Protein Intake Rate Research Articles

Food on a plate: Wild geese maintain higher food intake rates on uniform winter cereals fields versus diverse grasslands

Spring staging Greater White-fronted Geese Anser albifrons have increasingly shifted from traditional diverse grassland fields to monocultures of winter cereals, causing conflict with farmers. To account for this transition, we tested two key predictions, controlling for goose age effects and sward height. Firstly, that cereal is better quality than grass (based on crude protein content). Secondly, that geese show higher peck rate and step rate on grassland than cereal, enabling them to compensate for lower, less selective intake rates there compared to the uniform, dense, high quality arable sward where all blades are equally of high profitability. Laboratory analyses showed that winter cereal had 27 % higher crude protein content than grass. Based on data extracted from video sequences of spring foraging geese in NE Poland, first-year birds (“immatures”) showed significantly higher peck rates and step rates than adults in all situations, likely reflecting their less efficient foraging abilities. Both age classes showed significantly higher peck rates on grass than winter cereal as predicted. Combining differential protein content and lamina length/dry weight relationships of grass versus cereal showed that geese obtained 17–33 % more protein from cereal lamina of the same length. At observed peck rates, this equated to a 6 % greater hourly crude protein intake rate on cereals compared to grass at lamina length 2.5 cm, increasing to 29 % difference at 12.5 cm. Hence, at longer swards, cereals become increasingly profitable for foraging geese over grass swards, despite the higher peck rates observed on grass which failed to compensate for lower lamina quality. We contend that these interactions explain the simultaneous attraction of cereal over grass swards in this study area and likely elsewhere and we discuss the management implications of these findings.

MALNUTRITION IN PEDIATRIC PATIENTS WITH LOW RESPIRATORY TRACT INFECTIONS AT NATIONAL LUNG HOSPITAL, VIETNAM

Aims: To determine the nutritional status and the dietary intake of inpatient children with lower respiratory infections. Methods: This cross-sectional study was conducted in 106 children aged under 5 years admitted to the Pediatric Department of the National Lung Hospital in Hanoi, Vietnam, from August to December 2018. Body weight, height/length were measured; nutritional status was evaluated by using World Health Organization criteria and Subjective Global Assessment (SGA). Dietary intake was daily recorded during the first week of hospitalization. Results: The prevalence of malnutrition was 30.1%, 25.7%, and 17.8% respectively for underweight, stunting and wasting. According to the SGA, 20% of the patients were at risk for malnutrition. From the first day to seventh day of hospitalization, the rate of chidlren given 100% of requirement had a fluctuating upward trend from 30% to 40% in energy intake and from 66% to 84% in protein intake; the rates of energy intake under 80% of requirement were from 31% to 54% in patients, while the rates of protein intake over 1.5-fold requirement were from 37% to 50% in patients. Conclusions: The study indicated the alarmingly high prevalence of malnutrition in children aged under 5 years and the contrast between under energy intake and over protein intake in the hospitalized children.

Switching between Food Patches Suggests a Need to Balance Nutrients while Foraging in Wild Black Howler Monkeys (Alouatta pigra)

Studies of feeding patch choice in primates have traditionally analyzed individual foraging decisions in relation to patterns of social foraging,dominance, and feeding competition. However, information on detailed ecological and nutritional characteristics of the patches also is neededto understand the basis of feeding patch preferences. In particular, recent models of nutritional ecology have stressed the importance of nutrientbalancing as a primary driver of individual foraging decisions. Here we investigated the behavioral and nutritional factors affecting feeding patchchoice in black howler monkeys (Alouatta pigra) during a 15-month field study in Campeche, Mexico. We collected 1300 hours of behavioral dataon 14 focal animals, including full-day follows of one individual/day recording all feeding activities. We carried out nutritional analyses of foodsfrom feeding trees and calculated daily nutrient intake. A total of 690 trees (i.e., patches) were visited throughout the study period. The time spentfeeding and the amount of food consumed differed significantly according to patch type. Individuals consumed more food in mature and immaturefruit patches than in mature leaf, young leaf, and flower patches. Protein intake rates (kJoule/min) were similar in young and mature leaf patches,and higher than in mature fruit, immature fruit, and flower patches, among which the rate was similar. In the majority of the cases (80.3%), thefocal animals left the feeding patch prior to satiation. On those occasions, resource mixing, or moving from one food type to another food type,accounted for 49.4% of the patch leaving events. The fact that black howler monkeys alternated feeding bouts between fruit and leaf patches, aswell as alternating bouts of higher and lower protein intake, suggest that this pattern could be dictated by the need to balance nutrients.

Protein and energy intake and nutritional evolution of preterm infants after hospital discharge: A longitudinal study

BackgroundPreterm infants, especially those with very low birth weight, are more susceptible to nutritional deficiencies and growth restriction after hospital discharge than term infants. AimsTo investigate the association between energy and protein intake and nutritional evolution of preterm infants during the first year of life of corrected age after hospital discharge. Study designThis is a retrospective longitudinal study with 131 preterm infants born at a high-risk neonatal clinic. SubjectsNeonates born at <32 weeks of gestational age and with birth weight < 1500 g were included in the study. Outcomes measuresGrowth was assessed by z-scores for weight- and length-to age. Energy and protein intake were assessed by caloric and protein intake rate per kilogram of body weight. Changes in growth were evaluated according to caloric rate and energy intake using linear mixed-effect models. ResultsWe found that most of the followed-up children (62.3%) had an average daily energy intake <120 kcal/kg of body weight. At the end of the first year of life based on corrected age, the variation in weight gain was greater among those with more severe nutritional deficit at born and who had daily intakes over 130 kcal/kg of body weight (p=0.02) or over 3.5 g of protein/kg of body weight (p=0.03). ConclusionIndividualized dietary plans for preterm infants should be based on the continuous assessment of growth and weight gain.

Modelling of amino acid turnover in the horse during training and racing: A basis for developing a novel supplementation strategy.

Horses in heavy training in preparation for racing and competition have increased metabolic demands to support the more intensive levels of exercise and recovery. However, little is known at the metabolic level about amino acid turnover and the specific alterations of demand caused by high intensity exercise. During exercise, certain amino acids are required in greater quantities due to disproportionate losses via excretory systems and usage in biosynthetic pathways. This investigation has built a theoretical computer model in an attempt to bring together the published rates of protein intake and utilisation to try to understand how some amino acids might be in higher demand than others. The model indicated that after evaluation of the daily amino acid turnover, glutamine/glutamic acid (Glx), serine and ornithine were in negative nitrogen balance which identified these amino acids as critical limiting factors for anabolism. Adjustment of the modelling conditions to cater for high intensity training indicated that an additional demand was placed on eight amino acids, including GLx, valine, lysine, histidine and phenylalanine which could thus become limiting under these conditions. The modelling results indicated that an amino acid supplement with the correct amino acids to match demand could theoretically be beneficial to a 500Kg horse in quantities of 20-80g/day. These results open new avenues of research for specifically tailoring amino acid supplementation to meet demands for sports horses in heavy training and improving general well-being, especially in hotter climates.

Modelling of protein turnover provides insight for metabolic demands on those specific amino acids utilised at disproportionately faster rates than other amino acids

The nitrogen balance is regulated by factors such as diet, physical activity, age, pathogenic challenges, and climatic conditions. A paradigm was developed from published recommended rates of protein intake (g/kg/day) with corresponding rates of endogenous protein turnover and excretion, to extrapolate amino acid balances under various conditions. The average proportions of amino acids in the ingested proteins representing a well-balanced diet were used to assess intake and an average human composition profile from five major high-turnover proteins in the body to assess endogenous protein turnover. The amino acid excretion profiles for urine and sweat were constructed for males and females from published data. The model calculated the nitrogen balances for a range of amino acids to determine the amino acid requirements to support daily exertion. Histidine, serine, glycine, and ornithine were in negative balances in males and females and this potential deficit was greater in the higher body-mass ranges. Conversely, leucine, isoleucine, and valine were conserved during nitrogen flux and resulted in positive balances. The model was run under a scenario of high demand for the synthesis of IgG during a response to an infectious challenge which indicated that these were increased requirements for tyrosine, threonine, and valine. It was concluded that these amino acids represent points of limitation to anabolic metabolism by restriction of their supply at critical times of demand. This would especially occur under conditions of fitness training, maintaining intensive exercise regimes, facilitating responses to pathogenic challenge, or recovery from injury.

Association of Protein Intake in Three Meals with Muscle Mass in Healthy Young Subjects: A Cross-Sectional Study

Protein intake of >0.24 g/kg of body weight (BW) at a single meal is necessary to maximize muscle protein synthesis in a young population. However, the association between the protein intake rate for three meals and muscle mass in the young population has not been evaluated. We hypothesized that a protein intake of >0.24 g/kg BW at all three meals is effective for maintaining muscle mass. Therefore, we cross-sectionally examined the association between protein intake at all three meals with muscle mass in 266 healthy young subjects (aged 21.4 ± 2.4 years). Subjects were divided into the AP group, which achieved protein intake >0.24 g/kg BW at all three meals; and the NP group, which did not. We calculated total fat-free mass (FFM) and appendicular fat-free mass (AppFFM) with dual-energy X-ray absorptiometry, and the percentage of total FFM (TotalFFM%) and appendicular FFM (AppFFM%) were calculated as the percentage of BW (%BW). We demonstrated that TotalFFM% (77.0 ± 0.5 vs. 75.2 ± 0.4%, p = 0.008) and AppFFM% (34.7 ± 0.3 vs. 34.1 ± 0.2%, p = 0.058) were higher in the AP than in the NP group. This finding suggests that achieving protein intake of >0.24 g/kg BW at all three meals is important for muscle mass maintenance in young populations.

High rates of protein intake are associated with an accelerated rate of decline of residual kidney function in incident peritoneal dialysis patients.

Preservation of residual kidney function (RKF) is a relevant objective in peritoneal dialysis (PD) patients. The influence of dietary protein intake (PI) on this variable has not been adequately investigated. Following an observational design, we studied 336 patients incident on PD, with a minimum follow-up of 6 months. The main study variable was the mean PI [normalized rate of protein nitrogen appearance (nPNA)] during the first 4 months on PD. The main outcome variables were the absolute rate of decline of RKF and the proportion of patients presenting a >50% decay of their RKF during the first year of follow-up. We applied univariate and multivariate strategies of analysis, taking into consideration the main control variables bearing a correlation with nPNA and/or RKF. Mean nPNA (first 4 months) was 1.23 ± 0.33 g/kg/day, while the overall rate of decline of RKF was -0.13 ± 0.29 mL/min/month; 69 patients (25.1%) had lost >50% of their initial RKF by the end of the first year. Univariate analysis disclosed consistent associations between the main study variable on one hand and baseline RKF (r = 0.32, P < 0.0005) and its rate of decline (r = -0.23, P < 0.0005) on the other. The latter two variables were also significantly correlated (r = -0.36, P < 0.0005). Multivariate analysis identified mean nPNA as an independent predictor of the rate of decline of RKF [odds ratio 1.09 per 0.10 g/kg/day, 95% confidence interval (CI) 0.99-1.19, P = 0.058] and, in particular, of the probability of losing >50% of the baseline RKF during the first year of treatment (odds ratio 1.15 per 0.10 g/kg/day, 95% CI 1.04-1.27, P = 0.006). Higher rates of PI during the first months of therapy are associated with a faster decline of RKF among patients incident on PD. Our results underline the convenience of keeping an adequate balance between sufficient protein ingestion, to prevent malnutrition and wasting, and sensible restriction in stable, adequately nourished individuals with rates of intake in the higher range or above-recommended allowances.

Blood Markers In College Athletes According To Their Vegetable/Animal Protein Intake Rate

Blood Markers In College Athletes According To Their Vegetable/Animal Protein Intake Rate

Degradability and kinetics of fibrous particles in cattle fed diets based on corn silage and concentrates with or without addition of lipids

Eight rumen-cannulated steers were assigned to two 4 × 4 balanced Latin squares to evaluate degradability and kinetics of fiber particles from diets based on corn silage and supplements with or without addition of lipids. Dietary treatments were: only corn silage (T1), corn silage plus concentrate with no added lipids (T2), corn silage plus concentrate with added soybean oil (T3), and corn silage plus concentrate containing ground soybean seeds (T4). Kinetics of gastrointestinal transit of fibrous particles was evaluated based on chromium-mordanted fiber. Events of rumen degradation dynamics of fibrous carbohydrates were quantified using the in situ incubation procedure. The mixed models methodology from SAS was used to fit models and the Tukey test was used to compare means. The ruminal digestibility of fiber was lower in treatments T3 and T4 and, consequently, lower proportions of potentially digestible fraction of standardized fiber and higher proportions of indigestible fraction of standardized fiber for treatments T3 and T4 compared with T1 and T2 were observed. However, there were no differences in mean retention time of the rumen, total mean retention time, mean digestion time, and rumen fill among diets. Animals from T2, T3, and T4 showed higher dry matter intake, organic matter intake, and crude protein intake rates than animals receiving T1 diet, but there was no effect of the addition of lipid. Treatments did not differ regarding neutral detergent fiber intake. Animals from T1 had lower crude fat intake than animals from T2, which showed lower crude fat intake than those from T3 and T4. The addition of lipid to concentrate has no effect on passage rate, digestion rate, and intake, when a good quality roughage is used.

Nutritional ecology of elk during summer and autumn in the Pacific Northwest

Nutritional ecology of elk during summer and autumn in the Pacific Northwest

Foraging decisions underlying restricted space use: effects of fire and forage maturation on large herbivore nutrient uptake.

Recent models suggest that herbivores optimize nutrient intake by selecting patches of low to intermediate vegetation biomass. We assessed the application of this hypothesis to plains bison (Bison bison) in an experimental grassland managed with fire by estimating daily rates of nutrient intake in relation to grass biomass and by measuring patch selection in experimental watersheds in which grass biomass was manipulated by prescribed burning. Digestible crude protein content of grass declined linearly with increasing biomass, and the mean digestible protein content relative to grass biomass was greater in burned watersheds than watersheds not burned that spring (intercept; F 1,251 = 50.57, P < 0.0001). Linking these values to published functional response parameters, ad libitum protein intake, and protein expenditure parameters, Fryxell's (Am. Nat., 1991, 138, 478) model predicted that the daily rate of protein intake should be highest when bison feed in grasslands with 400–600 kg/ha. In burned grassland sites, where bison spend most of their time, availability of grass biomass ranged between 40 and 3650 kg/ha, bison selected foraging areas of roughly 690 kg/ha, close to the value for protein intake maximization predicted by the model. The seasonal net protein intake predicted for large grazers in this study suggest feeding in burned grassland can be more beneficial for nutrient uptake relative to unburned grassland as long as grass regrowth is possible. Foraging site selection for grass patches of low to intermediate biomass help explain patterns of uniform space use reported previously for large grazers in fire‐prone systems.

Individuality in nutritional preferences: a multi-level approach in field crickets.

Selection may favour individuals of the same population to differ consistently in nutritional preference, for example, because optimal diets covary with morphology or personality. We provided Southern field crickets (Gryllus bimaculatus) with two synthetic food sources (carbohydrates and proteins) and quantified repeatedly how much of each macronutrient was consumed by each individual. We then quantified (i) whether individuals were repeatable in carbohydrate and protein intake rate, (ii) whether an individual’s average daily intake of carbohydrates was correlated with its average daily intake of protein, and (iii) whether short-term changes in intake of carbohydrates coincided with changes in intake of protein within individuals. Intake rates were individually repeatable for both macronutrients. However, individuals differed in their relative daily intake of carbohydrates versus proteins (i.e., ‘nutritional preference’). By contrast, total consumption varied plastically as a function of body weight within individuals. Body weight—but not personality (i.e., aggression, exploration behaviour)—positively predicted nutritional preference at the individual level as large crickets repeatedly consumed a higher carbohydrate to protein ratio compared to small ones. Our finding of level-specific associations between the consumption of distinct nutritional components demonstrates the merit of applying multivariate and multi-level viewpoints to the study of nutritional preference.

Biological responses in mullet Mugil liza juveniles fed with guar gum supplemented diets

This study aimed to evaluate the effects of adding guar gum, a non-starch polysaccharide, to the diet of Mugil liza juveniles. The juveniles (mean weight=0.38±0.01g) were fed one of three diets with increasing supplement levels (4%, 8%, and 12%) and a control diet without additional gum for 60 days, in order to evaluate the effects on zootechnical performance, proximate composition, liver parameters, morphological alterations to the intestinal tract, and modulation of gastrointestinal microbiota. The animals fed 8% and 12% gum presented a significantly lower mean final weight, weight gain, specific growth rate, food intake rate, and protein intake rate than the control. Adding gum to the diets also reduced the dry matter, crude protein, and carcass fat levels. All treatments with added gum resulted in increased liver glycogen, and the cholesterol levels were significantly reduced in fish fed 4% and 8% supplement levels. No intestinal morphological alterations were observed in the animals. However, a modulating effect was noted on the microbial community, altering the bacterial quantity and composition throughout the tract segments. The use of guar gum is not recommended in Mugil liza diets, at least above 4%.

Foraging in a heterogeneous environment—An experimental study of the trade-off between intake rate and diet quality

Among the factors determining the choice of feeding sites by herbivores, the rate of intake of net energy and nutrients is a major one. For grazers, patches of tall grasses are ingested faster, but are digested less fully because of their high fibre contents; conversely, short grass is highly digestible but allows only low intake rates. Herbivores therefore face a trade-off between the quantity and the quality of their food. Little empirical information is available to test whether optimisation models of patch selection are applicable to horses. An experiment was therefore designed where the trade-off between sward height and quality was explored to test explanatory models based on rates of nutrient acquisition (digestible dry matter, energy and/or protein intake rates). Three groups of two 2-year-old saddle horses were grazed on pasture managed to produce three swards differing in both height and quality (vegetative to reproductive stages). They were offered binary choices in a Latin-square design to assess preferences; daily intake was measured to determine the consequences of their choices. Instantaneous intake rates (IIRs) were determined from bite rates at pasture, and bite mass estimated using trays indoors. The taller sward matured during the experiment, so the quality differences between swards increased. The horses selected the taller sward in the first period, and the shorter alternatives in the following ones. The rates of digestible dry matter (DM) and net energy intake were always higher on the tall swards; digestible protein was the best predictor of the horses’ choices. Patch selection thus depended on the nutritional context: when digestible protein was not limiting, the horses selected patches where food was ingested faster, and when protein supplies declined, they maximised their protein intake rate. Preferences were however partial: as the shorter swards allowed higher rates of digestible protein intake but lower net energy than the taller swards, the horses may have been balancing their protein and energy intake by feeding on both swards; alternative explanations are discussed.

Protein metabolism in adult patients with phenylketonuria

Objective Protein intake recommendations in phenylketonuria (PKU) are frequently the subject of discussion. For healthy adults, the recommended daily allowance (RDA) is 0.8 g · kg −1 · d −1, which is generally lower than that observed in the general Western population. We investigated whether whole-body protein metabolism in patients with PKU is comparable to that of healthy controls at a RDA rate of protein intake. Methods Six adult patients with well-controlled PKU and six healthy subjects of comparable age, height, and weight were studied using a primed continuous infusion of [1- 13C]-valine for 8 h after an overnight fast before and during frequent meals. Normal protein was given to controls, whereas patients with PKU received a combination of an amino acid mixture and natural protein. Results No significant differences were observed between patients with PKU and controls in preprandial and prandial rates of valine appearance and oxidation and protein breakdown, protein synthesis, and net protein balance. Feeding resulted in a significant ( P < 0.01) decrease in protein breakdown (PKU: 94 ± 15 μmol · kg −1 · h −1 preprandial to 49 ± 10 μmol · kg −1 · h −1 prandial; controls: 97 ± 10 μmol · kg −1 · h −1 preprandial to 55 ± 10 μmol · kg −1 · h −1 prandial), whereas no effects were observed in protein synthesis (PKU: 77 ± 10 μmol · kg −1 · h −1 preprandial to 73 ± 7 μmol · kg −1 · h −1 prandial; controls: 76 ± 8 μmol · kg −1 · h −1 preprandial to 71 ± 5 μmol · kg −1 · h −1 prandial). Net protein balance increased from negative prandial to positive preprandial values (PKU: −17 ± 6 μmol · kg −1 · h −1 preprandial to +23 ± 8 μmol · kg −1 · h −1 prandial; controls: −21 ± 4 μmol · kg −1 · h −1 preprandial to +16 ± 9 μmol · kg −1 · h −1 prandial). Conclusion Whole-body protein metabolism in adult patients with PKU is fully comparable to that in healthy controls at the RDA level of protein intake.

Amino acid supplementation prevents the loss of appetite for casein in old Lou/Cjall rats

A deleterious reduction of casein intake occurring earlier in males than in females had been previously observed in old Lou/Cjall rats. On the contrary, protein intake was observed to be maintained in old males when they were offered whey protein. Present studies were designed to investigate the effect of dietary casein modification on protein decrease. In two lifelong studies, male and female Lou/Cjall rats were tested every four months in order to study protein intake depending on the protein available: casein, whey protein or casein supplemented with an amino acid mixture (SC). In subsequent cross-sectional studies, young, adult, middle-aged and old rats were successively fed with casein, casein supplemented either with leucine or with alanine or with glycine. Supplementing casein with an amino acid mixture both globally increased protein intake and allowed old males to maintain a high rate of protein intake. In cross-sectional experiments, no effect of supplementation was seen in the young group. In older animals, the greatest effect was seen when casein was supplemented with alanine or glycine, independently of sex and age. We therefore, concluded that supplemented casein is more beneficial for old rats than casein alone, probably by increasing amino acid availability. We hypothesize that alanine could act through its effect on gluconeogenesis.

Autumn Foraging Dynamics of Woodland Caribou in Experimentally Manipulated Habitats, Northeastern Washington, USA

Foraging options of woodland caribou (Rangifer tarandus caribou) in the high snowpack ecosystems of western North America become narrowed after freezing temperatures in antumn precipitate leaf-drop in deciduous shrubs. The objectives of this research were to determine the influence of (1) removing arborca lichen (Ascompecytes) on windthrown trees and myrtle boxwood (Pachistime myrsinites) and (2) stand type (oldgrowth versus clearcnt) on woodland caribou foraging dynamics during autum. Foraging trials were conducted with 3 tame woodland caribou in 6 0.5-ha pens. In 3 treatment pens all windthrown arboreal lichen-bearing trees were removed from the old-growth portion of the pen and extant invrtle hoxwood plants were removed from the entire pen. In the 3 control pens all extant windthrown trees and invrtle boxwood plants were retained In addition, pens were constructed such that half of each pen was in an old-growth stand of western red-cedar (Thuja plicata)-western hemlock (Tsuga heterophylla) and half was in an adjacent clearent. Arboreal hcher had the greatest influence on dry-matter intake rate (DMIR) because of the large bite size provided by this forage. In control pens, caribou had higher DMIR (P = 0.006) and crude protein intake rate (CPIR) (P = 0.007) than in treatment pens where lichen-bearing windthrown trees had been removed. Arboreal lichen from windthrown trees was 52% (range 43-61) of the total DMI in the old-growth portious of control pens Arboreal lichen from windthrown trees comprised 81% (range = 75-92) of the arboreal lichen bites (i.e., 19% of arboreal lichen bites were from litterfall and standing trees), and 28% range = 16-48) of total bites in the timbered portion of control peus. The DMIR (P = 0.004) and CPIR (P = 0.004) of caribou was also greater in old-growth than in clearcat portions of pens. Search time was greater (P = 0.008) in clearent portions or pens than in old-growth portions. Myrtle boxwood comprised <0.4% of caribou diets. These data suggest that arboreal lichen is an important dietary component earlier in antamn than previously reported.

Monthly and diurnal variations in food choice byMacaca fuscata yakui during the major fruiting season at Yakushima Island, Japan

An ecological survey was conducted on two groups of wild Japanese macaques (Macaca fuscata yakui) inhabiting the warm-temperate, broad-leaved forest of Yakushima Island. The survey was designed to determine and explain monthly and diurnal variations in both duration of feeding and food choice, and to explain these variations from a nutritional perspective. Feeding activity increased during the hour before sunset, while leaf eating in particular tended to be observed later in the day throughout the study period. A diverse and unstable diet promoted monthly differences in fat and protein consumption. The mean lipid and calorific content of the food and the rate of protein intake were high in early autumn.Ficus fruits were not selected when unripeArdisia sieboldii fruits were available, but were an important food resource in a general context. Differences in nutritional intake at different times of the day were determined by the combination of species eaten although no single species was preferred at a particular time. Similarities with experimental results in laboratory animals suggest that a physiological, rather than a behavioural, response was regulating nutritional intake. A high consumption of proteins before rest might produce satiety in the macaques and give them the opportunity to digest and absorb complicated or toxic metabolites slowly during the night.

The effects of increased protein intake on kidney size and function.

In endothermic vertebrates, long-term increases in metabolic energy demand are often associated with increases in food intake and accompanied by increases in organ mass. Wide-scale increases in organ mass have often been attributed to a metabolic response to increased energy intake and utilization. On a constant diet, however, increased food intake is also associated with increased protein intake. We hypothesized that, while increased food intake itself may be responsible for increases in digestive tract mass, the consequent increased protein intake would be the factor responsible for increased kidney mass and function. Thus, we exposed male and female mice to diets differing in protein level (7 %, 15 % or 46 % casein by mass) at different acclimation temperatures (5 degrees C or 23 degrees C). Within an acclimation temperature, food intake rate remained constant over the entire range of dietary protein level, and protein intake rate increased as dietary content increased. The mice in the cold-acclimation group increased food intake rate by 48-120 % over those in the warm-acclimation group. Liver, kidney and stomach mass increased with protein intake rate, while digestive tract and other vital organ masses increased only in response to increased energy intake rate. Blood urea nitrogen levels increased with protein intake rate. Glomerular filtration rates increased with increases in dietary protein level in male mice but not female mice. Finally nitrogen filtration rate increased with protein intake rate for mice on the high-protein diet. We suggest that it is primarily the increased protein intake rate rather than the increased food intake rate that results in the changes in kidney and liver mass and kidney function observed to occur in situations of high energy demand.