Determinants of amino acid bioavailability from ingested protein in relation to gut health

Enhancing bioavailability and functionality of plant peptides and proteins: A review of novel strategies for food and pharmaceutical applications

Plant-derived peptides and proteins are emerging as versatile bioactive ingredients in functional food and pharmaceutical sectors due to their diverse health benefits. However, their practical applications are often limited by poor bioavailability and functional instability. This review evaluates key determinants of plant peptide/protein bioactivity, including physicochemical properties, anti-nutritional components, food matrix interactions, and gastrointestinal digestion conditions. Strategies to enhance their functionality and bioavailability are systematically discussed, focusing on absorption enhancers, structural modifications, protease inhibitors, and colloidal delivery systems (e.g., liposomes, emulsions, nanoparticles). Recent advancements highlight targeted enzymatic hydrolysis and fermentation as effective methods to generate bioactive peptides with improved therapeutic properties. Additionally, physical/chemical modifications enhance stability against proteolysis and improve functional performance. Innovations in plant-derived protein-based delivery systems, such as nanoparticles, demonstrate promise in protecting bioactive compounds and optimizing bioavailability. Collectively, these approaches provide a roadmap for developing next-generation plant-protein products, addressing challenges in bioactivity retention and gastrointestinal absorption.

Comparison of the Dual Isotope Tracer Approach with Oro-Ileal Balance Method for Determination of Amino Acid Digestibility in Cannulated Pigs

BACKGROUND

The dual isotope tracer approach was developed as a less invasive alternative for the measurement of ileal amino acid (AA) digestibility.

OBJECTIVES

This study aimed to validate the dual isotope tracer approach with the standardized oro-ileal balance method in growing pigs.

METHODS

Eight pigs were fitted with jugular catheters and ileal T-cannulas. On the test day, feed containing intrinsically labeled 15N-milk protein and 13C-spirulina was provided every half hour for 240 min. Ileal digesta and 10 jugular blood samples were collected between 0 min and 540 min. Digesta samples were analyzed for isotopic enrichment, AA, and titanium concentrations for balance method calculations. Serum AA isotopic enrichment was measured for dual stable isotope tracer calculations.

RESULTS

Using the oro-ileal balance method, the mean ileal AA digestibility of milk protein concentrate was 97.8 ± 0.59% and of spirulina 81.5 ± 2.44% (mean ± standard deviation). Lysine digestibility was specifically evaluated, as it does not transaminate. Lysine digestibility of milk protein concentrate calculated according to the dual isotope tracer approach was 88.9 ± 8.35%, 9% point lower than the value obtained with the oro-ileal method (98.1 ± 0.36, P = 0.04). Moreover, Bland-Altman analysis showed that the difference between methods was higher, with lower mean lysine digestibility.

CONCLUSIONS

This study observed differences between the dual isotope tracer approach and the oro-ileal balance method for estimating lysine digestibility under the current experimental conditions with 6 pigs. This result may be due to methodological issues. Considering the use of 15N protein, conclusions on other AA that do not transaminate could not be drawn.

Cottage cheese, a relatively underexplored cultured dairy product with potential health benefits?

Cottage cheese (CC) is a member of the "fresh cheese" family of cheeses and is widely consumed due to its culinary versatility and some perceived health benefits. However, the evidence of direct health effects of CC is not well established. This review describes the production and nutritional characteristics of CC, before exploring the evidence of health effects from human intervention, in vitro, and in vivo models. Despite widespread consumption and advocated health benefits, there is a dearth of evidence pertaining to the health effects of CC from high-quality human randomized controlled trials. To date, a limited number of human intervention models with CC have explored nutrient bioavailability, metabolic health, and appetite regulation, in small, niche study populations. Findings with in vitro and in vivo models suggest that CC may be an efficacious vehicle for bioactive compounds. In conclusion, CC is a cultured dairy product that could impose a myriad of benefits across health outcomes including cardiometabolic, gastrointestinal, body composition, appetite regulation, and nutrient status. However, there is a need for high-quality human randomized controlled trials to develop a substantiated evidence base relating to the full potential of CC in human health.

Ultrasound-treated hybrid protein gels from pea and whey: A comparison of gastric breakdown mechanisms with commercial protein-based foods

A novel hybrid protein gel was developed to sustainably meet the growing demands for protein with pea and whey protein isolates (3:2 in 15 % w/v protein content) which was ultrasound treated (7.5 and 15 min), and gelled (90 °C, 60 min). The study investigated the impact of ultrasound treatment on the structure and gastric breakdown kinetics of hybrid protein gels and compared these properties to commercial protein-based foods (ham, paneer, and mozzarella). Ultrasound treatment for 15 min significantly (p < 0.05) reduced particle size (d50: 5.4 µm vs 32.5 µm in control) and resulted in a higher initial Young's modulus than control. Protein hydrolysis at 180 min was ∼53 % lower (p < 0.05) with 15 min ultrasound treatment than control and 7.5 min ultrasound treatment. Hybrid protein gels exhibited similarities in initial Young's modulus to mozzarella (p > 0.05), while ham and paneer were significantly firmer (p < 0.05). Effective diffusivity of moisture from gastric fluid decreased (p < 0.05) in the order: ham > paneer and mozzarella > hybrid protein gels. In contrast, the effective acid diffusivity from gastric fluid was similar (p > 0.05) between hybrid protein gels and paneer, which were ∼74 % higher (p < 0.05) than ham and mozzarella. Digestion time influenced (p < 0.05) breakdown mechanisms (texture, dry matter loss, moisture, and acid uptake) during digestion. This study confirmed that hybrid protein gels were comparable to commercial protein-based foods and the limiting factor driving gastric breakdown is unique to different foods incorporating proteins.

Comprehensive review on the potential of ultrasound for blue food protein extraction, modification and impact on bioactive properties

Food security for the increasing global population is a significant challenge of the current times particularly highlighting the protein deficiencies. Plant-based proteins could be considered as alternate source of the protein. The digestibility and PDCASS value of these proteins are still a concern. Blue proteins, the new approach of utilizing the proteins from aquatic sources could be a possible solution as it contains all the essential amino acids. However, the conjugation of these proteins with fats and glycogen interferes with their techno-functional properties and consequently their applicability. The application of power ultrasound for extraction and modification of these proteins from aquatic sources to break open the cellular structure, increase extractability, alter the protein structure and consequently provide proteins with higher bioavailability and bioactive properties could be a potential approach for their effective utilization into food systems. The current review focuses on the application of power ultrasound when applied as extraction treatment, alters the sulphite and peptide bond and modifies protein to elevated digestibility. The degree of alteration is influenced by intensity, frequency, and exposure time. The extracted proteins will serve as a source of essential amino acids. Furthermore, modification will lead to the development of bioactive peptides with different functional applications. Numerous studies reveal that blue proteins have beneficial impacts on amino acid availability, and subsequently food security with higher PDCAAS values. In many cases, converted peptides give anti-hypertensive, anti-diabetic, and anti-oxidant activity. Therefore, researchers are concentrating on ultrasound-based extraction, modification, and application in food and pharmaceutical systems.

Impact of aging on the digestive system related to protein digestion in vivo

For the current aging population, protein is an important macronutrient to counteract the development of sarcopenia. Protein digestion is influenced by the capacity of the digestive system. The current evidence is reviewed about the impact of aging on the human digestive system and related to protein digestion in vivo. Aging changes the digestive organs which impacts protein digestion. Dentition decreases and mastication changes, potentially affecting particle size reduction. Stomach gastric acidity is unchanged, gastric emptying is delayed, while total transit time remains unchanged. Production of enzymes by the pancreas is decreased, but any changes in the small intestine remain unresolved. Animal studies showed decreased fecal protein digestion in older compared to young animals. Human studies showed decreased postprandial peripheral plasma appearance of ingested amino acids and increased splanchnic extraction. The findings suggest that the deteriorating digestive system with aging results in decreased protein digestion. Interpretation of the results should be taken with caution because of interindividual differences in the aging process, and because studies on protein digestion in aging humans are scarce. More information is needed on healthy aging and its relation to the digestive tract and protein digestion, several methods including in vitro experiments are valuable in this perspective.

Pea and soy fortified with leucine stimulates muscle protein synthesis comparable to whey in a murine ageing model

PURPOSE

To meet the global dietary protein demands, a trend towards plant-based protein (PBP) sources to replace animal-derived protein is currently ongoing. However, PBPs may not have the same anabolic capacity to stimulate muscle protein synthesis (MPS) as dairy proteins. For vulnerable populations with specific medical needs, it is especially important to validate the anabolic properties of PBPs. In this study, a blend of pea and soy protein isolate, with or without additional leucine, was compared to whey protein isolate on MPS in aged mice.

METHODS

25-Months aged C57BL/6J-mice received an oral gavage with 70 mg of whey protein isolate (W), PS protein isolate (PS; ratio 51:49), PS fortified with 19% leucine (PS + L), or 0.5mL water (F). Mice were subcutaneously injected with puromycin (0.04 µmol/g body weight, t = 30 min) and sacrificed 60 min thereafter. Left m. tibialis anterior (TA) was used to analyse MPS by the SUnSET method and mTOR signal transduction proteins. Amino acid concentrations were determined in plasma and right TA. Dried blood spots (DBS) were analysed for postprandial dynamics of amino acids at 10-20-45-60-min.

RESULTS

MPS was significantly increased by W and PS + L (p < 0.003), however not by PS. Pathway protein 4EBP1 showed significant increases with W, PS and PS + L to F (p < 0.0002). W and PS + L increased plasma and muscle free leucine equally, which was confirmed by DBS.

CONCLUSION

A PS blend fortified with leucine stimulates MPS comparable to whey protein in this acute murine ageing model. Leucine appears to be the main driver for the anabolic responses observed.

Technological advances in protein extraction, structure improvement and assembly, digestibility and bioavailability of plant-based foods

Plant-based foods are being considered seriously to replace traditional animal-origin foods for various reasons. It is well known that animals release large amounts of greenhouse gases into the environment during feeding, and eating animal-origin foods may also cause some health problems. Moreover, animal resources will likely be in short supply as the world population grows. It is highly likely that serious health problems ascribed to insufficient protein intake in some areas of the world will occur. Studies have shown that environmentally friendly, abundant, and customizable plant-based foods can be an effective alternative to animal-based foods. However, currently, available plant-based foods lack nutrients unique to animal-based foods. Innovative processing technologies are needed to improve the nutritional value and functionality of plant-based foods and make them acceptable to a wider range of consumers. Therefore, protein extraction technologies (e.g., high-pressure extraction, ultrasound extraction, enzyme extraction, etc.), structure improvement and assembly technologies (3D printing, micro-encapsulation, etc.), and technologies to improve digestibility and utilization of bioactive substances (microbial fermentation, physical, etc.) in the field of plant-based foods processing are reviewed. The challenges of plant-based food processing technologies are summarized. The advanced technologies aim to help the food industry solve production problems using efficient, environmentally friendly, and economical processing technologies and to guide the development of plant-based foods in the future.

A look inside the gut as a clue to nutritional status

PURPOSE OF REVIEW

Malabsorption and malnutrition are common gastrointestinal manifestations clinicians face, requiring diagnostic workup for effective diagnosis and management of the underlying cause. This review discusses recent advances in diagnostic approaches to malabsorption and maldigestion of macronutrients - lipids, proteins, and carbohydrates. We highlight underrecognized causes, available testing modalities, and ongoing diagnostic unmet needs.

RECENT FINDINGS

Innovations in the diagnostic landscape are enhancing our understanding of malabsorption syndromes. Stool collection and handling is uncomfortable and commonly avoided. The objective quantification of stool lipids, bile acids, and gut enzymes is therefore underused in the diagnosis and management of common disorders such as exocrine pancreatic insufficiency, bile acid diarrhea, protein-losing enteropathy, and more. We review the recent advancements in spot quantification of stool fat and bile acid content, endoscopic imaging techniques such as endocytoscopy, confocal laser endomicroscopy, and optical coherence tomography and the future place in clinical practice.

SUMMARY

Malabsorption and maldigestion represent significant challenges in clinical nutrition and gastroenterology. Through the integration of advanced diagnostic techniques, clinicians will be better equipped to tailor therapy and monitor treatment response, ultimately improving patient health outcomes. This review underscores the critical role of innovative diagnostic tools in accurately detecting and effectively managing gastrointestinal disorders linked to nutritional status.

Anthropometric, Body Composition, and Nutritional Indicators with and without Nutritional Intervention during Nitisinone Therapy in Alkaptonuria

INTRODUCTION

Protein nutrition disorder in alkaptonuria (AKU), resulting in increased homogentisic acid (HGA) before nitisinone therapy and increased tyrosine (TYR) during nitisinone therapy, may benefit from dietetic intervention. The aim of this study was to characterise the diet and their effects prospectively in those who received formal dietetic intervention in the nitisinone-receiving National Alkaptonuria Centre (NAC) patients with those who did not in no-nitisinone Suitability of Nitisinone in Alkaptonuria 2 (SN2 N-) and nitisinone-treated SN2 (SN2 N+) randomised study groups.

PATIENTS AND METHODS

A total of 63, 69, and 69 AKU patients from the NAC, SN2 N-, and SN2 N+ were studied for anthropometric (weight, BMI), body composition (including muscle mass, %body fat, hand grip strength), chemical characteristics (serum TYR, serum phenylalanine, urine urea or uUREA, and urine creatinine or uCREAT), and corneal keratopathy. Nitisinone 2 mg and 10 mg were employed in the NAC and SN2 N+ groups, respectively. Dieticians managed protein intake in the NAC, while the SN2 N- and SN2 N+ groups only received advice on self-directed protein restriction during four years of study duration.

RESULTS

uUREA decreased in the NAC, SN2 N-, and SN2 N+ groups, showing that protein restriction was achieved in these groups. Body weight and BMI increased in the NAC and SN2 N+ groups. uCREAT decreased significantly in SN2 N- and SN2 N+ compared with the NAC over four years of study. Corneal keratopathy was less frequent in the NAC than in the SN2 N+ group. Active dietetic intervention in NAC stabilised lean body mass (muscle mass, hand grip strength) despite a decrease in uUREA and uCREAT, as well as sTYR.

CONCLUSION

Ongoing dietetic intervention prevented loss of lean body mass despite protein restriction and moderated serum tyrosine increase, leading to less prevalent corneal keratopathy. Protein restriction risks fat mass gain.

Secondary Bioactive Metabolites from Foods of Plant Origin as Theravention Agents against Neurodegenerative Disorders

Neurodegenerative disorders (NDDs) such as Alzheimer's (AD) and Parkinson's (PD) are on the rise, robbing people of their memories and independence. While risk factors such as age and genetics play an important role, exciting studies suggest that a diet rich in foods from plant origin may offer a line of defense. These kinds of foods, namely fruits and vegetables, are packed with a plethora of powerful bioactive secondary metabolites (SBMs), including terpenoids, polyphenols, glucosinolates, phytosterols and capsaicinoids, which exhibit a wide range of biological activities including antioxidant, antidiabetic, antihypertensive, anti-Alzheimer's, antiproliferative, and antimicrobial properties, associated with preventive effects in the development of chronic diseases mediated by oxidative stress such as type 2 diabetes mellitus, respiratory diseases, cancer, cardiovascular diseases, and NDDs. This review explores the potential of SBMs as theravention agents (metabolites with therapeutic and preventive action) against NDDs. By understanding the science behind plant-based prevention, we may be able to develop new strategies to promote brain health and prevent the rise in NDDs. The proposed review stands out by emphasizing the integration of multiple SBMs in plant-based foods and their potential in preventing NDDs. Previous research has often focused on individual compounds or specific foods, but this review aims to present a comprehensive fingerprint of how a diet rich in various SBMs can synergistically contribute to brain health. The risk factors related to NDD development and the diagnostic process, in addition to some examples of food-related products and medicinal plants that significantly reduce the inhibition of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1), are highlighted.

Digestible indispensable amino acid score (DIAAS): 10 years on

The objective of the review is to revisit the findings of the 2011 Food and Agriculture Organization of the United Nations (FAO) Expert Consultation on Dietary Protein Quality Evaluation in Human Nutrition, and to report on progress on uptake of the findings. It is evident that since 2011 there has been a concerted research effort to enhance an understanding of the protein quality of foods. The validity of the growing pig ileal protein digestibility assay has been confirmed and numerous studies reported using the growing pig as a model to give true ileal amino acid digestibility values for foods as consumed by humans. This has allowed for the determination of digestible indispensable amino acid scores (DIAAS) for a range of foods. A new non-invasive true ileal amino acid digestibility assay in humans which can be applied in different physiological states, called the dual-isotope assay, has been developed and applied to determine the DIAAS values of foods. It is concluded that DIAAS is currently the most accurate score for routinely assessing the protein quality rating of single source proteins. In the future, the accuracy of DIAAS can be enhanced by improved information on: the ideal dietary amino acid balance including the ideal dispensable to indispensable amino acid ratio; dietary indispensable amino acid requirements; effects of processing on ileal amino acid digestibility and lysine bioavailability. There is a need to develop rapid, inexpensive in vitro digestibility assays. Conceptual issues relating DIAAS to food regulatory claims, and to holistic indices of food nutritional and health status are discussed. The first recommendation of the 2011 Consultation regarding treating each indispensable amino acid as an individual nutrient has received little attention. Consideration should be given to providing food label information on the digestible contents of specific indispensable amino acids.

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.

A review of dairy food intake for improving health among black geriatrics in the US

The transition to older adulthood is generally marked by progressive declines in body composition, metabolism, cognitive function, and immunity. For socially disadvantaged geriatric populations such as Black Americans, this life stage may also include additional stressors, including dealing with discrimination, poor access to healthcare, and food insecurity. These types of chronic stressors are linked to a higher allostatic load, which is associated with accelerated biological aging, higher rates of adverse health outcomes, and an overall lower quality of life. Of the numerous factors involved in healthy aging, a growing body of research indicates that consuming a higher quality diet that is rich in fruits, vegetables, whole grains, protein foods, and dairy foods, is one of the most potent factors for helping to protect against age-related disease progression. Among the food groups listed above that are recommended by the 2020-2025 Dietary Guidelines for Americans dairy foods are unique in their ability to provide several of the essential nutrients (e.g., high-quality protein, calcium, potassium, vitamin B12, and vitamin D in fortified products) that are most often inadequately consumed by older Black Americans. However, dairy is the most inadequately consumed food group in the US, with older Black adults consuming fewer than half of the 3 daily recommended servings. Therefore, this review examines the current body of evidence exploring the links between dairy intake and age-related disease risk, with a special focus on health and disparities among older Black Americans. Overall, the evidence from most systematic reviews and/or meta-analyses focused on dairy intake and musculoskeletal health suggest that higher dairy intake across the life span, and especially from fermented and fortified products, is associated with better bone and muscle health outcomes in older adults. The evidence on dairy intake and neurocognitive and immune outcomes among older adults holds significant promise for potential benefits, but most of these results are sourced from individual studies or narrative reviews and are not currently corroborated in systematic reviews or meta-analyses. Additionally, most of the research on dairy intake and age-related disease risk has been performed in White populations and can only be extrapolated to Black populations. Nonetheless, older Black populations who do not meet the DGA recommended 3 servings of dairy per day due to lactose intolerance, restrictive dietary patterns, or for other reasons, are likely falling short of several of the nutritional requirements necessary to support healthy aging.

Urine Metabolite Profiles after the Consumption of a Low- and a High-Digestible Protein Meal, and Comparison of Urine Normalization Techniques

In the context of dietary transition toward plant proteins, it is necessary to ensure protein security in populations. It would thus be of interest to identify biomarkers of altered protein digestibility in populations. We examined the association between urinary metabolites and the acute intake of low- or highly digestible protein in healthy volunteers. The urine samples were collected before and 9 h after the ingestion of a meal containing either no protein, zein (low-digestible) or whey protein isolate (highly digestible). The liquid chromatography-high resolution mass spectrometry metabolomics approach was used for the profiling of the urinary metabolites. For the standardization of metabolomics data sets, osmolality-based, standard normal variates (SNV) and probabilistic quotient normalization (PQN) techniques were used. The ANOVA-based factorial method, AComDim_ICA, was used for chemometrics analysis. The osmolality adjustment has a beneficial effect and the subsequent mathematical normalization improves the chemometric analysis further. Some changes in the urinary metabolomes were observed 9 h after the meal in the three groups. However, there was no difference in the urine metabolome between groups. No biomarker of protein digestibility can be identified after the ingestion of a single meal, even when marked differences in the digestion efficiency of protein have been observed.

Values for the Digestibility of Pea Protein Isolate or Casein Amino Acids Determined using the Dual Isotope Method Are Not Similar to Those Derived with the Standard Ileal Balance Method in Healthy Volunteers

BACKGROUND

The measurement of ileal amino acid (AA) digestibility is invasive and inappropriate when applied to vulnerable populations. The dual isotope method has been developed over the past 5 y as an alternative method.

OBJECTIVE

The aim of this work was to compare the indispensable amino acid (IAA) digestibility values of 2 different proteins obtained using the dual isotope and the standard ileal balance methods in the same subjects.

METHODS

Fifteen healthy adults completed the study. Over 4 h, they ingested 9 successive portions of mashed potatoes containing the test protein (pea protein or casein) labeled intrinsically with 15N and 2H, and a 13C-free AA mixture as a reference for the dual isotope method. Plasma was sampled regularly over the 8-h postprandial period, whereas the ileal digesta was collected continuously via a naso-ileal tube. Isotopic enrichments (15N and 13C) were measured in the digesta for the direct determination of ileal IAA digestibility, whereas plasma enrichments (2H and 13C) were measured to determine IAA digestibility using the dual isotope method.

RESULTS

The 4-h repeated meal procedure enabled the almost complete digestion of test proteins at 8 h and the attainment of a plasma isotopic plateau between 2.5 and 4 h. These conditions were necessary to perform the ileal balance and dual isotope methods simultaneously. For pea protein, the mean IAA digestibility was similar between the 2 methods, but significant differences (from 10% to 20%) were observed for individual IAA values. For casein, IAA digestibility was significantly lower with the dual isotope method for all the IAA analyzed.

CONCLUSIONS

Under our experimental conditions, the degree of agreement between the dual isotope and ileal balance methods varied among AAs and depended on the protein source. Further research is needed to validate the dual isotope method. This study was registered at clinicaltrials.gov as NCT04072770.

Effect of Soy Protein Supplementation on Muscle Adaptations, Metabolic and Antioxidant Status, Hormonal Response, and Exercise Performance of Active Individuals and Athletes: A Systematic Review of Randomised Controlled Trials

BACKGROUND

Protein supplements are important to maintain optimum health and physical performance, particularly in athletes and active individuals to repair and rebuild their skeletal muscles and connective tissues. Soy protein (SP) has gained popularity in recent years as an alternative to animal proteins.

OBJECTIVES

This systematic review evaluates the evidence from randomised controlled clinical trials of the effects of SP supplementation in active individuals and athletes in terms of muscle adaptations, metabolic and antioxidant status, hormonal response and exercise performance. It also explores the differences in SP supplementation effects in comparison to whey protein.

METHODS

A systematic search was conducted in PubMed, Embase and Web of Science, as well as a manual search in Google Scholar and EBSCO, on 27 June 2023. Randomised controlled trials that evaluated the applications of SPs supplementation on sports and athletic-related outcomes that are linked with exercise performance, adaptations and biomarkers in athletes and physically active adolescents and young adults (14 to 39 years old) were included, otherwise, studies were excluded. The risk of bias was assessed according to Cochrane's revised risk of bias tool.

RESULTS

A total of 19 eligible original research articles were included that investigated the effect of SP supplementation on muscle adaptations (n = 9), metabolic and antioxidant status (n = 6), hormonal response (n = 6) and exercise performance (n = 6). Some studies investigated more than one effect. SP was found to provide identical increases in lean mass compared to whey in some studies. SP consumption promoted the reduction of exercise-induced metabolic/blood circulating biomarkers such as triglycerides, uric acid and lactate. Better antioxidant capacity against oxidative stress has been seen with respect to whey protein in long-term studies. Some studies reported testosterone and cortisol fluctuations related to SP; however, more research is required. All studies on SP and endurance performance suggested the potential beneficial effects of SP supplementation (10-53.3 g) on exercise performance by improving high-intensity and high-speed running performance, enhancing maximal cardiac output, delaying fatigue and improving isometric muscle strength, improving endurance in recreational cyclists, increasing running velocity and decreasing accumulated lactate levels; however, studies determining the efficacy of soy protein on VO2max provided conflicted results.

CONCLUSION

It is possible to recommend SP to athletes and active individuals in place of conventional protein supplements by assessing their dosage and effectiveness in relation to different types of training. SP may enhance lean mass compared with other protein sources, enhance the antioxidant status, and reduce oxidative stress. SP supplementation had an inconsistent effect on testosterone and cortisol levels. SP supplementation may be beneficial, especially after muscle damage, high-intensity/high-speed or repeated bouts of strenuous exercise.

The impacts of partial replacement of red and processed meat with legumes or cereals on protein and amino acid intakes: a modelling study in the Finnish adult population

BACKGROUND

A shift towards more plant-based diets is considered healthy and environmentally sustainable but may cause a concern regarding protein and amino acid intakes. This modelling study aimed to assess the impacts of partial replacement of red and processed meat with legumes or cereals on the protein and indispensable amino acid intakes in the Finnish adult population.

MATERIALS AND METHODS

We used the cross-sectional data of the National FinDiet 2017 Survey (two non-consecutive 24-h recalls, n = 1655, 47% men, aged 18-74 years). Six replacement scenarios were created in which the amount of red and processed meat exceeding 70 g/day (Finnish nutrition recommendation), or 30 g/day (EAT-Lancet recommendation) was replaced with the same amounts of legumes, cereals or their combination. Differences to the reference diet were evaluated based on non-overlapping 95% confidence intervals. Population shares (%) below estimated average requirements (EAR) were calculated using the usual intake modelling methodology (SPADE).

RESULTS

The replacement scenarios decreased the protein and indispensable amino acid intakes depending on gender and age. At the 70-g level, decreases were observed only in men aged 18-64 years. At the 30-g level, decreases were observed in other gender and age groups except women aged 65-74 years. In the scenarios, the mean daily protein intake was 15-18% of total energy intake (E%) (reference 17-18 E%), and the proportions below the EAR were 7-10% in men and 8-10% in women aged 18-64 years (reference 5-7%) and 20-25% in men and 16-20% in women aged 65-74 years (reference 14-17%). For total indispensable amino acids, the proportions below the EAR were <5% in the reference diet and the scenarios.

CONCLUSIONS

The mean daily protein intake remained sufficient when red and processed meat was partially replaced with legumes or cereals in the Finnish adult population. However, protein adequacy in the elderly population warrants attention and more research.

The utility of algae as sources of high value nutritional ingredients, particularly for alternative/complementary proteins to improve human health

As the global population continues to grow, the demand for dietary protein is rapidly increasing, necessitating the exploration of sustainable and nutritious protein sources. Algae has emerged as a promising food source due to their high value ingredients such as proteins, as well as for their environmental sustainability and abundance. However, knowledge gaps surrounding dietary recommendations and food applications restrict algae's utilization as a viable protein source. This review aims to address these gaps by assessing the suitability of both microalgae and macroalgae as alternative/complementary protein sources and exploring their potential applications in food products. The first section examines the potential suitability of algae as a major food source by analyzing the composition and bioavailability of key components in algal biomass, including proteins, lipids, dietary fiber, and micronutrients. Secondly, the biological effects of algae, particularly their impact on metabolic health are investigated with an emphasis on available clinical evidence. While evidence reveals protective effects of algae on glucose and lipid homeostasis as well as anti-inflammatory properties, further research is required to understand the longer-term impact of consuming algal protein, protein isolates, and concentrates on metabolic health, including protein metabolism. The review then explores the potential of algal proteins in food applications, including ways to overcome their sensory limitations, such as their dark pigmentation, taste, and odor, in order to improve consumer acceptance. To maximize algae's potential as a valuable protein source in the food sector, future research should prioritize the production of more acceptable algal biomass and explore new advances in food sciences and technology for improved consumer acceptance. Overall, this paper supports the potential utility of algae as a sustainable and healthy ingredient source for widespread use in future food production.

Amino Acid Digestibility of Different Formulations of Torula Yeast in an In Vitro Porcine Gastrointestinal Digestion Model and Their Protective Effects on Barrier Function and Inflammation in a Caco-2/THP1Co-Culture Model

Single-cell protein from torula yeast (Cyberlindnera jadinii) grown on lignocellulosic biomass has been proven to be an excellent alternative protein source for animal feed. This study aimed to evaluate the amino acid (AA) digestibility by estimating intestinal absorption from three yeast-based ingredients, produced by cultivating C. jadinii on hydrolysate, using either mixed woody species (drum- (WDI) or spray-dried (WSI)) or corn dextrose (drum-dried (DDI)) as the carbon source. Further, the protective effect of intestinal digests on activated THP1-Blue™-induced epithelial damage and cytokine profile was evaluated. Total protein content from these three ingredients ranged from 34 to 45%, while the AA dialysis showed an estimated bioaccessibility between 41 and 58%, indicating good digestibility of all test products. A protective effect against epithelial-induced damage was observed for two of the three tested products. Torula yeast cultivated on wood and drum-dried (WDI) and torula yeast cultivated on wood and spray-dried (WSI) significantly increased transepithelial electrical resistance (TEER) values (111-147%, p < 0.05), recovering the epithelial barrier from the inflammation-induced damage in a dose-dependent manner. Further, WSI digests significantly reduced IL8 (250.8 ± 28.1 ng/mL), IL6 (237.9 ± 1.8 pg/mL) and TNF (2797.9 ± 216.3 pg/mL) compared to the blank control (IL8 = 485.7 ± 74.4 ng/mL, IL6 = 478.7 ± 58.9 pg/mL; TNF = 4273.5 ± 20.9 pg/mL) (p < 0.05). These results align with previous in vivo studies, supporting torula yeast-based ingredients as a high-quality protein source for pigs, protecting the intestinal barrier from inflammatory damage, and reducing the pro-inflammatory response. We provided novel insights into the mechanisms behind the health improvement of pigs fed on torula yeast-based ingredients, with potential applications for designing nutritional interventions to recover intestinal homeostasis during critical production periods, such as weaning.

Use of Isotope-Labeled Body or Dietary Proteins to Determine Dietary Amino Acid Digestibility

Amino acid (AA) digestibility in humans has been determined conventionally based on oro-ileal AA disappearance. With this approach, it is necessary to account for undigested AAs of body origin (endogenous AAs) found in the ileal digesta. Determination of the endogenous AAs under physiological conditions is not straightforward, and the use of isotopes (labeled foods or body tissues) has been pivotal to advancing our understanding. The application of isotopes for determining gut endogenous AAs and AA digestibility is discussed as well as the types of digestibility coefficient generated (apparent, true, real) dependent upon methodology. Recently a new dual isotope-based method for determining ileal AA digestibility in humans has been developed that obviates the collection of ileal digesta. The dual isotope method, which awaits full validation, offers considerable promise for making noninvasive measures of AA digestibility in humans of different ages and physiological states.

Sustainable emerging high-intensity sonication processing to enhance the protein bioactivity and bioavailability: An updated review

High-intensity ultrasound (HIU) is considered one of the promising non-chemical eco-friendly techniques used in food processing. Recently (HIU) is known to enhance food quality, extraction of bioactive compounds and formulation of emulsions. Various foods are treated with ultrasound, including fats, bioactive compounds, and proteins. Regarding proteins, HIU induces acoustic cavitation and bubble formation, causing the unfolding and exposure of hydrophobic regions, resulting in functional, bioactive, and structural enhancement. This review briefly portrays the impact of HIU on the bioavailability and bioactive properties of proteins; the effect of HIU on protein allergenicity and anti-nutritional factors has also been discussed. HIU can enhance bioavailability and bioactive attributes in plants and animal-based proteins, such as antioxidant activity, antimicrobial activity, and peptide release. Moreover, numerous studies revealed that HIU treatment could enhance functional properties, increase the release of short-chain peptides, and decrease allergenicity. HIU could replace the chemical and heat treatments used to enhance protein bioactivity and digestibility; however, its applications are still on research and small scale, and its usage in industries is yet to be implemented.

Oral bioavailability of bioactive compounds; modulating factors, in vitro analysis methods, and enhancing strategies

Foods are complex biosystems made up of a wide variety of compounds. Some of them, such as nutrients and bioactive compounds (bioactives), contribute to supporting body functions and bring important health benefits; others, such as food additives, are involved in processing techniques and contribute to improving sensory attributes and ensuring food safety. Also, there are antinutrients in foods that affect food bioefficiency and contaminants that increase the risk of toxicity. The bioefficiency of food is evaluated with bioavailability which represents the amount of nutrients or bioactives from the consumed food reaching the organs and tissues where they exert their biological activity. Oral bioavailability is the result of some physicochemical and biological processes in which food is involved such as liberation, absorption, distribution, metabolism, and elimination (LADME). In this paper, a general presentation of the factors influencing oral bioavailability of nutrients and bioactives as well as the in vitro techniques for evaluating bioaccessibility and is provided. In this context, a critical analysis of the effects of physiological factors related to the characteristics of the gastrointestinal tract (GIT) on oral bioavailability is discussed, such as pH, chemical composition, volumes of gastrointestinal (GI) fluids, transit time, enzymatic activity, mechanical processes, and so on, and the pharmacokinetics factors including BAC and solubility of bioactives, their transport across the cell membrane, their biodistribution and metabolism. The impact of matrix and food processing on the BAC of bioactives is also explained. The researchers' recent concerns for improving oral bioavailability of nutrients and food bioactives using both traditional techniques, for example, thermal treatments, mechanical processes, soaking, germination and fermentation, as well as food nanotechnologies, such as loading of bioactives in different colloidal delivery systems (CDSs), is also highlighted.

The impact of advanced age on gastrointestinal characteristics that are relevant to oral drug absorption: An AGePOP review

The purpose of this review is to summarize the current knowledge on three physiological determinants of oral drug absorption, i.e., gastric emptying, volumes and composition of luminal fluids, and intestinal permeability, in the advanced age population, so that potential knowledge gaps and directions for further research efforts are identified. Published data on gastric emptying rates in older people are conflicting. Also, there are significant knowledge gaps, especially on gastric motility and emptying rates of drugs and of non-caloric fluids. Compared with younger adults, volumes of luminal contents seem to be slightly smaller in older people. Our understanding on the impact of advanced age on luminal physicochemical characteristics is, at best, very limited, whereas the impact of (co)morbidities and geriatric syndromes in the advanced age population has not been addressed to date. The available literature on the effect of advanced age on intestinal permeability is limited, and should be approached with caution, primarily due to the limitations of the experimental methodologies used.

Non-destructive characterization of pulse flours-A review

The consumption of plant-based proteins sourced from pulses is sustainable from the perspective of agriculture, environment, food security, and nutrition. Increased incorporation of high-quality pulse ingredients into foods such as pasta and baked goods is poised to produce refined food products to satisfy consumer demand. However, a better understanding of pulse milling processes is required to optimize the blending of pulse flours with wheat flour and other traditional ingredients. A thorough review of the state-of-the-art on pulse flour quality characterization reveals that research is required to elucidate the relationships between the micro- and nanoscale structures of these flours and their milling-dependent properties, such as hydration, starch and protein quality, components separation, and particle size distribution. With advances in synchrotron-enabled material characterization techniques, there exist a few options that have the potential to fill knowledge gaps. To this end, we conducted a comprehensive review of four high-resolution nondestructive techniques (i.e., scanning electron microscopy, synchrotron X-ray microtomography, synchrotron small-angle X-ray scattering, and Fourier-transformed infrared spectromicroscopy) and a comparison of their suitability for characterizing pulse flours. Our detailed synthesis of the literature concludes that a multimodal approach to fully characterize pulse flours will be vital to predicting their end-use suitability. A holistic characterization will help optimize and standardize the milling methods, pretreatments, and post-processing of pulse flours. Millers/processors will benefit by having a range of well-understood pulse flour fractions to incorporate into food formulations.

Role of the Intestinal Microbiota in the Genesis of Major Depression and the Response to Antidepressant Drug Therapy: A Narrative Review

A major depressive disorder is a serious mental illness characterized by a pervasive low mood that negatively concerns personal life, work life, or education, affecting millions of people worldwide. To date, due to the complexity of the disease, the most common and effective treatments consist of a multi-therapy approach, including psychological, social, and pharmacological support with antidepressant drugs. In general, antidepressants are effective in correcting chemical imbalances of neurotransmitters in the brain, but recent evidence has underlined the pivotal role of gut microbiota (GM) also in the regulation of their pharmacokinetics/pharmacodynamics, through indirect or direct mechanisms. The study of these complex interactions between GM and drugs is currently under the spotlight, and it has been recently named "pharmacomicrobiomics". Hence, the purpose of this review is to summarize the contribution of GM and its metabolites in depression, as well as their role in the metabolism and activity of antidepressant drugs, in order to pave the way for the personalized administration of antidepressant therapies.

Available Lysine in Foods as Determined in Adult Ileostomates

BACKGROUND

When foods are subjected to heat and pressure, a proportion of lysine is structurally altered and some will revert to lysine because of acid hydrolysis during amino acid analysis. Altered lysine molecules may be partly absorbed but are not utilized post-absorption.

OBJECTIVES

A guanidination-based bioassay has been developed to determine true ileal digestible reactive lysine but it was only used in animal models (pig and rat). The objective of this study was to apply the assay and determine whether there is a difference between true ileal digestible total lysine and true ileal digestible reactive lysine in adult human ileostomates.

METHODS

Six cooked or processed foods were analyzed for total lysine and reactive lysine. Six adults with a fully functioning ileostomy (4 women and 2 men; age range: 41-70 y; BMI: 20.8-28.1) participated. Foods for which total lysine > reactive lysine (cooked black beans, toasted wheat bread, and processed wheat bran), as well as a protein-free diet, were consumed by the ileostomates (n = 5 to 8; test food meals contained 25 g protein) and ileal digesta was collected. Each food was ingested twice by each participant, and the digesta was pooled. The order of foods for each participant was determined according to a Youden square. True ileal digestible total lysine and true ileal digestible reactive lysine were determined and a 2-way ANOVA model was used to analyze data.

RESULTS

True ileal digestible reactive lysine was significantly lower than true ileal digestible total lysine for cooked black beans, toasted wheat bread, and processed wheat bran by 89%, 55%, and 85%, respectively (P< 0.05).

CONCLUSIONS

True ileal digestible reactive lysine was lower than true ileal digestible total lysine, similar to that previously reported in pigs and rats, demonstrating the importance of determining the true ileal digestible reactive lysine contents of processed foods.

Caecal digestibility as an approximation of ileal protein digestibility evaluation in rats

The rat model can be used to assess ileal protein digestibility rapidly and in first intention, but no standardised method exists. Our objective was to compare methods to assess protein digestibility, depending on collection site (ileum/caecum) and use of a non-absorbable marker. A meal containing either casein, gluten or pea protein and chromium oxide as non-absorbable marker was given to male Wistar rats and the entire digestive content was collected 6 h later. Total chromium recovery was incomplete and variable, depending on protein source. We observed no significant difference in digestibility between the methods for any of the protein sources tested. Although none of the methods tested is optimal, our results suggest that caecal digestibility can be used as a proxy of ileal digestibility in rats without using a non-absorbable marker. This simple method makes it possible to evaluate protein digestibility of new alternative protein sources for human consumption.

Measurement of True Indispensable Amino Acid Digestibility by the Dual Isotope Tracer Technique: A Methodological Review

The digestible indispensable amino acid score uses ileal digestibility of each indispensable amino acid (IAA) of a dietary protein to calculate its protein quality. However, true ileal digestibility, which is the exclusive sum of digestion and absorption of a dietary protein up to the terminal ileum, is difficult to measure in humans. It is traditionally measured using invasive oro-ileal balance methods but can be confounded by endogenous secreted protein in the intestinal lumen, although the use of intrinsically labeled protein corrects for this. A recent, minimally invasive dual isotope tracer technique is now available to measure true IAA digestibility of dietary protein sources. This method involves simultaneous ingestion of 2 intrinsically but differently (stable) isotopically labeled proteins, a (²H or ¹⁵N-labeled) test protein and (¹³C-labeled) reference protein whose true IAA digestibility is known. Using a plateau-feeding protocol, the true IAA digestibility is determined by comparing the steady state ratio of blood to meal test protein IAA enrichment to the similar reference protein IAA ratio. The use of intrinsically labeled protein also distinguishes between IAA of endogenous and dietary origin. The collection of blood samples makes this method minimally invasive. As the α-¹⁵N and α-²H atoms of AAs of the intrinsically labeled protein are prone to label loss because of transamination, underestimation of digestibility, appropriate correction factors need to be employed when using ¹⁵N or ²H labeled test protein. The true IAA digestibility values of highly digestible animal protein by the dual isotope tracer technique are comparable to that measured by direct oro-ileal balance measurements, but no data are yet available for proteins with lower digestibility. A major advantage is that the minimally invasive method allows for true IAA digestibility measurement in humans across different age groups and physiological conditions.

The association between dietary branched-chain amino acids and the risk of cardiovascular diseases in Chinese patients with type 2 diabetes: A hospital-based case-control study

Background

Previous studies showed conflicting evidence on the association between the intake of dietary branched-chain amino acid (BCAA) and the risk of cardiovascular disease (CVD). However, this relationship has not been studied in patients with type 2 diabetes. Therefore, we evaluated the effects of total and individual dietary BCAA (leucine, isoleucine, and valine) intake on CVD risk among individuals with type 2 diabetes in China.

Materials and methods

A total of 419 patients with type 2 diabetes who have been diagnosed with CVD (within 2 weeks) were recruited between March 2013 and September 2015 in China. Cases with CVD were 1:1 matched to controls with type 2 diabetes but without CVD by age (±5 years) and sex. A validated 79-item semiquantitative food frequency questionnaire (FFQ) was administered to assess the participants' dietary data. Total dietary BCAA per individual was the summation of the daily intake of isoleucine, leucine, and valine. OR and corresponding CIs were computed by conditional logistic regression models adjusted for potential confounders.

Results

Median values of the daily intake of total BCAA were 11.87 g, with an interquartile range of 10.46–13.15 g for cases, and 12.47 g, with an interquartile range of 11.08–13.79 g for controls (P = 0.001). Dietary BCAA was inversely related to CVD risk after multivariable adjustment (OR _Q4−Q1 = 0.23, 95%CI = 0.10, 0.51, P trend <0.001 for total BCAA; OR _Q4−Q1 = 0.20, 95%CI = 0.07, 0.53, P trend = 0.001 for leucine). For each 1-S.D. increase in total dietary BCAA, leucine or valine intake was associated with 54% (95%CI = 29%, 70%, P = 0.001), 64% (95%CI = 29%, 82%, P = 0.003), or 54% (95%CI = 1%, 79%, P = 0.049) decrease in the risk of CVD, respectively. Whole grains, starchy vegetables, mushrooms, fruit, eggs, and dairy and dairy product-derived BCAA were found to attenuate CVD risk (P ranged: = 0.002–0.027).

Conclusion

Higher BCAA intake, in particular leucine and valine, might be associated with a lower risk of CVD.

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.

Comparison of True Ileal Amino Acid Digestibility between Adult Humans and Growing Pigs

BACKGROUND

It is not feasible to determine the true ileal amino acid (AA) digestibility of protein sources in humans on a routine basis, and the growing pig has been recommended as an animal model for this purpose but requires further validation.

OBJECTIVES

To determine and compare true ileal AA digestibility between adult human ileostomates and growing cannulated pigs for a range of food proteins.

METHODS

Seven protein sources (black beans, bread, collagen, pigeon peas, wheat bran, whey protein isolate, and zein) that spanned the range of digestibilities typically seen in foods were evaluated. Six female growing pigs received each of the protein sources, as well as a protein-free diet, and digesta were collected via ileal T-cannula. Adult human ileostomates consumed the same protein sources (5-8 ileostomates, depending on the protein source), as well as a protein-free diet, and digesta were collected. Titanium dioxide and celite were included in the diets as indigestible markers. True ileal AA digestibility coefficients were determined.

RESULTS

There was a significant effect of protein source (P ≤ 0.001) for all AAs. The effect of species was not significant (P > 0.05) except for total lysine (but not for available lysine). When analyzed within diets, the statistically significant species effect for true lysine digestibility was found for black beans only. Pig and human digestibility values were generally highly and significantly (P ≤ 0.05) correlated. A linear regression equation derived for true ileal AA digestibility (given as coefficients) determined in the human and pig for the overall mean of all AAs was (y = human, x = pig) y = 1.00x - 0.010, with the slope not statistically significant (P > 0.05) from unity and the intercept not different (P > 0.05) from zero.

CONCLUSIONS

True ileal AA digestibility values determined in the growing pig can be directly used for predicting digestibility in adult humans.

Moderate adiposity levels counteract protein metabolism modifications associated with aging in rats

PURPOSE

Physiological parameters such as adiposity and age are likely to influence protein digestion and utilization. The aim of this study was to evaluate the combined effects of age and adiposity on casein protein and amino acid true digestibility and its postprandial utilization in rats.

METHODS

Four groups were included (n = 7/8): 2 months/normal adiposity, 2 months/high adiposity, 11 months/normal adiposity and 11 months/high adiposity. Rats were given a calibrated meal containing ¹⁵N-labeled casein (Ingredia, Arras, France) and were euthanized 6 h later. Digestive contents were collected to assess protein and amino acid digestibilities. ¹⁵N enrichments were measured in plasma and urine to determine total body deamination. Fractional protein synthesis rate (FSR) was determined in different organs using a flooding dose of ¹³C valine.

RESULTS

Nitrogen and amino acid true digestibility of casein was around 95-96% depending on the group and was increased by 1% in high adiposity rats (P = 0.04). Higher adiposity levels counteracted the increase in total body deamination (P = 0.03) that was associated with older age. Significant effects of age (P = 0.006) and adiposity (P = 0.002) were observed in the muscle FSR, with age decreasing it and adiposity increasing it.

CONCLUSION

This study revealed that a higher level of adiposity resulted in a slight increase in protein and individual amino acid true digestibility values and seemed to compensate for the metabolic postprandial protein alterations observed at older age.

The True Amino Acid Digestibility of 15N-Labelled Sunflower Biscuits Determined with Ileal Balance and Dual Isotope Methods in Healthy Humans

BACKGROUND

Sunflower is a promising protein source but data on amino acid (AA) digestibility are lacking in humans. Classically, the determination of AA digestibility requires ileal digesta sampling. The dual isotope method is minimally invasive but has not been compared to the conventional approach.

OBJECTIVES

This study aimed to determine the true ileal digestibility of sunflower AAs in healthy volunteers who ate biscuits containing 15nitrogen (N) protein isolate, in comparison with the dual isotope method.

METHODS

Twelve healthy volunteers (men and women; 40.4 ± 10.5 years old; BMI, 23.7 ± 2.9 kg/m2) were equipped with a naso-ileal tube. For 4 hours, they consumed 9 repeated meals comprising 15N-sunflower protein biscuits together with 13carbon (C)-AAs, carried either in chocolate (SUN + Ch; n = 7) or apple puree (SUN + P; n = 5). Ileal digesta and blood were sampled throughout 8 hours after ingestion of the first meal. The 15N and 13C AA enrichments were measured in digesta to determine ileal digestibility directly and in plasma to determine lysine and threonine digestibility using the dual isotope method. Differences between methods and between vector groups were analyzed using paired and unpaired t-tests, respectively.

RESULTS

The ileal digestibility of sunflower indispensable AAs (IAA) was 89% ± 5.3%, with threonine and lysine having the lowest digestibility. In the SUN + Ch meal, IAA digestibility was 3% below that of SUN + P (P < 0.05). The mean free 13C-AA ileal digestibility was 98.1% ± 0.9%. No matter which matrix was used to carry 13C-AAs, plasma 15N and 13C-AA kinetics displayed a 1-hour offset. Digestibility obtained with the dual isotope method (70.4% ± 6.0% for threonine and 75.9% ± 22.3% for lysine) was below the target values.

CONCLUSIONS

The ileal digestibility of IAAs from a sunflower isolate incorporated in a biscuit was close to 90% in healthy adults. Under our experimental conditions, the dual isotope method provided lower values than the usual method. Further protocol developments are needed to validate the equivalence between both methods. This trial was registered at clinicaltrials.gov as NCT04024605.

Protein Quality in Perspective: A Review of Protein Quality Metrics and Their Applications

For design of healthy and sustainable diets and food systems, it is important to consider not only the quantity but also the quality of nutrients. This is particularly important for proteins, given the large variability in amino acid composition and digestibility between dietary proteins. This article reviews measurements and metrics in relation to protein quality, but also their application. Protein quality methods based on concentrations and digestibility of individual amino acids are preferred, because they do not only allow ranking of proteins, but also assessment of complementarity of protein sources, although this should be considered only at a meal level and not a diet level. Measurements based on ileal digestibility are preferred over those on faecal digestibility to overcome the risk of overestimation of protein quality. Integration of protein quality on a dietary level should also be done based on measurements on an individual amino acid basis. Effects of processing, which is applied to all foods, should be considered as it can also affect protein quality through effects on digestibility and amino acid modification. Overall, protein quality data are crucial for integration into healthy and sustainable diets, but care is needed in data selection, interpretation and integration.

Real ileal amino acid digestibility of pea protein compared to casein in healthy humans: a randomized trial

BACKGROUND

It is necessary to propose plant alternatives to animal proteins that are of good nutritional quality. Pea is a good candidate owing to its high protein content and its well-balanced amino acid (AA) profile.

OBJECTIVES

This study aimed to assess the real ileal AA and nitrogen digestibility (RIDAA and RIDN) of pea protein isolate as compared to milk casein in humans. It also aimed to evaluate their nutritional quality through calculation of the digestible indispensable amino acid score (DIAAS) and to determine the net postprandial protein utilization (NPPU).

METHODS

Fifteen healthy volunteers were included in a randomized, single-blinded, 2-arm, parallel-design trial. They were equipped with a naso-ileal tube. They ingested the test meals, which consisted of 9 successive portions of mashed potatoes containing either pea protein or casein, intrinsically labeled with nitrogen 15. Ileal content, plasma, and urine samples were collected regularly over an 8-h postprandial period.

RESULTS

The mean RIDAA values were 93.6% ± 2.9% for pea protein and 96.8% ± 1.0% for casein, with no difference between the sources (P = 0.22). Leucine, valine, lysine, and phenylalanine were significantly less digestible in pea than in casein. The RIDN values were 92.0% ± 2.7% and 94.0% ± 1.7% for pea protein and casein, respectively, and were not different (P = 0.11). The DIAAS was 1.00 for pea protein and 1.45 for casein. The NPPU was 71.6% ± 6.2% and 71.2% ± 4.9% for pea protein and casein, respectively (P = 0.88).

CONCLUSIONS

Although some AAs are less digestible in pea protein than in casein, the real ileal digestibility and the NPPU were not different. The DIAAS of 1.00 obtained for pea protein demonstrated its ability to meet all AA requirements. This study shows the potential of pea isolate as a high-quality protein. This study was registered at clinicaltrials.gov as NCT04072770.

Intestinal dysfunction in chronic disease

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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