Dietary proteins contribute little to glucose production, even under optimal gluconeogenic conditions in healthy humans

A comprehensive review on the implications of Yogic/Sattvic diet in reducing inflammation in type 2 diabetes

Chronic inflammation in type 2 diabetes (T2D), characterized by constitutively activated immune cells and elevated pro-inflammatory mediators along with hyperglycaemia and increased free fatty acids and branched chain amino acid levels, significantly alters the immuno-metabolic axis. Over the years, dietary intervention has been explored as an effective strategy for managing T2D. Evidence from experimental and clinical studies indicates that various diets, including Mediterranean, Nordic, Palaeolithic and ketogenic diets, increase insulin sensitivity, decrease gluconeogenesis, and adiposity, and exert anti-inflammatory effects, thus preserving immuno-metabolic homeostasis in individuals with T2D. Indian dietary sources are categorized as Sattvic, Rajasic, and Tamasic, depending on their impact on health and behaviour. The Yogic diet, commonly recommended during yoga practice, is predominantly Sattvic, emphasizing plant-based whole foods while limiting processed and high-glycaemic-index items. Yogic diet is also recommended for Mitahara, emphasizing mindful eating, which is attributed to calorie restriction. Adopting a Yogic diet, featuring low-fat vegetarian principles, strongly reduces inflammatory mediator levels. This diet not only ameliorates insulin resistance and maintains a healthy body weight but also regulates immunomodulation, enhances gut microbiome diversity and provides essential phytonutrients, collectively preventing inflammation. Although, preliminary studies show aforementioned beneficial role of Yogic diet in improving diabetes associated metabolic and inflammatory changes, precise cellular and molecular mechanisms are not yet understood. Hence, further studies are warranted to decipher the mechanisms. This review summarizes the multiple roles of Yogic diet and related dietary components in mitigating inflammation and enhancing glycaemic control in T2D.

The Glycemic Impact of Protein Ingestion in People With Type 1 Diabetes

In individuals with type 1 diabetes, carbohydrate is commonly recognized as the primary macronutrient influencing postprandial glucose levels. Accumulating evidence indicates that protein ingestion also contributes to the increment in postprandial glucose levels, despite endocrine and metabolic responses different from those with carbohydrate ingestion. However, findings regarding protein ingestion's glycemic effect in people with type 1 diabetes are equivocal, with the magnitude of glycemic response seemingly dependent on the rate of absorption and composition of protein ingested. Therefore, the aim of this article is to outline the physiological mechanisms by which ingested protein influences blood glucose regulation in individuals with type 1 diabetes and provide clinical implications on use of dietary protein in the context of glycemic management. Specifically, protein ingestion raises plasma amino acid levels, which directly or indirectly (via gut hormones) stimulates glucagon secretion. Together with the increase in gluconeogenic precursors and an absent endogenous insulin response in individuals with type 1 diabetes, this provides a synergistic physiological environment for increased endogenous glucose production and subsequently increasing circulating glucose levels for several hours. While there is a dearth of well-controlled studies in this area, we provide clinical implications and directions for future research regarding the potential for using ingestion of fast-absorbing protein (such as whey protein) as a tool to prevent and mitigate overnight- and exercise-induced hypoglycemia in people with type 1 diabetes.

Postexercise Dietary Leucine Retention for Whole-Body Anabolism Is Greater With Whey Protein Isolate and Fish-Derived Protein Hydrolysate Than Nonessential Amino Acids in Trained Young Men

Marine-derived proteins, such as blue whiting-derived protein hydrolysates (BWPH), represent high-quality sources of dietary protein, but their ability to support postexercise anabolism is not established. The impact of BWPH on whole-body anabolism was compared with an isonitrogenous whey protein isolate (WPI) and nonessential amino acid (NEAA) control in 10 trained young males (31 ± 4 years) who, on three separate visits, performed a session of whole-body resistance exercise and then consumed, in randomized crossover fashion, BWPH, WPI, or NEAA (0.33 g/kg; 19, 33, and 0 mg/kg leucine, respectively) with L-[1-13C]leucine. Breath, blood, and urine samples were collected for 6-hr postprandial to assess dietary leucine oxidation, amino acid (AA) concentrations, and 3-methylhistidine: creatinine ratio. Peak and area under the curve concentrations for leucine, branched-chain amino acids, and essential amino acids were greater in WPI compared with BWPH (all p < .05) but with no differences in time to peak concentration. Total oxidation reflected leucine intake (WPI > BWPH > NEAA; p < .01), whereas relative oxidation was greater (p < .01) in WPI (28.6 ± 3.6%) compared with NEAA (21.3 ± 4.2%), but not BWPH (28.6 ± 8.8%). Leucine retention, a proxy for whole-body protein synthesis, was greater in WPI (185.6 ± 9.5 μmol/kg) compared with BWPH (109.3 ± 14.1 μmol/kg) and NEAA (5.74 ± 0.30 μmol/kg; both p < .01), with BWPH being greater than NEAA (p < .01). Urinary 3-methylhistidine: creatinine ratio did not differ between conditions. Both WPI and BWPH produced essential aminoacidemia and supported whole-body anabolism after resistance exercise, but a higher intake of BWPH to better approximate the leucine and EAA content of WPI may be needed to produce an equivalent anabolic response.

Clinical research framework proposal for ketogenic metabolic therapy in glioblastoma

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, with a universally lethal prognosis despite maximal standard therapies. Here, we present a consensus treatment protocol based on the metabolic requirements of GBM cells for the two major fermentable fuels: glucose and glutamine. Glucose is a source of carbon and ATP synthesis for tumor growth through glycolysis, while glutamine provides nitrogen, carbon, and ATP synthesis through glutaminolysis. As no tumor can grow without anabolic substrates or energy, the simultaneous targeting of glycolysis and glutaminolysis is expected to reduce the proliferation of most if not all GBM cells. Ketogenic metabolic therapy (KMT) leverages diet-drug combinations that inhibit glycolysis, glutaminolysis, and growth signaling while shifting energy metabolism to therapeutic ketosis. The glucose-ketone index (GKI) is a standardized biomarker for assessing biological compliance, ideally via real-time monitoring. KMT aims to increase substrate competition and normalize the tumor microenvironment through GKI-adjusted ketogenic diets, calorie restriction, and fasting, while also targeting glycolytic and glutaminolytic flux using specific metabolic inhibitors. Non-fermentable fuels, such as ketone bodies, fatty acids, or lactate, are comparatively less efficient in supporting the long-term bioenergetic and biosynthetic demands of cancer cell proliferation. The proposed strategy may be implemented as a synergistic metabolic priming baseline in GBM as well as other tumors driven by glycolysis and glutaminolysis, regardless of their residual mitochondrial function. Suggested best practices are provided to guide future KMT research in metabolic oncology, offering a shared, evidence-driven framework for observational and interventional studies.

Intermittent fasting influences immunity and metabolism

Intermittent fasting (IF) modifies cell- and tissue-specific immunometabolic responses that dictate metabolic flexibility and inflammation during obesity and type 2 diabetes (T2D). Fasting forces periods of metabolic flexibility and necessitates increased use of different substrates. IF can lower metabolic inflammation and improve glucose metabolism without lowering obesity and can influence time-dependent, compartmentalized changes in immunity. Liver, adipose tissue, skeletal muscle, and immune cells communicate to relay metabolic and immune signals during fasting. Here we review the connections between metabolic and immune cells to explain the divergent effects of IF compared with classic caloric restriction (CR) strategies. We also explore how the immunometabolism of metabolic diseases dictates certain IF outcomes, where the gut microbiota triggers changes in immunity and metabolism during fasting.

Ketogenic Diet Plus Resistance Training Applied to Physio-Pathological Conditions: A Brief Review

The ketogenic diet (KD) is a nutritional strategy characterized by a reduced intake of carbohydrates (between 30 and 45 g per day or ≈5% of one’s total calories from this macronutrient). The regimen induces physiological ketosis in which serum levels of ketone bodies increase from 0.5 to 3.0 mM, becoming an essential contributor to energy production. The popularity of using the KD to lose weight and its application in specific physio-pathological conditions, such as epilepsy, lipedema, and polycystic ovary syndrome, which is maintained over extended periods, gave us the impulse to write this brief review. In these types of physio-pathological conditions, subjects can achieve favorable training outcomes even if adhering to a KD. Therefore, performing resistance training under the KD to enhance muscle status and quality of life could be possible. It is important to note that, while some statements here suggest potential future directions, they are hypotheses that require experimental validation, even if they are supported by the independent benefits reported from the KD and resistance training and represent a promising area for future research.

Postprandial glycemic response to a high-protein diabetes-specific nutritional shake compared to isocaloric instant oatmeal in people with type 2 diabetes: a randomized, controlled, crossover trial

Introduction

Minimizing postprandial glucose response is an important goal for overall diabetes management. Diabetes-specific nutritional shakes (DSNS) have been clinically shown to minimize postprandial glucose response in people with type 2 diabetes (T2DM) compared to high-glycemic foods. However, it is unknown how a high-protein, low-fat DSNS impacts the GLP-1 response.

Methods

We tested the postprandial glucose, insulin, and GLP-1 response to a high-protein, low-fat diabetes-specific nutritional shake (DSNS-HP) compared to isocaloric instant oatmeal (IOM) in a randomized, controlled, crossover study in adults with T2DM (n = 24). Participants were randomly selected to receive IOM or DSNS-HP on two test days. Glucose, insulin, and total GLP-1 concentration were measured at baseline and 15, 30, 45, 60, 90, 120, 180, and 240 min postprandially.

Results

Compared to IOM, the glucose-positive area under the curve (pAUC) was significantly lower (P = .021). DSNS-HP significantly increased GLP-1 pAUC response by 213% (P <.001) with a corresponding increase in insulin pAUC (P = .033) compared to IOM.

Discussion

A high-protein, low-fat DSNS leads to favorable changes in GLP-1 response and is a suitable option to minimize blood glucose response in people with type 2 diabetes.

Protein quality, nutrition and health

Dietary proteins are energy macronutrients providing nitrogen, amino acids (AA), and energy. AAs are the main nitrogen-containing compounds in the body and are the precursors for the synthesis of body proteins and of several other AA-derived molecules. Among the 20 AAs included in protein sequence, 9 are classified as "nutritionally essential" or "indispensable" AA (IAA) because they cannot be synthesized in the body and must be provided by the diet. IAAs are limiting components for protein synthesis. An adequate intake of protein is required to support growth, maintenance, body functions, health and survival. Official definition of protein requirement is based on nitrogen balance. Protein quality is related to the capacity of protein to provide an adequate quantity of nitrogen and of each of the 9 IAAs for the different physiological situations in humans. Protein source is considered high quality for humans when the protein is readily digested, simultaneously providing an adequate quantity of nitrogen and of each of the 9 IAAs to maintain an adequate metabolic AA pool. The most accurate assessment of protein quality of foods for humans is through metabolic studies that measure nitrogen balance. The protein quality score is the ratio of the content of each IAA in the food and in a reference profile. This score corresponds to the calculated composition of a protein which, when meeting protein requirements, simultaneously meets the requirements of each of the 9 IAAs. AA scores as predictors of protein quality must be adjusted for protein and AA availability.

Adipose tissue in cortisol excess: What Cushing's syndrome can teach us?

Endogenous Cushing's syndrome (CS) is a rare condition due to prolonged exposure to elevated circulating cortisol levels that features its typical phenotype characterised by moon face, proximal myopathy, easy bruising, hirsutism in females and a centripetal distribution of body fat. Given the direct and indirect effects of hypercortisolism, CS is a severe disease burdened by increased cardio-metabolic morbidity and mortality in which visceral adiposity plays a leading role. Although not commonly found in clinical setting, endogenous CS is definitely underestimated leading to delayed diagnosis with consequent increased rate of complications and reduced likelihood of their reversal after disease control. Most of all, CS is a unique model for systemic impairment induced by exogenous glucocorticoid therapy that is commonly prescribed for a number of chronic conditions in a relevant proportion of the worldwide population. In this review we aim to summarise on one side, the mechanisms behind visceral adiposity and lipid metabolism impairment in CS during active disease and after remission and on the other explore the potential role of cortisol in promoting adipose tissue accumulation.

True Ileal Amino Acid Digestibility and Protein Quality of 15N-Labeled Faba Bean in Healthy Humans

BACKGROUND

The recommended transition toward more plant-based diets, particularly containing legumes, requires a wider knowledge of plant protein bioavailability. Faba beans are cultivated at different latitudes and are used increasingly in human nutrition.

OBJECTIVES

We aimed to assess the nutritional quality of faba bean protein in healthy volunteers equipped with an intestinal tube to implement the ileal 15N balance method.

METHODS

Nine volunteers completed the study (7 males, 2 females, aged 33 ± 10 y, BMI: 24.7 ± 2.6 kg/m2). They were equipped with a nasoileal tube. After fasting overnight, they ingested a test meal consisting of cooked mash of dehulled faba bean seeds (20 g protein per serving of approximately 250 g) intrinsically labeled with 15N. Samples of ileal contents, plasma, and urine were collected over an 8-h postprandial period. Undigested nitrogen (N) and amino acids (AAs) were determined using isotopic MS, and subsequently, ileal digestibility and digestible indispensable amino acid score (DIAAS) were calculated. The measurement of postprandial deamination allowed calculation of the net postprandial protein utilization (NPPU).

RESULTS

The ileal N digestibility was 84.1% ± 7.7%. Postprandial deamination represented 19.2% ± 3.6% of ingested N, and the NPPU was 64.7% ± 9.7%. The ileal digestibility of individual AAs varied from 85.1% ± 13.7% for histidine to 94.2% ± 3.6% for glutamine + glutamate. The mean AA digestibility was ∼6 percentage points higher than the digestibility of N, reaching 89.8% ± 5.9%, whereas indispensable AA digestibility was 88.0% ± 7.3%. Histidine and tryptophan were the first limiting AAs [DIAAS = 0.77 (calculated by legume-specific N-to-protein conversion factor 5.4); 0.67 (by default factor 6.25)]. Sulfur AAs were limiting to a lesser extent [DIAA ratio = 0.94 (N × 5.4); 0.81 (N × 6.25)].

CONCLUSIONS

Protein ileal digestibility of cooked, dehulled faba beans in humans was moderate (<85%), but that of AAs was close to 90%. Overall protein quality was restricted by the limited histidine and tryptophan content. This trial was registered at clinicaltrials.gov as NCT05047757.

The impact of a single dose of whey protein on glucose flux and metabolite profiles in normoglycemic males: insights into glucagon and insulin biology

Protein ingestion concurrently stimulates euglycemic glucagon and insulin secretion, a response that is particularly robust with rapidly absorbing proteins. Previously, we have shown that ingestion of repeated doses of rapidly absorbing whey protein equally stimulated endogenous glucose production (EGP) and glucose disposal (Rd), thus explaining the preservation of euglycemia. Here, we aimed to determine if a smaller single dose of whey could elicit a large enough glucagon and insulin response to stimulate glucose flux. Therefore, in normoglycemic young adult males (n = 10; age ∼26; BMI ∼25), using [6,6-2H2] glucose tracing and quantitative targeted metabolite profiling, we determined the metabolic response to a single 25 g "standard" dose of whey protein. Whey protein ingestion did not alter glycemia, but increased circulating glucagon (peak 4-fold basal), insulin (peak 6-fold basal), amino acids, and urea while also reducing free fatty acid (FFA) and glycerol concentrations. Interestingly, the postprandial insulin response was driven by both a stimulation of insulin secretion and marked reduction in hepatic insulin clearance. Whey protein ingestion resulted in a modest stimulation of EGP and Rd, both peaking at ∼20% above baseline 1 h after protein ingestion. These findings demonstrate that the ingestion of a single standard serving of whey protein can induce a euglycemic glucagon and insulin response that stimulates glucose flux. We speculate on a theory that could potentially explain how glucagon and insulin synergistically provide hardwired control of nitrogen and glucose homeostasis.NEW & NOTEWORTHY Protein ingestion concurrently stimulates glucagon and insulin secretion. Here we show that in normoglycemic males, ingestion of a single "standard" 25 g serving of rapidly absorbing whey protein drives a sufficiently large glucagon and insulin response, such that it simultaneously increases endogenous glucose production and glucose disposal. We speculate on a novel theory that could potentially explain how the antagonistic/synergistic actions of glucagon and insulin simultaneously provide tight control of glucose and nitrogen homeostasis.

Evaluation of Protein Quality in Humans and Insights on Stable Isotope Approaches to Measure Digestibility - A Review

The recent Food and Agricultural Organization/World Health Organization/United Nations University expert consultations on protein requirements and quality have emphasized the need for the new Digestible Indispensable Amino Acid Score (DIAAS), as a measure of protein quality. This requires human measurements of the true ileal digestibility of individual indispensable amino acids (IAAs) until the end of the small intestine. Digestibility is measured using standard oro-ileal balance methods, which can only be achieved by an invasive naso-ileal intubation in healthy participants or fistulation at the terminal ileum. Significant efforts have been made over the last 2 decades to develop noninvasive or minimally invasive methods to measure IAA digestibility in humans. The application of intrinsically labeled (with stable isotopes like 13C, 15N, and 2H) dietary proteins has helped in circumventing the invasive oro-ileal balance techniques and allowed the differentiation between endogenous and exogenous protein. The noninvasive indicator amino acid oxidation (IAAO) technique, which is routinely employed to measure IAA requirements, has been modified to estimate metabolic availability (a sum of digestibility and utilization) of IAA in foods, but provides an estimate for a single IAA at a time and is burdensome for participants. The recently developed minimally invasive dual isotope tracer method measures small intestinal digestibility of multiple amino acids at once and is suitable for use in vulnerable groups and disease conditions. However, it remains to be validated against standard oro-ileal balance techniques. This review critically evaluates and compares the currently available stable isotope-based protein quality evaluation methods with a focus on the digestibility and metabolic availability measurements in humans. In view of building a reliable DIAAS database of various protein sources and subsequently supporting protein content claims in food labeling, a re-evaluation and harmonization of the available methods are necessary.

Ketogenic diets, physical activity and body composition: a review

Obesity remains a serious relevant public health concern throughout the world despite related countermeasures being well understood (i.e. mainly physical activity and an adjusted diet). Among different nutritional approaches, there is a growing interest in ketogenic diets (KD) to manipulate body mass (BM) and to enhance fat mass loss. KD reduce the daily amount of carbohydrate intake drastically. This results in increased fatty acid utilisation, leading to an increase in blood ketone bodies (acetoacetate, 3-β-hydroxybutyrate and acetone) and therefore metabolic ketosis. For many years, nutritional intervention studies have focused on reducing dietary fat with little or conflicting positive results over the long term. Moreover, current nutritional guidelines for athletes propose carbohydrate-based diets to augment muscular adaptations. This review discusses the physiological basis of KD and their effects on BM reduction and body composition improvements in sedentary individuals combined with different types of exercise (resistance training or endurance training) in individuals with obesity and athletes. Ultimately, we discuss the strengths and the weaknesses of these nutritional interventions together with precautionary measures that should be observed in both individuals with obesity and athletic populations. A literature search from 1921 to April 2021 using Medline, Google Scholar, PubMed, Web of Science, Scopus and Sportdiscus Databases was used to identify relevant studies. In summary, based on the current evidence, KD are an efficient method to reduce BM and body fat in both individuals with obesity and athletes. However, these positive impacts are mainly because of the appetite suppressive effects of KD, which can decrease daily energy intake. Therefore, KD do not have any superior benefits to non-KD in BM and body fat loss in individuals with obesity and athletic populations in an isoenergetic situation. In sedentary individuals with obesity, it seems that fat-free mass (FFM) changes appear to be as great, if not greater, than decreases following a low-fat diet. In terms of lean mass, it seems that following a KD can cause FFM loss in resistance-trained individuals. In contrast, the FFM-preserving effects of KD are more efficient in endurance-trained compared with resistance-trained individuals.

Effects of Combining a Ketogenic Diet with Resistance Training on Body Composition, Strength, and Mechanical Power in Trained Individuals: A Narrative Review

Ketogenic diets (KD) have gained popularity in recent years among strength-trained individuals. The present review summarizes current evidence—with a particular focus on randomized controlled trials—on the effects of KD on body composition and muscle performance (strength and power output) in strength-trained individuals. Although long-term studies (>12 weeks) are lacking, growing evidence supports the effectiveness of an ad libitum and energy-balanced KD for reducing total body and fat mass, at least in the short term. However, no or negligible benefits on body composition have been observed when comparing hypocaloric KD with conventional diets resulting in the same energy deficit. Moreover, some studies suggest that KD might impair resistance training-induced muscle hypertrophy, sometimes with concomitant decrements in muscle performance, at least when expressed in absolute units and not relative to total body mass (e.g., one-repetition maximum). KD might therefore be a beneficial strategy for promoting fat loss, although it might not be a recommendable option to gain muscle mass and strength/power. More research is needed on the adoption of strategies for avoiding the potentially detrimental effect of KD on muscle mass and strength/power (e.g., increasing protein intake, reintroduction of carbohydrates before competition). In summary, evidence is as yet scarce to support a major beneficial effect of KD on body composition or performance in strength-trained individuals. Furthermore, the long-term effectiveness and safety of this type of diet remains to be determined.

RETRACTED: Whey protein preload enhances the active GLP-1 response and reduces circulating glucose in women with polycystic ovarian syndrome

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. The article is a duplicate of a paper that has already been published in Nutrients: (Nutrients 2021, 13(7), 2451. https://doi.org/10.3390/nu13072451. Redundant publications overweigh the relative importance of published findings and distort the academic record of the authors. One of the conditions of submission of a paper for publication is therefore that authors declare explicitly that the paper has not been previously published and is not under consideration for publication elsewhere. As such this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Effects of resistance training combined with a ketogenic diet on body composition: a systematic review and meta-analysis

We evaluated the effects of ketogenic diets (KDs) on body mass (BM), fat mass (FM), fat-free mass (FFM), body mass index (BMI), and body fat percentage (BFP) compared to non-KDs in individuals performing resistance training (RT). Online electronic databases including PubMed, the Cochrane Library, Web of Science, Embase, SCOPUS, and Ovid were searched to identify initial studies until February 2021. Data were pooled using both fixed and random-effects methods and were expressed as weighted mean difference (WMD) and 95% confidence intervals (CI). Out of 1372 studies, 13 randomized controlled trials (RCTs) that enrolled 244 volunteers were included. The pooled results demonstrated that KDs significantly decreased BM [(WMD = -3.67 kg; 95% CI: -4.44, -2.90, p < 0.001)], FM [(WMD = -2.21 kg; 95% CI: -3.09, -1.34, p < 0.001)], FFM [(WMD = -1.26 kg; 95% CI: -1.82, -0.70, p < 0.001)], BMI [(WMD = -1.37 kg.m^-2; 95% CI: -2.14, -0.59, p = 0.022)], and BFP [(WMD = -2.27%; 95% CI: -3.63, -0.90, p = 0.001)] compared to non-KDs. We observed beneficial effects of KDs compared to non-KDs on BM and body fat (both FM and BFP) in individuals performing RT. However, adherence to KDs may have a negative effect on FFM, which is not ameliorated by the addition of RT.

Efficacy of Popular Diets Applied by Endurance Athletes on Sports Performance: Beneficial or Detrimental? A Narrative Review

Endurance athletes need a regular and well-detailed nutrition program in order to fill their energy stores before training/racing, to provide nutritional support that will allow them to endure the harsh conditions during training/race, and to provide effective recovery after training/racing. Since exercise-related gastrointestinal symptoms can significantly affect performance, they also need to develop strategies to address these issues. All these factors force endurance athletes to constantly seek a better nutritional strategy. Therefore, several new dietary approaches have gained interest among endurance athletes in recent decades. This review provides a current perspective to five popular diet approaches: (a) vegetarian diets, (b) high-fat diets, (c) intermittent fasting diets, (d) gluten-free diet, and (e) low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diets. We reviewed scientific studies published from 1983 to January 2021 investigating the impact of these popular diets on the endurance performance and health aspects of endurance athletes. We also discuss all the beneficial and harmful aspects of these diets, and offer key suggestions for endurance athletes to consider when following these diets.

Very low ileal nitrogen and amino acid digestibility of zein compared to whey protein isolate in healthy volunteers

BACKGROUND

Whey protein and zein are of nutritional interest due to their high leucine content, but little data are available on their amino acid (AA) ileal digestibility.

OBJECTIVE

This study aimed to determine ileal digestibility of whey protein isolate (WPI) and zein in healthy volunteers by use of the naso-ileal intubation method, which allows continuous collection of postprandial ileal digesta.

METHODS

Twenty-two healthy volunteers were intubated with a naso-ileal sampling device positioned at the terminal ileum level. They received a single meal of protein-free biscuits and a drink containing zein (n = 8), WPI (n = 7), or no protein (protein free, n = 7). Ileal effluents and plasma samples were collected over a 9-h postprandial period. Total nitrogen and AA contents were quantified in effluents. True ileal digestibility was calculated after correction for endogenous losses evaluated in the protein-free group.

RESULTS

True ileal nitrogen digestibility of zein was markedly lower than WPI (60.2 ± 4.5% and 91.2 ± 2.6%, respectively, P = 0.0003). True ileal digestibility of AAs ranged from 87.4 ± 2.7% for threonine to 98.4 ± 1.0% for methionine in the WPI group, and from 59.3 ± 5.6% for methionine to 69.0 ± 5.8% for arginine in the zein group. The digestible indispensable AA (IAA) score was 1.03 (histidine) for WPI and close to 0 for zein, owing to its negligible lysine content. Plasma IAA concentration significantly increased after WPI intake (P = 0.0319), whereas no effect of zein on aminoacidemia was observed, including plasma leucine, despite its high leucine content.

CONCLUSIONS

Our findings provide data on ileal digestibility of WPI and zein AAs in healthy humans and, in contrast to WPI, zein is poorly digestible. This study was registered at clinicaltrials.gov as NCT03279211.

The Impact of Fasting on Major Metabolic Pathways of Macronutrients and Pharmacokinetics Steps of Drugs

In this review, we have investigated how fasting promotes an adaptive cross-talk between different hormones and metabolic pathways to supply and meet the body's daily energy demands. We highlight in biochemical terms and mechanisms how fasting impacts four metabolic pathways-glycogenolysis, gluconeogenesis, amino acid oxidation, and fatty acid β-oxidation-that are actively engaged in the metabolism of carbohydrates, proteins, and lipids. Fasting results in reduced insulin secretion and increased glucagon and epinephrine release to prevent or stimulate metabolic reaction(s). Fasting stimulates glycogenolysis, amino acid and glucose oxidation, aminotransferase reactions in skeletal muscle, and promotes gluconeogenesis and urea production in the liver. In addition, fasting promotes gene expression of lipid metabolism in skeletal muscle, the synthesis of ketone bodies in the liver, and intracellular hormone-sensitive lipase activity in adipose tissue. Furthermore, the impact of fasting on reducing cellular damage by mitochondrial reactive oxygen species is discussed. Lastly, we briefly describe the impact of fasting on the four steps of pharmacokinetics-the absorption, distribution, metabolism, and excretion of a few select drugs-with an emphasis on the elimination of drugs related to the cytochrome-P450 family of enzymes.

Scientific evidence underlying contraindications to the ketogenic diet: An update

First identified as a feasible treatment for intractable epilepsy, the ketogenic diet (KD) has recently gained popularity thanks to growing evidence on applications such as weight loss, most importantly, but also NAFLD, cancer, neurologic conditions and chronic pain. As with any treatment, whether pharmacologic or not, the KD might not be an appropriate intervention for every individual, and a number of contraindications have been proposed, now deeply rooted into clinical practice, excluding de facto many patients that could benefit from its use. However, many of these concerns were expressed due to the absence of clinical studies conducted on fragile populations, and an assessment of lately emerged evidence relative to KD safety is currently lacking and much needed. We herein provide a critical revision of the literature behind each safety alert, in order to guide through the treatment options in the case of subjects with an indication to the KD and a borderline safe situation. Based on available evidence, the possible use of this diet as a therapeutic intervention should be assessed on a patient-to-patient basis by adequately skilled medical doctors, keeping in mind current recommendations, but reading them through the knowledge of the current state of the art.

Nocturnal whey protein ingestion impairs post-prandial glucose tolerance at breakfast

Poor post-prandial glucose control is a risk factor for multiple health conditions. The second-meal effect refers to the progressively improved glycaemic control with repeated feedings, an effect which is achievable with protein ingestion at the initial eating occasion. The most pronounced glycaemic response each day therefore typically occurs following breakfast, so the present study investigated whether ingesting protein during the night could improve glucose control at the first meal of the day. In a randomised crossover design, fifteen adults (seven males, eight females; age, 22 (sd 3) years; BMI, 24·0 (sd 2·8) kg/m2; fasting blood glucose, 4·9 (sd 0·5) mmol/l) woke at 04.00 (sd 1) hours to ingest 300 ml water with or without 63 g whey protein. Participants then completed a mixed-macronutrient meal tolerance test (1 g carbohydrate/kg body mass, 2356 (sd 435) kJ), 5 h 39 min following the nocturnal feeding. Nocturnal protein ingestion increased the glycaemic response (incremental AUC) to breakfast by 43·5 (sd 55·5) mmol × 120 min/l (P = 0·009, d = 0·94). Consistent with this effect, individual peak blood glucose concentrations were 0·6 (sd 1·0) mmol/l higher following breakfast when protein had been ingested (P = 0·049, d = 0·50). Immediately prior to breakfast, rates of lipid oxidation were 0·02 (sd 0·03) g/min higher (P = 0·045) in the protein condition, followed by an elevated post-prandial energy expenditure (0·38 (sd 0·50) kJ/min, P = 0·018). Post-prandial appetite and energy intake were similar between conditions. The present study reveals a paradoxical second-meal phenomenon whereby nocturnal whey protein feeding impaired subsequent glucose tolerance, whilst increasing post-prandial energy expenditure.

Glucocorticoid-Induced Fatty Liver Disease

Glucocorticoids (GCs) are commonly used at high doses and for prolonged periods (weeks to months) in the treatment of a variety of diseases. Among the many side effects are increased insulin resistance with disturbances in glucose/insulin homeostasis and increased deposition of lipids (mostly triglycerides) in the liver. Here, we review the metabolic pathways of lipid deposition and removal from the liver that become altered by excess glucocorticoids. Pathways of lipid deposition stimulated by excess glucocorticoids include 1) increase in appetite and high caloric intake; 2) increased blood glucose levels due to GC-induced stimulation of gluconeogenesis; 3) stimulation of de novo lipogenesis that is augmented by the high glucose and insulin levels and by GC itself; and 4) increased release of free fatty acids from adipose stores and stimulation of their uptake by the liver. Pathways that decrease hepatic lipids affected by glucocorticoids include a modest stimulation of very-low-density lipoprotein synthesis and secretion into the circulation and inhibition of β-oxidation of fatty acids. Role of 11β-hydroxysteroid dehydrogenases-1 and -2 and the reversible conversion of cortisol to cortisone on intracellular levels of cortisol is examined. In addition, GC control of osteocalcin expression and the effect of this bone-derived hormone in increasing insulin sensitivity are discussed. Finally, research focused on gaining a better understanding of the dose and duration of treatment with glucocorticoids, which leads to increased triglyceride deposition in the liver, and the reversibility of the condition is highlighted.

Enzymatic Hydrolysis of a Collagen Hydrolysate Enhances Postprandial Absorption Rate-A Randomized Controlled Trial

Collagen is characterized by its high content of glycine, proline and hydroxyproline, and is found to exert beneficial effects on joint pain related to activity and osteoarthritis. However, to exert any beneficial effects it is essential that collagen is optimally absorbed. This study aimed to investigate the postprandial absorption of collagen and elucidate the impact of an exogenous enzymatic hydrolysis on absorption rate and bioavailability. A randomized, blinded, cross-over study was conducted where ten healthy male subjects received either 35 g enzymatically hydrolyzed collagen protein (EHC), 35 g non-enzymatically hydrolyzed collagen protein (NC) or placebo (250 mL water) on three nonconsecutive days. Blood samples were drawn before, and up to 240 min following, ingestion and the blood metabolome was characterized by nuclear magnetic resonance (NMR)-based metabolomics. A significant increase in the plasma concentration of nearly all amino acids (AAs) was observed over a 240 min period for both EHC and NC. In addition, the absorption rate and bioavailability of glycine, proline and hydroxyproline were significantly higher for EHC (p < 0.05). In conclusion, ingestion of collagen hydrolysates increases postprandial plasma concentrations of AAs over a period of 240 min, and an enzymatic hydrolysis increases the absorption rate and bioavailability of the collagen-rich AAs glycine, proline and hydroxyproline.

Postprandial Aminogenic Insulin and Glucagon Secretion Can Stimulate Glucose Flux in Humans

Insulin and glucagon exert opposing actions on glucose metabolism, and their secretion is classically viewed as being inversely regulated. This is, however, context specific as protein ingestion concomitantly stimulates euglycemic insulin and glucagon secretion. It remains enigmatic how euglycemia is preserved under these conditions. Accordingly, we examined the systems-level mechanisms governing such endocrine control of glucose homeostasis. Eight healthy participants completed a water (control) and multidose whey protein ingestion trial designed to augment the protein-induced endocrine response. Glucose kinetics were measured using stable isotope tracer methodology. Protein ingestion induced marked hyperaminoacidemia, hyperinsulinemia (approximately sixfold basal), and unprecedented hyperglucagonemia (approximately eightfold basal) while suppressing free fatty acids. Both glucose disposal (Rd) and endogenous glucose production (EGP) increased by ∼25%, thereby maintaining euglycemia. This demonstrates 1) that protein ingestion can stimulate glucose Rd and EGP, 2) that postprandial inhibition of adipose lipolysis does not suppress EGP, and 3) that physiological hyperglucagonemia can override the hepatic actions of insulin, rendering the liver unresponsive to insulin-mediated EGP suppression. Finally, we argue that glucagon is a bona fide postprandial hormone that evolved to concurrently and synergistically work with insulin to regulate glucose, amino acid, and nitrogen metabolism. These findings may have implications for glucagon receptor antagonist or agonist-based therapies.

Time course of fractional gluconeogenesis after meat ingestion in healthy adults: a D2O study

In the postprandial state, glucose homeostasis is challenged by macronutrient intake, including proteins that trigger insulin secretion and provide glucose precursors. However, little is known about the postprandial response of gluconeogenesis to a protein meal. We aimed to quantify the evolution of fractional gluconeogenesis after a meat meal. Thirteen healthy subjects received oral doses of D₂O. After fasting overnight, they ingested a steak (120 g). Glycemia, insulinemia, and ²H enrichments in glucose and plasma water were measured for 8 h after the meal. Fractional gluconeogenesis was assessed using the average method. Glucose was stable for 5 h and then decreased. There was a slight increase of insulin 1 h after the meal. ²H enrichment in the carbon 5 position of glucose (C5) increased after 2 h, whereas it decreased in plasma water. Consequently, fractional gluconeogenesis increased from 68.2 ± 7.2% before the meal to 75.5 ± 5.8% 8 h after the meal, the latter corresponding to 22 h without a glucose supply. These values are consistent with the exhaustion of glycogen stores after 24 h but represent the highest among values in the literature. The impact of methodological conditions is discussed.

Whole-body net protein balance plateaus in response to increasing protein intakes during post-exercise recovery in adults and adolescents

Background

Muscle protein synthesis and muscle net balance plateau after moderate protein ingestion in adults. However, it has been suggested that there is no practical limit to the anabolic response of whole-body net balance to dietary protein. Moreover, limited research has addressed the anabolic response to dietary protein in adolescents. The present study determined whether whole-body net balance plateaued in response to increasing protein intakes during post-exercise recovery and whether there were age- and/or sex-related dimorphisms in the anabolic response.

Methods

Thirteen adults [7 males (M), 6 females (F)] and 14 adolescents [7 males (AM), 7 females (AF) within ~ 0.4 y from peak height velocity] performed ~ 1 h variable intensity exercise (i.e., Loughborough Intermittent Shuttle Test) prior to ingesting hourly mixed meals that provided a variable amount of protein (0.02-0.25 g·kg^- 1·h^- 1) as crystalline amino acids modeled after egg protein. Steady-state protein kinetics were modeled noninvasively with oral L-[1-¹³C]phenylalanine. Breath and urine samples were taken at plateau to determine phenylalanine oxidation and flux (estimate of protein breakdown), respectively. Whole-body net balance was determined by the difference between protein synthesis (flux - oxidation) and protein breakdown. Total amino acid oxidation was estimated from the ratio of urinary urea/creatinine.

Results

Mixed model biphasic linear regression explained a greater proportion of net balance variance than linear regression (all, r ² ≥ 0.56; P < 0.01), indicating an anabolic plateau. Net balance was maximized at ~ 0.15, 0.12, 0.12, and 0.11 g protein·kg^- 1·h^- 1 in M, F, AM, and AF, respectively. When collapsed across age, the y-intercept (net balance at very low protein intake) was greater (overlapping CI did not contain zero) in adolescents vs. adults. Urea/creatinine excretion increased linearly (all, r ≥ 0.76; P < 0.01) across the range of protein intakes. At plateau, net balance was greater (P < 0.05) in AM vs. M.

Conclusions

Our data suggest there is a practical limit to the anabolic response to protein ingestion within a mixed meal and that higher intakes lead to deamination and oxidation of excess amino acids. Consistent with a need to support lean mass growth, adolescents appear to have greater anabolic sensitivity and a greater capacity to assimilate dietary amino acids than adults.

Urinary Metabolomics Profiles Associated to Bovine Meat Ingestion in Humans

SCOPE

The impact of meat consumption on human health is widely examined in nutritional epidemiological studies, especially due to the connection between the consumption of red and processed meat and the risk of colon cancer. Food questionnaires do not assess the exposure to different methods of meat cooking. This study aimed to identify biomarkers of the acute ingestion of bovine meat cooked with two different processes.

METHODS AND RESULTS

Non-targeted UPLC-MS metabolite profiling was done on urine samples obtained from 24 healthy volunteers before and 8 h after the ingestion of a single meal composed of intrinsically ¹⁵ N labelled bovine meat, either cooked at 55 °C for 5 min or at 90 °C for 30 min. A discriminant analysis extension of independent components analysis was applied to the mass spectral data. After meat ingestion, the urinary excretion of 1-methylhistidine, phenylacetylglutamine, and short- and medium-chained acylcarnitines was observed. ¹⁵ N labelling was detected in these metabolites, thus confirming their origin from ingested meat. However, no difference was observed in urinary metabolomic profiles according to the meat cooking process used.

CONCLUSION

Meat ingestion led to the excretion of several nitrogen-containing compounds, but although a metabolic signature was detected for meat ingestion, the impact of the cooking process was not detectable at the level of urinary metabolic signature in our experimental conditions.

Glutamine dipeptide and cortisol change the liver glucose metabolism and reduce the severity of insulin-induced hypoglycaemia in untreated T1DM Swiss mice

CONTEXT

Glutamine is conditionally essential in type 1 diabetes mellitus, and might be useful to counteract hypoglycaemia.

OBJECTIVE

To investigate the systemic and hepatic effects of counter-regulatory hormones and glutamine dipeptide (GDP) during hypoglycemic episodes.

MATERIALS AND METHODS

Diabetic Swiss mice made hypoglycaemic by insulin injection (1 U/kg) were given counter-regulatory hormones and/or GDP. Sixty minutes later, liver histology, liver glucose metabolism and plasma were assessed.

RESULTS

Combined, cortisol and GDP improved the hypoglycemic profile. During liver perfusion, gluconeogenesis was possibly the major pathway leading to glucose release. Perfusion with gluconeogenic precursors after glycogen depletion by adrenaline increased liver glucose and urea release.

DISCUSSION

The less severe hypoglycaemia could result from cortisol stimulating periportal gluconeogenesis and GDP inhibiting pericentral glycogenolysis, both favouring liver glucose release.

CONCLUSIONS

At least some benefits of GDP and cortisol during hypoglycaemia came from their hepatic actions, and their use in diabetic patients should be explored.

Dietary protein intake and human health

A protein consists of amino acids (AA) linked by peptide bonds. Dietary protein is hydrolyzed by proteases and peptidases to generate AA, dipeptides, and tripeptides in the lumen of the gastrointestinal tract. These digestion products are utilized by bacteria in the small intestine or absorbed into enterocytes. AA that are not degraded by the small intestine enter the portal vein for protein synthesis in skeletal muscle and other tissues. AA are also used for cell-specific production of low-molecular-weight metabolites with enormous physiological importance. Thus, protein undernutrition results in stunting, anemia, physical weakness, edema, vascular dysfunction, and impaired immunity. Based on short-term nitrogen balance studies, the Recommended Dietary Allowance of protein for a healthy adult with minimal physical activity is currently 0.8 g protein per kg body weight (BW) per day. To meet the functional needs such as promoting skeletal-muscle protein accretion and physical strength, dietary intake of 1.0, 1.3, and 1.6 g protein per kg BW per day is recommended for individuals with minimal, moderate, and intense physical activity, respectively. Long-term consumption of protein at 2 g per kg BW per day is safe for healthy adults, and the tolerable upper limit is 3.5 g per kg BW per day for well-adapted subjects. Chronic high protein intake (>2 g per kg BW per day for adults) may result in digestive, renal, and vascular abnormalities and should be avoided. The quantity and quality of protein are the determinants of its nutritional values. Therefore, adequate consumption of high-quality proteins from animal products (e.g., lean meat and milk) is essential for optimal growth, development, and health of humans.

High True Ileal Digestibility but Not Postprandial Utilization of Nitrogen from Bovine Meat Protein in Humans Is Moderately Decreased by High-Temperature, Long-Duration Cooking

BACKGROUND

Meat protein digestibility can be impaired because of indigestible protein aggregates that form during cooking. When the aggregates are subsequently fermented by the microbiota, they can generate potentially harmful compounds for the colonic mucosa.

OBJECTIVE

This study evaluated the quantity of bovine meat protein escaping digestion in the human small intestine and the metabolic fate of exogenous nitrogen, depending on cooking processes.

METHODS

Sixteen volunteers (5 women and 11 men; aged 28 ± 8 y) were equipped with a double lumen intestinal tube positioned at the ileal level. They received a test meal exclusively composed of 120 g of intrinsically (15)N-labeled bovine meat, cooked either at 55°C for 5 min (n = 8) or at 90°C for 30 min (n = 8). Ileal effluents and blood and urine samples were collected over an 8-h period after the meal ingestion, and (15)N enrichments were measured to assess the digestibility of meat proteins and the transfer of dietary nitrogen into the metabolic pools.

RESULTS

Proteins tended to be less digestible for the meat cooked at 90°C for 30 min than at 55°C for 5 min (90.1% ± 2.1% vs. 94.1% ± 0.7% of ingested N; P = 0.08). However, the particle number and size in ileal digesta did not differ between groups. The appearance of variable amounts of intact fibers was observed by microscopy. The kinetics of (15)N appearance in plasma proteins, amino acids, and urea were similar between groups. The amount of exogenous nitrogen lost through deamination did not differ between groups (21.2% ± 0.8% of ingested N).

CONCLUSIONS

Cooking bovine meat at a high temperature for a long time can moderately decrease protein digestibility compared with cooking at a lower temperature for a short time and does not affect postprandial exogenous protein metabolism in young adults. The study was registered at www.clinicaltrials.gov as NCT01685307.

PPARα via HNF4α regulates the expression of genes encoding hepatic amino acid catabolizing enzymes to maintain metabolic homeostasis

The liver is the main organ involved in the metabolism of amino acids (AA), which are oxidized by amino acid catabolizing enzymes (AACE). Peroxisome proliferator-activated receptor-α (PPARα) stimulates fatty acid β-oxidation, and there is evidence that it can modulate hepatic AA oxidation during the transition of energy fuels. To understand the role and mechanism of PPARα's regulation of AA catabolism, the metabolic and molecular adaptations of Ppara-null mice were studied. The role of PPARα on AA metabolism was examined by in vitro and in vivo studies. In wild-type and Ppara-null mice, fed increasing concentrations of the dietary protein/carbohydrate ratio, we measured metabolic parameters, and livers were analyzed by microarray analysis, histology and Western blot. Functional enrichment analysis, EMSA and gene reporter assays were performed. Ppara-null mice presented increased expression of AACE in liver affecting AA, lipid and carbohydrate metabolism. Ppara-null mice had increased glucagon/insulin ratio (7.2-fold), higher serum urea (73.1 %), lower body protein content (19.7 %) and decreased several serum AA in response to a high-protein/low-carbohydrate diet. A functional network of differentially expressed genes, suggested that changes in the expression of AACE were regulated by an interrelationship between PPARα and HNF4α. Our data indicated that the expression of AACE is down-regulated through PPARα by attenuating HNF4α transcriptional activity as observed in the serine dehydratase gene promoter. PPARα via HNF4α maintains body protein metabolic homeostasis by down-regulating genes involved in amino acid catabolism for preserving body nitrogen.

Dietary protein and blood glucose control

PURPOSE OF REVIEW

This review presents the different pathways by which protein and amino acid impact glucose control. The review more particularly discusses the contradictory effects reported in the literature on the involvement of amino acid on glucose production and in insulin secretion and sensitivity.

RECENT FINDINGS

Some recent findings allow a better understanding of the direct and indirect mechanisms involved in the insulinotropic activity of some amino acids in pancreatic β-cell and in the production of glucose through liver gluconeogenesis that participates to improve the control of glycemia. In contrast, the potential deleterious effects of branched chain amino acid, and particularly leucine, hypothesized in previous publications, have been discussed in some recent publications.

SUMMARY

These processes are of high clinical relevance since the role of protein and amino acid have been repeatedly discussed to improve insulin secretion in type 2 diabetes patients or in weight management strategy in overweight and obese individuals. In addition, whether blood amino acid could be used as biomarkers for the risk of type 2 diabetes needs to be discussed.