Evidence that protein requirements have been significantly underestimated

A new concept to establish protein requirements

There is an increased need to establish the protein requirements for body weight maintenance and optimal health in humans. Different methods were developed in the past to assess protein requirements in which known amounts of protein/amino acids were provided. The purpose of this paper is to propose a new concept of establishing protein requirements in healthy and diseased conditions using a novel stable isotope approach. In the past years, we consistently found that when using a novel stable isotope pulse approach the intracellular production of amino acids (i.e., phenylalanine and tyrosine) is more than double the plasma rate of appearance, as measured by the commonly used primed constant infusion approach, leading to a net protein breakdown that is more than twice than estimated in the past. Net protein breakdown in the fasted state may provide a good estimation of the actual net protein loss that would take place during the day and thus can be used to estimate daily protein requirements. Our recent study found that a net protein breakdown ∼1 g protein/kg body weight/day was equal to the habitual protein intake, suggesting that there is a relation between habitual protein intake and protein requirements. As net protein breakdown is lower with advanced aging and in patient populations with comorbidities, a lower protein requirement for body weight maintenance is suggested. We propose a new concept to establish actual protein requirements of healthy and disease conditions, using a pulse tracer administration and to consider individual habitual protein intake and health conditions.

European guidelines on diagnosis and treatment of phenylketonuria: First revision

Phenylketonuria (PKU) is an autosomal recessive inherited disorder of phenylalanine metabolism caused by deficiency of the enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine. Untreated, PKU results in elevated phenylalanine levels in blood and brain, which cause severe intellectual disability, epilepsy and behavioural problems. For this first revision of the European PKU Guidelines previous recommendations were re-evaluated and updated according to new research findings. Twenty-one professionals were divided across four working groups and supported by a coordinator and chair. In addition to an update of the previous 70 recommendations, 20 new topics were included, resulting in a total of 87 statements in this first revision of the guidelines. Research publications were reviewed up until September 2022. Evidence was graded as high, moderate, low, very low or expert opinion and the recommendations were graded conditional or strong according to GRADE methodology. All recommendations were discussed during 14 plenary online or in person meetings. Recommendations were accepted if more than 75 % of the professionals were in agreement. When recommendations were not amended, the text reported in the European guidelines of 2017 remains valid.

Toward a Dynamic Model of Indispensable Amino Acid Requirements of the Adult Human: A Factorial Estimate of Oxidative Amino Acid Losses

BACKGROUND

Consensus regarding the required intake of indispensable amino acids (IDAAs) and protein [representing total amino acids (AAs)] in the adult is lacking. Oxidation is a major, although not exclusive, source of IDAA loss in humans body and a primary factor determining requirements; a quantitative understanding of oxidative IDAA losses is required.

OBJECTIVES

This study aimed to develop a factorial diurnal model of total oxidative IDAA and protein losses in the adult human.

METHODS

A factorial diurnal model of oxidative losses of protein and each IDAA at maintenance was developed by estimating the magnitude and variability of sources of oxidative loss from existing literature: inevitable catabolism (constitutive oxidation of each absorbed dietary AA), and protein turnover in the postprandial and postabsorptive states. Total oxidative losses were calculated by summing individual losses, validated against published independent nitrogen balance data and compared with current IDAA requirements.

RESULTS

The factorial model predicted minimum oxidative total AA losses of 390 ± 60 mg/kg BW/d, 59% of the estimated average requirement for protein. Inevitable AA oxidation and oxidation associated with postabsorptive protein turnover were the major sources of the oxidative loss for protein, at 40% and 44%, respectively. Summed oxidative IDAA losses ranged from 64% (isoleucine) to 91% (tryptophan) of current requirements. Total oxidative losses predicted by the model were significant predictors of actual experimental oxidative losses obtained by nitrogen balance (R2 = 0.66; P = 0.049).

CONCLUSIONS

The use of a factorial model for estimation of minimum IDAA and protein oxidative losses in the adult human provides an essential starting point for an updated understanding of protein and IDAA requirements. Further iterations of the model will estimate total protein and IDAA requirements, and account for variations in dietary protein quantity and quality, as well as different populations and physiologic states. Additional data, especially for inevitable oxidation in humans, and particularly with respect to individual IDAAs, are needed.

Protein requirements in adults with phenylketonuria and bioavailability of glycomacropeptide compared to an l-amino acid-based product

BACKGROUND

Phenylketonuria (PKU) is caused by phenylalanine hydroxylase deficiency. Treatment is primarily a low-Phe diet combined with l-amino acid-based products (l-AA). Protein requirements in adults with PKU have not been directly determined. A formula with glycomacropeptide (GMP) and low phenylalanine is available, yet untested for optimal protein synthesis.

OBJECTIVES

To determine the protein requirements in adults with PKU and the bioavailability of GMP-AA in the same patients using the indicator amino acid oxidation (IAAO) technique.

METHODS

Each participant was allocated to 7 separate l-AA intakes (range: 0.1-1.8 g/kg/day) in Experiment 1. In Experiment 2, the same patients participated in 4 GMP-AA intakes (range: 0.1-0.9 g/kg/day). The IAAO method with l-[1-13C]-lysine as the indicator amino acid and its oxidation to 13CO2 was used as the primary indicator of protein synthesis. Protein requirements were identified with a breakpoint, and bioavailability was determined by comparing 13CO2 slope from GMP-AA versus l-AA.

RESULTS

Six adults with PKU (4 M: 2F) completed a total of 54 study days over the 2 experiments. The estimated average requirement (EAR) for protein was determined to be 1.11 g/kg/day (R2 = 0.20). The bioavailability of protein from GMP-AA was determined to be 99.98%, which was high and near to 100% comparable to l-AA; although, the results apply only to the tested GMP-AA blend.

CONCLUSIONS

To our knowledge, this is the first study to directly define a quantitative protein requirement and indicates that current PKU protein recommendations for adults with PKU may be underestimated. The bioavailability of protein in the GMP-AA blend was high and optimal for protein synthesis in adults with PKU.

Common questions and misconceptions about protein supplementation: what does the scientific evidence really show?

Protein supplementation often refers to increasing the intake of this particular macronutrient through dietary supplements in the form of powders, ready-to-drink shakes, and bars. The primary purpose of protein supplementation is to augment dietary protein intake, aiding individuals in meeting their protein requirements, especially when it may be challenging to do so through regular food (i.e. chicken, beef, fish, pork, etc.) sources alone. A large body of evidence shows that protein has an important role in exercising and sedentary individuals. A PubMed search of "protein and exercise performance" reveals thousands of publications. Despite the considerable volume of evidence, it is somewhat surprising that several persistent questions and misconceptions about protein exist. The following are addressed: 1) Is protein harmful to your kidneys? 2) Does consuming "excess" protein increase fat mass? 3) Can dietary protein have a harmful effect on bone health? 4) Can vegans and vegetarians consume enough protein to support training adaptations? 5) Is cheese or peanut butter a good protein source? 6) Does consuming meat (i.e., animal protein) cause unfavorable health outcomes? 7) Do you need protein if you are not physically active? 8) Do you need to consume protein ≤ 1 hour following resistance training sessions to create an anabolic environment in skeletal muscle? 9) Do endurance athletes need additional protein? 10) Does one need protein supplements to meet the daily requirements of exercise-trained individuals? 11) Is there a limit to how much protein one can consume in a single meal? To address these questions, we have conducted a thorough scientific assessment of the literature concerning protein supplementation.

Determining amino acid requirements in humans

Amino acids form the building blocks of body protein. Dietary protein sources provide the amino acids needed, but protein sources vary widely in amio acid composition. To ensure humans can meet body demands for amino acids, amino acid intake recommendations are provided by the Dietary Reference Intakes (DRI) and by Food and Agriculture Organization/World Health Organization/United Nations University (FAO/WHO/UNU). Current amino acid intake recommendations, however, are based on data collected predominantly from young adult males. The development of the minimally invasive indicator amino acid oxidation (IAAO) method has permitted the evaluation of amino acid requirements in various vulnerable populations. The purpose of this review is to discuss recent amino acid requirement studies in school-age children, pregnant females and the elderly determined using the IAAO technique. These requirements will help to inform evidence-based recommendations that will help to guide dietary guidelines.

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.

The Importance of Dietary Protein Quality in Mid- to High-Income Countries

In wealthy countries, the protein intake of adults is usually considered to be adequate, and considerations of protein quality are often deemed irrelevant. The objective was to examine dietary protein intakes of adults in developed countries in the context of dietary protein quality. An analysis of NHANES population data on actual protein intakes in the United States (a developed country) demonstrated that for a dietary Digestible Indispensable Amino Acid Score (DIAAS) of 100%, 11% of the adult (19-50 y) population had habitual protein intakes below the Estimated Average Requirement (EAR) and 22% below the Recommended Dietary Allowance. The percentage of the population with utilizable protein intakes potentially falling below the EAR increased as the assumed DIAAS declined. Analysis of the NHANES data and several other datasets also indicated that total protein intakes can be limiting or close to limiting for the elderly and some vegetarians and vegans. Here, lower dietary protein quality can potentially lead to inadequate utilizable protein intakes. For many people in specific physiological states (e.g., weight loss, endurance sports, resistance exercise) attempting to meet higher dietary protein targets often with accompanying lowered energy intakes, low dietary protein quality can lead to protein calories expressed as a proportion of total calories, falling outside what may be acceptable limits (maximum of 30% protein calories from total calories). In general, individuals within the adult population may be susceptible to macronutrient imbalance (whenever total protein intakes are high, daily energy intakes low) and for diets with lower protein quality (DIAAS <100%). Our analysis shows that dietary protein quality is relevant in mid- to high-income countries.

Protein intake affects erythrocyte glutathione synthesis in young healthy adults in a repeated-measures trial

BACKGROUND

In 2005, the Institute of Medicine advised using methods other than nitrogen balance (NB) for determining protein requirements. Since then, protein requirements using indicator amino acid oxidation (IAAO) have been published and are higher than NB. Glutathione (GSH), a tripeptide of cysteine, glutamate, and glycine, is a principal antioxidant that can be used as a functional indicator of protein adequacy.

OBJECTIVES

The aim of this study was to measure changes in erythrocyte GSH kinetics [fractional synthesis rate (FSR) and absolute synthesis rate (ASR)] in healthy adults following a range of protein intakes at and above the current recommendations.

METHODS

Sixteen healthy adults [8 males and 8 females, aged 25.6 ± 0.9 y (mean ± SEM)] were studied at 4 of 6 protein intakes ranging from 0.6 to 1.5 g⋅kg-1⋅d-1. Erythrocyte GSH kinetics were assessed during a 7-h infusion of [U-13C2-15N]glycine following 2 d of adaptation to each protein intake. Blood and urine tests were performed to measure oxidative stress markers, plasma homocysteine, triglycerides, plasma amino acid concentrations, 5-L-oxoproline (5-OP), and urinary sulfate. The protein intake that maximized GSH synthesis was determined using mixed-effect change-point regression in R. Primary and secondary outcomes were analyzed using linear mixed-effects and repeated-measures analysis of variance with Tukey's post hoc test.

RESULTS

The protein intake that maximized GSH FSR at 78%⋅d-1 was 1.0 g⋅kg-1⋅d-1 (95% confidence interval: 0.63, 1.39). GSH ASR was significantly lower at 0.6 and 0.8 g⋅kg-1⋅d-1 than at 1.5 g⋅kg-1⋅d-1 (2.03 and 2.17, respectively, compared with 3.71 mmol⋅L-1⋅d-1). Increasing the protein intake led to increased urinary sulfate but did not affect erythrocyte GSH concentration, plasma oxidative stress markers, triglycerides, homocysteine, or 5-OP.

CONCLUSIONS

A protein intake of 1.0 g⋅kg-1⋅d-1 maximized GSH synthesis, which is in agreement with earlier IAAO-derived protein requirements of 0.93 to 1.2 g⋅kg-1⋅d-1. These findings suggest that recommendations based on NB (0.66 g⋅kg-1⋅d-1) may underestimate protein needs for adequate health. This trial was registered at clinicaltrials.gov as NCT02971046.

Development of a diet quality score and adherence to the Swiss dietary recommendations for vegans

BACKGROUND

Vegan diets have recently gained popularity in Switzerland as well as globally. The aim of the present study was to develop a diet quality score for vegans (DQS-V) based on the Swiss dietary recommendations for vegans.

METHODS

The dataset included 52 healthy vegan adults. Dietary intake data were assessed by three-day weighed food records. Body weight and height were measured, and a venous blood sample for the analysis of vitamin and mineral status was collected. Spearman rank correlation coefficients were used due to not-normally distributed data. Dietary patterns were identified using principal component analysis (PCA).

RESULTS

The DQS-V score (mean ± SD) was 48.9 ± 14.7. Most vegans adhered to the recommended portions of vegetables, vitamin C-rich vegetables, fruits, omega-3-rich nuts, fats and oils, and iodized salt. However, the intake of green leafy vegetables, vitamin C-rich fruits, wholegrains, legumes, nuts and seeds, selenium-rich nuts, zero caloric liquid, and calcium-fortified foods was suboptimal. The sample overconsumed sweet-, salty-, fried foods, and alcohol. The DQS-V had a significantly positive correlation with intakes of fibre, polyunsaturated fatty acids, potassium, zinc, and phosphorus intakes (p's < 0.05) but was negatively correlated with vitamin B12 and niacin intakes (p's < 0.05). Two dietary patterns were derived from PCA: 1) refined grains and sweets and 2) wholegrains and nuts. The correlation between the DQS-V and the first dietary pattern was negative (- 0.41, p = 0.004) and positive for the second dietary pattern (0.37, p = 0.01). The refined grains and sweets dietary pattern was inversely correlated with beta-carotene status (- 0.41, p = 0.004) and vitamin C status (r = - 0.51, p = 0.0002).

CONCLUSION

The newly developed DQS-V provides a single score for estimating diet quality among vegan adults. Further validation studies examining the DQS-V in relation to an independent dietary assessment method and to biomarkers of nutritional intake and status are still needed before the general application of the DQS-V.

Optimal Protein Intake in Healthy Children and Adolescents: Evaluating Current Evidence

High protein intake might elicit beneficial or detrimental effects, depending on life stages and populations. While high protein intake in elder individuals can promote beneficial health effects, elevated protein intakes in infancy are discouraged, since they have been associated with obesity risks later in life. However, in children and adolescents (4–18 years), there is a scarcity of data assessing the effects of high protein intake later in life, despite protein intake being usually two- to three-fold higher than the recommendations in developed countries. This narrative review aimed to revise the available evidence on the long-term effects of protein intake in children and adolescents aged 4–18 years. Additionally, it discusses emerging techniques to assess protein metabolism in children, which suggest a need to reevaluate current recommendations. While the optimal range is yet to be firmly established, available evidence suggests a link between high protein intake and increased Body Mass Index (BMI), which might be driven by an increase in Fat-Free Mass Index (FFMI), as opposed to Fat Mass Index (FMI).

Is It Time to Reconsider the U.S. Recommendations for Dietary Protein and Amino Acid Intake?

Since the U.S. Institute of Medicine's recommendations on protein and amino acid intake in 2005, new information supports the need to re-evaluate these recommendations. New lines of evidence include: (1) re-analysis/re-interpretation of nitrogen balance data; (2) results from indicator amino acid oxidation studies; (3) studies of positive functional outcomes associated with protein intakes higher than recommended; (4) dietary guidance and protein recommendations from some professional nutrition societies; and (5) recognition that the synthesis of certain dispensable amino acids may be insufficient to meet physiological requirements more often than previously understood. The empirical estimates, theoretical calculations and clinical functional outcomes converge on a similar theme, that recommendations for intake of protein and some amino acids may be too low in several populations, including for older adults (≥65 years), pregnant and lactating women, and healthy children older than 3 years. Additional influential factors that should be considered are protein quality that meets operational sufficiency (adequate intake to support healthy functional outcomes), interactions between protein and energy intake, and functional roles of amino acids which could impact the pool of available amino acids for use in protein synthesis. Going forward, the definition of "adequacy" as it pertains to protein and amino acid intake recommendations must take into consideration these critical factors.

Macronutrient (im)balance drives energy intake in an obesogenic food environment: An ecological analysis

OBJECTIVE

The protein leverage hypothesis (PLH) postulates that strong regulation of protein intake drives energy overconsumption and obesity when human diets are diluted by fat and carbohydrates. The two predictions of the PLH are that humans (i) regulate intake to maintain protein within a narrow range and that (ii) energy intake is an inverse function of percentage energy from protein because absolute protein intake is maintained within narrow limits.

METHODS

Multidimensional nutritional geometry was used to test the predictions of the PLH using dietary data from the Australian National Nutrition and Physical Activity Survey.

RESULTS

Both predictions of the PLH were confirmed in a population setting: the mean protein intake was 18.4%, and energy intake decreased with increasing energy from protein (L = -0.18, p &lt; 0.0001). It was demonstrated that highly processed discretionary foods are a significant diluent of protein and associated with increased energy but not increased protein intake.

CONCLUSIONS

These results support an integrated ecological and mechanistic explanation for obesity, in which low-protein highly processed foods lead to higher energy intake because of the biological response to macronutrient imbalance driven by a dominant appetite for protein. This study supports a central role for protein in the obesity epidemic, with significant implications for global health.

Review of protein intake and suitability of foods for protein-fortification in older adults in the UK

Protein is a vital dietary component for combating negative health outcomes associated with malnutrition in older adults, including sarcopenia, functional decline and reduced quality of life. Yet, recommended daily protein intake is consistently unmet, as evidenced in the literature and reaffirmed in this review. Poor appetite is recognized as a major determinant of protein-energy undernutrition and thus fortification of regular food or drinks provides a flexible and relevant approach for older adults with reduced appetite. To increase the likelihood of fortified products being successfully incorporated into the diets of older adults, they must be adaptable to older adults eating patterns, cater for their preferences and take the specific age-related problems that complicate food intake into account. This paper aims to highlight older adults' current sources of protein, shopping habits, typical eating patterns and commonly consumed foods, and hence consider appropriate carriers for protein enrichment. Data were reanalyzed from a combination of freely available UK datasets, including the National Dietary and Nutrition Survey and the Food and You Survey, alongside data purchased from market research consultancy, Kantar. These insights draw attention to the potential suitability of foods for fortification purposes, with the ultimate objective to promote eating pleasure and prevent malnutrition.

Association of Dietary Protein Intake and Grip Strength Among Adults Aged 19+ Years: NHANES 2011–2014 Analysis

Background

Research on the role of protein in the diet has evolved beyond a focus on quantity to include the impact of its quality and distribution across meal times in an effort to optimize dietary protein recommendations.

Objective

To determine the association of dietary protein amount, type, and intake pattern with grip strength in adults.

Design

Data from the National Health and Nutrition Examination Survey (NHANES) 2011–2014 for adults 19 + years (N = 9,214) were used with exclusions for pregnant and lactating women. Intakes of dietary total protein (TP), animal protein (AP, including dairy), plant protein (PP), and leucine (Leu) were determined using day 1 24 h dietary recall data after adjusting for the complex sample design of NHANES. Regression analyses were used to assess the association of dietary protein and leucine intake quartiles, and whether consuming &gt; 20 g of dietary protein at one or more meals was related to grip strength with adjustment for age, gender, and ethnicity.

Results

Mean intake of TP among adults aged 19 + years was 83.6 ± 0.5 g/day, and 2/3rd of this was from animal sources (including dairy). Grip strength increased (p &lt; 0.05) with increasing quartiles of TP, AP, PP, and leucine among all adults 19 + years (β = 1.340.19, 1.27 ± 0.19, 0.76 ± 0.20, and 1.33 ± 0.23, respectively), 19–50 years (β = 1.14 ± 0.27, 1.06 ± 0.25, 0.77 ± 0.30, and 1.18 ± 0.27, respectively), and 51 + years (β = 0.95 ± 0.26, 1.08 ± 0.27, and 1.05 ± 0.27, respectively, for TP, AP, and Leu); however, the increase was more pronounced for AP than PP. Grip strength also increased (p &lt; 0.05) with increasing the number of meal occasions containing &gt; 20 g of dietary protein (β = 1.50 ± 0.20, 1.41 ± 0.25, and 0.91 ± 0.37 for 19+, 19–50, and 51 + years, respectively), and significant increases were detected for two meals compared to zero meals.

Conclusion

Dietary protein quantity, quality, and distribution should be considered collectively when looking to optimize protein intake to support muscle strength and function.

Perspective: Soybeans Can Help Address the Caloric and Protein Needs of a Growing Global Population

Feeding a growing global population with projected rising socioeconomic status will require additional sources of calories and especially protein. These sources need to align with the Sustainable Development Goals established by the Food and Agriculture Organization of the United Nations. The soybean is uniquely positioned to meet this challenge based on the following criteria: (1) Global soybean production exceeds by ~4 times the production of all pulses combined (2) Soybeans are higher in protein than other legumes and soy protein quality is similar to animal protein quality (3) Soybeans are an excellent source of healthy fat, including both essential fatty acids (4) Soybeans, like other legumes, symbiotically fix atmospheric nitrogen thereby reducing the need for fertilizer inputs (5) Greenhouse gas emissions per unit protein are lower than for nearly all other foods (6) Soybeans, like other legumes, are also recognized as an affordable food that can be incorporated into diverse diets regardless of economic standing and (7) The range of foods produced from soybeans constitutes an important position in historic and contemporary cuisines, cultures and emerging consumer trends for plant-based protein. Although most soybeans are currently used for animal feed, soybean use is dictated by consumer demand. Therefore, soybeans are well positioned to meet future global needs for energy and protein. Armed with this knowledge, health professionals can feel justified in encouraging greater consumption of soyfoods for both personal and planetary reasons.

Dietetic Management of Adults with Phenylketonuria (PKU) in the UK: A Care Consensus Document

There is an increasing number of adults and elderly patients with phenylketonuria (PKU) who are either early, late treated, or untreated. The principal treatment is a phenylalanine-restricted diet. There is no established UK training for dietitians who work with adults within the specialty of Inherited Metabolic Disorders (IMDs), including PKU. To address this, a group of experienced dietitians specializing in IMDs created a standard operating procedure (SOP) on the dietetic management of adults with PKU to promote equity of care in IMD dietetic services and to support service provision across the UK. The group met virtually over a period of 12 months until they reached 100% consensus on the SOP content. Areas of limited evidence included optimal blood phenylalanine reporting times to patients, protein requirements in older adults, management of weight and obesity, and management of disordered eating and eating disorders. The SOP does not include guidance on maternal PKU management. The SOP can be used as a tool for training dietitians new to the specialty and to raise the standard of education and care for patients with PKU in the UK.

Meal-to-meal and day-to-day macronutrient variation in an ad libitum vending food paradigm

BACKGROUND

Theory posits that macronutrient intake is regulated by protein consumption and adequate intake of protein results in consumption of less carbohydrates and fat. The current study investigates the effect of protein intake on calorie and macronutrient content using an ad libitum vending machine paradigm.

METHODS

Healthy volunteers (n = 287; 177 m; Age = 36 ± 11; BMI = 32 ± 8) were admitted to our clinical research unit. Macronutrient meal content (grams) and energy intake (Kcal) were quantified by specialized food processing software and collected on an hourly basis over a three-day period using a validated ad libitum vending machine paradigm. Body composition was assessed by DXA. Lagged multi-level models accounting for age, sex, race/ethnicity, fat and fat free mass indices were fitted to examine the impact of prior macronutrient content on subsequent meals.

RESULTS

Protein intake was associated with decreased energy intake (Kcal; B = -1.67 kcal, p = 0.0048), lower protein and carbohydrate intake (B = -0.08 g, p = 0.0006; B = -0.21 g, p = 0.0003, respectively) at subsequent meals. Daily Macronutrient intake and subsequent intake were positively associated.

CONCLUSIONS

Dietary protein exhibits a negative regulatory effect on a short-term meal-to-meal rather than day-to-day basis. In the setting of readily available food, protein intake impacts energy intake only over very short time courses.

A new high protein-to-energy enteral formula with a whey protein hydrolysate to achieve protein targets in critically ill patients: a prospective observational tolerability study

OBJECTIVES

Current guidelines and expert recommendations stress the need to implement enteral feeds with a higher protein-to-energy ratio to meet protein requirements as recommended while avoiding gastrointestinal side effects and energy overfeeding in ICU patients.

MATERIALS AND METHODS

Prospective tolerability study in 18 critically ill patients with a high protein formula (high protein-to-energy (HP:E) formula = Fresubin® Intensive; HPG) compared to a contemporary matched conventional therapy group (CTG). The primary outcome was GI intolerance defined as ≥300 ml daily gastric residual volume (GRV), vomiting, or diarrhea on days 1 and 2. Secondary outcomes were the percentage of patients reaching their protein target on day 4 and overall protein intake.

RESULTS

Groups were comparable regarding demographic characteristics, disease severity, organ failures, mechanical ventilation, and NUTRIC score at baseline. Eighteen patients completed the 4-day feeding period. The number of events of GRV of ≥300 ml/day was equal in both groups (33.3%). The incidence of diarrhea and vomiting was low in the HPG (two patients concerned). EN did not need to be discontinued due to intolerance in any group. Seventy-two percent of patients reached protein targets ≥1.3 g/kgBW/d within 4 days after initiation of enteral feeding, which was superior to the CTG (33%). Post-hoc testing showed group differences of protein intake between HPG and CTG were significant at t = 72 h and t = 96 h. Energy targets were met in both groups.

CONCLUSION

The HP:E formula containing 33% whey protein hydrolysate is well tolerated in this tolerability study. Due to the HP:E ratio protein targets can be reached faster. Larger randomized trials are needed to confirm preliminary results.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02678325. Registered 2 May 2016.

Resistance to lean mass gain in constitutional thinness in free-living conditions is not overpassed by overfeeding

BACKGROUND

Constitutional thinness (CT), a non-malnourished underweight state with no eating disorders, is characterized by weight gain resistance to high fat diet. Data issued from muscle biopsies suggested blunted anabolic mechanisms in free-living state. Weight and metabolic responses to protein caloric supplementation has not been yet explored in CT.

METHODS

A 2 week overfeeding (additional 600 kcal, 30 g protein, 72 g carbohydrate, and 21 g fat) was performed to compare two groups of CTs (12 women and 11 men) to normal-weight controls (12 women and 10 men). Bodyweight, food intake, energy expenditure, body composition, nitrogen balance, appetite hormones profiles, and urine metabolome were monitored before and after overfeeding.

RESULTS

Before overfeeding, positive energy gap was found in both CT genders (309 ± 370 kcal in CT-F and 332 ± 709 kcal in CT-M) associated with higher relative protein intake per kilo (1.74 ± 0.32 g/kg/day in CT-F vs. 1.16 ± 0.23 in C-F, P < 0.0001; 1.56 ± 0.36 in CT-M vs. 1.22 ± 0.32 in C-M, P = 0.03), lower nitrogen (7.26 ± 2.36 g/day in CT-F vs. 11.41 ± 3.64 in C-F, P = 0.003; 9.70 ± 3.85 in CT-M vs. 14.14 ± 4.19 in C-M, P = 0.02), but higher essential amino acids urinary excretion (CT/C fold change of 1.13 for leucine and 1.14 for arginine) in free-living conditions. After overfeeding, CTs presented an accentuated positive energy gap, still higher than in controls (675 ± 540 in CTs vs. 379 ± 427 in C, P = 0.04). Increase in lean mass was induced in both controls genders but not in CTs (a trend was noticed in CT women), despite a similar nitrogen balance after overfeeding (5.06 ± 4.33 g/day in CTs vs. 4.28 ± 3.15 in controls, P = 0.49). Higher anorectic gut hormones' tone, glucagon-like peptide 1 and peptide tyrosine tyrosine, during test meal and higher snacking frequency were noticed before and after overfeeding in CTs.

CONCLUSIONS

The blunted muscle energy mechanism, previously described in CTs in free-living state, is associated with basal saturated protein turn over suggested by the concordance of positive nitrogen balance and an increased urine excretion of several essential amino acids. This saturation cannot be overpassed by increasing this spontaneous high-protein intake suggesting a resistance to lean mass gain in CT phenotype.

Bioavailable Methionine Assessed Using the Indicator Amino Acid Oxidation Method Is Greater When Cooked Chickpeas and Steamed Rice Are Combined in Healthy Young Men

BACKGROUND

In general, pulse protein is limiting in the indispensable amino acid methionine, and antinutritional factors in pulses can affect methionine bioavailability. Complementation with grains such as rice can improve pulse protein quality, but knowledge of methionine bioavailability in pulses and grains is necessary to correct for available methionine when planning and assessing dietary protein intake.

OBJECTIVES

The study objectives were to determine the bioavailability of methionine in rice and chickpeas separately and to assess the effect of complementation of chickpeas and rice.

METHODS

Eleven healthy young men (<30 y, BMI <25 kg/m2) were studied in a repeated-measures design using the indicator amino acid oxidation (IAAO) method, with l-[1-13C]phenylalanine as the indicator. Each received 7 or 10 methionine intakes in random order: 4 intakes of l-methionine-0.5, 1, 2, and 3 mg⋅kg-1⋅d-1 (reference diet); 3 intakes of methionine from rice and from chickpeas; and 3 intakes from the mixed meal of chickpeas plus rice (test diets). The bioavailability of methionine and the effect of complementation were assessed by comparing the IAAO response to varying intakes of methionine in rice, in cooked Canadian chickpeas, and in rice plus chickpeas combined compared with the IAAO response to l-methionine intakes in the reference protein (crystalline amino acid mixture patterned after egg protein) using the slope ratio method.

RESULTS

The bioavailability of methionine from rice and from chickpeas was 100% and 63%, respectively. Complementation of cooked chickpeas with rice decreased the oxidation of l-[1-13C]phenylalanine by up to 14% (P < 0.05), suggesting an improved protein quality of the combined chickpeas plus rice protein.

CONCLUSIONS

When chickpeas are the main protein source in the diet of young adult men, the combination of rice and chickpeas in a 3:1 ratio is recommended to improve dietary protein quality. This trial was registered at clinicaltrials.gov as NCT03339154 and NCT03674736.

Translating "protein foods" from the new Canada's Food Guide to consumers: knowledge gaps and recommendations

The revised version of Canada's Food Guide, released in January 2019, issued new guidance by combining meat and alternatives with milk and alternatives into a single group called "protein foods" and emphasized selecting plant-based foods from this category more often. Though the changes represent a simple depiction of a healthy plate, the new Food Guide has opened knowledge gaps about protein foods and exposed new concerns about the interpretation and implementation of the Food Guide among vulnerable groups, particularly children and the elderly. To address key knowledge and research gaps, nutrition leaders need to reach a consensus on key messages to best inform the development of tools and resources to support practitioners in translating messages to consumers, including foodservice standards. Among consumers, families with young children are a primary target for these resources as they develop their life-long habits to ensure they have the knowledge and skills to select, prepare, and consume nutrient-rich protein foods. The new Food Guide provides an opportunity to address the existing knowledge gaps, develop tools and resources to support health professionals, and design interventions that will help Canadian families choose, prepare, and eat nutrient-rich protein foods. Novelty An updated Canadian regulatory framework is needed for protein labelling and content/health claims. There are knowledge gaps about protein foods consumption and food literacy needed to optimize nutritional health. Mandatory nutrition policies are needed to safeguard the provision of high-quality protein foods across institutions that serve children and older adults.

An Acute Reduction in Habitual Protein Intake Attenuates Post Exercise Anabolism and May Bias Oxidation-Derived Protein Requirements in Resistance Trained Men

Protein recommendations for resistance-trained athletes are generally lower than their habitual intakes. Excess protein consumption increases the capacity to oxidize amino acids, which can attenuate post-exercise anabolism and may impact protein requirements determined by stable isotope techniques predicated on amino acid tracer oxidation. We aimed to determine the impact of an acute (5d) reduction in dietary protein intake on post-exercise anabolism in high habitual consumers using the indicator amino acid oxidation (IAAO) technique. Resistance trained men [n = 5; 25 ± 7 y; 73.0 ± 5.7 kg; 9.9 ± 2.9% body fat; 2.69 ± 0.38 g·kg⁻¹·d⁻¹ habitual protein intake) consumed a high (H; 2.2 g·kg⁻¹·d⁻¹) and moderate (M; 1.2 g·kg⁻¹·d⁻¹) protein diet while training every other day. During the High protein phase, participants consumed a 2d controlled diet prior to determining whole body phenylalanine turnover, net balance (NB), and ¹³CO₂ excretion (F¹³CO₂) after exercise via oral [¹³C]phenylalanine. During the Moderate phase, participants consumed 2.2 g protein·kg⁻¹·d⁻¹ for 2d prior to consuming 1.2 g protein·kg⁻¹·d⁻¹ for 5d. Phenylalanine metabolism was measured on days 1, 3, and 5 (M1, M3, and M5, respectively) of the moderate intake. F¹³CO₂, the primary outcome for IAAO, was ~72 and ~55% greater on the 1st day (M1, P < 0.05) and the third day of the moderate protein diet (M3, P = 0.07), respectively, compared to the High protein trial. Compared to the High protein trial, NB was ~25% lower on the 1st day (M1, P < 0.01) and 15% lower on the third day of the moderate protein diet (M3, P = 0.09). High habitual protein consumption may bias protein requirements determined by traditional IAAO methods that use only a 2d pre-trial controlled diet. Post-exercise whole body anabolism is attenuated following a reduction in protein intake in resistance trained men and may require ~3–5d to adapt. This trial is registered at clinicaltrials.gov as NCT03845569.

Higher dietary protein intake preserves lean body mass, lowers liver lipid deposition, and maintains metabolic control in participants with long-chain fatty acid oxidation disorders

Medical nutrition therapy for long-chain fatty acid oxidation disorders (LC-FAODs) currently emphasizes fasting avoidance, restricted dietary long-chain fatty acid intake, supplementation with medium chain triglycerides, and increased carbohydrate intake. We hypothesize that increasing dietary protein intake relative to carbohydrate intake would preserve metabolic control yet induce physical benefits including reduced hepatic lipogenesis. Therefore, we compared two dietary approaches with similar fat intake but different carbohydrate to protein ratios in participants diagnosed with LC-FAODs. Thirteen participants were enrolled and randomized into either a high-protein (PRO) or a high-carbohydrate (CHO) diet for 4 months. Baseline and 4-month assessments included body composition, ectopic lipid deposition, and resting energy expenditure. End of study assessments also included total energy expenditure, metabolic responses to oral feedings, and whole-body fatty acid oxidation capacity. At the end of the dietary intervention, both groups had similar energy expenditure, fat and glucose oxidation rates, and glucolipid responses to mixed meal and oral glucose loads. Neither dietary group experienced worsening symptoms related to their LC-FAOD. Compared to the CHO group, the PRO group exhibited increased blood levels of short-chain acylcarnitines, reduced intrahepatic lipid content, and maintained lean body mass while the CHO group lost lean mass. In patients with LC-FAODs, increasing protein intake maintained metabolic control, reduced liver fat without risk of metabolic decompensation, and helped preserve lean body mass. We propose that a modest increase in dietary protein along with fasting avoidance and fat restriction may improve body composition and energy expenditure in patients with LC-FAODs.

Protein Leverage: Theoretical Foundations and Ten Points of Clarification

Much attention has been focused on fats and carbohydrates as the nutritional causes of energy overconsumption and obesity. In 2003, a model of intake regulation was proposed in which the third macronutrient, protein, is not only involved but is a primary driver of calorie intake via its interactions with carbohydrates and fats. This model, called protein leverage, posits that the strong regulation of protein intake causes the overconsumption of fats and carbohydrates (hence total energy) on diets with a low proportion of energy from protein and their underconsumption on diets with a high proportion of protein. Protein leverage has since been demonstrated in a range of animal studies and in several studies of human macronutrient regulation, and its potential role in contributing to the obesity epidemic is increasingly attracting discussion. Over recent years, however, several misconceptions about protein leverage have arisen. Our aim in this paper is to briefly outline some key aspects of the underlying theory and clarify 10 points of misunderstanding that have the potential to divert attention from the substantive issues.

The redox-dependent regulation of satellite cells following aseptic muscle trauma (SpEED): study protocol for a randomized controlled trial

Background

Muscle satellite cells (SCs) are crucial for muscle regeneration following muscle trauma. Acute skeletal muscle damage results in inflammation and the production of reactive oxygen species (ROS) which may be implicated in SCs activation. Protection of these cells from oxidative damage is essential to ensure sufficient muscle regeneration. The aim of this study is to determine whether SCs activity under conditions of aseptic skeletal muscle trauma induced by exercise is redox-dependent.

Methods/design

Based on the SCs content in their vastus lateralis skeletal muscle, participants will be classified as either high or low respondents. In a randomized, double-blind, crossover, repeated-measures design, participants will then receive either placebo or N-acetylcysteine (alters redox potential in muscle) during a preliminary 7-day loading phase, and for eight consecutive days following a single bout of intense muscle-damaging exercise. In both trials, blood samples and muscle biopsies will be collected, and muscle performance and soreness will be measured at baseline, pre-exercise, 2 and 8 days post exercise. Biological samples will be analyzed for redox status and SCs activity. Between trials, a 4-week washout period will be implemented.

Discussion

This study is designed to investigate the impact of redox status on SCs mobilization and thus skeletal muscle potential for regeneration under conditions of aseptic inflammation induced by exercise. Findings of this trial should provide insight into (1) molecular pathways involved in SCs recruitment and muscle healing under conditions of aseptic skeletal muscle trauma present in numerous catabolic conditions and (2) whether skeletal muscle’s potential for regeneration depends on its basal SCs content.

Trial registration

ClinicalTrials.gov, ID: NCT03711838. Registered on 19 Oct 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3557-3) contains supplementary material, which is available to authorized users.

Dietary Protein and Muscle Mass: Translating Science to Application and Health Benefit

Adequate consumption of dietary protein is critical for the maintenance of optimal health during normal growth and aging. The current Recommended Dietary Allowance (RDA) for protein is defined as the minimum amount required to prevent lean body mass loss, but is often misrepresented and misinterpreted as a recommended optimal intake. Over the past two decades, the potential muscle-related benefits achieved by consuming higher-protein diets have become increasingly clear. Despite greater awareness of how higher-protein diets might be advantageous for muscle mass, actual dietary patterns, particularly as they pertain to protein, have remained relatively unchanged in American adults. This lack of change may, in part, result from confusion over the purported detrimental effects of higher-protein diets. This manuscript will highlight common perceptions and benefits of dietary protein on muscle mass, address misperceptions related to higher-protein diets, and comment on the translation of academic advances to real-life application and health benefit. Given the vast research evidence supporting the positive effects of dietary protein intake on optimal health, we encourage critical evaluation of current protein intake recommendations and responsible representation and application of the RDA as a minimum protein requirement rather than one determined to optimally meet the needs of the population.

Are Canadian protein and physical activity guidelines optimal for sarcopenia prevention in older adults?

Aging is characterized by physiological and morphological changes that affect body composition, strength, and function, ultimately leading to sarcopenia. This condition results in physical disability, falls, fractures, poor quality of life, and increased health care costs. Evidence suggests that increased consumption of dietary protein and physical activity levels, especially resistance exercise, can counteract the trajectory of sarcopenia. Canadian guidelines for protein intake and physical activity were last updated in 2005 and 2011, respectively, and new evidence on sarcopenia diagnosis, prevention, and treatment is rapidly evolving. Protein recommendations are set as “one-size-fits-all” for both young and older adults. Recent evidence demonstrates that current recommendations are insufficient to meet the minimum protein requirement to counteract muscle loss and to stimulate hypertrophy in healthy older adults. Beyond quantity, protein quality is also essential to benefit muscle anabolism in older adults. In terms of physical activity, resistance exercise training is a potential strategy to counteract age-related effects, as it can elicit muscle hypertrophic response in addition to increases in muscle strength and function in older adults. Canadian physical activity guidelines lack details on how this modality of training should be performed. Current guidelines for protein intake and physical activity do not reflect recent knowledge on sarcopenia prevention. The gap between guidelines and the latest evidence on the maintenance and promotion of older adult’s health highlight the need for updated protein and physical activity recommendations.

QUALITY ASSESSMENT OF PROTEINS IN COOKED SAUSAGES WITH FOOD COMPOSITIONS

. In the article, the data are given of research carried out in vitro to determine the amino acid composition and the degree of digestibility of the reference and experimental samples of cooked sausage, with the use of the protein-containing composition developed. The protein digestibility-corrected amino acid score (PDCAAS) has been calculated to clarify the assimilation of amino acids that enter the body as part of proteins in experimental cooked sausage samples.It has been established that replacing a part of the meat raw material with the protein-containing composition in the formula of cooked sausages does not affect significantly the amino acid composition of the finished product. The addition of mechanically deboned poultry meat reduces the amount of such essential amino acids as isoleucine by 68 %, compared with the control formula, leucine by 38 %, and valine by 48 %. At the same time, the content of lysine significantly increases by 1.5 times.  The in vitro index of digestibility for an experimental sample of cooked sausages with protein-containing composition at the pepsinolysis stage is slightly reduced compared with the reference sample (by an average of 7 %). At the second stage of hydrolysis (trypsin enzyme), this parameter does not differ from the reference one. During the two stages of hydrolysis, this parameter, with mechanically deboned poultry meat introduced, decreased by an average of 20 %, compared with the reference sample.Calculated PDCAAS has allowed establishing that the true efficiency of proteins in cooked sausages is different from the in vitro index of digestibility, which is due to the presence of limiting values of the essential amino acids content in the product.

Branched-Chain Amino Acids Are the Primary Limiting Amino Acids in the Diets of Endurance-Trained Men after a Bout of Prolonged Exercise

Background

The indicator amino acid oxidation (IAAO) method estimates the protein intake required to maximize whole-body protein synthesis and identify the daily protein requirement in a variety of populations. However, it is unclear whether the greater requirements for endurance athletes previously determined by the IAAO reflect an increased demand for all or only some amino acids.

Objective

The aim of this study was to determine the primary rate-limiting amino acids in endurance-trained athletes after prolonged exercise, by measuring the oxidation of ingested [1-13C]phenylalanine in response to variable amino acid intake.

Methods

Five endurance-trained men (means ± SDs: age, 26 ± 7 y; body weight, 66.9 ± 9.5 kg; maximal oxygen consumption, 63.3 ± 4.3 mL · kg-1 · min-1) performed 5 trials that involved 2 d of controlled diet (1.4 g protein · kg-1 · d-1) and running (10 km on day 1 and 5 km on day 2) prior to performing an acute bout of endurance exercise (20-km treadmill run) on day 3. During recovery on day 3, participants consumed test diets as 8 isocaloric hourly meals providing sufficient energy and carbohydrate but a variable amino acid intake. The test diets, consumed in random order, were deficient (BASE: 0.8 g · kg-1 · d-1) and sufficient (SUF; 1.75 g · kg-1 · d-1) amino acid diets modeled after egg protein, and BASE supplemented with branched-chain amino acids (BCAA diet; 1.03 g · kg-1 · d-1), essential amino acids (EAA diet; 1.23 g · kg-1 · d-1), or nonessential amino acids (NEAA diet; 1.75 g · kg-1 · d-1). Whole-body phenylalanine flux (Q), 13CO2 excretion (F13CO2), and phenylalanine oxidation (OX) were determined according to standard IAAO methodology.

Results

There was no effect of amino acid intake on Q (P = 0.43). F13CO2 was significantly (all P < 0.01) lower than BASE for the BCAA (∼32%), EAA (∼31%), and SUF (∼36%) diet treatments. F13CO2 for the NEAA diet was ∼18% lower than for BASE (P < 0.05) but ∼28% greater than for SUF (P < 0.05). OX was similarly decreased (∼24-41%) in all conditions compared with BASE (all P < 0.05).

Conclusion

Our results suggest that the BCAAs may be the primary rate-liming amino acids in the greater daily protein requirement of endurance trained men. This trial was registered at clinicaltrials.gov as NCT02628249.

Post-Game High Protein Intake May Improve Recovery of Football-Specific Performance during a Congested Game Fixture: Results from the PRO-FOOTBALL Study

The effects of protein supplementation on performance recovery and inflammatory responses during a simulated one-week in-season microcycle with two games (G1, G2) performed three days apart were examined. Twenty football players participated in two trials, receiving either milk protein concentrate (1.15 and 0.26 g/kg on game and training days, respectively) (PRO) or an energy-matched placebo (1.37 and 0.31 g/kg of carbohydrate on game and training days, respectively) (PLA) according to a randomized, repeated-measures, crossover, double-blind design. Each trial included two games and four daily practices. Speed, jump height, isokinetic peak torque, and muscle soreness of knee flexors (KF) and extensors (KE) were measured before G1 and daily thereafter for six days. Blood was drawn before G1 and daily thereafter. Football-specific locomotor activity and heart rate were monitored using GPS technology during games and practices. The two games resulted in reduced speed (by 3–17%), strength of knee flexors (by 12–23%), and jumping performance (by 3–10%) throughout recovery, in both trials. Average heart rate and total distance covered during games remained unchanged in PRO but not in PLA. Moreover, PRO resulted in a change of smaller magnitude in high-intensity running at the end of G2 (75–90 min vs. 0–15 min) compared to PLA (P = 0.012). KE concentric strength demonstrated a more prolonged decline in PLA (days 1 and 2 after G1, P = 0.014–0.018; days 1, 2 and 3 after G2, P = 0.016–0.037) compared to PRO (days 1 after G1, P = 0.013; days 1 and 2 after G2, P = 0.014–0.033) following both games. KF eccentric strength decreased throughout recovery after G1 (PLA: P=0.001–0.047—PRO: P =0.004–0.22) in both trials, whereas after G2 it declined throughout recovery in PLA (P = 0.000–0.013) but only during the first two days (P = 0.000–0.014) in PRO. No treatment effect was observed for delayed onset of muscle soreness, leukocyte counts, and creatine kinase activity. PRO resulted in a faster recovery of protein and lipid peroxidation markers after both games. Reduced glutathione demonstrated a more short-lived reduction after G2 in PRO compared to PLA. In summary, these results provide evidence that protein feeding may more efficiently restore football-specific performance and strength and provide antioxidant protection during a congested game fixture.

Protein in the Hospital: Gaining Perspective and Moving Forward

Provision of adequate protein is crucial for optimizing outcomes in hospitalized patients. However, the methodologies upon which current recommendations are based have limitations, and little is known about true requirements in any clinical population. In this tutorial, we aim to give clinicians an understanding of how current protein recommendations were developed, an appreciation for the limitations of these recommendations, and an overview of more sophisticated approaches that can be applied to better define protein requirements. A broader perspective of the challenges and opportunities in determining clinical protein requirements can help clinicians think critically about the individualized nutrition care they provide to their patients with the goal of administering adequate protein to optimize outcomes.

High Dietary Protein Intake and Protein-Related Acid Load on Bone Health

PURPOSE OF REVIEW

Consumption of high-protein diets is increasingly popular due to the benefits of protein on preserving lean mass and controlling appetite and satiety. The paper is to review recent clinical research assessing dietary protein on calcium metabolism and bone health.

RECENT FINDINGS

Epidemiological studies show that long-term, high-protein intake is positively associated with bone mineral density and reduced risk of bone fracture incidence. Short-term interventional studies demonstrate that a high-protein diet does not negatively affect calcium homeostasis. Existing evidence supports that the negative effects of the acid load of protein on urinary calcium excretion are offset by the beneficial skeletal effects of high-protein intake. Future research should focus on the role and the degree of contribution of other dietary and physiological factors, such as intake of fruits and vegetables, in reducing the acid load and further enhancing the anabolic effects of protein on the musculoskeletal system.

Protein ingestion preserves proteasome activity during intense aseptic inflammation and facilitates skeletal muscle recovery in humans

The ubiquitin–proteasome system (UPS) is the main cellular proteolytic system responsible for the degradation of normal and abnormal (e.g. oxidised) proteins. Under catabolic conditions characterised by chronic inflammation, the UPS is activated resulting in proteolysis, muscle wasting and impaired muscle function. Milk proteins provide sulphur-containing amino acid and have been proposed to affect muscle inflammation. However, the response of the UPS to aseptic inflammation and protein supplementation is largely unknown. The aim of this study was to investigate how milk protein supplementation affects UPS activity and skeletal muscle function under conditions of aseptic injury induced by intense, eccentric exercise. In a double-blind, cross-over, repeated measures design, eleven men received either placebo (PLA) or milk protein concentrate (PRO, 4×20 g on exercise day and 20 g/d for the following 8 days), following an acute bout of eccentric exercise (twenty sets of fifteen eccentric contractions at 30°/s) on an isokinetic dynamometer. In each trial, muscle biopsies were obtained from the vastus lateralis muscle at baseline, as well as at 2 and 8 d post exercise, whereas blood samples were collected before exercise and at 6 h, 1 d, 2 d and 8 d post exercise. Muscle strength and soreness were assessed before exercise, 6 h post exercise and then daily for 8 consecutive days. PRO preserved chymotrypsin-like activity and attenuated the decrease of strength, facilitating its recovery. PRO also prevented the increase of NF-κB phosphorylation and HSP70 expression throughout recovery. We conclude that milk PRO supplementation following exercise-induced muscle trauma preserves proteasome activity and attenuates strength decline during the pro-inflammatory phase.

Current Concepts and Unresolved Questions in Dietary Protein Requirements and Supplements in Adults

Protein needs for otherwise healthy individuals older than 19 years are defined by the recommended dietary allowance (RDA) at 0.80 g protein/kg/day. There is no recommendation in the current RDA for subpopulations of older adults or people in various pathological situations. Despite the lack of a separate recommendation, there exists a growing body of evidence that is strongly suggestive of an increased need and/or benefit for protein in older persons. That is, intakes beyond the RDA are, in older persons, associated with benefits. In addition, a number of catabolic states including critical illness also result in a sharp elevation in the needs for protein and amino acids. An underappreciated issue in protein nutrition is the impact of protein quality on clinically relevant outcomes. The introduction of a new protein scoring system-the digestible indispensable amino acid score (DIAAS)-for protein quality has raised a forgotten awareness of protein quality. The DIAAS, which replaces the protein digestibility-corrected amino acid score (PDCAAS), is based on ileal digestibility of protein and a different test protein than PDCAAS and has values greater than 1.0. The aim of this article is a brief review and summary recommendations for protein nutrition and protein requirements in populations who would benefit from more protein than the RDA. The emphasis of the review is on muscle protein turnover, and there is a discussion of the impact of protein quality, particularly as it applies to commercially available protein sources. The evidence for more optimal protein intakes is considered in light of the potential health risks of consumption of protein at levels greater than the RDA.

The dietary protein, IGF-I, skeletal health axis

Dietary protein represents an important nutrient for bone health and thereby for the prevention of osteoporosis. Besides its role as a brick provider for building the organic matrix of skeletal tissues, dietary protein stimulates the production of the anabolic bone trophic factor IGF-I (insulin-like growth factor I). The liver is the main source of circulating IGF-I. During growth, protein undernutrition results in reduced bone mass and strength. Genetic defect impairing the production of IGF-I markedly reduces bone development in both length and width. The serum level of IGF-I markedly increases and then decreases during pubertal maturation in parallel with the change in bone growth and standing height velocity. The impact of physical activity on bone structure and strength is enhanced by increased dietary protein consumption. This synergism between these two important environmental factors can be observed in prepubertal boys, thus modifying the genetically determined bone growth trajectory. In anorexia nervosa, IGF-I is low as well as bone mineral mass. In selective protein undernutrition, there is a resistance to the exogenous bone anabolic effect of IGF-I. A series of animal experiments and human clinical trials underscore the positive effect of increased dietary intake of protein on calcium-phosphate economy and bone balance. On the contrary, the dietary protein-induced acidosis hypothesis of osteoporosis is not supported by several experimental and clinical studies. There is a direct effect of amino acids on the local production of IGF-I by osteoblastic cells. IGF-I is likely the main mediator of the positive effect of parathyroid hormone (PTH) on bone formation, thus explaining the reduction in fragility fractures as observed in PTH-treated postmenopausal women. In elderly women and men, relatively high protein intake protects against spinal and femoral bone loss. In hip fracture patients, isocaloric correction of the relatively low protein intake results in: increased IGF-I serum level, significant attenuation of postsurgical bone loss, improved muscle strength, better recovery, and shortened hospital stay. Thus, dietary protein contributes to bone health from early childhood to old age. An adequate intake of protein should be recommended in the prevention and treatment of osteoporosis.

Optimizing Protein Intake in Adults: Interpretation and Application of the Recommended Dietary Allowance Compared with the Acceptable Macronutrient Distribution Range

The adult RDA is defined as the average daily level of intake sufficient to meet the nutrient requirements of nearly all healthy people. The RDA for protein for adults ≥18 y of age (0.8 g/kg) has been essentially unchanged for >70 y. In practice, the RDA for protein was derived to estimate the minimum amount of protein that must be eaten to avoid a loss of body nitrogen. The Acceptable Macronutrient Distribution Range (AMDR) (10-35% of calories as protein) was developed to express dietary recommendations in the context of a complete diet. It is noteworthy that the lowest level of protein intake reflected in the AMDR is higher than that of the RDA. Furthermore, recent studies, particularly in older individuals, suggest specific health benefits at levels of protein intake that significantly exceed the RDA. Translation of protein intake recommendations for the general adult population into dietary guidance for individuals requires an understanding of the derivation and intended use of both the protein RDA and AMDR. The following discussion will describe limitations to the derivation and practical application of the RDA compared with the use of the AMDR to help maximize health benefits associated with higher protein intake by using flexible calories inherent in different dietary patterns.

Effect of a High-Protein Energy-Restricted Diet Combined with Resistance Training on Metabolic Profile in Older Individuals with Metabolic Impairments

Adequate protein intake and resistance training are effective strategies to maintain muscle mass, but the effect of their combination on metabolic profile during weight loss remains to be determined in older adults. The main objective of this study was to determine the effect of a 16-week high-protein caloric restriction combined with resistance training on chronic disease risk factors in obese older individuals with metabolic impairments. A total of 26 overweight adults aged between 60 and 75 years (BMI 32.4 ± 3.9 kg/m2) with at least 2 factors of the metabolic syndrome participated in this study and were randomized into two groups: 1) high-protein caloric restriction (HP; n= 12) and 2) high-protein caloric restriction combined with dynamic-resistance training (HP+RT; n=14). Caloric intake was reduced by 500 kcal/d in all participants and protein intake equated 25-30% of total calories (~1.4 g/kg/d). Exercise training consisted of 3 session/week of resistance training on pulley machines. Outcome measures included total and trunk fat mass (FM), total and appendicular lean body mass (LBM), fasting glucose level, lipid profile and blood pressure. Our results showed that total and trunk FM (all p<0.0001) as well as fasting glucose (p<0.0001), triglycerides (p=0.002) and total cholesterol (p=0.03) levels decreased similarly in both groups. However, total (p=0.04) and appendicular (p=0.02) LBM decreased in the HP group only. Our data show that high-protein energy restriction improves health profile of obese elderly at high risk of chronic disease but needs to be combined with resistance training to maintain LBM.

The biological standard of living in Suriname, c. 1870-1975

The physical stature of Surinamese soldiers is estimated to have increased by more than 3cm between 1870 and 1909. In the subsequent four decades, the increase in adult male and female height amounted to 0.3-0.5cm and 0.9-1.0cm per decade, respectively. This increase in height continued and accelerated during the second half of the twentieth century. Height increase among African and Hindustani Surinamese males and females was similar. Height differences between African and Hindustani Surinamese were therefore fairly constant over time, at 4-5cm. Other indicators of nutritional and health status, such as infant mortality, showed continuous improvement, whereas per capita calorie and protein availability improved in the twentieth century.

Protein Requirements during Aging

Protein recommendations for elderly, both men and women, are based on nitrogen balance studies. They are set at 0.66 and 0.8 g/kg/day as the estimated average requirement (EAR) and recommended dietary allowance (RDA), respectively, similar to young adults. This recommendation is based on single linear regression of available nitrogen balance data obtained at test protein intakes close to or below zero balance. Using the indicator amino acid oxidation (IAAO) method, we estimated the protein requirement in young adults and in both elderly men and women to be 0.9 and 1.2 g/kg/day as the EAR and RDA, respectively. This suggests that there is no difference in requirement on a gender basis or on a per kg body weight basis between younger and older adults. The requirement estimates however are ~40% higher than the current protein recommendations on a body weight basis. They are also 40% higher than our estimates in young men when calculated on the basis of fat free mass. Thus, current recommendations may need to be re-assessed. Potential rationale for this difference includes a decreased sensitivity to dietary amino acids and increased insulin resistance in the elderly compared with younger individuals.

Protein Requirements Are Elevated in Endurance Athletes after Exercise as Determined by the Indicator Amino Acid Oxidation Method

A higher protein intake has been recommended for endurance athletes compared with healthy non-exercising individuals based primarily on nitrogen balance methodology. The aim of this study was to determine the estimated average protein requirement and recommended protein intake in endurance athletes during an acute 3-d controlled training period using the indicator amino acid oxidation method. After 2-d of controlled diet (1.4 g protein/kg/d) and training (10 and 5km/d, respectively), six male endurance-trained adults (28±4 y of age; Body weight, 64.5±10.0 kg; VO₂peak, 60.3±6.7 ml·kg^-1·min^-1; means±SD) performed an acute bout of endurance exercise (20 km treadmill run) prior to consuming test diets providing variable amounts of protein (0.2–2.8 g·kg^-1·d^-1) and sufficient energy. Protein was provided as a crystalline amino acid mixture based on the composition of egg protein with [1-¹³C]phenylalanine provided to determine whole body phenylalanine flux, ¹³CO₂ excretion, and phenylalanine oxidation. The estimated average protein requirement was determined as the breakpoint after biphasic linear regression analysis with a recommended protein intake defined as the upper 95% confidence interval. Phenylalanine flux (68.8±8.5 μmol·kg^-1·h^-1) was not affected by protein intake. ¹³CO₂ excretion displayed a robust bi-phase linear relationship (R² = 0.86) that resulted in an estimated average requirement and a recommended protein intake of 1.65 and 1.83 g protein·kg^-1·d^-1, respectively, which was similar to values based on phenylalanine oxidation (1.53 and 1.70 g·kg^-1·d^-1, respectively). We report a recommended protein intake that is greater than the RDA (0.8 g·kg^-1·d^-1) and current recommendations for endurance athletes (1.2–1.4 g·kg^-1·d^-1). Our results suggest that the metabolic demand for protein in endurance-trained adults on a higher volume training day is greater than their sedentary peers and current recommendations for athletes based primarily on nitrogen balance methodology.

Trial Registration: ClinicalTrial.gov NCT02478801

Developmental contributions to macronutrient selection: a randomized controlled trial in adult survivors of malnutrition

Background and objectives: Birthweight differences between kwashiorkor and marasmus suggest that intrauterine factors influence the development of these syndromes of malnutrition and may modulate risk of obesity through dietary intake. We tested the hypotheses that the target protein intake in adulthood is associated with birthweight, and that protein leveraging to maintain this target protein intake would influence energy intake (EI) and body weight in adult survivors of malnutrition.

Methodology: Sixty-three adult survivors of marasmus and kwashiorkor could freely compose a diet from foods containing 10, 15 and 25 percentage energy from protein (percentage of energy derived from protein (PEP); Phase 1) for 3 days. Participants were then randomized in Phase 2 (5 days) to diets with PEP fixed at 10%, 15% or 25%.

Results: Self-selected PEP was similar in both groups. In the groups combined, selected PEP was 14.7, which differed significantly (P < 0.0001) from the null expectation (16.7%) of no selection. Self-selected PEP was inversely related to birthweight, the effect disappearing after adjusting for sex and current body weight. In Phase 2, PEP correlated inversely with EI (P = 0.002) and weight change from Phase 1 to 2 (P = 0.002). Protein intake increased with increasing PEP, but to a lesser extent than energy increased with decreasing PEP.

Conclusions and implications: Macronutrient intakes were not independently related to birthweight or diagnosis. In a free-choice situation (Phase 1), subjects selected a dietary PEP significantly lower than random. Lower PEP diets induce increased energy and decreased protein intake, and are associated with weight gain.

Recent developments in understanding protein needs - How much and what kind should we eat?

A novel method has been developed to determine protein requirements, which is called indicator amino acid oxidation (IAAO). This technique has been validated by comparison with the "gold standard" nitrogen balance. Using IAAO we have shown that minimum protein requirements have been underestimated by 30%-50%. The National Academy of Sciences has for macro-nutrients proposed "Acceptable Macronutrient Distribution Ranges", which for protein is 10% to 35% of total energy. In practice, we suggest 1.5-2.2 g/(kg·day) of a variety of high-quality proteins.

Protein requirements of healthy pregnant women during early and late gestation are higher than current recommendations

BACKGROUND

Adequate maternal dietary protein intake is necessary for healthy pregnancy. However, current protein intake recommendations for healthy pregnant women are based on factorial calculations of nitrogen balance data derived from nonpregnant adults. Thus, an estimate of protein requirements based on pregnancy-specific data is needed.

OBJECTIVE

The objective of this study was to determine protein requirements of healthy pregnant women at 11-20 (early) and 31-38 (late) wk of gestation through use of the indicator amino acid oxidation method.

METHODS

Twenty-nine healthy women (24-37 y) each randomly received a different test protein intake (range: 0.22-2.56 g · kg(-1) · d(-1)) during each study day in early (n = 35 observations in 17 women) and late (n = 43 observations in 19 women) gestation; 7 women participated in both early and late gestation studies. The diets were isocaloric and provided energy at 1.7 × resting energy expenditure. Protein was given as a crystalline amino acid mixture based on egg protein composition, except phenylalanine and tyrosine, which were maintained constant across intakes. Protein requirements were determined by measuring the oxidation rate of L-[1-(13)C]phenylalanine to (13)CO2 (F(13)CO2). Breath and urine samples were collected at baseline and isotopic steady state. Linear regression crossover analysis identified a breakpoint (requirement) at minimal F(13)CO2 in response to different protein intakes.

RESULTS

The estimated average requirement (EAR) for protein in early and late gestation was determined to be 1.22 (R(2) = 0.60; 95% CI: 0.79, 1.66 g · kg(-1) · d(-1)) and 1.52 g · kg(-1) · d(-1) (R(2) = 0.63; 95% CI: 1.28, 1.77 g · kg(-1) · d(-1)), respectively.

CONCLUSIONS

These estimates are considerably higher than the EAR of 0.88 g · kg(-1) · d(-1) currently recommended by the Dietary Reference Intakes. To our knowledge, this study is the first to directly estimate gestational stage-specific protein requirements in healthy pregnant women and suggests that current recommendations based on factorial calculations underestimate requirements. This trial was registered at clinicaltrials.gov as NCT01784198.