglutaminase (MTGase) catalyzes isopeptide bond formation via acyl transfer reactions, conferring resistance to gastrointestinal digestion. However, the in vivo sustained release potential of MTGase-modified fish gelatin (MTGase-modified-FG) remains uncertain. In this study, enzymatic modification was performed using MTGase at graded concentrations (0.00 % (Nor), 0.06 % (LD), 0.12 % (MD), and 0.21 % (HD)), with sustained release of collagen evaluated through pharmacokinetic analysis. The results indicated that the MTGase-modified-FG supplementation exhibited a dose-dependent sustained release, extending Tmax from 2.00 ± 0.00 h (Nor) to 5.33 ± 1.15 h (HD). Notably, suboptimal crosslinking (LD/MD) enhanced skin collagen deposition, whereas excessive modification (HD) induced malabsorptive phenomena that may be attributed to the presence of excessive isopeptide bonds. Metabolomic analysis identified MTGase-modified-FG modulated the serum metabolome in collagen-related metabolites (LysoPC, Lysine, succinate), mechanistically linked to choline metabolism in cancer and lysine catabolism. Additionally, the gut microbiota remodeling was modulated by the suppression of Ruminococcus and Blautia, as well as by the expansion of Faecalibaculum and Bifidobacterium at the genus level. RT-qPCR analysis indicated that MTGase-modified-FG enhanced collagen deposition via the TGF-β/Smads and MAPK/AP-1/MMP pathways in human dermal fibroblast cells. These findings suggest that MTGase-modified confers the sustained release properties to fish gelatin, and provides a new collagen supplementation strategy for individuals with malabsorption syndromes.

The Microbiota-Human Health Axis

Trillions of microorganisms play a pivotal role in maintaining health and preventing disease in humans. Their presence influences daily life, habits, energy levels, and pathologies. The present narrative review synthesized recent studies of microbial diversity across organ systems. The composition of the microbiota regulates the intestinal barrier, modulates the immune response, influences metabolism, and produces essential compounds such as short-chain fatty acids and neurotransmitters. Dysbiosis is associated with numerous pathologies, including metabolic, autoimmune, neurodegenerative, and cardiovascular diseases. The microbiota is key to maintaining physiological balance and reducing disease risk. Therapeutic interventions, such as probiotics, prebiotics, postbiotics, and microbiome transplantation, offer promising perspectives in restoring microbial homeostasis and preventing chronic diseases.

Prolonged postweaning protein restriction induces gut dysbiosis and colonic dysfunction in male mice

Insufficient or imbalanced protein can disrupt gut microbiota, potentially compromising gut barrier function and increasing health risks. Herein, we investigated the effects of protein restriction on cecal microbiota and colon morphofunction in male mice. From 30 to 120 days of age, C57Bl/6 mice were fed a control protein diet [14% protein, control (C) group] or a low-protein diet [6% protein, protein-restricted (R) group]. At the end of the experimental period, R mice exhibited typical features of undernutrition, such as reduced body weight, hypoalbuminemia, and hypoproteinemia. In addition, despite the hyperphagia displayed in the R group, these mice presented a decreased amount of excreted feces and less energy content in feces. Cecal microbiota analysis demonstrated that protein restriction led to reductions in Shannon and Simpson indices and, therefore, dysbiosis. This effect was accompanied by morphological modifications in the proximal colon of R mice, such as 1) reduction in the total area of neurons of myenteric plexus; 2) increased number of goblet cells, with mucin droplets less developed; 3) reductions in crypt depth and diameter; 4) decreases in gene expressions for mucins and in the tight junction proteins expression; 5) enhanced paracellular permeability and expression of pro-inflammatory cytokines (tumor necrosis factor α, toll-like receptor 4, interferon γ, interleukin 1β, and interleukin 6), decreased anti-inflammatory cytokines (interleukins 4 and 10) in the colon, and increased plasma LPS binding protein concentrations. Therefore, protein restriction induced gut dysbiosis and may result in structural and functional negative impacts on the proximal colon barrier against luminal bacteria.NEW & NOTEWORTHY Prolonged postweaning protein restriction induced gut dysbiosis and led to a reduced neuron area in the myenteric plexus, with increased but underdeveloped goblet cells. Protein restriction decreased colonic crypt depth and diameter, and increased paracellular permeability due to lower expression of mucin-related genes and tight junction proteins. The diminished barrier function resulted in systemic inflammation, evidenced by elevated plasma LPS-binding protein and pro-inflammatory markers in the colon.

The interaction between various food components and intestinal microbiota improves human health through the gut-X axis: independently or synergistically

Food contains various components that improve health by affecting the gut microbiota, primarily by modulating its abundance or altering its diversity. Active substances in food have different effects on the gut microbiota when they act alone or in synergy, resulting in varying impacts on health. The bioactive compounds in food exert different effects on various gut microbiota through multiple pathways, thereby delaying or preventing different kinds of disease. The combination of two or more active compounds may have a synergistic effect, which can more effectively alter the gut microbiota and alleviate diseases through the microbiota-gut-organ axis. According to reports, multiple different food components have similar effects, some of which have been shown to have a synergistic effect on the gut microbiota to promote health. However, there is currently no systematic review of its synergistic effects and mechanisms. There may be more compounds with synergistic effects that have not yet been discovered, while their mechanisms of synergy and ways of impacting host health through the gut microbiota deserve further investigation. The purpose of this review is to systematically summarize the effects of different food components on intestinal flora and health, and further analyze the potential synergies between different food components. PubMed and Google Scholar databases were searched in this review.

The effectiveness and safety of natural food and food-derived extract supplements for treating functional gastrointestinal disorders-current perspectives

Functional gastrointestinal disorders (FGIDs) were highly prevalent and involve gastrointestinal discomfort characterized by non-organic abnormalities in the morphology and physiology of the gastrointestinal tract. According to the Rome IV criteria, irritable bowel syndrome and functional dyspepsia are the most common FGIDs. Complementary and alternative medicines are employed by increasing numbers of individuals around the world, and they include herbal and dietary supplements, acupuncture, and hypnosis. Of these, herbal and dietary supplements seem to have the greatest potential for relieving FGIDs, through multiple modes of action. However, despite the extensive application of natural extracts in alternative treatments for FGIDs, the safety and effectiveness of food and orally ingested food-derived extracts remain uncertain. Many randomized controlled trials have provided compelling evidence supporting their potential, as detailed in this review. The consumption of certain foods (eg, kiwifruit, mentha, ginger, etc) and food ingredients may contribute to the alleviation of symptoms associated with FGID,. However, it is crucial to emphasize that the short-term consumption of these components may not yield satisfactory efficacy. Physicians are advised to share both the benefits and potential risks of these alternative therapies with patients. Furthermore, larger randomized clinical trials with appropriate comparators are imperative.

Large Quantities of Bacterial DNA and Protein in Common Dietary Protein Source Used in Microbiome Studies

Diet has been shown to greatly impact the intestinal microbiota. To understand the role of individual dietary components, defined diets with purified components are frequently used in diet-microbiota studies. Defined diets frequently use purified casein as the protein source. Previous work indicated that casein contains microbial DNA potentially impacting results of microbiome studies. Other diet-based microbially derived molecules that may impact microbiome measurements, such as proteins detected by metaproteomics, have not been determined for casein. Additionally, other protein sources used in microbiome studies have not been characterized for their microbial content. We used metagenomics and metaproteomics to identify and quantify microbial DNA and protein in a casein-based defined diet to better understand potential impacts on metagenomic and metaproteomic microbiome studies. We further tested six additional defined diets with purified protein sources with an integrated metagenomic-metaproteomic approach and found that contaminating microbial protein is unique to casein within the tested set as microbial protein was not identified in diets with other protein sources. We also illustrate the contribution of diet-derived microbial protein in diet-microbiota studies by metaproteomic analysis of stool samples from germ-free mice (GF) and mice with a conventional microbiota (CV) following consumption of diets with casein and non-casein protein. This study highlights a potentially confounding factor in diet-microbiota studies that must be considered through evaluation of the diet itself within a given study.

Impact of commercial gut health interventions on caecal metagenome and broiler performance

BACKGROUND

Maintaining gut health is a persistent and unresolved challenge in the poultry industry. Given the critical role of gut health in chicken performance and welfare, there is a pressing need to identify effective gut health intervention (GHI) strategies to ensure optimal outcomes in poultry farming. In this study, across three broiler production cycles, we compared the metagenomes and performance of broilers provided with ionophores (as the control group) against birds subjected to five different GHI combinations involving vaccination, probiotics, prebiotics, essential oils, and reduction of ionophore use.

RESULTS

Using a binning strategy, 84 (≥ 75% completeness, ≤ 5% contamination) metagenome-assembled genomes (MAGs) from 118 caecal samples were recovered and annotated for their metabolic potential. The majority of these (n = 52, 61%) had a differential response across all cohorts and are associated with the performance parameter - European poultry efficiency factor (EPEF). The control group exhibited the highest EPEF, followed closely by the cohort where probiotics are used in conjunction with vaccination. The use of probiotics B, a commercial Bacillus strain-based formulation, was determined to contribute to the superior performance of birds. GHI supplementation generally affected the abundance of microbial enzymes relating to carbohydrate and protein digestion and metabolic pathways relating to energy, nucleotide synthesis, short-chain fatty acid synthesis, and drug-transport systems. These shifts are hypothesised to differentiate performance among groups and cycles, highlighting the beneficial role of several bacteria, including Rikenella microfusus and UBA7160 species.

CONCLUSIONS

All GHIs are shown to be effective methods for gut microbial modulation, with varying influences on MAG diversity, composition, and microbial functions. These metagenomic insights greatly enhance our understanding of microbiota-related metabolic pathways, enabling us to devise strategies against enteric pathogens related to poultry products and presenting new opportunities to improve overall poultry performance and health. Video Abstract.

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).

A pilot study of metaproteomics and DNA metabarcoding as tools to assess dietary intake in humans

Objective biomarkers of food intake are a sought-after goal in nutrition research. Most biomarker development to date has focused on metabolites detected in blood, urine, skin, or hair, but detection of consumed foods in stool has also been shown to be possible via DNA sequencing. An additional food macromolecule in stool that harbors sequence information is protein. However, the use of protein as an intake biomarker has only been explored to a very limited extent. Here, we evaluate and compare measurement of residual food-derived DNA and protein in stool as potential biomarkers of intake. We performed a pilot study of DNA sequencing-based metabarcoding and mass spectrometry-based metaproteomics in five individuals' stool sampled in short, longitudinal bursts accompanied by detailed diet records (n = 27 total samples). Dietary data provided by stool DNA, stool protein, and written diet record independently identified a strong within-person dietary signature, identified similar food taxa, and had significantly similar global structure in two of the three pairwise comparisons between measurement techniques (DNA-to-protein and DNA-to-diet record). Metaproteomics identified proteins including myosin, ovalbumin, and beta-lactoglobulin that differentiated food tissue types like beef from dairy and chicken from egg, distinctions that were not possible by DNA alone. Overall, our results lay the groundwork for development of targeted metaproteomic assays for dietary assessment and demonstrate that diverse molecular components of food can be leveraged to study food intake using stool samples.

Dietary protein source alters gut microbiota composition and function

The source of protein in a person's diet affects their total life expectancy. However, the mechanisms by which dietary protein sources differentially impact human health and life expectancy are poorly understood. Dietary choices impact the composition and function of the intestinal microbiota that ultimately modulate host health. This raises the possibility that health outcomes based on dietary protein sources might be driven by interactions between dietary protein and the gut microbiota. In this study, we determined the effects of seven different sources of dietary protein on the gut microbiota of mice using an integrated metagenomics-metaproteomics approach. The protein abundances measured by metaproteomics can provide microbial species abundances, and evidence for the molecular phenotype of microbiota members because measured proteins indicate the metabolic and physiological processes used by a microbial community. We showed that dietary protein source significantly altered the species composition and overall function of the gut microbiota. Different dietary protein sources led to changes in the abundance of microbial proteins involved in the degradation of amino acids and the degradation of glycosylations conjugated to dietary protein. In particular, brown rice and egg white protein increased the abundance of amino acid degrading enzymes. Egg white protein increased the abundance of bacteria and proteins usually associated with the degradation of the intestinal mucus barrier. These results show that dietary protein sources can change the gut microbiota's metabolism, which could have major implications in the context of gut microbiota mediated diseases.

Stable isotope fingerprinting can directly link intestinal microorganisms with their carbon source and captures diet-induced substrate switching in vivo

Diet has strong impacts on the composition and function of the gut microbiota with implications for host health. Therefore, it is critical to identify the dietary components that support growth of specific microorganisms in vivo. We used protein-based stable isotope fingerprinting (Protein-SIF) to link microbial species in gut microbiota to their carbon sources by measuring each microbe's natural 13C content (δ13C) and matching it to the 13C content of available substrates. We fed gnotobiotic mice, inoculated with a 13 member microbiota, diets in which the 13C content of all components was known. We varied the source of protein, fiber or fat to observe 13C signature changes in microbial consumers of these substrates. We observed significant changes in the δ13C values and abundances of specific microbiota species, as well as host proteins, in response to changes in 13C signature or type of protein, fiber, and fat sources. Using this approach we were able to show that upon switching dietary source of protein, fiber, or fat (1) some microbial species continued to obtain their carbon from the same dietary component (e.g., protein); (2) some species switched their main substrate type (e.g., from protein to carbohydrates); and (3) some species might derive their carbon through foraging on host compounds. Our results demonstrate that Protein-SIF can be used to identify the dietary-derived substrates assimilated into proteins by microbes in the intestinal tract; this approach holds promise for the analysis of microbiome substrate usage in humans without the need of substrate labeling.

Significance

The gut microbiota plays a critical role in the health of animals including humans, influencing metabolism, the immune system, and even behavior. Diet is one of the most significant factors in determining the function and composition of the gut microbiota, but our understanding of how specific dietary components directly impact individual microbes remains limited. We present the application of an approach that measures the carbon isotope "fingerprint" of proteins in biological samples. This fingerprint is similar to the fingerprint of the substrate used to make the proteins. We describe how we used this approach in mice to determine which dietary components specific intestinal microbes use as carbon sources to make their proteins. This approach can directly identify components of an animal's diet that are consumed by gut microbes.

Review of the Relationships Between Human Gut Microbiome, Diet, and Obesity

Obesity is a complex disease that increases the risk of other pathologies. Its prevention and long-term weight loss maintenance are problematic. Gut microbiome is considered a potential obesity modulator. The objective of the present study was to summarize recent findings regarding the relationships between obesity, gut microbiota, and diet (vegetable/animal proteins, high-fat diets, restriction of carbohydrates), with an emphasis on dietary fiber and resistant starch. The composition of the human gut microbiome and the methods of its quantification are described. Products of the gut microbiome metabolism, such as short-chain fatty acids and secondary bile acids, and their effects on the gut microbiota, intestinal barrier function and immune homeostasis are discussed in the context of obesity. The importance of dietary fiber and resistant starch is emphasized as far as effects of the host diet on the composition and function of the gut microbiome are concerned. The complex relationships between human gut microbiome and obesity are finally summarized.

Behind the scenes: metagenomic analysis of bacterial communities in sustainable depilation of sheepskin

AIM

The leather industry is embracing eco-friendly technologies for both regulatory compliance and sustainable growth. While enzymatic depilation provides a greener alternative to traditional beamhouse methods, its complexity often leads to higher costs. To address this, we examined the performance of sheepskins' native bacterial flora in acetic acid conditions with low-environmental impact.

METHODS AND RESULTS

Utilizing metagenomic techniques, we analyzed the bacterial community dynamics during the depilation process. This investigation revealed a notable increase in microbial diversity and richness in acetic acid treatments compared to water treatments. At the class level, a post-processing decrease in Gammaproteobacteria dominance was observed, while Actinomycetia numbers surged in the acetic acid group. In contrast, the water group showed an increase in Bacteroidia. Order-level analysis indicated reductions in Pseudomonadales and increases in Actinomycetales with acetic acid treatment, whereas Flavobacteriales was more prevalent in water-treated liquors. At the family level, Moraxellaceae decreased and Micrococcaceae increased in the acetic acid group, in contrast to the marked rise of Weeksellaceae in the water group. Temporal analyses further highlighted the evolving bacterial landscapes under different treatments. Moreover, acetic acid treatment fostered a stable microbial community, beneficial for sustainable leather processing. Functional pathways were predicted using PICRUSt2. It showed that significantly enriched degradation pathways in the water group were less abundant in the acetic acid group, potentially preventing substrate matrix damage during depilation.

CONCLUSION

The study underscores the transformative potential of acetic acid for the leather industry, offering a pathway to reduce pollution while maintaining economic viability. By enhancing our understanding of microbial interactions during depilation, this study opens avenues for refining these eco-friendly techniques. Our findings advocate for a shift towards greener depilation methods and contribute to the broader dialogue on sustainable manufacturing practices, emphasizing the importance of leveraging indigenous microbial communities for environmental and economic gains.

Dietary soy protein reverses obesity-induced liver steatosis and alters fecal microbial composition independent of isoflavone level

Introduction

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a major public health concern that is exacerbated by the obesity pandemic. Dietary interventions have the potential to alleviate obesity-associated MASLD through variable mechanisms, including optimizing the gut microbiota. Previously, we reported that soy protein concentrate (SPC) with low or high levels of isoflavone (LIF or HIF) protected young obese Zucker rats from developing liver steatosis. The current study was designed to test whether SPC-LIF and SPC-HIF diets would reverse liver steatosis and alter fecal microbial composition in adult obese Zucker rats with existing steatosis.

Methods

Six-week-old male obese Zucker rats (n = 26) were fed a casein control diet (CAS) for 8 weeks and 7 rats were randomly selected and sacrificed to confirm liver steatosis. The remaining rats were randomly assigned to receive CAS, SPC-LIF, or SPC-HIF diet (n = 6-7/group) for an additional 10 weeks.

Results

Compared to CAS diet, feeding SPC-LIF and SPC-HIF diets resulted in significantly lower liver weight, liver steatosis score, and liver microvesicular score (p < 0.05), but did not lead to difference in body weight, liver macrovesicular score, serum ALT, or serum AST. Isoflavone levels (e.g., LIF vs. HIF) did not affect any of these measurements except in the SPC-HIF group, which had an additional decrease in liver weight (p < 0.05) compared to the SPC-LIF group. The SPC-HIF group also had significantly higher levels of the aglycone forms of daidzein, genistein, and equol as well as the total levels of daidzein, genistein, and equol compared to SPC-LIF or CAS diet fed rats (p < 0.05). The distribution of microbial communities based on measures of beta diversity of both SPC-LIF and SPC-HIF groups were significantly different to that of the CAS group (p ≤ 0.005). Alpha-diversity did not differ between any of the groups.

Conclusion

Taken together, dietary soy protein can reverse liver steatosis in adult Zucker rats, and the reversal of steatosis is accompanied by alterations in gut microbial composition.

Opinion Piece: New Plant-Based Food Products Between Technology and Physiology

The rapid growth of product sectors for plant-based meat and dairy alternatives has raised significant scientific interest in their nutritional and ecological benefits. Here, it outlines the fractionation of plant-based raw materials and describes the technologies applied in the production of meat and dairy substitutes. Moreover, the study describes the effects of these new products on human nutrient supply and metabolic responses. Examples of meat-like products produced by extrusion technology and dairy alternatives are provided, addressing production challenges and the effects of processing on nutrient digestibility and bioavailability. In contrast to animal-based products, plant-based protein ingredients can contain many compounds produced by plants for defense or symbiotic interactions, such as lectins, phytates, and a wide range of secondary metabolites. The intake of these compounds as part of a plant-based diet can influence the digestion, bioaccessibility, and bioavailability of essential nutrients such as minerals and trace elements but also of amino acids. This is a critical factor, especially in regions with limited plant species for human consumption and inadequate technologies to eliminate these compounds. To fully understand these impacts and ensure that plant-based diets meet human nutritional needs, well-controlled human studies are needed.

The role of fiber in modulating plant protein-induced metabolic responses

The rising consumption of plant protein foods and the emergence of meat alternatives have prompted interest in the health benefits of such products, which contain fiber in addition to protein. This review investigates the effect of fiber on plant-based protein metabolism and evaluates its contribution to gut-derived health impacts. Plant proteins, which often come with added fiber, can have varying health outcomes. Factors such as processing and the presence of fiber and starch influence the digestibility of plant proteins, potentially leading to increased proteolytic fermentation in the gut and the production of harmful metabolites. However, fermentable fiber can counteract this effect by serving as a primary substrate for gut microbes, decreasing proteolytic activity. The increased amount of fiber, rather than the protein source itself, plays a significant role in the observed health benefits of plant-based diets in human studies. Differences between extrinsic and intrinsic fiber in the food matrix further impact protein fermentation and digestibility. Thus, in novel protein products without naturally occurring fiber, the health impact may differ from conventional plant protein sources. The influence of various fibers on plant-based protein metabolism throughout the gastrointestinal tract is not fully understood, necessitating further research.

Gastrointestinal digestion of food proteins: Anticancer, antihypertensive, anti-obesity, and immunomodulatory mechanisms of the derived peptides

Food proteins and their peptides play a significant role in the important biological processes and physiological functions of the body. The peptides show diverse biological benefits ranging from anticancer to antihypertensive, anti-obesity, and immunomodulatory, among others. In this review, an overview of food protein digestion in the gastrointestinal tract and the mechanisms involved was presented. As some proteins remain resistant and undigested, the multifarious factors (e.g. protein type and structure, microbial composition, pH levels and redox potential, host factors, etc.) affecting their colonic fermentation, the derived peptides, and amino acids that evade intestinal digestion are thus considered. The section that follows focuses on the mechanisms of the peptides with anticancer, antihypertensive, anti-obesity, and immunomodulatory effects. As further considerations were made, it is concluded that clinical studies targeting a clear understanding of the gastrointestinal stability, bioavailability, and safety of food-based peptides are still warranted.

Experimental Protocols Used to Mimic Gastrointestinal Protein Digestion: A Systematic Review

Bioactive peptides derived from native proteins modulate physiological processes in the metabolic pathways. Given that multiple protocols in the literature mimic the digestion of dietary components, gathering studies that use such models directed at protein digestion processes is critical. This systematic review aimed to gather evidence that adopted adequate experimental models to simulate human protein digestion. The databases searched were PubMed, Web of Science, ScienceDirect, Embase, Virtual Health Library, and Scopus. A total of 1985 articles were found, resulting in 20 eligible in vitro studies. The Office of Health Assessment and Translation was used to evaluate methodological quality. Seven studies used plant-based protein sources, twelve used animal protein sources, and one used both. The duration of the oral phase varied, although 60% of the studies employed a protein digestion period of 120 min. Amylase, pepsin, and pancreatin enzymes were utilized in 40% of the studies, with pH levels of 7, 3, and 7, respectively, during the oral, gastric, and intestinal phases. The INFOGEST harmonized static model was adopted by 65% of the studies; INFOGEST is the most effective model for simulating gastrointestinal protein processes in humans and can be used to answer several research questions because it describes experimental conditions close to the human physiological situation.

Dietary protein from different sources escapes host digestion and is differentially modified by the microbiota

Protein is an essential macronutrient and variations in its source and quantity have been shown to impact long-term health outcomes. Differential health impacts of dietary proteins from various sources are likely driven by differences in their digestibility by the host and subsequent availability to the intestinal microbiota. However, our current understanding regarding the fate of dietary proteins from different sources in the gut, specifically how component proteins within these sources interact with the host and the gut microbiota, is limited. To determine which dietary proteins are efficiently digested by the host and which proteins escape host digestion and are used by the gut microbiota, we used high-resolution mass spectrometry to quantify the proteins that make up different dietary protein sources before and after digestion in germ-free and conventionally raised mice. Contrary to expectation, we detected proteins from all sources in fecal samples of both germ-free and conventional mice suggesting that even protein sources with a high digestive efficiency make it in part to the colon where they can serve as a substrate for the microbiota. Additionally, we found clear patterns where specific component proteins of the dietary protein sources were used as a preferred substrate by the microbiota or were not as accessible to the microbiota. We found that specific proteins with functions that could impact host health and physiology were differentially enriched in germ-free or conventionally raised mice. These findings reveal large differences in the fate of dietary protein from various sources in the gut that could explain some of their differential health impacts.

Exploring animal protein sources against prevent age-related short-term memory decline in mice: Dietary fish (Alaska Pollock) protein exhibits superior protective effects

Dietary factors, particularly proteins, have been extensively explored to combat cognitive impairment. We have previously reported that dietary fish (Alaska Pollock) protein (APP) is more effective than casein (CAS) or fish oil in maintaining short-term memory in senescence-accelerated mice prone 10 (SAMP10). To examine the specificity of the protective effect of APP intakes against short-term memory decline, we assessed the impact of various dietary animal proteins, including APP, CAS, chicken breast protein (CP), and whey protein (WP), against age-related cognitive function in SAMP10 mice. After feeding the experimental diets for 5 months, memory was assessed using the Y-maze. The APP group exhibited a significant increase in spontaneous alternation behavior as an indicator of working memory when group compared with groups fed with other protein source. Additionally, the APP group displayed significantly higher neurofilament heavy chain positivity than the CAS and CP groups, as evidenced immunohistochemical analysis. Gut microbiota analysis indicated that dietary APP significantly enhanced the relative abundance of Lactobacillus, which positively correlated with spontaneous alternation behavior. Collectively, these findings suggest that dietary APP is more effective than CAS, CP, or WP in preventing age-related short-term memory decline and morphological abnormalities in the hippocampal axons of SAMP10 mice. Moreover, APP-mediated improvements in cognitive deficits may be associated with changes in microbiota diversity. PRACTICAL APPLICATION: This research suggests that dietary fish protein from Alaska Pollock may be more efficient in prevention short-term memory decline in mice, compared to other animal proteins. This finding has practical implications for nutritional optimization, developing the new health food products, and elucidating the relationship between the impact of specific proteins on gut microbiota and prevention of age-related cognitive decline.

Digestive dynamics: Unveiling interplay between the gut microbiota and the liver in macronutrient metabolism and hepatic metabolic health

Although the liver is the largest metabolic organ in the body, it is not alone in functionality and is assisted by "an organ inside an organ," the gut microbiota. This review attempts to shed light on the partnership between the liver and the gut microbiota in the metabolism of macronutrients (i.e., proteins, carbohydrates, and lipids). All nutrients absorbed by the small intestines are delivered to the liver for further metabolism. Undigested food that enters the colon is metabolized further by the gut microbiota that produces secondary metabolites, which are absorbed into portal circulation and reach the liver. These microbiota-derived metabolites and co-metabolites include ammonia, hydrogen sulfide, short-chain fatty acids, secondary bile acids, and trimethylamine N-oxide. Further, the liver produces several compounds, such as bile acids that can alter the gut microbial composition, which can in turn influence liver health. This review focuses on the metabolism of these microbiota metabolites and their influence on host physiology. Furthermore, the review briefly delineates the effect of the portosystemic shunt on the gut microbiota-liver axis, and current understanding of the treatments to target the gut microbiota-liver axis.

Development strategy of non-GMO organism for increased hemoproteins in Corynebacterium glutamicum: a growth-acceleration-targeted evolution

Heme, found in hemoproteins, is a valuable source of iron, an essential mineral. The need for an alternative hemoprotein source has emerged due to the inherent risks of large-scale livestock farming and animal proteins. Corynebacterium glutamicum, regarded for Qualified Presumption of Safety or Generally Recognized as Safe, can biosynthesize hemoproteins. C. glutamicum single-cell protein (SCP) can be a valuable alternative hemoprotein for supplying heme iron without adversely affecting blood fat levels. We constructed the chemostat culture system to increase hemoprotein content in C. glutamicum SCP. Through adaptive evolution, hemoprotein levels could be naturally increased to address oxidative stress resulting from enhanced growth rate. In addition, we used several specific plasmids containing growth-accelerating genes and the hemA promoter to expedite the evolutionary process. Following chemostat culture for 15 days, the plasmid in selected descendants was cured. The evolved strains showed improved specific growth rates from 0.59 h-1 to 0.62 h-1, 20% enhanced resistance to oxidative stress, and increased heme concentration from 12.95 µg/g-DCW to 14.22-15.24 µg/g-DCW. Notably, the putative peptidyl-tRNA hydrolase-based evolved strain manifested the most significant increase (30%) of hemoproteins. This is the first report presenting the potential of a growth-acceleration-targeted evolution (GATE) strategy for developing non-GMO industrial strains with increased bio-product productivity.

Differential Roles of Diet on Development and Spinal Cord Regeneration in Larval Zebrafish

The zebrafish is a powerful model organism for studying development and regeneration. However, there is a lack of a standardized reference diet for developmental and regeneration experiments. Most studies evaluate the rate of growth, survival, and fecundity. In this study, we compare three diets and their effects on growth and regeneration after a spinal cord injury (SCI). Fish were fed daily for 1 week with daily measurements of overall length and width of spinal injury. Fish fed a live rotifer diet grew 32%, whereas a commercially available diet only led to a 4% increase in body length. Similarly, differences in rate of regeneration were observed with over 80% of rotifer-fed larvae forming a glial bridge after injury compared to <10% of zebrafish fed with the commercial diet. Our data highlight the need for establishing a standardized diet for regeneration studies to improve research reproducibility.

Cross-sectional analyses of metabolites across biological samples mediating dietary acid load and chronic kidney disease

Chronic kidney disease (CKD) is a major public health burden, with dietary acid load (DAL) and gut microbiota playing crucial roles. As DAL can affect the host metabolome, potentially via the gut microbiota, we cross-sectionally investigated the interplay between DAL, host metabolome, gut microbiota, and early-stage CKD (TwinsUK, n = 1,453). DAL was positively associated with CKD stage G1-G2 (Beta (95% confidence interval) = 0.34 (0.007; 0.7), p = 0.046). After adjusting for covariates and multiple testing, we identified 15 serum, 14 urine, 8 stool, and 7 saliva metabolites, primarily lipids and amino acids, associated with both DAL and CKD progression. Of these, 8 serum, 2 urine, and one stool metabolites were found to mediate the DAL-CKD association. Furthermore, the stool metabolite 5-methylhexanoate (i7:0) correlated with 26 gut microbial species. Our findings emphasize the gut microbiota's therapeutic potential in countering DAL's impact on CKD through the host metabolome. Interventional and longitudinal studies are needed to establish causality.

Gut microbiota in overweight and obesity: crosstalk with adipose tissue

Overweight and obesity are characterized by excessive fat mass accumulation produced when energy intake exceeds energy expenditure. One plausible way to control energy expenditure is to modulate thermogenic pathways in white adipose tissue (WAT) and/or brown adipose tissue (BAT). Among the different environmental factors capable of influencing host metabolism and energy balance, the gut microbiota is now considered a key player. Following pioneering studies showing that mice lacking gut microbes (that is, germ-free mice) or depleted of their gut microbiota (that is, using antibiotics) developed less adipose tissue, numerous studies have investigated the complex interactions existing between gut bacteria, some of their membrane components (that is, lipopolysaccharides), and their metabolites (that is, short-chain fatty acids, endocannabinoids, bile acids, aryl hydrocarbon receptor ligands and tryptophan derivatives) as well as their contribution to the browning and/or beiging of WAT and changes in BAT activity. In this Review, we discuss the general physiology of both WAT and BAT. Subsequently, we introduce how gut bacteria and different microbiota-derived metabolites, their receptors and signalling pathways can regulate the development of adipose tissue and its metabolic capacities. Finally, we describe the key challenges in moving from bench to bedside by presenting specific key examples.

Dietary Protein Quality Affects the Interplay between Gut Microbiota and Host Performance in Nile Tilapia

Dietary protein quality plays a key role in maintaining intestinal mucosal integrity, but also modulates the growth of luminal microorganisms. This work assessed the effect of dietary protein sources on the performance, gut morphology, and microbiome in Nile tilapia. Four isonitrogenous and isolipidic diets comprising equivalent amounts of the protein supply derived from either PLANT, ANIMAL, INSECT, or BACTERIAL (bacterial biomass) sources were fed to triplicate groups of fish (IBW: 12 g) for 46 days. Fish fed the ANIMAL and BACTERIAL diets showed significantly higher weight gains than those fed the PLANT and INSECT diets (p < 0.05). Relative abundance at the phylum level showed that Bacteroidetes, Fusobacteria, and Proteobacteria were the more abundant phyla in tilapia's intestine, while Cetobacterium was the most representative genus in all treatments. Interesting patterns were observed in the correlation between amino acid intake and genus and species abundance. Metabolism prediction analysis showed that BACTERIAL amine and polyamine degradation pathways are modulated depending on diets. In conclusion, different protein sources modulate the relationship between bacteria functional pathways and amino acid intake.

A review of mitigation technologies and management strategies for greenhouse gas and air pollutant emissions in livestock production

One of the key issues in manure management of livestock production is to reduce greenhouse gas (GHG) and air pollutant emissions, which lead to significant environmental footprint and human/animal health threats. This study provides a review of potentially efficacious technologies and management strategies that reduce GHG and air pollutant emissions during the three key stages of manure management in livestock production, i.e., animal housing, manure storage and treatment, and manure application. Several effective mitigation technologies and practices for each manure management stage are identified and analyzed in detail, including feeding formulation adjustment, frequent manure removal and air scrubber during animal housing stage; solid-liquid separation, manure covers for storage, acidification, anaerobic digestion and composting during manure storage and treatment stage; land application techniques at appropriate timing during manure application stage. The results indicated several promising approaches to reduce multiple gas emissions from the entire manure management. Removing manure 2-3 times per week or every day during animal housing stage is an effective and simple way to reduce GHG and air pollutant emissions. Acidification during manure storage and treatment stage can reduce ammonia and methane emissions by 33%-93% and 67%-87%, respectively and proper acid, such as lactic acid can also reduce nitrous oxide emission by about 90%. Shallow injection of manure for field application has the best performance in reducing ammonia emission by 62%-70% but increase nitrous oxide emission. The possible trade-off brings insight to the prioritization of targeted gas emissions for the researchers, stakeholders and policymakers, and also highlights the importance of assessing the mitigation technologies across the entire manure management chain. Implementing a combination of the management strategies needs comprehensive considerations about mitigation efficiency, technical feasibility, local regulations, climate condition, scalability and cost-effectiveness.

The Effects of Yeast Protein on Gut Microbiota in Mice When Compared with Soybean Protein and Whey Protein Isolates

Different protein sources can impact gut microbiota composition and abundance, and also participate in health regulation. In this study, mice were gavaged with yeast protein (YP), soybean protein isolate (SPI), and whey protein isolate (WPI) for 28 days. Body weights showed similar patterns across different protein administration groups. The ileum in YP-supplemented mice exhibited good morphology, and tight-junction (TJ) proteins were slightly upregulated. Immunoglobulin (Ig)A, IgM, and IgG levels in the ileum of different protein groups were significantly increased (p < 0.05). Interleukin (IL)-10 levels were significantly increased, whereas IL-6 levels were significantly reduced in the YP group when compared with the control (C) (p < 0.05). Glutathione peroxidase (GSH-Px) levels in the ileum were significantly increased in the YP group (p < 0.05). These results indicate that YP potentially improved intestinal immunity and inflammatory profiles. The relative abundances of Parabacteroides, Prevotella, and Pseudobutyrivibrio in the YP group were more enriched when compared with the C and SPI groups, and Parabacteroides was significantly upregulated when compared with the WPI group (p < 0.05). Overall, the results indicate that YP upregulates the beneficial bacteria and improves ileal immunity and anti-inflammatory capabilities.

microbeMASST: a taxonomically informed mass spectrometry search tool for microbial metabolomics data

microbeMASST, a taxonomically informed mass spectrometry (MS) search tool, tackles limited microbial metabolite annotation in untargeted metabolomics experiments. Leveraging a curated database of >60,000 microbial monocultures, users can search known and unknown MS/MS spectra and link them to their respective microbial producers via MS/MS fragmentation patterns. Identification of microbe-derived metabolites and relative producers without a priori knowledge will vastly enhance the understanding of microorganisms' role in ecology and human health.

Microbiota Implications in Endocrine-Related Diseases: From Development to Novel Therapeutic Approaches

This comprehensive review article delves into the critical role of the human microbiota in the development and management of endocrine-related diseases. We explore the complex interactions between the microbiota and the endocrine system, emphasizing the implications of microbiota dysbiosis for the onset and progression of various endocrine disorders. The review aims to synthesize current knowledge, highlighting recent advancements and the potential of novel therapeutic approaches targeting microbiota-endocrine interactions. Key topics include the impact of microbiota on hormone regulation, its role in endocrine pathologies, and the promising avenues of microbiota modulation through diet, probiotics, prebiotics, and fecal microbiota transplantation. We underscore the importance of this research in advancing personalized medicine, offering insights for more tailored and effective treatments for endocrine-related diseases.

Effect of a Probiotic Beverage Enriched with Cricket Proteins on the Gut Microbiota: Composition of Gut and Correlation with Nutritional Parameters

The health and balance of the gut microbiota are known to be linked to diet composition and source, with fermented products and dietary proteins potentially providing an exceptional advantage for the gut. The purpose of this study was to evaluate the effect of protein hydrolysis, using a probiotic beverage enriched with either cricket protein (CP) or cricket protein hydrolysates (CP.Hs), on the composition of the gut microbiota of rats. Taxonomic characterization of the gut microbiota in fecal samples was carried out after a 14-day nutritional study to identify modifications induced by a CP- and CP.H-enriched fermented probiotic product. The results showed no significant differences (p > 0.05) in the diversity and richness of the gut microbiota among the groups fed with casein (positive control), CP-enriched, and fermented CP.H-enriched probiotic beverages; however, the overall composition of the microbiota was altered, with significant modifications in the relative abundance of several bacterial families and genera. In addition, fermented CP.H-enriched probiotic beverages could be related to the decrease in the number of potential pathogens such as Enterococcaceae. The association of gut microbiota with the nutritional parameters was determined and the results showed that digestibility and the protein efficiency ratio (PER) were highly associated with the abundance of several taxa.

Dietary Amino Acid Source Elicits Sex-Specific Metabolic Response to Diet-Induced NAFLD in Mice

SCOPE

Non-alcoholic fatty liver disease (NAFLD) is a sexually dimorphic disease influenced by dietary factors. Here, the metabolic and hepatic effects of dietary amino acid (AA) source is assessed in Western diet (WD)-induced NAFLD in male and female mice.

METHODS AND RESULTS

The AA source is either casein or a free AA mixture mimicking the composition of casein. As expected, males fed a casein-based WD display glucose intolerance, fasting hyperglycemia, and insulin-resistance and develop NAFLD associated with changes in hepatic gene expression and microbiota dysbiosis. In contrast, males fed the AA-based WD show no steatosis, a similar gene expression profile as males fed a control diet, and a distinct microbiota composition compared to males fed a casein-based WD. Females are protected against WD-induced liver damage, hepatic gene expression, and gut microbiota changes regardless of the AA source.

CONCLUSIONS

Free dietary AA intake prevents the unhealthy metabolic outcomes of a WD preferentially in male mice.

Effect of diet on the evolution of gut commensal bacteria

The gut microbiota, comprising trillions of diverse microorganisms inhabiting the intestines of animals, forms a complex and indispensable ecosystem with profound implications for the host's well-being. Its functions include contributing to developing the host's immune response, aiding in nutrient digestion, synthesizing essential compounds, acting as a barrier against pathogen invasion, and influencing the development or regression of various pathologies. The dietary habits of the host directly impact this intricate community of gut microbes. Diet influences the composition and function of the gut microbiota through alterations in gene expression, enzymatic activity, and metabolome. While the impact of diet on gut ecology is well-established, the investigation into the relationship between dietary consumption and microbial genotypic diversity has been limited. This review provides an overview of the relationship between diet and gut microbiota, emphasizing the impact of host nutrition on both short- and long-term evolution in the mammalian gut. It is evident that the evolution of the gut microbiota occurs even on short timescales through the acquisition of novel mutations, within the gut bacteria of individual hosts. Consequently, we discuss the importance of considering alterations in bacterial genomic diversity when analyzing microbiota-dependent effects on host physiology. Future investigations into the various microbiota-related traits shall greatly benefit from a deeper understanding of commensal bacterial evolutionary adaptation.

Large Quantities of Bacterial DNA and Protein in Common Dietary Protein Source Used in Microbiome Studies

Diet has been shown to greatly impact the intestinal microbiota. To understand the role of individual dietary components, defined diets with purified components are frequently used in diet-microbiota studies. Many of the frequently used defined diets use purified casein as the protein source. Previous work indicated that this casein contains microbial DNA potentially impacting results of microbiome studies. Other diet-based microbially derived molecules that may impact microbiome measurements, such as proteins detected by metaproteomics, have not been determined for casein. Additionally, other protein sources used in microbiome studies have not been characterized for their microbial content. We used metagenomics and metaproteomics to identify and quantify microbial DNA and protein in a casein-based defined diet to better understand potential impacts on metagenomic and metaproteomic microbiome studies. We further tested six additional defined diets with purified protein sources with an integrated metagenomic-metaproteomic approach and show that contaminating microbial protein is unique to casein within the tested set as microbial protein was not identified in diets with other protein sources. We also illustrate the contribution of diet-derived microbial protein in diet-microbiota studies by metaproteomic analysis of stool samples from germ-free mice (GF) and mice with a conventional microbiota (CV) following consumption of diets with casein and non-casein protein. This study highlights a potentially confounding factor in diet-microbiota studies that must be considered through evaluation of the diet itself within a given study.

Bridging the Gap from Enterotypes to Personalized Dietary Recommendations: A Metabolomics Perspective on Microbiome Research

Advances in high-throughput DNA sequencing have propelled research into the human microbiome and its link to metabolic health. We explore microbiome analysis methods, specifically emphasizing metabolomics, how dietary choices impact the production of microbial metabolites, providing an overview of studies examining the connection between enterotypes and diet, and thus, improvement of personalized dietary recommendations. Acetate, propionate, and butyrate constitute more than 95% of the collective pool of short-chain fatty acids. Conflicting data on acetate's effects may result from its dynamic signaling, which can vary depending on physiological conditions and metabolic phenotypes. Human studies suggest that propionate has overall anti-obesity effects due to its well-documented chemistry, cellular signaling mechanisms, and various clinical benefits. Butyrate, similar to propionate, has the ability to reduce obesity by stimulating the release of appetite-suppressing hormones and promoting the synthesis of leptin. Tryptophan affects systemic hormone secretion, with indole stimulating the release of GLP-1, which impacts insulin secretion, appetite suppression, and gastric emptying. Bile acids, synthesized from cholesterol in the liver and subsequently modified by gut bacteria, play an essential role in the digestion and absorption of dietary fats and fat-soluble vitamins, but they also interact directly with intestinal microbiota and their metabolites. One study using statistical methods identified primarily two groupings of enterotypes Bacteroides and Ruminococcus. The Prevotella-dominated enterotype, P-type, in humans correlates with vegetarians, high-fiber and carbohydrate-rich diets, and traditional diets. Conversely, individuals who consume diets rich in animal fats and proteins, typical in Western-style diets, often exhibit the Bacteroides-dominated, B-type, enterotype. The P-type showcases efficient hydrolytic enzymes for plant fiber degradation but has limited lipid and protein fermentation capacity. Conversely, the B-type features specialized enzymes tailored for the degradation of animal-derived carbohydrates and proteins, showcasing an enhanced saccharolytic and proteolytic potential. Generally, models excel at predictions but often struggle to fully elucidate why certain substances yield varied responses. These studies provide valuable insights into the potential for personalized dietary recommendations based on enterotypes.

A Taxonomically-informed Mass Spectrometry Search Tool for Microbial Metabolomics Data

MicrobeMASST, a taxonomically-informed mass spectrometry (MS) search tool, tackles limited microbial metabolite annotation in untargeted metabolomics experiments. Leveraging a curated database of >60,000 microbial monocultures, users can search known and unknown MS/MS spectra and link them to their respective microbial producers via MS/MS fragmentation patterns. Identification of microbial-derived metabolites and relative producers, without a priori knowledge, will vastly enhance the understanding of microorganisms' role in ecology and human health.

Amino Acid Catabolism: An Overlooked Area of Metabolism

Amino acids have been extensively studied in nutrition, mainly as key elements for maintaining optimal protein synthesis in the body as well as precursors of various nitrogen-containing compounds. However, it is now known that amino acid catabolism is an important element for the metabolic control of different biological processes, although it is still a developing field to have a deeper understanding of its biological implications. The mechanisms involved in the regulation of amino acid catabolism now include the contribution of the gut microbiota to amino acid oxidation and metabolite generation in the intestine, the molecular mechanisms of transcriptional control, and the participation of specific miRNAs involved in the regulation of amino acid degrading enzymes. In addition, molecules derived from amino acid catabolism play a role in metabolism as they are used in the epigenetic regulation of many genes. Thus, this review aims to examine the mechanisms of amino acid catabolism and to support the idea that this process is associated with the immune response, abnormalities during obesity, in particular insulin resistance, and the regulation of thermogenesis.

Dietary Supplementation with Popped Amaranth Modulates the Gut Microbiota in Low Height-for-Age Children: A Nonrandomized Pilot Trial

Amaranth has been recognized as a nutraceutical food because it contains high-quality proteins due to its adequate amino acid composition that covers the recommended requirements for children and adults. Since pre-Hispanic times, amaranth has been consumed as popped grain; the popping process improves its nutritive quality and improves its digestibility. Popped amaranth consumption has been associated with the recovery of malnourished children. However, there is no information on the impact that popped amaranth consumption has on gut microbiota composition. A non-randomized pilot trial was conducted to evaluate the changes in composition, structure, and function of the gut microbiota of stunted children who received four grams of popped amaranth daily for three months. Stool and serum were collected at the beginning and at the end of the trial. Short-chain fatty acids (SCFA) were quantified, and gut bacterial composition was analyzed by 16S rRNA gene sequencing. Biometry and hematology results showed that children had no pathology other than low height-for-age. A decrease in the relative abundance of Alistipes putredinis, Bacteroides coprocola, and Bacteroides stercoris bacteria related to inflammation and colitis, and an increase in the relative abundance of Akkermansia muciniphila and Streptococcus thermophiles bacteria associated with health and longevity, was observed. The results demonstrate that popped amaranth is a nutritious food that helps to combat childhood malnutrition through gut microbiota modulation.

Novel plant-based meat alternatives: Implications and opportunities for consumer nutrition and health

Against the backdrop of the global protein transition needed to remain within planetary boundaries, there is an influx of plant-based meat alternatives that seek to approximate the texture, flavor and/or nutrient profiles of conventional animal meat. These novel plant-based meat alternatives, enabled by advances in food technology, can be fundamentally different from the whole-plant foods from which they are derived. One of the reasons is the necessity to use food additives on various occasions, since consumers' acceptance of plant-based meat products primarily depends on the organoleptic properties. Consequently, a high degree of heterogeneity in formulation and nutritional profiles exists both within and between product categories of plant-based meat alternatives with unknown effects on several aspects of human health. This is further complicated by the differences in digestibility and bioavailability between proteins from animal and plant sources, which have a profound impact on colonic fermentation, nutritional adequacy and potential health effects. On the other hand, emerging strategies provide opportunities to develop affordable, delicious and nutritious plant-based meat alternatives that align with consumer interests.

Modulatory Effects of A1 Milk, A2 Milk, Soy, and Egg Proteins on Gut Microbiota and Fermentation

Milk can be divided into A1 and A2 types according to β-casein variants, and there is a debate about whether A1 milk consumption exacerbates gut environments. This study examined the cecum microbiota and fermentation in mice fed A1 casein, A2 casein, mixed casein (commercial casein), soy protein isolate, and egg white. The cecum acetic acid concentration was higher, and the relative abundances of Muribaculaceae and Desulfovibrionaceae were greater in mice fed A1 versus A2 casein. The other parameters of cecum fermentation and microbiota composition were similar among the mice fed A1, A2, and mixed caseins. The differences were more distinctive among the three caseins, soy, and egg feedings. Chao 1 and Shannon indices of the cecum microbiota were lowered in egg white-fed mice, and the microbiota of mice fed milk, soy, and egg proteins were separately grouped by principal coordinate analysis. Mice fed the three caseins were characterized by a high abundance of Lactobacillaceae and Clostridiaceae, those fed soy were characterized by Corynebacteriaceae, Muribaculaceae, and Ruminococcaceae, and those fed egg white were characterized by Eggerthellaceae, Rikenellaceae, and Erysipelatoclostridiaceae. Thus, although several differences can arise between A1 and A2 caseins in terms of their modulatory effects on gut environments, the differences between milk, soy, and egg proteins can be more distinctive and are worth further consideration.

Different Approaches to Ergogenic, Pre-, and Probiotic Supplementation in Sports with Different Metabolism Characteristics: A Mini Review

Sport disciplines with different metabolic characteristics require different dietary approaches. Bodybuilders or sprinters ("anaerobic" athletes) need a high-protein diet (HPD) in order to activate muscle protein synthesis after exercise-induced muscle damage and use nitric oxide enhancers (such as citrulline and nitrates) to increase vasodilatation, whereas endurance athletes, such as runners or cyclists ("aerobic" athletes), prefer a high-carbohydrate diet (HCHD), which aims to restore the intramuscular glycogen, and supplements containing buffering agents (such as sodium bicarbonate and beta-alanine). In both cases, nutrient absorption, neurotransmitter and immune cell production and muscle recovery depend on gut bacteria and their metabolites. However, there is still insufficient data on the impact of an HPD or HCHD in addition to supplements on "anaerobic" and "aerobic" athletes' gut microbiota and how this impact could be affected by nutritional interventions such as pre- and probiotic therapy. Additionally, little is known about the role of probiotics in the ergogenic effects of supplements. Based on the results of our previous research on an HPD in amateur bodybuilders and an HCHD in amateur cyclists, we reviewed human and animal studies on the effects of popular supplements on gut homeostasis and sport performance.

Red Meat Intake, Indole-3-Acetate, and Dorea longicatena Together Affect Insulin Resistance after Gastric Bypass

Roux-en-Y Gastric bypass (RYGB) promotes improvement in type 2 diabetes (T2D) shortly after surgery, with metabolic mechanisms yet to be elucidated. This study aimed to investigate the relationship between food intake, tryptophan metabolism, and gut microbiota on the glycemic control of obese T2D women after RYGB surgery. Twenty T2D women who underwent RYGB were evaluated before and three months after surgery. Food intake data were obtained by a seven-day food record and a food frequency questionnaire. Tryptophan metabolites were determined by untargeted metabolomic analysis, and the gut microbiota was determined by 16S rRNA sequencing. The glycemic outcomes were fasting blood glucose, HbA1C, HOMA-IR, and HOMA-beta. Linear regression models were applied to assess the associations between the changes in food intake, tryptophan metabolism, and gut microbiota on glycemic control after RYGB. All variables changed after RYGB (p < 0.05), except for tryptophan intake. Jointly, the variation in red meat intake, plasma indole-3-acetate, and Dorea longicatena was associated with postoperative HOMA-IR {R² 0.80, R² adj 0.74; p < 0.01}. Red meat intake decreased three months after bariatric surgery while indole-3-acetate and Dorea longicatena increased in the same period. These combined variables were associated with better insulin resistance in T2D women after RYGB.

The gut microbiota in obesity and weight management: microbes as friends or foe?

Obesity is caused by a long-term difference between energy intake and expenditure - an imbalance that is seemingly easily restored by increasing exercise and reducing caloric consumption. However, as simple as this solution appears, for many people, losing excess weight is difficult to achieve and even more difficult to maintain. The reason for this difficulty is that energy intake and expenditure, and by extension body weight, are regulated through complex hormonal, neural and metabolic mechanisms that are under the influence of many environmental factors and internal responses. Adding to this complexity, the microorganisms (microbes) that comprise the gut microbiota exert direct effects on the digestion, absorption and metabolism of food. Furthermore, the gut microbiota exerts a miscellany of protective, structural and metabolic effects both on the intestinal milieu and peripheral tissues, thus affecting body weight by modulating metabolism, appetite, bile acid metabolism, and the hormonal and immune systems. In this Review, we outline historical and recent advances in understanding how the gut microbiota is involved in regulating body weight homeostasis. We also discuss the opportunities, limitations and challenges of using gut microbiota-related approaches as a means to achieve and maintain a healthy body weight.