A low-protein diet exerts a beneficial effect on diabetic status and prevents diabetic nephropathy in Wistar fatty rats, an animal model of type 2 diabetes and obesity

Amino Acid Composition of Thirty Food Fishes of the Ganga Riverine Environment for Addressing Amino Acid Requirement through Fish Supplementation

Amino acids are significant biomolecules that govern the major metabolic processes and act as precursors for macromolecules such as proteins that are crucial to life. Fish is an integral component of human nutrition and a dietary source of high-quality animal proteins and amino acids. In this context, the crude protein and amino acid compositions of food fish from different landing stations of the Ganga river have been determined. The Kjeldahl method was utilized to determine the crude protein content and the amino acids were analyzed using high-performance liquid chromatography (HPLC); data on 30 food fish were assessed. The study showed that among the fish studied, Eleotris fusca, Macrobrachium malcomsonii, and Mystus cavasius were rich in most of the amino acids important for human nutrition, such as glycine, glutamic acid, cysteine, threonine, phenylalanine, methionine, lysine, leucine, isoleucine, histidine, and valine. Further, it was observed that the daily consumption of these fish (approximately 50 g) can fulfil the daily requirement of these individual amino acids for an adult human with a body weight of 60 kg. Therefore, the amino acid composition analyzed in the present study could be utilized for recommendation by clinicians according to the requirement for specific amino acids, and fish can be prescribed as a natural supplement against the amino acid requirement.

Critical role of FGF21 in diabetic kidney disease: from energy metabolism to innate immunity

Diabetic kidney disease (DKD) stands as the predominant cause of chronic kidney disease (CKD) on a global scale, with its incidence witnessing a consistent annual rise, thereby imposing a substantial burden on public health. The pathogenesis of DKD is primarily rooted in metabolic disorders and inflammation. Recent years have seen a surge in studies highlighting the regulatory impact of energy metabolism on innate immunity, forging a significant area of research interest. Within this context, fibroblast growth factor 21 (FGF21), recognized as an energy metabolism regulator, assumes a pivotal role. Beyond its role in maintaining glucose and lipid metabolism homeostasis, FGF21 exerts regulatory influence on innate immunity, concurrently inhibiting inflammation and fibrosis. Serving as a nexus between energy metabolism and innate immunity, FGF21 has evolved into a therapeutic target for diabetes, nonalcoholic steatohepatitis, and cardiovascular diseases. While the relationship between FGF21 and DKD has garnered increased attention in recent studies, a comprehensive exploration of this association has yet to be systematically addressed. This paper seeks to fill this gap by summarizing the mechanisms through which FGF21 operates in DKD, encompassing facets of energy metabolism and innate immunity. Additionally, we aim to assess the diagnostic and prognostic value of FGF21 in DKD and explore its potential role as a treatment modality for the condition.

Activation of brown adipose tissue by a low-protein diet ameliorates hyperglycemia in a diabetic lipodystrophy mouse model

Long-term ad libitum dietary restrictions, such as low-protein diets (LPDs), improve metabolic health and extend the life span of mice and humans. However, most studies conducted thus far have focused on the preventive effects of LPDs on metabolic syndromes. To test the therapeutic potential of LPD, we treated a lipodystrophy mouse model IRFKO (adipose-specific insulin receptor knockout) in this study. We have previously shown that IRFKO mice have profound insulin resistance, hyperglycemia, and whitening of interscapular brown adipose tissue (BAT), closely mimicking the phenotypes in lipoatrophic diabetic patients. Here, we demonstrate that 14-day of LPD (5.1% kcal from protein) feeding is sufficient to reduce postprandial blood glucose, improve insulin resistance, and normalize glucose tolerance in the IRFKO mice. This profound metabolic improvement is associated with BAT activation and increase in whole body energy expenditure. To confirm, we showed that surgical denervation of BAT attenuated the beneficial metabolic effects of LPD feeding in IRFKO mice, including the 'browning' effects on BAT and the glucose-ameliorating results. However, BAT denervation failed to affect the body weight-lowering effects of LPD. Together, our results imply a therapeutic potential to use LPD for the treatment of lipoatrophic diabetes.

Activation of brown adipose tissue by a low-protein diet ameliorates hyperglycemia in a diabetic lipodystrophy mouse model

Long-term ad libitum dietary restrictions, such as low-protein diets (LPDs), improve metabolic health and extend the life span of mice and humans. However, most studies conducted thus far have focused on the preventive effects of LPDs on metabolic syndromes. To test the therapeutic potential of LPD, we treated a lipodystrophy mouse model IR ^FKO (adipose-specific insulin receptor knockout) in this study. We have previously shown that IR ^FKO mice have profound insulin resistance, hyperglycemia, and whitenng of interscapular brown adipose tissue (BAT), closely mimicking the phenotypes in lipoatrophic diabetic patients. Here, we demonstrate that 14-day of LPD (5.1% kcal from protein) feeding is sufficient to reduce postprandial blood glucose, improve insulin resistance, and normalize glucose tolerance in the IR ^FKO mice. This profound metabolic improvement is associated with BAT activation and increase in whole body energy expenditure. To confirm, we showed that surgical denervation of BAT attenuated the beneficial metabolic effects of LPD feeding in IR ^FKO mice, including the 'browning' effects on BAT and the glucose-ameliorating results. However, BAT denervation failed to affect the body weight-lowering effects of LPD. Together, our results imply a therapeutic potential to use LPD for the treatment of lipoatrophic diabetes.

Methionine-Restricted Diet: A Feasible Strategy Against Chronic or Aging-Related Diseases

Dietary methionine restriction (MR) has been associated with multifaceted health-promoting effects. MR is conducive to prevention of several chronic diseases and cancer, and extension of lifespan. A growing number of studies on new phenotypes and mechanisms of MR have become available in the past five years, especially in angiogenesis, neurodegenerative diseases, intestinal microbiota, and intestinal barrier function. In this review, we summarize the characteristics and advantages of MR, and current knowledge on the physiological responses and effects of MR on chronic diseases and aging-associated pathologies. Potential mechanisms, in which hydrogen sulfide, fibroblast growth factor 21, gut microbiota, short-chain fatty acids, and so on are involved, are discussed. Moreover, directions for epigenetics and gut microbiota in an MR diet are presented in future perspectives. This review comprehensively summarizes the novel roles and interpretations of the mechanisms underlying MR in the prevention of chronic diseases and aging.

An Association Between FNDC5, PGC-1α Genetic Variants and Obesity in Chinese Children: A Case-Control Study

BACKGROUND

Fibronectin type III domain containing protein 5 (FNDC5) gene encodes irisin that regulates adipose tissue metabolism. Peroxide-proliferator-activated receptor γ coactivator 1α (PGC-1α) is a powerful promoter of mitochondrial biosynthesis and oxidative metabolism, which plays an important role in inducing heat production and energy consumption of brown fat. PGC1-α expression stimulated an increase in expression of FNDC5.

PURPOSE

The aims of this study were to analyze the association between FNDC5, PGC-1α genetic variants and overweight or obesity in Chinese children and adolescents.

METHODS

A total of 198 children and adolescents with overweight or obesity and 198 children and adolescents with normal weight were screened according to gender and age 1:1. The healthy eating behaviors, moderate-to-vigorous physical activity time were surveyed using food frequency questionnaire and CLASS questionnaire, respectively. Genotypes of FNDC5 and PGC-1α gene were detected using SNaPshot method.

RESULTS

GT genotype of FNDC5 (rs16835198) increased the risk of overweight or obesity in boys (OR (95% CI): 1.68 (1.00, 2.93)) based on overdominant model; GG genotype of FNDC5 (rs16835198) decreased the risk of overweight or obesity in girls and boys (OR (95% CI): 0.45 (0.21,0.97), 0.45 (0.24, 0.83), respectively) based on dominant model; TT genotype of FNDC5 (rs16835198) increased the risk of overweight or obesity in girls based on recessive model (OR (95% CI): 2.46 (1.19, 5.05)), and based on the additive model (OR (95% CI): 3.82 (1.49, 9.80)). There was significant interaction between FNDC5 (rs16835198) and PGC-1α (rs3755863, rs8192678), healthy eating behaviors, moderate-to-vigorous physical activity time, interaction between PGC-1α (rs8192678) and moderate-to-vigorous physical activity time in the occurrence of overweight or obesity in Chinese children and adolescents.

CONCLUSION

FNDC5 (rs16835198) played an independent or interactive role with PGC-1α (rs3755863, rs8192678), healthy eating behaviors, moderate-to-vigorous physical activity time in the occurrence of overweight or obesity in Chinese children and adolescents.

Dietary interventions and molecular mechanisms for healthy musculoskeletal aging

Over the past decade, extensive efforts have focused on understanding age-associated diseases and how to prolong a healthy lifespan. The induction of dietary protocols such as caloric restriction (CR) and protein restriction (PR) has positively affected a healthy lifespan. These intervention ideas (nutritional protocols) have been the subject of human cohort studies and clinical trials to evaluate their effectiveness in alleviating age-related diseases (such as type II diabetes, cardiovascular disease, obesity, and musculoskeletal fragility) and promoting human longevity. This study summarizes the literature on the nutritional protocols, emphasizing their impacts on bone and muscle biology. In addition, we analyzed several CR studies using Gene Expression Omnibus (GEO) database and identified common transcriptome changes to understand the signaling pathway involved in musculoskeletal tissue. We identified nine novel common genes, out of which five were upregulated (Emc3, Fam134b, Fbxo30, Pip5k1a, and Retsat), and four were downregulated (Gstm2, Per2, Fam78a, and Sel1l3) with CR in muscles. Gene Ontology enrichment analysis revealed that CR regulates several signaling pathways (e.g., circadian gene regulation and rhythm, energy reserve metabolic process, thermogenesis) involved in energy metabolism. In conclusion, this study summarizes the beneficiary role of CR and identifies novel genes and signaling pathways involved in musculoskeletal biology.

Impacts of essential amino acids on energy balance

BACKGROUND

Obesity develops due to an imbalance in energy homeostasis, wherein energy intake exceeds energy expenditure. Accumulating evidence shows that manipulations of dietary protein and their component amino acids affect the energy balance, resulting in changes in fat mass and body weight. Amino acids are not only the building blocks of proteins but also serve as signals regulating multiple biological pathways.

SCOPE OF REVIEW

We present the currently available evidence regarding the effects of dietary alterations of a single essential amino acid (EAA) on energy balance and relevant signaling mechanisms at both central and peripheral levels. We summarize the association between EAAs and obesity in humans and the clinical use of modifying the dietary EAA composition for therapeutic intervention in obesity. Finally, similar mechanisms underlying diets varying in protein levels and diets altered of a single EAA are described. The current review would expand our understanding of the contribution of protein and amino acids to energy balance control, thus helping discover novel therapeutic approaches for obesity and related diseases.

MAJOR CONCLUSIONS

Changes in circulating EAA levels, particularly increased branched-chain amino acids (BCAAs), have been reported in obese human and animal models. Alterations in dietary EAA intake result in improvements in fat and weight loss in rodents, and each has its distinct mechanism. For example, leucine deprivation increases energy expenditure, reduces food intake and fat mass, primarily through regulation of the general control nonderepressible 2 (GCN2) and mammalian target of rapamycin (mTOR) signaling. Methionine restriction by 80% decreases fat mass and body weight while developing hyperphagia, primarily through fibroblast growth factor 21 (FGF-21) signaling. Some effects of diets with different protein levels on energy homeostasis are mediated by similar mechanisms. However, reports on the effects and underlying mechanisms of dietary EAA imbalances on human body weight are few, and more investigations are needed in future.

Amino acid transporters as modulators of glucose homeostasis

Amino acids modulate glucose homeostasis. Cytosolic levels of amino acids are regulated by amino acid transporters, modulating insulin release, protein synthesis, cell proliferation, cell fate, and metabolism. In β-cells, amino acid transporters modulate incretin-stimulated insulin release. In the liver, amino acid transporters provide glutamine and alanine for gluconeogenesis. Intestinal amino acid transporters facilitate the intake of amino acids causing protein restriction when inactive. Adipocyte development is regulated by amino acid transporters through activation of mechanistic target of rapamycin (mTORC1) and amino acid-related metabolites. The accumulation and metabolism of branched-chain amino acids (BCAAs) in muscle depends on transporters. The integration between amino acid metabolism and transport is critical for the maintenance and function of tissues and cells involved in glucose homeostasis.

Dietary protein and amino acid restriction: Roles in metabolic health and aging-related diseases

The prevalence of obesity is a worldwide phenomenon in all age groups and is associated with aging-related diseases such as type 2 diabetes, as well metabolic and cardiovascular diseases. The use of dietary restriction (DR) while avoiding malnutrition has many profound beneficial effects on aging and metabolic health, and dietary protein or specific amino acid (AA) restrictions, rather than overall calorie intake, are considered to play key roles in the effects of DR on host health. Whereas comprehensive reviews of the underlying mechanisms are limited, protein restriction and methionine (Met) restriction improve metabolic health and aging-related neurodegenerative diseases, and may be associated with FGF21, mTOR and autophagy, improved mitochondrial function and oxidative stress. Circulating branched-chain amino acids (BCAAs) are inversely correlated with metabolic health, and BCAAs and leucine (Leu) restriction promote metabolic homeostasis in rodents. Although tryptophan (Trp) restriction extends the lifespan of rodents, the Trp-restricted diet is reported to increase inflammation in aged mice, while severe Trp restriction has side effects such as anorexia. Furthermore, inadequate protein intake in the elderly increases the risk of muscle-centric health. Therefore, the restriction of specific AAs may be an effective and executable dietary manipulation for metabolic and aging-related health in humans, which warrants further investigation to elucidate the underlying mechanisms.

Dapagliflozin Restores Impaired Autophagy and Suppresses Inflammation in High Glucose-Treated HK-2 Cells

Sodium-glucose cotransporter2 (SGLT2) inhibitors have a reno-protective effect in diabetic kidney disease. However, the detailed mechanism remains unclear. In this study, human proximal tubular cells (HK-2) were cultured in 5 mM glucose and 25 mM mannitol (control), 30 mM glucose (high glucose: HG), or HG and SGLT2 inhibitor, dapagliflozin-containing medium for 48 h. The autophagic flux was decreased, accompanied by the increased phosphorylation of S6 kinase ribosomal protein (p-S6RP) and the reduced phosphorylation of AMP-activated kinase (p-AMPK) expression in a HG condition. Compared to those of the control, dapagliflozin and SGLT2 knockdown ameliorated the HG-induced alterations of p-S6RP, p-AMPK, and autophagic flux. In addition, HG increased the nuclear translocation of nuclear factor-κB p65 (NF-κB) p65 and the cytoplasmic nucleotide-binding oligomerization domain-like receptor 3 (NLRP3), mature interleukin-1β (IL-1β), IL-6, and tumor necrosis factorα (TNFα) expression. Dapagliflozin, SGLT2 knockdown, and NF-κB p65 knockdown reduced the extent of these HG-induced inflammatory alterations. The inhibitory effect of dapagliflozin on the increase in the HG-induced nuclear translocation of NF-κB p65 was abrogated by knocking down AMPK. These data indicated that in diabetic renal proximal tubular cells, dapagliflozin ameliorates: (1) HG-induced autophagic flux reduction, via increased AMPK activity and mTOR suppression; and (2) inflammatory alterations due to NF-κB pathway suppression.

Typical gut indigenous bacteria in ICR mice fed a soy protein-based normal or low-protein diet

For patients with inflammatory bowel disease, cow’s milk allergy, and lactose intolerance, soymilk is a potential alternative to cow’s milk. In this study, we aimed to identify the effects of a soy protein-based low-protein diet on the body and organ weights and the gut microbiome of six-week-old mice fed a diet containing 20% (SP) or 5% (LP) soy protein for 14 days via 16S rRNA (V4) amplicon sequencing. Body weight gain (growth) and liver, spleen, and fat tissue weight were significantly suppressed by the LP diet. Operational taxonomic unit numbers and α-diversity were lower in the LP group than in the SP group. A principal coordinate analysis revealed differences in the gut microbiome compositions of SP and LP mice. The abundances of caecal Roseburia sp., Alistipes sp., and bacteria from the family Muribaculaceae were lower in the LP group than in the SP group. In contrast, the abundance of Desulfovibrionaceae, which is positively correlated with inflammation, was higher in the LP group than in the SP group. These results differed from the effects of a milk casein-based low-protein diet (reported previously). Based on these findings, we conclude that the undesirable effects of a low-protein diet and/or protein deficiency are related to changes in the gut microbiome composition and may differ depending on the kind of proteins used.

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Six-week-old ICR mice were fed a diet containing 20% (SP) or 5% (LP) soy protein for 14 days.

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Body weight gain and liver, spleen, and fat tissue weight were significantly suppressed by the LP diet.

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Caecal Roseburia sp., Alistipes sp., and bacteria from the family Muribaculaceae was lower in the LP.

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Desulfovibrionaceae, which is positively correlated with inflammation, was higher in the LP group.

Macronutrient Determinants of Obesity, Insulin Resistance and Metabolic Health

Obesity caused by the overconsumption of calories has increased to epidemic proportions. Insulin resistance is often associated with an increased adiposity and is a precipitating factor in the development of cardiovascular disease, type 2 diabetes, and altered metabolic health. Of the various factors contributing to metabolic impairments, nutrition is the major modifiable factor that can be targeted to counter the rising prevalence of obesity and metabolic diseases. However, the macronutrient composition of a nutritionally balanced "healthy diet" are unclear, and so far, no tested dietary intervention has been successful in achieving long-term compliance and reductions in body weight and associated beneficial health outcomes. In the current review, we briefly describe the role of the three major macronutrients, carbohydrates, fats, and proteins, and their role in metabolic health, and provide mechanistic insights. We also discuss how an integrated multi-dimensional approach to nutritional science could help in reconciling apparently conflicting findings.

Association of fourteen years diet quality trajectories and type 2 diabetes mellitus with related biomarkers

Diet quality fluctuates throughout one’s adulthood, yet it remains unclear how long-term diet quality changes are related to type 2 diabetes mellitus (T2DM) and its biomarkers. We aimed to examine the association of long-term diet quality with T2DM and its biomarkers. Diet quality was assessed by the revised DBI-07, in which diet quality distance levels (DQD) represented the overall diet quality. Participants were clustered into classes sharing similar DQD levels using latent class mixed model. We used Cox regression and random effect linear regression to assess DQD trajectories’ association with T2DM and its biomarkers. Three DQD trajectories were derived: moderate to gradual decrease, high to moderate, high stable DQD level representing 2.14%, 6.18% and, 91.68% of the population. Compared to class 1, class 2 and 3 were associated with an increased risk of T2DM [HR=4.40; 95%CI: 2.02-9.59]; [HR=3.68; 95% CI: 2.11-6.43]. When class 3 was used as a reference, class 1 was also associated with an increased risk of TDM [HR=2.71; 95%CI: 1.55-4.73]. Our findings suggest that a long-term unhealthy diet is associated with an increased risk of T2DM. Gradually reducing DQD level may not make a difference, which establishes the importance of promoting healthy eating habits at early adulthood.

Restriction of essential amino acids dictates the systemic metabolic response to dietary protein dilution

Dietary protein dilution (DPD) promotes metabolic-remodelling and -health but the precise nutritional components driving this response remain elusive. Here, by mimicking amino acid (AA) supply from a casein-based diet, we demonstrate that restriction of dietary essential AA (EAA), but not non-EAA, drives the systemic metabolic response to total AA deprivation; independent from dietary carbohydrate supply. Furthermore, systemic deprivation of threonine and tryptophan, independent of total AA supply, are both adequate and necessary to confer the systemic metabolic response to both diet, and genetic AA-transport loss, driven AA restriction. Dietary threonine restriction (DTR) retards the development of obesity-associated metabolic dysfunction. Liver-derived fibroblast growth factor 21 is required for the metabolic remodelling with DTR. Strikingly, hepatocyte-selective establishment of threonine biosynthetic capacity reverses the systemic metabolic response to DTR. Taken together, our studies of mice demonstrate that the restriction of EAA are sufficient and necessary to confer the systemic metabolic effects of DPD.

Dietary protein dilution, where protein is reduced and replaced by other nutrient sources without caloric restriction, promotes metabolic health via the hepatokine Fgf21. Here, the authors show that essential amino acids threonine and tryptophan are necessary and sufficient to induce these effects.

Methionine abrogates the renoprotective effect of a low-protein diet against diabetic kidney disease in obese rats with type 2 diabetes

Dietary interventions, including a low-protein diet (LPD) and methionine (Met) restriction, have shown longevity, anti-aging and metabolic health effects. We previously reported that the LPD has a renoprotective effect against diabetic kidney disease (DKD) in rats with type 2 diabetes and obesity. However, it is unclear whether the beneficial effect of the LPD is mediated by low-Met intake or how Met is related to the pathogenesis for DKD. We herein show that the addition of Met with the LPD abrogates the beneficial effects induced by the LPD such as anti-oxidative stress, anti-inflammation and anti-fibrosis, in diabetic kidney. Additionally, the increased levels of S-adenosylmethionine (SAM) in renal tubular cells, which are associated with the reduced expression of glycine N-methyltransferase (Gnmt) and non-restricted Met intake, contributes to the activation of mechanistic target of rapamycin complex 1 (mTORC1) and impaired autophagy, in diabetic kidney. Moreover, starvation-induced autophagy was suppressed in renal cortex of Gnmt null mice and amino acid free-induced autophagy was also suppressed by administration of SAM in cultured HK-2 cells. A LPD could exert a renoprotective effect through the suppression of mTORC1 and restoration of autophagy, which is associated with reduced levels of SAM due to low-Met intake, in diabetic kidney.

Rodent models of obesity

Obese or overweight people exceed one-third of the global population and obesity along with diabetes mellitus consist basic components of metabolic syndrome, both of which are known cardio-cerebrovascular risk factors with detrimental consequences. These data signify the pandemic character of obesity and the necessity for effective treatments. Substantial advances have been accomplished in preclinical research of obesity by using animal models, which mimic the human disease. In particular, rodent models have been widely used for many decades with success for the elucidation of the pathophysiology of obesity, since they share physiological and genetic components with humans and appear advantageous in their husbandry. The most representative rodents include the laboratory mouse and rat. Within this review, we attempted to consolidate the most widely used mice and rat models of obesity and highlight their strengths as well as weaknesses in a critical way. Our aim was to bridge the gap between laboratory facilities and patient's bed and help the researcher find the appropriate animal model for his/her obesity research. This tactful selection of the appropriate model of obesity may offer more translational derived results. In this regard, we included, the main diet induced models, the chemical/mechanical ones, as well as a selection of monogenic or polygenic models.

Amino Acid Nutrition and Metabolism in Health and Disease

Here an overview of the special issue "Amino acid nutrition and metabolism in health and disease" is given. In addition to several comprehensive and timely reviews, this issue had some original research contributions on fundamental research in animal models as well as human clinical trials exploring how the critical nutrients amino acids affect various traits.

Dietary restriction regimens for fighting kidney disease: Insights from rodent studies

This review critically discusses the research findings on the effects of various dietary restriction regimens in rodent models of kidney disease. Long-term caloric restriction executed at both early and progressive stages of kidney disease was found to exert beneficial effects in rodents. Moreover, some studies have also demonstrated the efficacy of short-term caloric restriction in treating the kidney disease of variable aetiologies possibly by improving mitochondrial dysfunction, autophagy process and suppression of inflammation. However, the mechanisms underlying these short-term caloric restriction mediated protective effects in rodent models of kidney disease are not completely understood. Importantly, few available evidences have also suggested that carbohydrate restriction can exert beneficial effects in aging and experimentally induced renal injury models, but the mechanisms are not explored yet. Interestingly, the benefits of low protein diet in kidney disease models are extensively reported in literature. However, in most of these studies implementation of the low protein dietary regimen was found to associated with increased high carbohydrate and caloric intake (non-isocaloric). Thus, testing the effects of low protein diet under isocaloric conditions might further help to particularly understand the role of dietary protein content in pathology of kidney disease. Moreover, the direct evidences comparing the efficacy of various dietary restriction regimens in rodent models of kidney diseases are also scarce at present.

The impact of dietary protein intake on longevity and metabolic health

Lifespan and metabolic health are influenced by dietary nutrients. Recent studies show that a reduced protein intake or low-protein/high-carbohydrate diet plays a critical role in longevity/metabolic health. Additionally, specific amino acids (AAs), including methionine or branched-chain AAs (BCAAs), are associated with the regulation of lifespan/ageing and metabolism through multiple mechanisms. Therefore, methionine or BCAAs restriction may lead to the benefits on longevity/metabolic health. Moreover, epidemiological studies show that a high intake of animal protein, particularly red meat, which contains high levels of methionine and BCAAs, may be related to the promotion of age-related diseases. Therefore, a low animal protein diet, particularly a diet low in red meat, may provide health benefits. However, malnutrition, including sarcopenia/frailty due to inadequate protein intake, is harmful to longevity/metabolic health. Therefore, further study is necessary to elucidate the specific restriction levels of individual AAs that are most effective for longevity/metabolic health in humans.

Methionine restriction prevents onset of type 2 diabetes in NZO mice

Dietary methionine restriction (MR) is well known to reduce body weight by increasing energy expenditure (EE) and insulin sensitivity. An elevated concentration of circulating fibroblast growth factor 21 (FGF21) has been implicated as a potential underlying mechanism. The aims of our study were to test whether dietary MR in the context of a high-fat regimen protects against type 2 diabetes in mice and to investigate whether vegan and vegetarian diets, which have naturally low methionine levels, modulate circulating FGF21 in humans. New Zealand obese (NZO) mice, a model for polygenic obesity and type 2 diabetes, were placed on isocaloric high-fat diets (protein, 16 kcal%; carbohydrate, 52 kcal%; fat, 32 kcal%) that provided methionine at control (Con; 0.86% methionine) or low levels (0.17%) for 9 wk. Markers of glucose homeostasis and insulin sensitivity were analyzed. Among humans, low methionine intake and circulating FGF21 levels were investigated by comparing a vegan and a vegetarian diet to an omnivore diet and evaluating the effect of a short-term vegetarian diet on FGF21 induction. In comparison with the Con group, MR led to elevated plasma FGF21 levels and prevented the onset of hyperglycemia in NZO mice. MR-fed mice exhibited increased insulin sensitivity, higher plasma adiponectin levels, increased EE, and up-regulated expression of thermogenic genes in subcutaneous white adipose tissue. Food intake and fat mass did not change. Plasma FGF21 levels were markedly higher in vegan humans compared with omnivores, and circulating FGF21 levels increased significantly in omnivores after 4 d on a vegetarian diet. These data suggest that MR induces FGF21 and protects NZO mice from high-fat diet–induced glucose intolerance and type 2 diabetes. The normoglycemic phenotype in vegans and vegetarians may be caused by induced FGF21. MR akin to vegan and vegetarian diets in humans may offer metabolic benefits via increased circulating levels of FGF21 and merits further investigation.—Castaño-Martinez, T., Schumacher, F., Schumacher, S., Kochlik, B., Weber, D., Grune, T., Biemann, R., McCann, A., Abraham, K., Weikert, C., Kleuser, B., Schürmann, A., Laeger, T. Methionine restriction prevents onset of type 2 diabetes in NZO mice.

Brown and Brite: The Fat Soldiers in the Anti-obesity Fight

Brown adipose tissue (BAT) is proposed to maintain thermal homeostasis through dissipation of chemical energy as heat by the uncoupling proteins (UCPs) present in their mitochondria. The recent demonstration of the presence of BAT in humans has invigorated research in this area. The research has provided many new insights into the biology and functioning of this tissue and the biological implications of its altered activities. Another finding of interest is browning of white adipose tissue (WAT) resulting in what is known as beige/brite cells, which have increased mitochondrial proteins and UCPs. In general, it has been observed that the activation of BAT is associated with various physiological improvements such as a reduction in blood glucose levels increased resting energy expenditure and reduced weight. Given the similar physiological functions of BAT and beige/ brite cells and the higher mass of WAT compared to BAT, it is likely that increasing the brite/beige cells in WATs may also lead to greater metabolic benefits. However, development of treatments targeting brown fat or WAT browning would require not only a substantial understanding of the biology of these tissues but also the effect of altering their activity levels on whole body metabolism and physiology. In this review, we present evidence from recent literature on the substrates utilized by BAT, regulation of BAT activity and browning by circulating molecules. We also present dietary and pharmacological activators of brown and beige/brite adipose tissue and the effect of physical exercise on BAT activity and browning.

Regulation of metabolic health by essential dietary amino acids

Although the beneficial effects of calorie restriction (CR) on health and aging were first observed a century ago, the specific macronutrients and molecular processes that mediate the effect of CR have been heavily debated. Recently, it has become clear that dietary protein plays a key role in regulating both metabolic health and longevity, and that both the quantity and quality - the specific amino acid composition - of dietary protein mediates metabolic health. Here, we discuss recent findings in model organisms ranging from yeast to mice and humans regarding the influence of dietary protein as well as specific amino acids on metabolic health, and the physiological and molecular mechanisms which may mediate these effects. We then discuss recent findings which suggest that the restriction of specific dietary amino acids may be a potent therapy to treat or prevent metabolic syndrome. Finally, we discuss the potential for dietary restriction of specific amino acids - or pharmaceuticals which harness these same mechanisms - to promote healthy aging.