The incidence of cognitive decline is rising, leading to increased attention on the preventive role of healthy foods on brain function. Previous reviews including primarily observational studies suggested that dietary proteins may improve cognitive performance, but evidence from individual randomised controlled trials (RCT) is less consistent. Therefore, this systematic review examined the long-term effects of dietary proteins from RCT, considering both their amount and type, on cognitive performance (psychomotor speed and attention, executive function, memory and global cognition). Alterations in cerebral blood flow (CBF) – a validated brain vascular function marker – were also considered. A total of 4747 studies were identified through a systematic search, resulting in twenty-three included papers reporting effects on cognitive performance (n = 23) and CBF (n = 3). Improvements were observed in three out of the nine studies that evaluated psychomotor speed which compared a dietary protein intervention with a non-protein or lower-protein control. Of the six beneficial observations on working memory (n = 12), declarative memory (n = 10) and visuospatial memory (n = 10), five were nut interventions from three different trials. Limited studies focusing on global cognition suggested that specific target populations, namely subacute stroke or dementia, may benefit more than healthy individuals from increased dietary protein intake. From the three studies involving CBF, improvements in regional blood flow were associated with most cognitive performance outcomes. The comparative effects of different protein types warrant further investigation. Overall, this review encourages additional research into protein-rich foods or supplements which could potentially prevent or mitigate cognitive decline.

Previous investigations on protein associations with diet quality and obesity still have inconclusive findings, possibly due to how protein intake was expressed. This study aimed to compare how different ways of expressing total protein intake may influence its relationships with diet quality and obesity. Usual protein intake was estimated from the 2011–12 Australian National Nutrition and Physical Activity Survey (n = 7637 adults, ≥19 years), expressed in grams (g/d), percent energy (%EI), and grams per actual kilogram body weight (g/kgBW/d). Diet quality was assessed using the 2013 Dietary Guidelines Index, and obesity measures included Body Mass Index (BMI) and waist circumference (WC). Sex-stratified multiple linear and logistic regressions were performed and adjusted for potential confounders. Total protein (g/d) was directly associated with diet quality (males, β = 0.15 (95% CI 0.12, 0.19); females, β = 0.25 (0.22, 0.29)), and this association was consistent across units. Protein intake (g/d) was directly associated with BMI (males, β = 0.07% (0.04%, 0.11%); females, β = 0.09% (0.04%, 0.15%)), and WC (males, β = 0.04 (0.01, 0.06); females, β = 0.05 (0.00, 0.09)). While in males, protein as %EI was associated with higher WC, no association was found in females. Adults with higher protein intake (g/d) had higher odds of overweight/obesity (males, OR = 1.01 (1.00, 1.01); females, OR = 1.01 (1.00, 1.01)), and central overweight/obesity (females, OR = 1.01 (1.00, 1.01)), but no significant association with females odds of overweight/obesity when protein was expressed in %EI. In conclusion, protein intake was positively associated with diet quality and obesity, yet these associations were stronger for women. The effect sizes also varied by measurement unit due to the different scales of those units.

More than two-thirds of women during childbearing years (20–39 years old) are overweight or obese in the United States, with protein intake among 20–49-year-old women being 1.6 times higher than recommended (75.4 g/day versus 46 g/day) that can be considered as a relatively high-protein diet (HPD). Both gestational obesity and HPDs during gestation adversely affect offspring health. This study investigates the impact of HPDs fed during gestation and lactation on obese mothers and their offspring in Wistar rats. Dams randomized to either a normal-protein diet (NPD) or HPD (n = 12/group). Pups from each maternal group were weaned to either NPD or HPD for 17 weeks (n = 12/group). No effect of maternal or weaning diet on food intake, body weight, or body fat/weight ratio was observed. However, NPD dams exhibited higher glucose area under the curve compared with HPD dams (p < 0.03). At weaning, offspring born to NPD dams showed higher fasting plasma glucose (P < 0.03) and insulin/glucose ratio (P = 0.05) than those born to HPD dams. The Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) index was higher in offspring born to NPD dams (P < 0.04) and weaned to NPD (P < 0.05) at week 17. These findings underscore the role of high-protein maternal and weaning diets in pregnancy outcomes for obese mothers, particularly in glucose homeostasis, although gestational obesity may overshadow other parameters. Further research is needed to fully understand the impact on both maternal and offspring health and their underlying mechanisms in this context.

Restriction of dietary carbohydrates, fat and/or protein is often used to reduce body weight and/or treat (metabolic) diseases. Since diet is a key modulator of the human gut microbiome, which plays an important role in health and disease, this review aims to provide an overview of current knowledge of the effects of macronutrient-restricted diets on gut microbial composition and metabolites. A structured search strategy was performed in several databases. After screening for inclusion and exclusion criteria, thirty-six articles could be included. Data are included in the results only when supported by at least three independent studies to enhance the reliability of our conclusions. Low-carbohydrate (<30 energy%) diets tended to induce a decrease in the relative abundance of several health-promoting bacteria, including Bifidobacterium, as well as a reduction in short-chain fatty acid (SCFA) levels in faeces. In contrast, low-fat diets (<30 energy%) increased alpha diversity, faecal SCFA levels and abundance of some beneficial bacteria, including Faecalibacterium prausnitzii. There were insufficient data to draw conclusions concerning the effects of low-protein (<10 energy%) diets on gut microbiota. Although the data of included studies unveil possible benefits of low-fat and potential drawbacks of low-carbohydrate diets for human gut microbiota, the diversity in study designs made it difficult to draw firm conclusions. Using a more uniform methodology in design, sample processing and sharing raw sequence data could foster our understanding of the effects of macronutrient restriction on gut microbiota composition and metabolic dynamics relevant to health. This systematic review was registered at https://www.crd.york.ac.uk/prospero as CRD42020156929.

Gestational obesity has major negative impacts on both mothers and their offspring. More than two-thirds of women of reproductive age in the United States are overweight and/or obese. We previously reported that the source of protein in the maternal diet influences the phenotype of offspring born to normal-weight dams. However, whether it has the same effect in obese mothers was unclear. The casein- and soya protein-based diets were fed to obese pregnant Wistar rats and compared for their effects on characteristics of the metabolic syndrome in male offspring. Dams randomized to either a casein (CD) or soya protein (SD) diet (n 12). Pups were weaned to either a CD or SD for 16 weeks. Offspring of SD dams had higher birthweight (P < 0⋅01). Glucose metabolism was not altered at birth but fasting blood glucose (FBG) (P < 0⋅02), insulin (P < 0⋅0002), insulin/glucose ratio (P < 0⋅03), and HOMA-IR index (P < 0⋅0002) were higher in offspring of SD dams at week 17. The pulse rate was higher in dams (P < 0⋅03). Food intake and body weight of offspring were affected by interactive effects of time and dams’ diet (P < 0⋅05). Food intake was not influenced by maternal diet, but it was higher in pups weaned to SD dams (P < 0⋅03) The results of this study indicate that although the source of protein in the maternal diet is still an influencing factor in the outcome of the pregnancy in obese mothers, gestational obesity may mask this effect possibly by imposing general detrimental effects on measured parameters regardless of the source of protein in maternal diet.

Plant-based substitutes (PBS) are seen as a convenient way to transition to a more plant-based diet, but their potential health benefits and nutritional concerns remain debated. Based on a review of the literature, it is concluded here that the primary risk of insufficient nutrient intake with PBS concerns iron and calcium, which are critical to the nutritional value of PBS. Other risks were identified but these would depend on the characteristics of the overall diet, as is the case for iodine in a diet containing no seafood or dairy, and vitamin B12 in a vegetarian/vegan diet. Conversely, the use of PBS is also expected to confer some benefits for long-term health because it would result in higher fibre intakes (in the case of meat PBS) and lower SFA intakes (but higher PUFA/MUFA intakes), but attention should be paid to a potential increase in sodium intake with PBS of meat products. In fact, a recurring finding in this review was that PBS is a very heterogeneous food category involving considerable variations in ingredient and nutrient composition, and whose design could be improved in order to foster nutritional and health benefits. The latter also depend on the animal food that is being replaced and are only deemed likely when PBS replace red meat. The fortification of PBS with key nutrients such as iron and calcium may constitute an actionable public health solution to further shift the balance in favour of PBS in the context of the current dietary transition in western countries.

The present study was aimed at (1) the differences between current weight v. ideal weight, (2) total energy intake and comparing it with required energy (Rkeer), (3) absolute protein intake in g/kg per d and g/1000 calories, (4) how energy and protein intake relate to the nutritional status of the subjects in terms of overall overweight (OEW) [overweight + obesity] and conservative overweight (CEW) [obesity] and (5) the contribution (%) of protein to total energy intake based on the acceptable macronutrient distribution range (AMDR). A dietary study was carried out in Colombia with 29 259 subjects between 1 and 64 years of age, based on cross-sectional data collected in 2015 by a 24-h dietary recall (24HR) administered as part of the National Nutrition Survey. Energy and protein intake did not differ by nutritional status. In the general population, energy intake was 2117 kcal/d (95 % CI 1969, 2264). The total protein intake was 64⋅3 g/d (95 % CI 61⋅4, 67⋅3). Adequate energy intake ranged from 90 to 100 %, except for the 1–4-year-old group, which ranged from 144 to 155 %. Protein intake was 1⋅64 g/kg per d (95 % CI 1⋅53, 1⋅75). The mean AMDR for protein to total energy intake was 13⋅3 % (95 % CI 12⋅9, 13⋅7). Excess weight began during the first 4 years of age. In conclusion, it is worth reviewing and updating energy and protein intake recommendations and dietary guidelines for the Colombian population and designing and modifying public policy.

During ageing, skeletal muscle develops anabolic resistance towards the stimulation of protein synthesis induced by dietary amino acids. The stimulation of muscle protein synthesis after food intake remains insufficient, even with a protein intake recommended for healthy adults. This alteration is one of the mechanisms known to be responsible for the decrease of muscle mass and function during ageing, namely sarcopenia. Increasing dietary protein intake above the current RDA(0⋅83 g/kg/d) has been strongly suggested to overcome the anabolic resistance observed. It is also specified that the dietary protein ingested should be of good quality. A protein of good quality is a protein whose amino acid (AA) composition covers the requirement of each AA when ingested at the RDA. However, the biological value of proteins may vary among dietary sources in which AA composition could be unbalanced. In the present review, we suggest that the quality of a dietary protein is also related to several other determinants. These determinants include the speed of digestion of dietary proteins, the presence of specific AA, the food matrix in which the dietary proteins are included, the processes involved in the production of food products (milk gelation and cooking temperature), the energy supply and its nature, and the interaction between nutrients before ingestion. Particular attention is given to plant proteins for nutrition of the elderly. Finally, the timing of protein intake and its association with the desynchronized intake of energetic nutrients are discussed.

A low-glycaemic-index (GI) breakfast has been shown to lower blood glucose levels throughout the day. A wide variety of breakfast foods are consumed, but their GI values are largely unknown, hence limiting consumers’ ability to select healthier options. This study investigated the GI values of ten common breakfast (five Asian and five Western) foods in this region using a randomised, cross-over study design. Participants arrived after an overnight fast, and fasting blood sample was taken before participants consumed test foods. Next, blood samples were taken at fixed intervals for 180 min. Glycaemic and insulinaemic responses to test foods were calculated as incremental AUC over 120 min, which were subsequently reported as glycaemic and insulinaemic indices. In all, nineteen healthy men (nine Chinese and ten Indians) aged 24·7 (sem 0·4) years with a BMI of 21·7 (sem 0·4) kg/m2 completed the study. Asian breakfast foods were of medium (white bun filled with red bean paste=58 (sem 4); Chinese steamed white bun=58 (sem 3)) to high GI (rice idli=85 (sem 4); rice dosa=76 (sem 5); upma=71 (sem 6)), whereas Western breakfast foods were all of low GI (whole-grain biscuit=54 (sem 5); whole-grain biscuit filled with peanut butter=44 (sem 3); whole-grain oat muesli=55 (sem 4); whole-grain oat protein granola=51 (sem 4); whole-grain protein cereal=49 (sem 3)). The GI of test foods negatively correlated with protein (r s −0·366), fat (r s −0·268) and dietary fibre (r s −0·422) (all P<0·001). GI values from this study contribute to the worldwide GI database, and may assist healthcare professionals in recommending low-GI breakfast to assist in lower daily glycaemia among Asians who are susceptible to type 2 diabetes mellitus.

The loss of lean body mass, muscle strength and physical function causes significant problems in older adults. Protein and amino acid supplements can preserve muscle strength but the effect on function is variable. We conducted a systematic literature review and meta-analysis to investigate the effect of protein and amino acid supplementation on fat-free mass, muscle strength and physical function in malnourished, frail, sarcopenic, dependent or elderly with acute or chronic conditions, with or without rehabilitation exercise. Databases searched included Medline, BIOSIS, CINAHL, Cochrane Library, EBM Reviews, Embase, Pre-Medline, ProQuest, PubMed and Scopus. Retrieved articles were assessed by two reviewers using the Cochrane Risk of Bias (ROB) Tool. In all, thirty nine randomised controlled trails (n 4274) were included. The studies used a range of protein or essential amino acid (EAA) supplements in a variety of settings, including hospital, community and long-term care. Only seven studies had low ROB and no effect of supplementation was found on any outcomes. Analysis of all thirty-nine studies suggest protein and EAA supplements may improve fat-free mass, muscle strength and physical function (standardised mean difference 0·21–0·27, all P<0·005), but significant heterogeneity and ROB was evident. Predetermined subgroup analysis found undernourished elderly benefitted most; EAA were the most effective supplements and small beneficial effects were seen without rehabilitation exercise. The high heterogeneity and few studies with low ROB limits the conclusions and more high quality studies are needed to determine the best nutritional strategies for the maintenance of strength and function with increasing age.

Resistance training (RT) and increased dietary protein are recommended to attenuate age-related muscle loss in the elderly. This study examined the effect of a lean red meat protein-enriched diet combined with progressive resistance training (RT+Meat) on health-related quality of life (HR-QoL) in elderly women. In this 4-month cluster randomised controlled trial, 100 women aged 60–90 years (mean 73 years) from self-care retirement villages participated in RT twice a week and were allocated either 160 g/d (cooked) lean red meat consumed across 2 meals/d, 6 d/week or ≥1 serving/d (25–30 g) carbohydrates (control group, CRT). HR-QoL (SF-36 Health Survey questionnaire), lower limb maximum muscle strength and lean tissue mass (LTM) (dual-energy X-ray absorptiometry) were assessed at baseline and 4 months. In all, ninety-one women (91 %) completed the study (RT+Meat (n 48); CRT (n 43)). Mean protein intake was greater in RT+Meat than CRT throughout the study (1·3 (sd 0·3) v. 1·1 (sd 0·3) g/kg per d, P<0·05). Exercise compliance (74 %) was not different between groups. After 4 months there was a significant net benefit in the RT+Meat compared with CRT group for overall HR-QoL and the physical component summary (PCS) score (P<0·01), but there were no changes in either group in the mental component summary (MCS) score. Changes in lower limb muscle strength, but not LTM, were positively associated with changes in overall HR-QoL (muscle strength, β: 2·2 (95 % CI 0·1, 4·3), P<0·05). In conclusion, a combination of RT and increased dietary protein led to greater net benefits in overall HR-QoL in elderly women compared with RT alone, which was because of greater improvements in PCS rather than MCS.

The effect of protein intake on growth velocity in infancy may be mediated by insulin-like growth factor-1 (IGF-1). This study aimed to determine the effects of formulae containing 1·8 (F1·8) or 2·7 g (F2·7) protein/418·4 kJ (100 kcal) on IGF-1 concentrations and growth. Healthy term infants were randomly assigned to receive F1·8 (n 74) or F2·7 (n 80) exclusively for the first 4 months of life. A group of breast-fed infants (n 84) was followed-up simultaneously (reference). Growth and body composition were measured at 0·5, 4, 6, 12, 36, 48 and 60 months of life. The IGF-1 concentrations at 4 months (primary outcome) were similar in the F1·8 (67·1 (sd 20·8) ng/l; n 70) and F2·7 (71·2 (sd 27·5) ng/l; n 73) groups (P=0·52). Both formula groups had higher IGF-1 concentrations than the breast-fed group at 4 and 9 months of age (P≤0·0001). During the first 60 months of life, anthropometric parameters in the F1·8 group were lower compared with the F2·7 group, and the differences were significant for head circumference from 2 to 60 months, body weight at 4 and 6 months and length at 9, 12 and 36 months of age. There were no significant differences in body composition between these two groups at any age. We conclude that, in formula-fed infants, although increased protein intake did not affect the IGF-1 concentration during the first 12 months of life, it did affect length and head circumference growth, suggesting that factors other than IGF-1 could play roles in determining growth velocity.

The aim of the present study was to investigate the effect of a protein-free diet in the induction of food allergy and oral tolerance in BALB/c mice. The experimental model used was mice that were fed, since weaning up to adulthood, a balanced diet in which all dietary proteins were replaced by amino acid diet (Aa). The absence of dietary proteins did not prevent the development of food allergy to ovalbumin (OVA) in these mice. However, Aa-fed mice produced lower levels of IgE, secretory IgA and cytokines. In addition, when compared with mice from control group, Aa-fed mice had a milder aversive reaction to the allergen measured by consumption of OVA-containing solution and weight loss during food allergy development. In addition, mice that did not have dietary proteins in their diets were less susceptible to induction of oral tolerance. One single oral administration was not enough to suppress specific serum Ig and IgG1 levels in the Aa-fed group, although it was efficient to induce suppression in the control group. The present results indicate that the stimulation by dietary proteins alters both inflammatory reactivity and regulatory immune reactivity in mice probably due to their effect in the maturation of the immune system.

Resistance training is recognised as a good strategy for retarding age-related declines in muscle mass and strength. Recent studies have also highlighted the potential value of protein intakes in excess of present recommendations. The roles that leisure-time physical activity and protein quality play in the preservation of skeletal muscle during ageing, and how such influences interact in free-living people are unclear. We sought to clarify these issues using data collected on 2425 participants aged ≥ 50 years in the US National Health and Nutrition Examination Survey (2003–2006). We estimated subjects’ usual intakes of total protein and beef from two 24 h diet recalls and computed the appendicular skeletal muscle mass index from anthropometric measures. Participants self-reported their physical activity levels. Analyses accounted for demographic factors and smoking. The association between muscle-strengthening activity and the appendicular skeletal muscle mass index varied with protein intake. Furthermore, among obese subjects with protein intakes < 70 g/d, those who performed such activities had a lower appendicular skeletal muscle mass index than those who were physically inactive. Protein intakes above the present recommendations were associated with benefits to obese subjects only. The appendicular skeletal muscle mass index of non-obese subjects who performed vigorous aerobic activities was consistently high; in obese subjects, it varied with protein intake. High-protein intake was associated with a modest increase in the appendicular skeletal muscle mass index in non-obese, physically inactive subjects. The present findings reinforce the idea that muscle-strengthening exercise preserves muscle when combined with adequate dietary protein. Vigorous aerobic activity may also help.

Indian diets derive almost 60 % of their protein from cereals with relatively low digestibility and quality. There have been several surveys of diets and protein intakes in India by the National Nutrition Monitoring Board (NNMB) over the last 25 years, in urban and rural, as well as in slum dwellers and tribal populations. Data of disadvantaged populations from slums, tribals and sedentary rural Indian populations show that the protein intake (mainly from cereals) is about 1 gm/kg/day. However, the protein intake looks less promising in terms of the protein digestibility corrected amino acid score (PDCAAS), using lysine as the first limiting amino acid, where all populations, particularly rural and tribal, appear to have an inadequate quality to their protein intake. The protein: energy (PE) ratio is a measure of dietary quality, and has been used in the 2007 WHO/FAO/UNU report to define reference requirement values with which the adequacy of diets can be evaluated in terms of a protein quality corrected PE ratio. It is likely that about one third of this sedentary rural population is at risk of not meeting their requirements. These levels of risk of deficiency are in a population with relatively low BMI populations, whose diets are also inadequate in fruits and vegetables. Therefore, while the burden of enhancing the quality of protein intake in rural India exists, the quality of the diet, in general, represents a challenge that must be met.

Diets high in protein have shown positive effects on short-term weight reduction and glycaemic control. However, the understanding of how dietary macronutrient composition relates to long-term risk of type 2 diabetes is limited. The aim of the present study was to examine intakes of macronutrients, fibre and protein sources in relation to incident type 2 diabetes. In total, 27 140 individuals, aged 45–74 years, from the population-based Malmö Diet and Cancer cohort, were included. Dietary data were collected with a modified diet history method, including registration of cooked meals. During 12 years of follow-up, 1709 incident type 2 diabetes cases were identified. High protein intake was associated with increased risk of type 2 diabetes (hazard ratio (HR) 1·27 for highest compared with lowest quintile; 95 % CI 1·08, 1·49; P for trend = 0·01). When protein consumption increased by 5 % of energy at the expense of carbohydrates (HR 1·20; 95 % CI 1·09, 1·33) or fat (HR 1·21; 95 % CI 1·09, 1·33), increased diabetes risk was observed. Intakes in the highest quintiles of processed meat (HR 1·16; 95 % CI 1·00, 1·36; P for trend = 0·01) and eggs (HR 1·21; 95 % CI 1·04, 1·41; P for trend = 0·02) were associated with increased risk. Intake of fibre-rich bread and cereals was inversely associated with type 2 diabetes (HR 0·84; 95 % CI 0·73, 0·98; P for trend = 0·004). In conclusion, results from the present large population-based prospective study indicate that high protein intake is associated with increased risk of type 2 diabetes. Replacing protein with carbohydrates may be favourable, especially if fibre-rich breads and cereals are chosen as carbohydrate sources.

The effect of dietary protein on enzyme activity of pancreatic juice was studied in ten growing, castrated, Large White male pigs. Animals, fitted with permanent cannulas in the pancreatic duct and in the duodenum, were divided into two groups receiving either casein or rapeseed concentrate as a protein source. After a 15 d adaptation period to the experimental diet, the volume of pancreatic secretion was significantly higher, whereas the protein concentration was lower in the casein group compared with the rapeseed group. No statistical difference was observed in the daily protein output between groups. Total secreted activities of carboxypeptidase A (EC 3.4.17.1), and elastase (EC 3.4.21.36) were higher in the casein group during the nocturnal period, whereas total activities of trypsin (EC 3.4.21.4), chymotrypsin (EC 3.4.21.1), carboxypeptidase B (EC 3.4.17.2) and amylase (EC 3.2.1.1) in pancreatic secretions during the post-prandial periods were increased by the ingestion of the rapeseed diet. It is concluded that the pancreatic enzyme secretion is sensitive to the nature of the protein ingested.