Protein, amino acids, vagus nerve signaling, and the brain

A 12-month, longitudinal, intervention study examining a tablet protein substitute preparation in the management of tyrosinemia

Protein substitutes (PS) without tyrosine (Tyr) and phenylalanine (Phe), are an essential source of synthetic protein in the treatment of tyrosinemia (HT). In the UK, the only available protein substitutes for HT are Tyr/ Phe free amino acid liquid or powders or formulations based on glycomacropeptide (CGMP). A tablet Tyr/ Phe free amino acid supplement (AAT) has now been introduced. The aim of this two-part prospective, longitudinal intervention study was to assess the efficacy, acceptability, and tolerance of AAT in children aged >8 years with HTI. Part 1: was a 28-day acceptability/ tolerance study, part 2, was a 12-month extension study examining efficacy of AAT. Anthropometry and blood Tyr/ Phe were assessed. All subjects were taking NTBC [2-(2-nitro-4-triflourothybenzoyl) cyclohexane-1, 3-dione] with a Tyr restricted diet. Eight subjects with HTI were recruited 4 boys, and 4 girls with a median age of 14.3y (range 10.4-17.3); 3 were Caucasian and 5 of Pakistani origin. The median (range) protein equivalent from PS was 60 g/d (50-60), natural protein 20 g/d (15-30), and NTBC 30 mg/d (25-80). No subjects were taking Phe supplements. Five (63%) subjects completed part 1, with 4 taking all their PS requirements as AAT. Subjects reported AAT were tasteless and had no odour. No adverse gastrointestinal symptoms were recorded, with two reporting improvements in abdominal discomfort. At 12 months, 4 subjects had a non-significant decrease in blood Tyr/ Phe compared to the 12 months pre-treatment. Median blood Tyr (μmol/ L) pre-intervention was 500 (320-590); and at 12 months, 450 (290-530). Median blood Phe (μmol/L) pre-intervention was 40 (30-40); and at 12 months 30 (30-50). Median height z scores remained unchanged, but there was a small decrease in weight z score (pre-study weight - 0.1 (-1.4 to1.1), 12 m - 0.3 (-1.4 to 1.3) and BMI (pre- study BMI 0.2 (-2 to 1.4), and 12 m, -0.1 (-2.5 to 1.5)).

Conclusion

AAT were useful for some adolescents with HTI who struggled with the taste and volume of conventional powdered and liquid PS.

Examining the Direct and Indirect Effects of Postprandial Amino Acid Responses on Markers of Satiety following the Acute Consumption of Lean Beef-Rich Meals in Healthy Women with Overweight

The consumption of protein-rich foods stimulates satiety more than other macronutrient-rich foods; however, the underlying mechanisms-of-action are not well-characterized. The objective of this study was to identify the direct and indirect effects of postprandial amino acid (AA) responses on satiety. Seventeen women (mean ± SEM, age: 33 ± 1 year; BMI: 27.8 ± 0.1 kg/m2) consumed a eucaloric, plant-based diet containing two servings of lean beef/day (i.e., 7.5 oz (207 g)) for 7 days. During day 6, the participants completed a 12 h controlled-feeding, clinical testing day including repeated satiety questionnaires and blood sampling to assess pre- and postprandial plasma AAs, PYY, and GLP-1. Regression and mediation analyses were completed to assess AA predictors and hormonal mediators. Total plasma AAs explained 41.1% of the variance in perceived daily fullness (p < 0.001), 61.0% in PYY (p < 0.001), and 66.1% in GLP-1 (p < 0.001) concentrations, respectively. Several individual AAs significantly predicted fluctuations in daily fullness, PYY, and GLP-1. In completing mediation analyses, the effect of plasma leucine on daily fullness was fully mediated by circulating PYY concentrations (indirect effect = B: 0.09 [Boot 95% CI: 0.032, 0.17]) as no leucine-fullness direct effect was observed. No other mediators were identified. Although a number of circulating AAs predict satiety, leucine was found to do so through changes in PYY concentrations in middle-aged women.

Evolution of human genes encoding cell surface receptors involved in the regulation of appetite: an analysis based on the phylostratigraphic age and divergence indexes

Genes encoding cell surface receptors make up a significant portion of the human genome (more than a thousand genes) and play an important role in gene networks. Cell surface receptors are transmembrane proteins that interact with molecules (ligands) located outside the cell. This interaction activates signal transduction pathways in the cell. A large number of exogenous ligands of various origins, including drugs, are known for cell surface receptors, which accounts for interest in them from biomedical researchers. Appetite (the desire of the animal organism to consume food) is one of the most primitive instincts that contribute to survival. However, when the supply of nutrients is stable, the mechanism of adaptation to adverse factors acquired in the course of evolution turned out to be excessive, and therefore obesity has become one of the most serious public health problems of the twenty-first century. Pathological human conditions characterized by appetite violations include both hyperphagia, which inevitably leads to obesity, and anorexia nervosa induced by psychosocial stimuli, as well as decreased appetite caused by neurodegeneration, inflammation or cancer. Understanding the evolutionary mechanisms of human diseases, especially those related to lifestyle changes that have occurred over the past 100-200 years, is of fundamental and applied importance. It is also very important to identify relationships between the evolutionary characteristics of genes in gene networks and the resistance of these networks to changes caused by mutations. The aim of the current study is to identify the distinctive features of human genes encoding cell surface receptors involved in appetite regulation using the phylostratigraphic age index (PAI) and divergence index (DI). The values of PAI and DI were analyzed for 64 human genes encoding cell surface receptors, the orthologs of which were involved in the regulation of appetite in model animal species. It turned out that the set of genes under consideration contains an increased number of genes with the same phylostratigraphic age (PAI = 5, the stage of vertebrate divergence), and almost all of these genes (28 out of 31) belong to the superfamily of G-protein coupled receptors. Apparently, the synchronized evolution of such a large group of genes (31 genes out of 64) is associated with the development of the brain as a separate organ in the first vertebrates. When studying the distribution of genes from the same set by DI values, a significant enrichment with genes having a low DIs was revealed: eight genes (GPR26, NPY1R, GHSR, ADIPOR1, DRD1, NPY2R, GPR171, NPBWR1) had extremely low DIs (less than 0.05). Such low DI values indicate that most likely these genes are subjected to stabilizing selection. It was also found that the group of genes with low DIs was enriched with genes that had brain-specific patterns of expression. In particular, GPR26, which had the lowest DI, is in the group of brain-specific genes. Because the endogenous ligand for the GPR26 receptor has not yet been identified, this gene seems to be an extremely interesting object for further theoretical and experimental research. We believe that the features of the genes encoding cell surface receptors we have identified using the evolutionary metrics PAI and DI can be a starting point for further evolutionary analysis of the gene network regulating appetite.

The Potential of Flavonoids and Flavonoid Metabolites in the Treatment of Neurodegenerative Pathology in Disorders of Cognitive Decline

Flavonoids are a biodiverse family of dietary compounds that have antioxidant, anti-inflammatory, antiviral, and antibacterial cell protective profiles. They have received considerable attention as potential therapeutic agents in biomedicine and have been widely used in traditional complimentary medicine for generations. Such complimentary medical herbal formulations are extremely complex mixtures of many pharmacologically active compounds that provide a therapeutic outcome through a network pharmacological effects of considerable complexity. Methods are emerging to determine the active components used in complimentary medicine and their therapeutic targets and to decipher the complexities of how network pharmacology provides such therapeutic effects. The gut microbiome has important roles to play in the generation of bioactive flavonoid metabolites retaining or exceeding the antioxidative and anti-inflammatory properties of the intact flavonoid and, in some cases, new antitumor and antineurodegenerative bioactivities. Certain food items have been identified with high prebiotic profiles suggesting that neutraceutical supplementation may be beneficially employed to preserve a healthy population of bacterial symbiont species and minimize the establishment of harmful pathogenic organisms. Gut health is an important consideration effecting the overall health and wellbeing of linked organ systems. Bioconversion of dietary flavonoid components in the gut generates therapeutic metabolites that can also be transported by the vagus nerve and systemic circulation to brain cell populations to exert a beneficial effect. This is particularly important in a number of neurological disorders (autism, bipolar disorder, AD, PD) characterized by effects on moods, resulting in depression and anxiety, impaired motor function, and long-term cognitive decline. Native flavonoids have many beneficial properties in the alleviation of inflammation in tissues, however, concerns have been raised that therapeutic levels of flavonoids may not be achieved, thus allowing them to display optimal therapeutic effects. Dietary manipulation and vagal stimulation have both yielded beneficial responses in the treatment of autism spectrum disorders, depression, and anxiety, establishing the vagal nerve as a route of communication in the gut-brain axis with established roles in disease intervention. While a number of native flavonoids are beneficial in the treatment of neurological disorders and are known to penetrate the blood–brain barrier, microbiome-generated flavonoid metabolites (e.g., protocatechuic acid, urolithins, γ-valerolactones), which retain the antioxidant and anti-inflammatory potency of the native flavonoid in addition to bioactive properties that promote mitochondrial health and cerebrovascular microcapillary function, should also be considered as potential biotherapeutic agents. Studies are warranted to experimentally examine the efficacy of flavonoid metabolites directly, as they emerge as novel therapeutic options.

A gut-brain axis mediates sodium appetite via gastrointestinal peptide regulation on a medulla-hypothalamic circuit

Salt homeostasis is orchestrated by both neural circuits and peripheral endocrine factors. The colon is one of the primary sites for electrolyte absorption, while its potential role in modulating sodium intake remains unclear. Here, we revealed that a gastrointestinal hormone, secretin, is released from colon endocrine cells under body sodium deficiency and is indispensable for inducing salt appetite. As the neural substrate, circulating secretin activates specific receptors in the nucleus of the solitary tracts, which further activates the downstream paraventricular nucleus of the hypothalamus, resulting in enhanced sodium intake. These results demonstrated a previously unrecognized gut-brain pathway for the timely regulation of sodium homeostasis.

Effects of whey protein supplementation on adiposity, body weight, and glycemic parameters: A synthesis of evidence

AIMS

The aim of this review was to analyze the evidence of whey protein supplementation on body weight, fat mass, lean mass and glycemic parameters in subjects with overweight or type 2 diabetes mellitus (T2DM) undergoing calorie restriction or with ad libitum intake.

DATA SYNTHESIS

Overweight and obesity are considered risk factors for the development of chronic noncommunicable diseases such as T2DM. Calorie restriction is a dietary therapy that reduces weight and fat mass, promotes the improvement of glycemic parameters, and decreases muscle mass. The maintenance of muscle mass during weight loss is necessary in view of its implication in preventing chronic diseases and improving functional capacity and quality of life. The effects of increased protein consumption on attenuating muscle loss and reducing body fat during calorie restriction or ad libitum intake in overweight individuals are discussed. Some studies have demonstrated the positive effects of whey protein supplementation on improving satiety and postprandial glycemic control in short term; however, it remains unclear whether long-term whey protein supplementation can positively affect glycemic parameters.

CONCLUSIONS

Although whey protein is considered to have a high nutritional quality, its effects in the treatment of overweight, obese individuals and those with T2DM undergoing calorie restriction or ad libitum intake are still inconclusive.

Liangxue Tongyu Prescription Alleviates Brain Damage in Acute Intracerebral Hemorrhage Rats by Regulating Intestinal Mucosal Barrier Function

Background

Liangxue Tongyu prescription (LTP) is a commonly used formula for acute intracerebral hemorrhage (AICH) in clinical practice that has significant ameliorative effects on neurological deficits and gastrointestinal dysfunction, yet the mechanism remains elusive. The aim of this study was to investigate the pathway by which LTP alleviates brain damage in AICH rats.

Methods

The AICH rat models were established by autologous caudal arterial blood injection. The neurological function scores were evaluated before and after treatment. The water content and the volume of Evans blue staining in the brain were measured to reflect the degree of brain damage. RT-PCR was used to detect the inflammatory factors of the brain. Western blotting was used to detect the expression of the tight junction proteins zonula occludens 1 (ZO-1), occludin (OCLN), and claudin (CLDN) in the brain and colon, followed by mucin 2 (MUC2), secretory immunoglobulin A (SIgA), and G protein-coupled receptor 43 (GPR43) in the colon. Flow cytometry was used to detect the ratios of helper T cells 17 (Th17) and regulatory T cells (Treg) in peripheral blood, and the vagus nerve (VN) discharge signals were collected.

Results

LTP reduced the brain damage of the AICH rats. Compared with the model group, LTP significantly improved the permeability of the colonic mucosa, promoted the secretion of MUC2, SigA, and GPR43 in the colon, and regulated the immune balance of peripheral T cells. The AICH rats had significantly faster VN discharge rates and lower amplitudes than normal rats, and these abnormalities were corrected in the LTP and probiotics groups.

Conclusion

LTP can effectively reduce the degree of brain damage in AICH rats, and the mechanism may be that it can play a neuroprotective role by regulating the function of the intestinal mucosal barrier.

Role of the duodenal microbiota in functional dyspepsia

BACKGROUND

Functional dyspepsia (FD) is a common and debilitating gastrointestinal disorder attributed to altered gut-brain interactions. While the etiology of FD remains unknown, emerging research suggests the mechanisms are likely multifactorial and heterogenous among patient subgroups. Small bowel motor disturbances, visceral hypersensitivity, chronic microinflammation, and increased intestinal tract permeability have all been linked to the pathogenesis of FD. Recently, alterations to the gut microbiome have also been implicated to play an important role in the disease. Changes to the duodenal microbiota may either trigger or be a consequence of immune and neuronal disturbances observed in the disease, but the mechanisms of influence of small intestinal flora on gastrointestinal function and symptomatology are unknown.

PURPOSE

This review summarizes and synthesizes the literature on the link between the microbiota, low-grade inflammatory changes in the duodenum and FD. This review is not intended to provide a complete overview of FD or the small intestinal microbiota, but instead outline some of the key conceptual advances in understanding the interactions between altered gastrointestinal bacterial communities; dietary factors; host immune activation; and stimulation of the gut-brain axes in patients with FD versus controls. Current and emerging treatment approaches such as dietary interventions and antibiotic or probiotic use that have demonstrated symptom benefits for patients are reviewed, and their role in modulating the host-microbiota is discussed. Finally, suggested opportunities for diagnostic and therapeutic improvements for patients with this condition are presented.

Are Dietary Proteins the Key to Successful Body Weight Management? A Systematic Review and Meta-Analysis of Studies Assessing Body Weight Outcomes after Interventions with Increased Dietary Protein

The primary aim was to systematically review the current evidence investigating if dietary interventions rich in protein lead to improved body weight management in adults with excessive body weight. The secondary aim was to investigate potential modifying effects of phenotyping. A systematic literature search in PubMed, Web of Science, and Cochrane Library identified 375 randomized controlled trials with 43 unique trials meeting the inclusion criteria. The Cochrane collaboration tool was used for a thorough risk of bias assessment. Based on 37 studies evaluating effects of dietary protein on body weight, the participants with increased protein intake (ranging from 18–59 energy percentage [E%]) were found to reduce body weight by 1.6 (1.2; 2.0) kg (mean [95% confidence interval]) compared to controls (isocaloric interventions with energy reduction introduced in certain studies). Individuals with prediabetes were found to benefit more from a diet high in protein compared to individuals with normoglycemia, as did individuals without the obesity risk allele (AA genotype) compared to individuals with the obesity risk alleles (AG and GG genotypes). Thus, diets rich in protein would seem to have a moderate beneficial effect on body weight management.

Compositional Characteristics of Mediterranean Buffalo Milk and Whey

The main objective of this review is to summarize the compositional characteristics and the health and functional properties of Mediterranean buffalo milk and whey derived from mozzarella cheese production. Several studies have investigated the composition of buffalo milk and in particular its fat, protein, and carbohydrates contents. These characteristics may change depending on the breed, feeding regime, and rearing system of the animals involved in the study, and also with the seasons. In particular, buffalo milk showed a higher nutritional value and higher levels of proteins, vitamins, and minerals when compared to milks produced by other animal species. Additionally, buffalo milk contains beneficial compounds such as gangliosides that can provide antioxidant protection and neuronal protection, and can improve bone, heart, and gastrointestinal health in humans.

Mechanisms of Food-Induced Symptom Induction and Dietary Management in Functional Dyspepsia

Functional dyspepsia (FD) is a common disorder of gut-brain interaction, characterised by upper gastrointestinal symptom profiles that differentiate FD from the irritable bowel syndrome (IBS), although the two conditions often co-exist. Despite food and eating being implicated in FD symptom induction, evidence-based guidance for dietetic management of FD is limited. The aim of this narrative review is to collate the possible mechanisms for eating-induced and food-related symptoms of FD for stratification of dietetic management. Specific carbohydrates, proteins and fats, or foods high in these macronutrients have all been reported as influencing FD symptom induction, with removal of 'trigger' foods or nutrients shown to alleviate symptoms. Food additives and natural food chemicals have also been implicated, but there is a lack of convincing evidence. Emerging evidence suggests the gastrointestinal microbiota is the primary interface between food and symptom induction in FD, and is therefore a research direction that warrants substantial attention. Objective markers of FD, along with more sensitive and specific dietary assessment tools will contribute to progressing towards evidence-based dietetic management of FD.

Intact vagal gut-brain signalling prevents hyperphagia and excessive weight gain in response to high-fat high-sugar diet

Aim

The tools that have been used to assess the function of the vagus nerve lack specificity. This could explain discrepancies about the role of vagal gut‐brain signalling in long‐term control of energy balance. Here we use a validated approach to selectively ablate sensory vagal neurones that innervate the gut to determine the role of vagal gut‐brain signalling in the control of food intake, energy expenditure and glucose homoeostasis in response to different diets.

Methods

Rat nodose ganglia were injected bilaterally with either the neurotoxin saporin conjugated to the gastrointestinal hormone cholecystokinin (CCK), or unconjugated saporin as a control. Food intake, body weight, glucose tolerance and energy expenditure were measured in both groups in response to chow or high‐fat high‐sugar (HFHS) diet. Willingness to work for fat or sugar was assessed by progressive ratio for orally administered solutions, while post‐ingestive feedback was tested by measuring food intake after an isocaloric lipid or sucrose pre‐load.

Results

Vagal deafferentation of the gut increases meal number in lean chow‐fed rats. Switching to a HFHS diet exacerbates overeating and body weight gain. The breakpoint for sugar or fat solution did not differ between groups, suggesting that increased palatability may not drive HFHS‐induced hyperphagia. Instead, decreased satiation in response to intra‐gastric infusion of fat, but not sugar, promotes hyperphagia in CCK‐Saporin‐treated rats fed with HFHS diet.

Conclusions

We conclude that intact sensory vagal neurones prevent hyperphagia and exacerbation of weight gain in response to a HFHS diet by promoting lipid‐mediated satiation.

High protein diet: benefits and risks

The nature of human nutrition has become increasingly important as an effective element in the prevention and treatment of many pathologies, especially obesity, type 2 diabetes and cardiovascular diseases. High protein diets are some of the most popular eating patterns and the Dukan diet has taken the lead in popularity among the diets of this type. An increase of protein in the diet is effective in reducing body weight, primarily due to the loss of adipose tissue, without a significant effect on muscle mass. Another advantage of a high-protein diet is earlier and longer satiety compared to other diets, which makes it comfortable for use. Besides obesity, high protein diets are presumably effective for treating such diseases as nonalcoholic fatty liver disease, diabetes mellitus and cardiovascular diseases However, despite the important advantages, this nutritional model is not universal and is contraindicated in patients with diseases of liver, kidneys and osteoporosis. Besides, the prolonged use of a high protein diet may increase the risks of urolithiasis and reduced mineral bone density even for healthy individuals. Thus, the increase in the proportion of protein in the diet should take place exclusively under the supervision of a physician.

Role of Amino Acids in Blood Glucose Changes in Young Adults Consuming Cereal with Milks Varying in Casein and Whey Concentrations and Their Ratio

BACKGROUND

Increasing the total protein content and reducing the casein to whey ratio in milks consumed with breakfast cereal reduce postprandial blood glucose (BG).

OBJECTIVES

We aimed to explore associations between plasma amino acids (AAs), BG, and glucoregulatory hormones.

METHODS

In this repeated-measures design, 12 healthy adults consumed cereal (58 g) and milks (250 mL) with 3.1 wt% or high 9.3 wt% protein concentrations and with casein to whey ratios of either 80:20 or 40:60. Blood was collected at 0, 30, 60, 120, 140, 170, and 200 min for measurement of the primary outcome, BG, and for the exploratory outcomes such as plasma AA, gastric emptying, insulin (INS), and glucoregulatory hormones. Measures were made prior to and after an ad libitum lunch at 120 min. Exploratory correlations were conducted to determine associations between outcomes.

RESULTS

Pre-lunch plasma AA groups [total (TAA), essential (EAA), BCAA, and nonessential (NEAA)] were higher after 9.3 wt% than 3.1 wt% milks by 12.7%, 21.4%, 20.9%, and 7.6%, respectively (P ≤ 0.05), while post-lunch AA groups were higher by 10.9%, 19.8%, 18.8%, and 6.0%, respectively (P ≤ 0.05). Except for NEAA, pre-lunch AAs were higher after 40:60 than 80:20 ratio milks by 4.5%, 8.3%, and 9.3% (P ≤ 0.05). When pooled by all treatments, pre-lunch AA groups associated negatively with BG (r/ρ ≥ -0.45, P ≤ 0.05), but post-lunch only TAA and NEAA correlated (r ≥ -0.37, P < 0.05). Pre-lunch BG was inversely associated with Leu, Ile, Lys, Met, Thr, Cys-Cys, Asn, and Gln (r/ρ ≥ -0.46, P ≤ 0.05), but post-lunch, only with Thr, Ala, and Gly (r ≥ -0.50, P ≤ 0.05). Pre-lunch associations between AA groups and INS were not found.

CONCLUSIONS

Protein concentration and the ratio of casein to whey in milks consumed at breakfast with cereal affect plasma AA concentrations and their associations with decreased BG. The decrease in BG could be explained by INS-independent mechanisms. This trial was registered at www.clinicaltrials.gov as NCT02471092.

Protein metabolism and related body function: mechanistic approaches and health consequences

The development and maintenance of body composition and functions require an adequate protein intake with a continuous supply of amino acids (AA) to tissues. Body pool and AA cellular concentrations are tightly controlled and maintained through AA supply (dietary intake, recycled from proteolysis and de novo synthesis), AA disposal (protein synthesis and other AA-derived molecules) and AA losses (deamination and oxidation). Different molecular regulatory pathways are involved in the control of AA sufficiency including the mechanistic target of rapamycin complex 1, the general control non-derepressible 2/activating transcription factor 4 system or the fibroblast growth factor 21. There is a tight control of protein intake, and human subjects and animals appear capable of detecting and adapting food and protein intake and metabolism in face of foods or diets with different protein contents. A severely protein deficient diet induces lean body mass losses and ingestion of sufficient dietary energy and protein is a prerequisite for body protein synthesis and maintenance of muscle, bone and other lean tissues and functions. Maintaining adequate protein intake with age may help preserve muscle mass and strength but there is an ongoing debate as to the optimal protein intake in older adults. The protein synthesis response to protein intake can also be enhanced by prior completion of resistance exercise but this effect could be somewhat reduced in older compared to young individuals and gain in muscle mass and function due to exercise require regular training over an extended period.

The Impact of the Use of Glycomacropeptide on Satiety and Dietary Intake in Phenylketonuria

Protein is the most satiating macronutrient, increasing secretion of gastrointestinal hormones and diet induced thermogenesis. In phenylketonuria (PKU), natural protein is restricted with approximately 80% of intake supplied by a synthetic protein source, which may alter satiety response. Casein glycomacropeptide (CGMP-AA), a carbohydrate containing peptide and alternative protein substitute to amino acids (AA), may enhance satiety mediated by its bioactive properties. Aim: In a three-year longitudinal; prospective study, the effect of AA and two different amounts of CGMP-AA (CGMP-AA only (CGMP100) and a combination of CGMP-AA and AA (CGMP50) on satiety, weight and body mass index (BMI) were compared. Methods: 48 children with PKU completed the study. Median ages of children were: CGMP100; (n = 13), 9.2 years; CGMP50; (n = 16), 7.3 years; and AA (n = 19), 11.1 years. Semi-quantitative dietary assessments and anthropometry (weight, height and BMI) were measured every three months. Results: The macronutrient contribution to total energy intake from protein, carbohydrate and fat was similar across the groups. Adjusting for age and gender, no differences in energy intake, weight, BMI, incidence of overweight or obesity was apparent between the groups. Conclusion: In this three-year longitudinal study, there was no indication to support a relationship between CGMP and satiety, as evidenced by decreased energy intake, thereby preventing overweight or obesity. Satiety is a complex multi-system process that is not fully understood.

Effects of cultured dairy and nondairy products added to breakfast cereals on blood glucose control, satiation, satiety, and short-term food intake in young women

Breakfast cereals are often consumed with dairy products or nondairy alternatives; however, the effect of the combination on blood glucose and food intake control is not well investigated. In a randomized, crossover study, 24 healthy women (age: 22.7 ± 2.5 years; body mass index: 22.1 ± 1.5 kg/m²) consumed, to satiation, 1 of 3 treatments: Greek yogurt with granola (150 kcal, 9.2 g protein, 2.6 g fat, 2.0 g dietary fibre, and 21.5 g available carbohydrate/100 g); cultured coconut product with granola (146 kcal, 3.2 g protein, 3.2 g fat, 5.6 g dietary fibre, and 21.9 g available carbohydrate/100 g); or water control. The data were analyzed with repeated-measures ANOVA. The 2 h blood glucose iAUC was 52% lower after the dairy compared with nondairy treatment (P < 0.0001). While there were no differences in food intake between the caloric treatments consumed to satiation, protein intake was 3 times higher and fibre intake was 4 times lower after the dairy compared with nondairy treatment. Both caloric treatments resulted in similar suppression of ad libitum food intake at 2 h (P < 0.003) and subjective appetite over 2 h (P < 0.0001) compared with water. The cumulative food intake over 2 h was lower after water (P < 0.05). The 1.8-fold increase in postprandial insulin after dairy compared with nondairy treatment may explain the reduction in blood glucose without an increase in subsequent energy intake. Novelty Blood glucose in young females is lower after a breakfast with granola in a high-protein cultured dairy than when in a high-fibre nondairy cultured product. Subjective appetite over 2 h and food intake 2 h later was similarly lower after both breakfasts but cumulative intake was higher compared with breakfast skipping.

Protein Status Modulates an Appetite for Protein To Maintain a Balanced Nutritional State-A Perspective View

Protein sufficiency is tightly controlled through different sensing and signaling processes that modulate and adapt protein and energy metabolism and feeding behavior to reach and maintain a well-balanced protein status. High-protein diets, often discussed in the context of body weight management, usually activate anorexigenic pathways, leading to higher satiety, decreased food and energy intake, and decreased body weight and adiposity. Diets marginally low in protein (3-8% energy) or marginally deficient in some indispensable amino acid more often activate orexigenic pathways, with higher appetite and a specific appetite for protein, a response that leads to an increase in protein intake to partially compensate for the deficit in protein and amino acid. Diets severely deficient in protein (2-3% energy as protein) usually depress food intake and induce lower weight and lower fat mass and lean tissues that characterize a status of protein deficiency. The control of protein sufficiency involves various peripheral and central signals, including modulation of both metabolic pathways at the periphery as well as central pathways of the control of food and protein intake, including a reward-driven specific sensitivity to the protein content of foods.

The Metabolic Concept of Meal Sequence vs. Satiety: Glycemic and Oxidative Responses with Reference to Inflammation Risk, Protective Principles and Mediterranean Diet

With increasing exposure to eating opportunities and postprandial conditions becoming dominant states, acute effects of meals are garnering interest. In this narrative review, meal components, combinations and course sequence were questioned vis-à-vis resultant postprandial responses, including satiety, glycemic, oxidative and inflammatory risks/outcomes vs. protective principles, with reference to the Mediterranean diet. Representative scientific literature was reviewed and explained, and corresponding recommendations discussed and illustrated. Starting meals with foods, courses and/or preloads high in innate/added/incorporated water and/or fibre, followed by protein-based courses, delaying carbohydrates and fatty foods and minimizing highly-processed/sweetened hedonic foods, would increase satiety-per-calorie vs. obesogenic passive overconsumption. Similarly, starting with high-water/fibre dishes, followed by high-protein foods, oils/fats, and delayed/reduced slowly-digested whole/complex carbohydrate sources, optionally closing with simpler carbohydrates/sugars, would reduce glycaemic response. Likewise, starting with foods high in innate/added/incorporated water/fibre/antioxidants, high monounsaturated fatty acid foods/oils, light proteins and whole/complex carbohydrate foods, with foods/oils low in n-6 polyunsaturated fatty acids (PUFA) and n-6:n-3 PUFA ratios, and minimal-to-no red meat and highly/ultra-processed foods/lipids, would reduce oxidative/inflammatory response. Pyramids illustrating representative meal sequences, from most-to-least protective foods, visually communicate similarities between axes, suggesting potential unification for optimal meal sequence, consistent with anti-inflammatory nutrition and Mediterranean diet/meal principles, warranting application and outcome evaluation.

Whey Protein Supplementation Compared to Collagen Increases Blood Nesfatin Concentrations and Decreases Android Fat in Overweight Women: A Randomized Double-Blind Study

Protein supplements are usually used to control body weight, however, the impact of protein quality on body fat attenuation is unknown. We investigated the effects of isocaloric isoproteic supplementation of either whey protein (WG) or hydrolysed collagen supplementation (CG) on dietary intake, adiposity and biochemical markers in overweight women. Methods: In this randomized double-blind study, 37 women, [mean ± SE, age 40.6 ± 1.7 year; BMI (kg/m²) 30.9 ± 0.6], consumed sachets containing 40 g/day of concentrated whey protein (25 g total protein, 2.4 leucine, 1.0 valine, 1.5 isoleucine, n = 17) or 38 g/day of hydrolysed collagen (26 g total protein, 1.02 leucine, 0.91 valine, 0.53 isoleucine, n = 20) in the afternoon snack. The compliance was set at >70% of the total theoretical doses. The dietary intake was evaluated by a 6-day food record questionnaire. At the beginning and after eight weeks of follow-up, body composition was evaluated by using dual-energy X-ray absorptiometry and lipid profile, insulin resistance, C-reactive protein, adiponectin, leptin and nesfastin plasma concentrations were analyzed. Results: Supplements were isocaloric and isoproteic. There were no differences in caloric intake (p = 0.103), protein (p = 0.085), carbohydrate (p = 0.797) and lipids (p = 0.109) intakes. The branched chain amino acids (BCAA) (GC: 1.8 ± 0.1 g vs. WG: 5.5 ± 0.3 g, p < 0.001) and leucine intake (CG: 0.1 ± 0.1 g vs. WG: 2.6 ± 0.1 g, p < 0.001) were higher in WG compared to CG. BMI increased in the CG (0.2 ± 1.1 kg/m², p = 0.044) but did not change in WG. WG decreased the android fat (−0.1 ± 0.3 kg, p = 0.031) and increased nesfatin concentrations (4.9 ± 3.2 ng/mL, p = 0.014) compared to CG. Conclusions: Whey protein supplementation in overweight women increased nesfatin concentrations and could promote increase of resting metabolic rate as part of body composition improvement programs compared to collagen supplementation for 8 weeks. Additionally, our findings suggest that collagen may not be an effective supplement for overweight women who are attempting to alter body composition.

Selected Food/Herb-Drug Interactions: Mechanisms and Clinical Relevance

BACKGROUND

Food/Herb-drug interactions have become a major problem in health care. These interactions can lead to loss of therapeutic efficacy or toxic effects of drugs.

AREAS OF UNCERTAINTY

To probe the clinical relevance of such interactions, the impact of food/herb intake on the clinical effects of drug administration has to be evaluated. Failure to identify and efficiently manage food-drug interactions can lead to serious consequences. A comprehensive knowledge of the mechanisms that underpin variability in disposition will help optimize therapy.

DATA SOURCES

Electronic search of literatures from relevant databases were conducted. A total of 58 original scientific reports/review articles were obtained with the search strategy; of which 25 were found eligible to be included in the present review. Required data were extracted from these studies, and their methodologies were assessed.

RESULTS AND CONCLUSIONS

This review updates our knowledge on clinical food-drug interactions with emphasis on mechanism and clinical implications. Results obtained from literature search identified interactions with selected foods/herbs generated from in vivo and in vitro studies. For example, interaction studies in humans revealed a reduction in the bioavailability of mercaptopurine when taken concurrently with substances containing xanthine oxidase (eg, cow milk); a reduction in the bioavailability of quinine with Garcinia kola; increased bioavailability/toxicity of felodipine, nifedipine, saquinavir, sildenafil with grape juice; increased bioavailability of felodipine, cisapride with red wine and diminished bioavailability of fexofenadine with apple. Pharmacokinetic and/or pharmacodynamic mechanisms are implicated in many of these interactions. By evaluating the dietary patterns of patients and use of prescribed medications, health professionals will be well informed of potential interactions and associated adverse effects.

Neurocognitive effects of umami: association with eating behavior and food choice

Free glutamate, a key substance underlying the umami taste of foods, fulfills a number of physiological functions related to energy balance. Previous experimental studies have shown that intake of a broth or soup supplemented with monosodium glutamate (MSG) prior to a meal can decrease appetite and food intake, particularly in women with propensity to overeat and gain weight. In this study, we examined potential neurocognitive mechanisms underlying this effect. We evaluated changes after intake of a chicken broth with or without MSG added (MSG+/MSG-) in a sample of healthy young women. Subjects were assessed with a food-modified computerized inhibitory control task, a buffet meal test with eye-tracking, and brain responses during a food choice paradigm evaluated with functional neuroimaging. We found evidence for improvement in key parameters related to inhibitory control following intake of the MSG+ broth, particularly in subjects with high levels of eating disinhibition, who also showed lower intake of saturated fat during the meal. Additionally, consumption of the MSG+ broth led to a reduction of the rate of fixation switches between plates at the meal, and increased engagement of a brain region in the left dorsolateral prefrontal cortex previously associated with successful self-control during dietary decisions. Altogether, these results, while preliminary, suggest potential facilitating effects of glutamate (MSG) on cognitive executive processes that are relevant for the support of healthy eating behaviors and food choice.

Satiety and gastrointestinal hormones during a Mixed Meal Tolerance Test after gastric bypass surgery: association with plasma amino acid concentrations

BACKGROUND

Circulating amino acids have been associated with both appetite and the secretion of anorexigenic hormones in healthy and obese populations. This effect has not been investigated in subjects having undergone Roux-en-Y gastric bypass surgery (RYGB).

OBJECTIVE

To investigate the association between postprandial plasma concentrations of amino acids and the anorexigenic hormones glucagon-like peptide-1 (GLP-1) and peptide tyrosine tyrosine (PYY), the orexigenic hormone ghrelin, and satiety and hunger in post-RYGB subjects.

SETTING

A Dutch surgical department.

METHODS

Participants after primary RYGB were studied during a Mixed Meal Tolerance Test (MMTT). Satiety and hunger were assessed every 30 minutes on visual analogue scales. Blood samples were collected at baseline, every 10 minutes during the first half hour and every 30 minutes until 210 minutes after the start. The samples were assessed for 24 amino acids and 3 gastrointestinal hormones. Incremental areas under the curve (iAUCs) were calculated. Exploratory analyses were performed in which subjects were divided into high and low responders depending on the median iAUC.

RESULTS

42 subjects, aged 48 ± 11 (mean ± SD) years, 31 to 76 months post-RYGB and with total weight loss of 30 ± 9% completed the MMTT. Subjects with high satiety scores had more than a 25% higher net iAUC of PYY and GLP-1 and at least a 10% higher net iAUC of 10 amino acids compared to subjects with low scores (P < 0.05). The net iAUC of five of these amino acids (i.e. arginine, asparagine, histidine, serine and threonine) was more than 10% higher in subjects with high responses on GLP-1 and/or PYY (P < 0.05).

CONCLUSIONS

Certain postprandial amino acids were associated with satiety and anorexigenic hormones and could therefore play a role in appetite regulation after RYGB; either by a direct effect on satiety, indirectly through gastrointestinal hormones, or both.

Studying heating effects on desi ghee obtained from buffalo milk using fluorescence spectroscopy

Characterisation and thermal deterioration of desi ghee obtained from buffalo milk is presented for the first time using the potential of Fluorescence spectroscopy. The emission bands in non-heated desi ghee centred at 375 nm is labelled for vitamin D, 390 nm for vitamin K, 440–460 nm for isomers of conjugated linoleic acid (CLA), 490 nm for vitamin A and the region 620–700 nm is assigned to chlorophyll contents. Fluorescence emission spectra from all the heated and non-heated ghee samples were recorded using excitation wavelengths at 280, and 410 nm which were found best for getting maximum spectral signatures. Heating of desi ghee affects its molecular composition, however, the temperature range from 140 to 170°C may be defined safe for cooking /frying where it does not lose much of its molecular composition. Further, the rise in temperature induces prominent spectral variations which confirm the deterioration of valuable vitamins, isomers of CLA and chlorophyll contents. Fluorescence emission peak at 552 nm shows oxidation product and an increase in its intensity with the rise in temperature is observed. In order to classify heated samples at different temperatures, principal component analysis (PCA) has been applied on heated and non-heated ghee samples that further elucidated the temperature effects.

Raman spectroscopy combined with a support vector machine for differentiating between feeding male and female infants mother's milk

This study presents differentiation in milk samples of mother's feeding male and female infants using Raman spectroscopy combined with a support vector machine (SVM). Major differences have been observed in the Raman spectra of both types of milk based on their chemical compositions. Overall, it has been found that milk samples of mother's having a female infant are richer in fatty acids, phospholipids, and tryptophan. In contrast, milk samples of mother's having a male infant contain more carotenoids and saccharides. Principal component analysis and SVM further highlighted the differences between the two groups on the basis of differentiating features obtained from their Raman spectra. The SVM model with two different kernels, i.e. polynomial kernel function (order-2) and Gaussian radial basis function (RBF sigma-2), are used for gender based milk differentiations. The performance of the proposed model in terms of accuracy, precision, sensitivity, and specificity using the polynomial kernel function of order-2 have been found to be 86%, 88%, 85% and 88%, respectively.

Increased Protein Consumption during the Day from an Energy-Restricted Diet Augments Satiety but Does Not Reduce Daily Fat or Carbohydrate Intake on a Free-Living Test Day in Overweight Women

Background: Higher-protein (HP) energy-restriction diets improve weight management to a greater extent than normal-protein (NP) versions. Potential mechanisms of action with regard to assessment of eating behaviors across the day have not been widely examined during energy restriction.Objectives: The objectives of this study were to test whether the consumption of an HP energy-restriction diet reduces carbohydrate and fat intakes through improvements in daily appetite, satiety, and food cravings compared with NP versions and to test whether protein type within the NP diets alters protein-related satiety.Methods: Seventeen overweight women [mean ± SEM age: 36 ± 1 y; body mass index (kg/m2): 28.4 ± 0.1] completed a randomized, controlled-feeding crossover study. Participants were provided with the following ∼1250-kcal/d energy-restricted (-750-kcal/d deficit) diets, each for 6 d: HP [124 g protein/d; 60% from beef and 40% from plant sources (HP-BEEF)] or NP (48 g protein/d) that was protein-type matched (NP-BEEF) or unmatched [100% from plant-based sources (NP-PLANT)]. On day 6 of each diet period, participants completed a 12-h testing day containing repetitive appetite, satiety, and food-craving questionnaires. On day 7, the participants were asked to consume their protein requirement within each respective diet but were provided with a surplus of carbohydrate- and fat-rich foods to consume, ad libitum, at each eating occasion across the day. All outcomes reported were primary study outcomes.Results: The HP-BEEF diet reduced daily hunger by 16%, desire to eat by 15%, prospective food consumption by 14%, and fast-food cravings by 15% but increased daily fullness by 25% compared with the NP-BEEF and NP-PLANT diets (all P < 0.05). However, consuming more protein throughout the day did not reduce the energy consumed ad libitum from the fat- and carbohydrate-rich foods (HP-BEEF: 2000 ± 180 kcal/d; NP-BEEF: 2120 ± 190 kcal/d; NP-PLANT: 2070 ± 180 kcal/d). None of the outcomes differed between the NP-BEEF and NP-PLANT treatments.Conclusions: Although appetite control, satiety, and food cravings improved after an HP energy-restriction diet, increased protein consumption did not reduce carbohydrate and fat intakes throughout the free-living test day in overweight healthy women exposed to highly palatable foods. This trial was registered at clinicaltrials.gov as NCT02614729.

Identification of cow and buffalo milk based on Beta carotene and vitamin-A concentration using fluorescence spectroscopy

The current study presents the application of fluorescence spectroscopy for the identification of cow and buffalo milk based on β-carotene and vitamin-A which is of prime importance from the nutritional point of view. All samples were collected from healthy animals of different breeds at the time of lactation in the vicinity of Islamabad, Pakistan. Cow and buffalo milk shows differences at fluorescence emission appeared at band position 382 nm, 440 nm, 505 nm and 525 nm both in classical geometry (right angle) setup as well as front face fluorescence setup. In front face fluorescence geometry, synchronous fluorescence emission shows clear differences at 410 nm and 440 nm between the milk samples of both these species. These fluorescence emissions correspond to fats, vitamin-A and β-carotene. Principal Component Analysis (PCA) further highlighted these differences by showing clear separation between the two data sets on the basis of features obtained from their fluorescence emission spectra. These results indicate that classical geometry (fixed excitation wavelength) as well as front face (synchronous fluorescence emission) of cow and buffalo milk nutrients could be used as fingerprint from identification point of view. This same approach can effectively be used for the determination of adulterants in the milk and other dairy products.

Effects of dietary urea concentration and zilpaterol hydrochloride on performance and carcass characteristics of finishing steers

Cattle receiving zilpaterol hydrochloride () may recycle less N and require a greater supply of RDP. This study evaluated effects of ZH on performance and carcass characteristics of steers fed diets with increasing dietary RDP concentrations supplied as urea. Steers (429 animals; BW = 423 ± 4.5 kg) were sorted into 3 blocks according to BW and assigned to 1 of 6 treatments (6 pens per treatment) in a randomized complete block design. Treatments were a 2 × 3 factorial arrangement of either no ZH or ZH (75 mg ZH per steer daily) supplemented to finishing diets containing 0, 0.5, or 1.0% urea of dietary DM. Pen weights were recorded before treatment initiation; urea was fed for 27 d, and ZH treatments were fed for 24 d with a 3-d withdrawal period. Pen weights were recorded before transporting steers to a commercial abattoir. Continuous response variables were analyzed using the MIXED procedure and categorical data were analyzed using the GLIMMIX procedure of SAS. No ZH × dietary urea interactions ( ≥ 0.14) occurred for all performance and carcass response variables. Feeding ZH for the last 27 d (included a 3-d withdrawal period) of the finishing period increased ( < 0.01) ADG, decreased ( < 0.01) DMI, and increased ( < 0.01) G:F compared with no ZH. In addition, ZH increased HCW ( < 0.01), dressing percentage ( < 0.01), LM area ( < 0.01), and decreased ( = 0.01) yield grade. Increasing dietary urea linearly decreased ( = 0.01) ADG and DMI. A tendency for a linear decrease ( = 0.10) in HCW, and a tendency for a quadratic increase ( = 0.07) in marbling score were observed as urea increased in the diet. Results indicate that cattle supplemented with ZH do not require additional RDP in the diet, and that performance and carcass characteristics were negatively affected when urea was increased in the diet.

Acute and Long-Term Impact of High-Protein Diets on Endocrine and Metabolic Function, Body Composition, and Exercise-Induced Adaptations

BACKGROUND

High-protein diets have been shown to improve body composition through alterations in satiety, muscle protein synthesis, and the thermic effect of food.

AIM

Given these findings, the purpose of this review is to discuss the integration of the specific hormonal and metabolic effects of high-protein diets following both acute and long-term usage, especially with regard to body composition.

METHODS

Full-text articles were obtained through PubMed by using the terms "high-protein diet and body composition," "high-protein diet and exercise," "high-protein diet risk," "high-protein diet side effects," "protein quality PDCAAS," "RDA for protein," and "daily protein recommendation." Articles were initially screened according to their title and abstract; careful evaluation of the full manuscripts was then used to identify relevant articles.

RESULTS

The higher satiety exerted by high-protein diets is generated through increments in anorexigenic, as well as decrements in orexigenic hormones. Improvements in muscle mass are achieved by activation of muscle protein synthesis acting through the mTOR pathway. High thermic effect of food is caused due to necessary deamination, gluconeogenesis, and urea synthesis caused by high-protein diets. Interestingly, high-protein diets in both hypo- and normocaloric conditions have shown to improve body composition, whereas in combination with hypercaloric conditions does not seem to increase fat mass, when the excess energy comes from protein.

CONCLUSIONS

High protein diets effectively improve body composition by acting through different pathways.

The pathogenesis of proventricular dilatation disease

Bornaviruses cause neurologic diseases in several species of birds, especially parrots, waterfowl and finches. The characteristic lesions observed in these birds include encephalitis and gross dilatation of the anterior stomach — the proventriculus. The disease is thus known as proventricular dilatation disease (PDD). PDD is characterized by extreme proventricular dilatation, blockage of the passage of digesta and consequent death by starvation. There are few clinical resemblances between this and the bornaviral encephalitides observed in mammals. Nevertheless, there are common virus-induced pathogenic pathways shared across this disease spectrum that are explored in this review. Additionally, a review of the literature relating to gastroparesis in humans and the control of gastric mobility in mammals and birds points to several plausible mechanisms by which bornaviral infection may result in extreme proventricular dilatation.

Dietary guidance for pulses: the challenge and opportunity to be part of both the vegetable and protein food groups

Pulses are a dry, edible variety of beans, peas, and lentils that have been consumed for 10,000 years. Pulses are rich in plant-based protein and fiber, as well as micronutrients such as iron and potassium. The satiating effect of both fiber and protein assists in managing weight and combating obesity. The high fiber content and low glycemic index of pulses aid people with diabetes in maintaining blood glucose and insulin levels. Pulse consumption may improve serum lipid levels to reduce the risk of cardiovascular disease. Pulses developed as a member of both the protein and vegetable food groups as a result of its high content of plant-based protein and dietary fiber. The last two revisions of the Dietary Guidelines saw the transformation from the MyPyramid "meat and beans group" to the MyPlate "protein foods group," a nutrient name rather than a food source. Research suggests that consumers better identify with food source examples rather than nutrient names. The 2015 Dietary Guidelines also came with a new area: sustainable diets. Encouraging the consumption of sustainable food sources, like pulses, is imperative to ensuring a secure, healthy food supply for the U.S. population over time and for future generations.

Measurement of Behavioral Taste Responses in Mice: Two-Bottle Preference, Lickometer, and Conditioned Taste-Aversion Tests

The natural like and dislike of foods based on taste is one of the most easily observed behaviors in animals. Animals eat palatable foods and reject aversive foods, which makes measurement of taste perception possible using various behavioral techniques. Three different methods to accurately measure taste behavior are described here. First, two-bottle preference tests evaluate whether a taste compound (tastant) is preferred over water. Second, lickometer tests quantify the like and dislike for multiple concentrations of the same tastant or multiple tastants at the same time. Finally, conditioned taste aversion tests accurately determine the perceived taste threshold for palatable tastants. Together, these diverse methods enable researchers to observe and measure behavioral taste responses in mice to any tastant. © 2016 by John Wiley & Sons, Inc.

Satiety Effects of Lentils in a Calorie Matched Fruit Smoothie

The food environment is changing, with consumers being more health conscious and concerned about the wholesomeness of their food than ever before. Consumers are looking for nutritious whole food alternatives to fill their plates and stomachs. Pulse grains, rich in both protein and fiber, may be the ideal candidate to promote satiety at meals. In a crossover feeding study, participants consumed calorie-matched fruit smoothies prepared with either an ice cream base or pureed red lentils. Self-reported satiety, blood glucose response, and ad libitum food intake at a secondary meal were all measured along with breath hydrogen and methane and gastrointestinal tolerance. While there was no significant difference in satiety response or energy intake at the secondary meal, the nutrient profile of the lentil smoothie was improved with increased protein and fiber and dramatically lower fat content. Blood glucose response was not statistically different between the 2 treatments. Both smoothies were generally well tolerated; however, there was a slightly elevated AUC for perceived gastrointestinal tolerance over 24 h in the lentil smoothie. No difference in breath hydrogen or methane response was seen between treatments. The substitution of lentils into a meal is not likely to improve satiety; however lentils are a good source of fiber and protein and can greatly improve nutritional content of the meal.

L-arginine promotes gut hormone release and reduces food intake in rodents

AIMS

To investigate the anorectic effect of L-arginine (L-Arg) in rodents.

METHODS

We investigated the effects of L-Arg on food intake, and the role of the anorectic gut hormones glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), the G-protein-coupled receptor family C group 6 member A (GPRC6A) and the vagus nerve in mediating these effects in rodents.

RESULTS

Oral gavage of L-Arg reduced food intake in rodents, and chronically reduced cumulative food intake in diet-induced obese mice. Lack of the GPRC6A in mice and subdiaphragmatic vagal deafferentation in rats did not influence these anorectic effects. L-Arg stimulated GLP-1 and PYY release in vitro and in vivo. Pharmacological blockade of GLP-1 and PYY receptors did not influence the anorectic effect of L-Arg. L-Arg-mediated PYY release modulated net ion transport across the gut mucosa. Intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) administration of L-Arg suppressed food intake in rats.

CONCLUSIONS

L-Arg reduced food intake and stimulated gut hormone release in rodents. The anorectic effect of L-Arg is unlikely to be mediated by GLP-1 and PYY, does not require GPRC6A signalling and is not mediated via the vagus. I.c.v. and i.p. administration of L-Arg suppressed food intake in rats, suggesting that L-Arg may act on the brain to influence food intake. Further work is required to determine the mechanisms by which L-Arg suppresses food intake and its utility in the treatment of obesity.

A hepatic amino acid/mTOR/S6K-dependent signalling pathway modulates systemic lipid metabolism via neuronal signals

Metabolism is coordinated among tissues and organs via neuronal signals. Levels of circulating amino acids (AAs), which are elevated in obesity, activate the intracellular target of rapamycin complex-1 (mTORC1)/S6kinase (S6K) pathway in the liver. Here we demonstrate that hepatic AA/mTORC1/S6K signalling modulates systemic lipid metabolism via a mechanism involving neuronal inter-tissue communication. Hepatic expression of an AA transporter, SNAT2, activates the mTORC1/S6K pathway, and markedly elevates serum triglycerides (TGs), while downregulating adipose lipoprotein lipase (LPL). Hepatic Rheb or active-S6K expression have similar metabolic effects, whereas hepatic expression of dominant-negative-S6K inhibits TG elevation in SNAT2 mice. Denervation, pharmacological deafferentation and β-blocker administration suppress obesity-related hypertriglyceridemia with adipose LPL upregulation, suggesting that signals are transduced between liver and adipose tissue via a neuronal pathway consisting of afferent vagal and efferent sympathetic nerves. Thus, the neuronal mechanism uncovered here serves to coordinate amino acid and lipid levels and contributes to the development of obesity-related hypertriglyceridemia.

Nutrients, satiety, and control of energy intake

In the context of the worldwide epidemic of obesity affecting men and women of all ages, it is important to understand the mechanisms that control human appetite, particularly those that allow the adjustment of energy intake to energy needs. Satiety is one important psycho-biological mechanism whose function is to inhibit intake following the ingestion of a food or a beverage. According to the classical theories of appetite control, satiety is influenced by macronutrient intake and/or metabolism. Satiety also seems to be modified by micronutrients, non-nutrients, and some bioactive food constituents. Under optimal conditions, satiety should be well connected with hunger and satiation in a way that spontaneously leads to a close match between energy intake and expenditures. However, the current obesity epidemic suggests that dysfunctions often affect satiety and energy intake. In this regard, this paper presents a conceptual integration that hopefully will help health professionals address satiety issues and provide the public with informed advice to facilitate appetite control.

Protein-dependent regulation of feeding and metabolism

Free-feeding animals often face complex nutritional choices that require the balancing of competing nutrients, but the mechanisms driving macronutrient-specific food intake are poorly defined. A large number of behavioral studies indicate that both the quantity and quality of dietary protein can markedly influence food intake and metabolism, and that dietary protein intake may be prioritized over energy intake. This review focuses on recent progress in defining the mechanisms underlying protein-specific feeding. Considering the evidence that protein powerfully regulates both food intake and metabolism, uncovering these protein-specific mechanisms may reveal new molecular targets for the treatment of obesity and diabetes while also offering a more complete understanding of how dietary factors shape both food intake and food choice.