Variations In Protein Intake Research Articles

Protein intake affects erythrocyte glutathione synthesis in healthy adults aged ≥60 years in a repeated-measures trial

BackgroundProtein recommendations for older adults are based on nitrogen balance data from young adults. Physiological studies using the indicator amino acid oxidation method suggest they need 30% to 50% more protein than current recommendations. We herein present glutathione (GSH) as a physiological estimate of protein adequacy in older adults. ObjectivesThe objective was to measure GSH kinetics in response to varying protein intakes in a repeated-measures design in healthy adults aged ≥60 y using the precursor-product method. MethodsSixteen healthy older adults (n = 8 male and n = 8 female; body mass index ≤30 kg/m2) were studied. Each received 4 of 6 protein intakes in random order (0.66, 0.8, 0.9, 1.1, 1.3 and 1.5 g⋅kg−1⋅d−1). At each intake level, participants underwent isotope infusion studies of 7 h duration following a 3-d adaptation to the test level of protein. On the fourth day, GSH fractional (FSR) and absolute synthesis (ASR) rates were quantified by measuring the incorporation of U-[13C2-15N]glycine into GSH at isotopic steady state. A mixed-effect change-point regression model was used to determine a breakpoint in FSR and ASR. Secondary outcomes included plasma concentrations of oxidative stress markers, homocysteine, 5-L-oxoproline (5-OP), and urinary sulfate. The effect of secondary outcomes on GSH kinetics was analyzed using a joint linear mixed-effect model and Tukey’s post hoc test. ResultsA protein intake of 1.08 g⋅kg−1⋅d−1 (95% confidence interval [CI]: 0.83, 1.32; Rm2 = 0.207; Rc2 = 0.671; P < 0.001) maximized GSH FSR. There was no effect of protein intake on concentrations of erythrocyte GSH, plasma homocysteine, oxidative stress markers, or 5-OP (P > 0.05). Protein intake had a positive effect on urinary sulfate excretion (P < 0.0001). ConclusionA protein intake of 1.08 g⋅kg−1⋅d−1 from a high-quality protein maximized GSH synthesis in adults ≥60 y. This lends support to data suggesting a requirement higher than the current recommendation.This study was registered at clinicaltrials.gov as NCT02971046.

Vitamin B-6 Status of Women with a Constant Intake of Vitamin B-6 Changes with Three Levels of Dietary Protein

To determine the effect of varying levels of dietary protein with a constant intake of vitamin B-6 (B-6) on B-6 status, nine women were fed diets providing daily intakes of 1.25 mg B-6 and 0.5, 1.0 and 2.0 g protein/kg body weight. After an 8-d adjustment period, the women consumed each level of dietary protein for 14 d in a Latin-square design. Several direct and indirect B-6 status indicators were measured in blood and urine. Significant differences among protein levels were found for urinary 4-pyridoxic acid (4-PA) excretion (P < 0.01), plasma pyridoxal 5′-phosphate (PLP) concentration (P < 0.05), and urinary excretion of volatile amines (VA, kynurenine plus acetylkynurenine) after a 2-g L-tryptophan load (P < 0.05). Nitrogen intake was significantly negatively correlated with urinary 4-PA excretion (r = -0.619, P < 0.001) and plasma PLP concentration (r = -0.549, P < 0.01), and positively correlated with erythrocyte alanine aminotransferase percentage stimulation (r = 0.418, P < 0.05) and urinary post-tryptophan load excretion of xanthurenic acid (r = 0.535, P < 0.05), kynurenic acid (r = 0.563, P < 0.05) and VA (r = 0.626, P < 0.01). Compared with men consuming diets with similar B-6 to protein ratios in a previous study, the women excreted a greater percentage of the B-6 intake as 4-PA, had lower plasma PLP concentrations and excreted greater amounts of postload urinary tryptophan metabolites at all three protein levels. If the Recommended Dietary Allowance (RDA) of vitamin B-6 is to be based on the dietary B-6 to protein ratio, gender differences in response to varying protein intakes should be considered. For the levels of protein intake used in this study and a B-6 intake of 1.25 mg/d, a B-6 to protein ratio of greater than 0.020 mg/g is required for adequate vitamin B-6 status in women.

Role of liver AMPK and GCN2 kinases in the control of postprandial protein metabolism in response to mid-term high or low protein intake in mice.

Protein synthesis and proteolysis are known to be controlled through mammalian target of rapamycin, AMP-activated kinase (AMPK) and general control non-derepressible 2 (GCN2) pathways, depending on the nutritional condition. This study aimed at investigating the contribution of liver AMPK and GCN2 on the adaptation to high variations in protein intake. To evaluate the answer of protein pathways to high- or low-protein diet, male wild-type mice and genetically modified mice from C57BL/6 background with liver-specific AMPK- or GCN2-knockout were fed from day 25 diets differing in their protein level as energy: LP (5%), NP (14%) and HP (54%). Two hours after a 1g test meal, protein synthesis rate was measured after a 13C valine flooding dose. The gene expression of key enzymes involved in proteolysis and GNC2 signaling pathway were quantified. The HP diet but not the LP diet was associated with a decrease in fractional synthesis rate by 29% in the liver compared to NP diet. The expression of mRNA encoding ubiquitin and Cathepsin D was not sensitive to the protein content. The deletion of AMPK or GCN2 in the liver did not affect nor protein synthesis rates and neither proteolysis markers in the liver or in the muscle, whatever the protein intake. In the postprandial state, protein level alters protein synthesis in the liver but not in the muscle. Taken together, these results suggest that liver AMPK and GCN2 are not involved in this adaptation to high- and low-protein diet observed in the postprandial period.

Protein requirements for critically ill ventilator‐dependent patients with COVID‐19

BackgroundRecent studies indicate critically ill patients with coronavirus disease 2019 (COVID‐19) are hypermetabolic; however, protein requirements in critically ill COVID‐19 patients are unknown. Our intent was to evaluate the nitrogen accretion response to varying protein intakes for critically ill ventilator‐dependent patients with COVID‐19.MethodsAdult patients (age ≥ 18 years) with COVID‐19, admitted to the intensive care unit (ICU) and who required mechanical ventilation were retrospectively evaluated. Patients received continuous enteral nutrition (EN), including supplemental protein boluses, and had a 24‐h urine collection for determination of nitrogen balance (NBAL). Data are expressed as mean ± SD with a P‐value < .05 as significant.ResultsTwenty‐two patients provided 29 NBAL determinations. Protein intake from EN and protein supplements was 0.9 ± 0.7 g/kg/day at the time of the NBAL with an NBAL of –12.1 ± 10.9 g/day at 7 ± 4 days in the ICU. Combined caloric intake from EN and propofol at the time of the NBAL was 12 ± 8 kcal/kg/day. Nitrogen equilibrium (NBAL of –4 g/day or better) occurred in five patients. Patients achieving nitrogen equilibrium received more protein than those with a negative NBAL (1.2 ± 0.4 g/kg/day vs 0.8 ± 0.8 g/kg/day, P = .046). The linear regression for NBAL in response to graded increases in protein intake was as follows: NBAL = 8.5 × protein intake (g/kg/day) – 18.8 (r = 0.450, P < .001).ConclusionCritically ill ventilator‐dependent patients with COVID‐19 exhibit significant variability in nitrogen accretion response to increases in protein intake and often have a markedly negative NBAL.

Estimated Protein Intake From Animal and Plant Foods by U.S. Adults, What We Eat in America, NHANES, 2015–2016

Abstract Objectives The 2020–2025 Dietary Guidelines for Americans encourage varying protein intake to include both animal foods and plant foods for the range of nutrients provided. The objective of this study is to estimate proportions of adults’ protein intake from animal and plant sources and the contribution of foods to each. Methods One day dietary intake data of adults 20+ years (N = 5017) in What We Eat in America (WWEIA), NHANES 2015–2016 were used. Proportions of protein intake from animal and plant sources were estimated from the ingredients for the foods in the Food and Nutrient Database for Dietary Studies (FNDDS) 2015–2016. Single ingredient foods such as chicken or beans were classified as 100% animal or plant, respectively. Proportions from multi-ingredient foods were determined from the amounts of animal and plant food ingredients in each item. If ingredients were not specified, the proportions from a similar food were applied. The proportions were applied to the dietary intakes to determine the population intake of protein from animal and plant sources. The WWEIA food categories were used to describe contribution of foods to animal and plant protein intake. Results Animal and plant foods accounted for 67% and 33% of total protein intake, respectively. Excluding mixed dishes, animal protein intake was contributed by dairy products (14%); meats (12%); poultry (16%); seafood (6%); cured meats (8%); and eggs (6%). Mixed dishes contributed 31% of animal protein intake. Protein from plant foods, excluding mixed dishes, was contributed by grains (24%); plant-based protein foods including legumes (4%), nuts and seeds (7%) soy products (1%); vegetables (9%); and fruit (2%). Mixed dishes accounted for 30% of plant protein intake; snacks and sweets contributed 14%. Conclusions Although protein intake from animal sources is relatively diverse, encouraging greater variety of protein intake from plant-based protein foods appears warranted. Funding Sources ARS-USDA.

Prevalence of low protein intake in 80+-year-old community-dwelling adults and association with dietary patterns and modifiable risk factors: a cross-sectional study

Low protein intake may accelerate age-related loss of lean mass and physical function. We investigated the prevalence of low protein intake (<1·0 g/kg/day) and the associations between dietary patterns, modifiable risk factors and low protein intake in self-reliant community-dwelling adults ≥ 80 years. This cross-sectional study consisted of two home visits. Data collection consisted of physical measurements (e.g. physical function, physical activity) and self-report of nutritional intake (4-d food records), appetite, eating symptoms and medical conditions. Binary analyses were performed to compare participants with low and normal protein intake. Multiple logistic regression analyses were performed to investigate associations between low protein intake, dietary patterns and modifiable risk factors adjusted for age, sex, BMI categories and diseases. One hundred twenty-six were included in the study. Prevalence of low protein intake was 54 %. A greater day-to-day variation in protein intake was associated with low protein intake (adjusted OR 2·5; 95 % CI 1·14, 5·48). Participants with low protein intake had a higher prevalence of nausea, diarrhoea and mouth dryness. Reduced appetite, mouth dryness and pain increased odds of low protein intake (adjusted OR 3·06, 95 % CI 1·23, 7·63; OR 3·41, 95 % CI 1·51, 7·7; OR 1·54, 95 % CI 1·00, 2·36, respectively). There was a high prevalence of low protein intake in community-dwelling adults aged ≥ 80 years. Day-to-day variability, appetite, mouth dryness and pain may be potentially modifiable risk factors. Targeting dietary patterns and risk factors in primary prevention strategies may potentially improve intake of protein and minimise risk of physical frailty.

Daily protein prioritization and long-term nutrient balancing in a dietary generalist, the blue monkey

Abstract Animals make dietary choices to achieve adequate nutrient intake; however, it is challenging to study such nutritional strategies in wild populations. We explored the nutritional strategy of a generalist social primate, the blue monkey (Cercopithecus mitis). We hypothesized that females balance intake of nutrients, specifically non-protein energy and protein, both on a daily and long-term basis. When balancing was not possible, we expected subjects to prioritize constant protein intake, allowing non-protein energy to vary more. To understand the ecology of nutrient balancing, we examined how habitat use, food availability, diet composition, social dominance rank, and reproductive demand influenced nutrient intake. Over 9 months, we conducted 371 all-day focal follows on 24 subjects in Kakamega Forest, Kenya. Females exhibited short- and long-term nutritional strategies. Daily, they balanced non-protein energy to protein intake but when balancing was impossible, monkeys prioritized protein intake. Longer term, they balanced non-protein energy:protein intake in a 3.8:1 ratio. The ratio related positively to fruit in the diet and negatively to time in near-natural forest, but we found no evidence that it related to food availability, reproductive demand, or dominance rank. Lower-ranked females had broader daily diets, however, which may reflect behavioral feeding strategies to cope with social constraints. Overall, females prioritized daily protein, allowing less variation in protein intake than other aspects such as non-protein energy:protein ratio and non-protein energy intake. The emerging pattern in primates suggests that diverse dietary strategies evolved to allow adherence to a nutrient balance of non-protein energy:protein despite various social and environmental constraints.

Analysis of Human Faecal Host Proteins: Responsiveness to 10-Week Dietary Intervention Modifying Dietary Protein Intake in Elderly Males.

Faecal proteomics targeting biomarkers of immunity and inflammation have demonstrated clinical application for the identification of changes in gastrointestinal function. However, there are limited comprehensive analyses of the host faecal proteome and how it may be influenced by dietary factors. To examine this, the Homo sapiens post-diet proteome of older males was analysed at the completion of a 10-week dietary intervention, either meeting the minimum dietary protein recommendations (RDA; n = 9) or twice the recommended dietary allowance (2RDA, n = 10). The host faecal proteome differed markedly between individuals, with only a small subset of proteins present in ≥ 60% of subjects (14 and 44 proteins, RDA and 2RDA, respectively, with only 7 common to both groups). No differences were observed between the diet groups on the profiles of host faecal proteins. Faecal proteins were detected from a wide range of protein classes, with high inter-individual variation and absence of obvious impact in response to diets with markedly different protein intake. This suggests that well-matched whole food diets with two-fold variation in protein intake maintained for 10 weeks have minimal impact on human faecal host proteins.

Role of Peptide Hormones in the Adaptation to Altered Dietary Protein Intake.

Dietary protein profoundly influences organismal traits ultimately affecting healthspan. While intracellular signalling downstream of altered amino acid supply is undoubtedly important, peptide hormones have emerged as critical factors determining systemic responses to variations in protein intake. Here the regulation and role of certain peptides hormones in such responses to altered dietary protein intake is reviewed.

The Effect of Dietary Protein on Protein Metabolism and Performance in Endurance-trained Males.

This study aimed to determine how varying protein intakes, including a new tracer-derived safe intake, alter whole body protein metabolism and exercise performance during training. Using a double-blind randomized crossover design, 10 male endurance-trained runners (age, 32 ± 8 yr; V˙O2peak, 65.9 ± 7.9 mL O2·kg·min) performed three trials consisting of 4 d of controlled training (20, 5, 10, and 20 km·d, respectively) while consuming diets providing 0.94 (LOW), 1.20 (MOD), and 1.83 (HIGH) g protein·kg·d. Whole body protein synthesis, breakdown, and net balance were determined by oral [N]glycine on the first and last day of the 4-d controlled training period, whereas exercise performance was determined from maximum voluntary isometric contraction, 5-km time trial, and countermovement jump impulse (IMP) and peak force before and immediately after the 4-d intervention. Synthesis and breakdown were not affected by protein intake, whereas net balance showed a dose-response (HIGH > MOD > LOW, P < 0.05) with only HIGH being in positive balance (P < 0.05). There was a trend (P = 0.06) toward an interaction in 5-km Time Trial with HIGH having a moderate effect over LOW (effect size = 0.57) and small effect over MOD (effect size = 0.26). IMP decreased with time (P < 0.01) with no effect of protein (P = 0.56). There was no effect of protein intake (P ≥ 0.06) on maximum voluntary isometric contraction, IMP, or peak force performance. Our data suggest that athletes who consume dietary protein toward the upper end of the current recommendations by the American College of Sports Medicine (1.2-2 g·kg) would better maintain protein metabolism and potentially exercise performance during training.

Nutrition of marine mesograzers: integrating feeding behavior, nutrient intake and performance of an herbivorous amphipod.

Consumers can regulate the acquisition and use of nutrients through behavioral and physiological mechanisms. Here, we present an experimental approach that simultaneously integrates multiple nutritional traits, feeding assays, and juvenile performance to assess whether a marine herbivore (the amphipod Ampithoe valida) regulates the intake of elements (carbon and nitrogen), macronutrients (protein and non-protein) or both when offered freeze-dried tissues of seaweeds varying in nutritional content. We assessed behavioral regulation of nutrients in three ways. First, during no-choice assays, we found that amphipods ingested similar amounts of carbon, but not nitrogen, non-protein and protein, across algal diets. Second, herbivore intake rates of carbon, protein and non-protein components across no-choice assays was similar to intake rates when offered a choice of foods. Third, variation in intake rates of carbon and non-protein components among algal diets was significantly greater than was tissue content of these components, while variation in intake rates of nitrogen was significantly lower; differences in protein intake variation was equivocal. While these analytical approaches are not uniformly consistent, carbon and nitrogen seem to emerge as the nutrient components that are more strongly regulated by A. valida. Juveniles reared on single diets shown patterns of survivorship, growth and reproduction that could not be predicted by these feeding preferences, nor nutrient content. We conclude that an integrative approach that considers the intake of multiple nutrients potentially yields insights into feeding behavior and its performance consequences.

Diet has independent effects on the pace and shape of aging in Drosophila melanogaster

Studies examining how diet affects mortality risk over age typically characterise mortality using parameters such as aging rates, which condense how much and how quickly the risk of dying changes over time into a single measure. Demographers have suggested that decoupling the tempo and the magnitude of changing mortality risk may facilitate comparative analyses of mortality trajectories, but it is unclear what biologically meaningful information this approach offers. Here, we determine how the amount and ratio of protein and carbohydrate ingested by female Drosophila melanogaster affects how much mortality risk increases over a time-standardised life-course (the shape of aging) and the tempo at which animals live and die (the pace of aging). We find that pace values increased as flies consumed more carbohydrate but declined with increasing protein consumption. Shape values were independent of protein intake but were lowest in flies consuming ~90 μg of carbohydrate daily. As protein intake only affected the pace of aging, varying protein intake rescaled mortality trajectories (i.e. stretched or compressed survival curves), while varying carbohydrate consumption caused deviation from temporal rescaling (i.e. changed the topography of time-standardised survival curves), by affecting pace and shape. Clearly, the pace and shape of aging may vary independently in response to dietary manipulation. This suggests that there is the potential for pace and shape to evolve independently of one another and respond to different physiological processes. Understanding the mechanisms responsible for independent variation in pace and shape, may offer insight into the factors underlying diverse mortality trajectories.

Gyrfalcons Falco rusticolus adjust CTNS expression to food abundance: a possible contribution to cysteine homeostasis.

Melanins form the basis of animal pigmentation. When the sulphurated form of melanin, termed pheomelanin, is synthesized, the sulfhydryl group of cysteine is incorporated to the pigment structure. This may constrain physiological performance because it consumes the most important intracellular antioxidant (i.e., glutathione, GSH), of which cysteine is a constitutive amino acid. However, this may also help avoid excess cysteine, which is toxic. Pheomelanin synthesis is regulated by several genes, some of them exerting this regulation by controlling the transport of cysteine in melanocytes. We investigated the possibility that these genes are epigenetically labile regarding protein intake and thus contribute to cysteine homeostasis. We found in the Icelandic population of gyrfalcon Falco rusticolus, a species that pigments its plumage with pheomelanin, that the expression of a gene regulating the export of cystine out of melanosomes (CTNS) in feather melanocytes of developing nestlings increases with food abundance in the breeding territories where they were reared. The expression of other genes regulating pheomelanin synthesis by different mechanisms of influence on cysteine availability (Slc7a11 and Slc45a2) or by other processes (MC1R and AGRP) was not affected by food abundance. As the gyrfalcon is a strict carnivore and variation in food abundance mainly reflects variation in protein intake, we suggest that epigenetic lability in CTNS has evolved in some species because of its potential benefits contributing to cysteine homeostasis. Potential applications of our results should now be investigated in the context of renal failure and other disorders associated with cystinosis caused by CTNS dysfunction.

The relationship between protein quantity, BMD and fractures in older adults.

Previously, no large-scale literature reviews have focussed on the relationship between dietary protein and its impact on bone mineral density (BMD) and fracture risk-as measures of bone health-in older adults and its potential impact as a primary prevention tool. The aim of this study was to assess the impact of varying dietary protein levels on bone health. A literature review of trials concerning older adults' (>50years of age) and animals' varying protein intake in the diet and its effect on BMD (human and animal) and fracture risk (human only) was carried out. Additionally, a review of dietary assessment tools used in these studies was also analysed. Ten out of fourteen trials assessing BMD and dietary protein quantity in humans and 3/4 in animal trials found a positive relationship between these two parameters. Four out of seven trials investigating the relationship between dietary protein quantity and fracture risk displayed a positive, protective effect of dietary protein levels on fracture risk. Sixty-two percent of studies used the Food-Frequency Questionnaire assessment method. Increased protein intake in the diet is beneficial to bone health and reduces morbidity and mortality. The importance of using dietary protein, along with calcium and vitamin D, as a primary preventative strategy should be stressed, given the health and cost benefits that this would deliver, with a possible need for a higher level of protein in the diet of an elderly person than what is currently recommended.

Relationship between Dietary Protein or Essential Amino Acid Intake and Training-Induced Muscle Hypertrophy among Older Individuals.

Dietary protein intake is critical for maintaining an optimal muscle mass, especially among older individuals. Although protein supplementation during resistance training (RT) has been shown to further augment training-induced muscle mass in older individuals, the impact of daily variations in protein intake on training-induced muscle mass has not been explored thus far. Therefore, this study aimed to investigate the relationship between the dietary protein and amino acid intake and RT-induced muscle hypertrophy among older individuals. Ten healthy older men (n=10; mean age=69±2 y; body weight (BW)=61.5±2.2 kg; height=1.65±0.02 m) participated in progressive RT performed 3 times/wk for 12 wk. Body composition (using DXA) and nutritional assessments (using a 3-d dietary record) were performed before and after the training period. Leg lean mass (LLM) increased significantly (15.0±0.8 vs. 15.4±0.8 kg, p<0.05) after RT, with no change in dietary nutrient intake. The average dietary protein intake was 1.62±0.11 g/kg BW/d, while essential amino acids was 600±51 mg/kg BW/d. Although the correlation between the increase in LLM and dietary protein intake was not significant, a significant correlation was found between the increase in LLM and dietary essential amino acid (EAA) intake. Furthermore, there were significant correlations between the increase in LLM and protein as well as EAA (especially leucine) intake at breakfast among subjects with suboptimal protein intake (p<0.05). Our study findings indicate that dietary protein as well as EAA intake may be significant contributing factors in muscle hypertrophic response during RT among healthy older men.

Protein requirements and aging 1

Protein requirements and aging 1

Reduced consumption of protein-rich foods follows immune challenge in a polyphagous caterpillar.

Advances in ecological immunity have illustrated that, like vertebrates, insects exhibit adaptive immunity, including induced changes in feeding behavior that aid the immune system. In particular, recent studies have pointed to the importance of protein intake in mounting an immune response. In this study, we tested the hypothesis that the polyphagous caterpillar Grammia incorrupta (H. Edwards) (Family: Erebidae) would adaptively change its feeding behavior in response to immune challenge, predicting that caterpillars would increase their intake of dietary protein. We further predicted that this response would enhance the melanization response, a component of the immune system that acts against parasitoids. We challenged the immune system using either tachinid fly parasitoids or a bead injection technique that has been used in studies to simulate parasitism, and measured feeding before and after immune challenge on diets varying in their macronutrient content. To evaluate the effects of diet on melanization, we quantified melanization of beads following feeding assays. Contrary to our prediction, we found that parasitized or injected caterpillars given a choice between high- and low-protein foods reduced their intake of the high-protein food. Furthermore, in a no-choice experiment, caterpillars offered food with a protein concentration that is optimal for growth reduced feeding following immune challenge, whereas those offered a low-protein food did not. Although variation in protein intake did not change the caterpillars' melanization response, increased carbohydrate intake did increase melanization, suggesting a prophylactic role for carbohydrates. We discuss alternative mechanisms by which variation in protein intake could negatively or positively affect parasitized caterpillars, including nutritional interactions with the caterpillar's self-medication response.

Influence of Aging on Nitrogen Accretion During Critical Illness

Aging adversely affects nitrogen accretion during health, but its effect during critical illness is unknown. Nitrogen balance (NB) response to varying protein intakes was compared between critically ill, older and younger patients. Adult patients admitted to the trauma intensive care unit, given enteral or parenteral nutrition, and who had a NB determination within 5-14 days after injury were evaluated. Patients with renal or hepatic disease were excluded. Patients were categorized as older (≥60 years) or younger (18-59 years of age). Data are given as mean ± SD or median [interquartile range]. Fifty-four older (69 [65, 77] years) and 195 younger (35 [27, 47] years) patients were evaluated. NB was blunted for the older patients with an observed trending improvement in NB from -13.5 ± 5.5 to -5.6 ± 8.8 g/d (P = NS) noted at 1.5-1.99 g/kg/d. NB improved from -22.2 ± 8.2 to -11.8 ± 9.9 g/d (P = .05) at 1-1.49 g/kg/d and modestly thereafter for each 0.5-g/kg/d increase in protein intake for the younger patients. Serum urea nitrogen concentration during the NB was highly variable but overall greater for the older patients (20 [14, 33] vs 15 [10, 20] mg/dL, P = .001). Improvement in nitrogen accretion was blunted at lower protein intakes in critically ill, older patients compared with younger patients. Individualization of protein intake is warranted.

Effects of energy deficit, dietary protein, and feeding on intracellular regulators of skeletal muscle proteolysis

This study was undertaken to characterize the ubiquitin proteasome system (UPS) response to varied dietary protein intake, energy deficit (ED), and consumption of a mixed meal. A randomized, controlled trial of 39 adults consuming protein at 0.8 (recommended dietary allowance [RDA]), 1.6 (2×-RDA), or 2.4 (3×-RDA) g · kg(-1) · d(-1) for 31 d. A 10-d weight maintenance (WM) period was followed by 21 d of 40% ED. Ubiquitin (Ub)-mediated proteolysis and associated gene expression were assessed in the postabsorptive (fasted) and postprandial (fed; 480 kcal, 20 g protein) states after WM and ED by using muscle biopsies, fluorescence-based assays, immunoblot analysis, and real-time qRT-PCR. In the assessment of UPS responses to varied protein intakes, ED, and feeding, the RDA, WM, and fasted measures served as appropriate controls. ED resulted in the up-regulation of UPS-associated gene expression, as mRNA expression of the atrogenes muscle RING finger-1 (MuRF1) and atrogin-1 were 1.2- and 1.3-fold higher (P<0.05) for ED than for WM. However, mixed-meal consumption attenuated UPS-mediated proteolysis, independent of energy status or dietary protein, as the activities of the 26S proteasome subunits β1, β2, and β5 were lower (P<0.05) for fed than for fasted. Muscle protein ubiquitylation was also 45% lower (P<0.05) for fed than for fasted, regardless of dietary protein and energy manipulations. Independent of habitual protein intake and despite increased MuRF1 and atrogin-1 mRNA expression during ED, consuming a protein-containing mixed meal attenuates Ub-mediated proteolysis.

Variation in protein intake induces variation in spider silk expression.

BackgroundIt is energetically expensive to synthesize certain amino acids. The proteins (spidroins) of spider major ampullate (MA) silk, MaSp1 and MaSp2, differ in amino acid composition. Glutamine and proline are prevalent in MaSp2 and are expensive to synthesize. Since most orb web spiders express high proline silk they might preferentially attain the amino acids needed for silk from food and shift toward expressing more MaSp1 in their MA silk when starved.Methodology/Principal FindingsWe fed three spiders; Argiope aetherea, Cyrtophora moluccensis and Leucauge blanda, high protein, low protein or no protein solutions. A. aetherea and L. blanda MA silks are high in proline, while C. moluccesnsis MA silks are low in proline. After 10 days of feeding we determined the amino acid compositions and mechanical properties of each species' MA silk and compared them between species and treatments with pre-treatment samples, accounting for ancestry. We found that the proline and glutamine of A. aetherea and L. blanda silks were affected by protein intake; significantly decreasing under the low and no protein intake treatments. Glutmaine composition in C. moluccensis silk was likewise affected by protein intake. However, the composition of proline in their MA silk was not significantly affected by protein intake.ConclusionsOur results suggest that protein limitation induces a shift toward different silk proteins with lower glutamine and/or proline content. Contradictions to the MaSp model lie in the findings that C. moluccensis MA silks did not experience a significant reduction in proline and A. aetherea did not experience a significant reduction in serine on low/no protein. The mechanical properties of the silks could not be explained by a MaSp1 expressional shift. Factors other than MaSp expression, such as the expression of spidroin-like orthologues, may impact on silk amino acid composition and spinning and glandular processes may impact mechanics.