Influence Of Protein Intake Research Articles

Influence of Protein Intake and Timing on Whole Body Protein Turnover in Middle‐Aged Men and Women

Meal protein consumption may be more important than total daily protein intake (TPI) in older adults. This study characterized effects of TPI and protein timing on whole body protein turnover (WBPT) in healthy middle‐aged (50–70 y) adults. WBPT (15N glycine method; flux, Q, protein synthesis, PS, and breakdown, PB) was determined following 2 wk diet intervention with TPI at or double the RDA (AP: 0.8, HP: 1.6 g/kg). AP was further grouped by % TPI consumed at meals (even distribution, APE or back loaded at dinner, APD). TPI was estimated from 7 d diet records. Comparisons (mean ± SE) were made between APE, APD and HP. Age and BMI (kg/m2) were similar for APE (n=6, 58 ± 2 y, 24.3 ± 1.0), APD (n=9, 54 ± 2 y, 25.8 ± 1.0) and HP (n=10, 56 ± 2 y, 25.2 ± 1.0). Q (1.23 ± .16 vs .54 ± .07 vs .75 ± .11), PS (6.49 ± .94 vs 2.69 ± .41 vs 3.86 ± .73) and PB (6.57 ± 1.09 vs 2.95 ± .34 vs 3.60 ± .72 p ≤ .02) was higher for HP vs AP but was similar for APE vs APD (p ≥ 0.1). NET balance (PS‐PB) was not different for HP vs AP. NET was lower for APE vs APD (−.26 ± .20 vs .25 ± .20, p = .05). Higher TPI increased WBPT. APD had a positive NET possibly related to a physiologically significant increase in PS (p = 0.1). Although preliminary in nature, the latter finding suggests when TPI approximates the RDA a single protein bolus may beneficially stimulate PS in middle‐aged adults. Caution in applying this information is warranted until findings are validated with the respective stable isotope method.

Nutrient-Mediated Architectural Plasticity of a Predatory Trap

BackgroundNutrients such as protein may be actively sought by foraging animals. Many predators exhibit foraging plasticity, but how their foraging strategies are affected when faced with nutrient deprivation is largely unknown. In spiders, the assimilation of protein into silk may be in conflict with somatic processes so we predicted web building to be affected under protein depletion.Methodology/Principal FindingsTo assess the influence of protein intake on foraging plasticity we fed the orb-web spiders Argiope aemula and Cyclosa mulmeinensis high, low or no protein solutions over 10 days and allowed them to build webs. We compared post-feeding web architectural components and major ampullate (MA) silk amino acid compositions. We found that the number of radii in webs increased in both species when fed high protein solutions. Mesh size increased in A. aemula when fed a high protein solution. MA silk proline and alanine compositions varied in each species with contrasting variations in alanine between the two species. Glycine compositions only varied in C. mulmeinensis silk. No spiders significantly lost or gained mass on any feeding treatment, so they did not sacrifice somatic maintenance for amino acid investment in silk.Conclusions/SignificanceOur results show that the amount of protein taken in significantly affects the foraging decisions of trap-building predators, such as orb web spiders. Nevertheless, the subtle differences found between species in the association between protein intake, the amino acids invested in silk and web architectural plasticity show that the influence of protein deprivation on specific foraging strategies differs among different spiders.

Low dietary protein intake during pregnancy differentially affects mitochondrial copy number in stromal vascular cells from subcutaneous versus visceral adipose tissue in the offspring

The present study examined the influence of protein intake during pregnancy on mitochondrial metabolism in stromal vascular cells from subcutaneous (SVSu) and visceral (SVVi) adipose tissue of offspring fed a high fat diet. Obese‐prone Sprague‐Dawley rats were fed diets containing either 8% or 20% protein throughout pregnancy and lactation. Male weanling offspring were fed diets with 20% protein and and either 10% fat (NF) or 45% fat (HF) for 12 wks. The mitochondrial copy number showed a 5X increase in SVCu in offspring fed HE whose dams were fed normal protein compared to a 1.5X increase in offspring in offspring fed HE but whose dams were fed low protein. Neither pre‐ nor postnatal diets influenced mitochondrial number in SVVi. This finding suggests that prenatal protein intake and postnatal fat intake may differentially affect mitochondrial metabolism in SVSu versus SVVi. Although dietary treatments did not affect cellular respiration as measured with a Seahorse XF24 Analyzer with 5 mM glucose and 1mM pyruvate using cultured cells, SVSu exhibited lower maximum O2 consumption and lower reserve respiratory capacity than SVVi. Lower reserve capacity suggests that SVSu in offspring may not be able to sufficiently respond metabolically to HE diets and adapt by increasing mitochondrial biogenesis. Low prenatal protein intake during pregnancy may impair this adaptation in the offspring.

Milk protein intake, the metabolic-endocrine response, and growth in infancy: data from a randomized clinical trial

Protein intake in early infancy has been suggested to be an important risk factor for later obesity, but information on potential mechanisms is very limited. This study examined the influence of protein intake in infancy on serum amino acids, insulin, and the insulin-like growth factor I (IGF-I) axis and its possible relation to growth in the first 2 y of life. In a multicenter European study, 1138 healthy, formula-fed infants were randomly assigned to receive cow-milk-based infant and follow-on formulas with lower protein (LP; 1.77 and 2.2 g protein/100 kcal) or higher protein (HP; 2.9 and 4.4 g protein/100 kcal) contents for the first year. Biochemical variables were measured at age 6 mo in 339 infants receiving LP formula and 333 infants receiving HP formula and in 237 breastfed infants. Essential amino acids, especially branched-chain amino acids, IGF-I, and urinary C-peptide:creatinine ratio, were significantly (P < 0.001) higher in the HP group than in the LP group, whereas IGF-binding protein (IGF-BP) 2 was lower and IGF-BP3 did not differ significantly. The median IGF-I total serum concentration was 48.4 ng/mL (25th, 75th percentile: 27.2, 81.8 ng/mL) in the HP group and 34.7 ng/mL (17.7, 57.5 ng/mL) in the LP group; the urine C-peptide:creatinine ratios were 140.6 ng/mg (80.0, 203.8 ng/mg) and 107.3 ng/mg (65.2, 194.7 ng/mg), respectively. Most essential amino acids, IGF-I, C-peptide, and urea increased significantly in both the LP and HP groups compared with the breastfed group. Total IGF-I was significantly associated with growth until 6 mo but not thereafter. HP intake stimulates the IGF-I axis and insulin release in infancy. IGF-I enhances growth during the first 6 mo of life. This trial was registered at clinicaltrials.gov as NCT00338689.

Nutrition for power sports: Middle-distance running, track cycling, rowing, canoeing/kayaking, and swimming

Contemporary training for power sports involves diverse routines that place a wide array of physiological demands on the athlete. This requires a multi-faceted nutritional strategy to support both general training needs – tailored to specific training phases – as well as the acute demands of competition. Elite power sport athletes have high training intensities and volumes for most of the training season, so energy intake must be sufficient to support recovery and adaptation. Low pre-exercise muscle glycogen reduces high-intensity performance, so daily carbohydrate intake must be emphasized throughout training and competition phases. There is strong evidence to suggest that the timing, type, and amount of protein intake influence post-exercise recovery and adaptation. Most power sports feature demanding competition schedules, which require aggressive nutritional recovery strategies to optimize muscle glycogen resynthesis. Various power sports have different optimum body compositions and body weight requirements, but increasing the power-to-weight ratio during the championship season can lead to significant performance benefits for most athletes. Both intra- and extracellular buffering agents may enhance performance, but more research is needed to examine the potential long-term impact of buffering agents on training adaptation. Interactions between training, desired physiological adaptations, competition, and nutrition require an individual approach and should be continuously adjusted and adapted.

Influence of protein intake and muscle mass on survival in chronic dialysis patients

Introduction: Some studies suggest that high body mass index (BMI) confers survival advantage in dialysis patients, but BMI does not differentiate muscle from fat mass, and the survival advantage conferred by its increase seems to be limited to patients with high muscle mass. Thus, discriminating body components when evaluating nutritional status and survival is highly important. This study evaluated the influence of nutritional parameters on survival in patients on chronic dialysis. Subjects and methods: Anthropometry, bioimpedance, biochemistry, and dietary recall were used to investigate the influence of nutritional parameters on survival in 79 prevalent patients on chronic dialysis. Results: Protein intake <1.2 g/kg/day and creatinine <9.7 mg/dL were independent predictors of mortality in all patients. Regarding dialysis method, protein intake <1.2 g/kg/day was predictive of mortality among hemodialysis patients, and percent standard mid-arm muscle circumference <80% was identified as a risk factor among peritoneal dialysis patients. Conclusion: Higher muscle mass, possibly favored by a higher protein intake, conferred survival advantage in dialysis patients.

Protein Intake, Body Composition, and Protein Status Following Bariatric Surgery

Daily protein intake recommendations have recently been proposed for the bariatric patient. We aimed to evaluate the accomplishment of these recommendations, and the influence of protein intake (PI) on fat free mass (FFM) and protein status changes following bariatric surgery. We examined 101 consecutive patients undergoing laparoscopic Roux-in-Y gastric gypass (LGBP) or laparoscopic sleeve gastrectomy (LSG). Based on 3-day food records, PI from food and supplements were quantified at 4, 8, and 12months after surgery. The association between PI and body composition (bioelectrical impedance), plasma albumin and pre-albumin was evaluated at all study time points. A PI <60g/day was present respectively in 45%, 35%, and 37% of the cohort at 4, 8, and 12months after surgery (p < 0.001 relative to baseline). Despite our universal recommendation of protein supplementation, supplements were taken only by 63.4, 50.5, and 33.7% of the participants at 4, 8, and 12months. However, protein supplementation was effective in helping patients to achieve the daily protein intake goal. In linear regression analysis, male gender and weight loss, but not PI, were significantly associated with loss of FFM (p < 0.001). No significant correlation between PI and plasma albumin or pre-albumin was found. Our study underscores the value of protein supplementation for the achievement of the recommended daily protein intake in the bariatric patient. However, our data does not help to define a PI goal as critical in determining the FFM and protein status changes following LGBP or LSG.

The Effects of Dietary Protein on Bone Mineral Mass in Young Adults May Be Modulated by Adolescent Calcium Intake ,

The effect of dietary protein on bone mass measures at different life stages is controversial. We investigated the influence of protein intake on bone mass measures in young adults, considering the influence of calcium intake through adolescence. Subjects were 133 young adults (59 males, 74 females) who were participating in the Saskatchewan Pediatric Bone Mineral Accrual Study (1991–1997, 2003–2006). At adulthood, their mean age was 23 y. We assessed dietary intake via serial 24-h recalls carried out at least once yearly. Total body (TB) bone mineral content (BMC) and TB bone mineral density (BMD) were assessed annually using Dual energy X-ray absorptiometry. We determined TB-BMC net gain from the age of peak height velocity (PHV) to early adulthood. We analyzed data from all subjects and subsets based on sex and calcium intake using multiple regression. TB-BMC significantly increased from age at PHV to early adulthood by 41% in males and 37% in females. Height, weight, physical activity, and sex were significant predictors of TB-BMC, TB-BMC net gain, and TB-BMD among all subjects. Protein intake predicted TB-BMC net gain in all subjects (β = 0.11; P = 0.015). In females at peri-adolescence or early adulthood with adequate calcium intake (>1000 mg/d), protein intake positively predicted TB-BMC, TB-BMC net gain, and TB-BMD (P < 0.05). Our results indicate that when calcium intake is adequate, protein intake has a beneficial effect on the bone mass of young adult females. Protein, in the absence of sufficient calcium, does not confer as much benefit to bone.

Does protein intake alter the precursors for synthesis of lactose and non‐essential amino acids by the mammary glands of lactating mice?

The aims were to: 1) develop a [U-13C]glucose tracer approach to establish the pathways of and substrates used for milk lactose and casein synthesis in the mouse mammary gland and 2) determine the influence of protein intake on this partition and use for milk synthesis. In Study 1, we determined the time-course to reach isotopic plateau in milk lactose and casein during the feeding of [U-13C]glucose. Four mid-lactation mice (C57/BL) were fed a standard diet with 10% of dextrose replaced by [U-13C]glucose for 5 d with milk collected after 1, 3 and 5 d of tracer feeding. 13C-Isotopic and isotopomer plateau was attained in milk lactose (glucose, galactose) and all non-essential amino acids (NEAA) in milk casein by 3 d. In Study 2, six paired (intake and pups equal) sets of lactating mice were fed either a normal (N, 20%) or low (L, 10%) protein diet from d 2 to 15 of lactation. The last 3 d, [U-13C]glucose replaced 10% of diet dextrose. On d 15, milk and mammary tissue were collected. In Study 1 and 2, 13C-mass isotopomer distribution (MID) in lactose-derived glucose and galactose did not differ, indicating common mammary metabolic pools. In Study 2, L mothers and pups weighed less (P<0.01). In addition, 13C-MID in blood vs. casein indicated significant mammary synthesis of glutamate (N:51%, L:50%), alanine (N:32%, L:29%), and serine (N:18%, L:37%, P<0.05). This NEAA synthesis suggests additional requirements for glucose and(or) EAA.

Mediterranean Diet and the Metabolic Syndrome: The Role of Protein

The traditional Mediterranean diet is suggested to be associated with the lowest prevalence of metabolic syndrome, coronary heart disease, and type 2 diabetes and is suggested to be the optimal diet for the general public. This diet is considered to be a moderate protein diet. It has been suggested that the Mediterranean diets protein content is partly responsible for the beneficial effects on health, but the level of protein intake to induce a cardioprotective effect is not yet well known. Nevertheless, there are current studies that support the hypothesis that high protein intake, particularly of plant origin, may have beneficial health effects, which provides some insight on the role of protein in modulating cardiovascular disease risk factors. Therefore, in this work current information about the role of the adoption of the traditional Mediterranean diet on the prevalence of Metabolic Syndrome as a risk factor for coronary heart disease is reviewed. Also special attention is given on the influence of protein intake in relation to the incidence of this syndrome.

Relationship between Zinc Parameters and Either Body Weight Gain, Protein Intake or Survival Time in Zinc-Deficient Rats

This study was undertaken to examine the relationships between zinc parameters (serum alkaline phosphatase activity, and zinc concentration in serum and femur) and either body weight gain, protein intake or survival time in zinc deficient rats. Demineralized soy protein (DP) and alkali-treated soy protein (AP) were used as dietary protein sources in order to make zinc deficient diets (< 0.5 mg zinc/kg diet). The same diets (DP and AP diets) supplemented with lysine or cystine were also given freely to rats. Moreover, in other experiments, the above relationships were examined. During the early stages, a significant negative correlation between body weight gain and survival time in zinc-deficient rats was demonstrated. The significant negative correlation coefficient between protein intake and survival time increased gradually, and the maximum value of this correlation coefficient was higher than that between body weight gain and survival time. The significant correlations between protein intake and femur zinc concentration were recognized throughout the longer periods. These results show that the number of zinc-deficient rats which survive decreases as protein intake increases throughout the feeding period, that the influence of protein intake is greater than that of body weight in early stages, and that the zinc requirements of rats rise with the increase in protein intake.

Fasting vs nonfasting plasma homocysteine concentrations for diagnosis of hyperhomocysteinemia.

Hyperhomocysteinemia, a risk factor for cardiovascular and thrombotic disease, pregnancy complications, and cognitive disorders, is defined as a fasting plasma total Hcy (tHcy) above a chosen cutoff value (1)(2). Reducing both the analytical and biological variation may add to the diagnostic value of any test. tHcy analytical variation (CVa) is method-dependent and ranges from 2.7% to 4.9% for fluorescence polarization immunoassays and from 2.5% to 14% for HPLC assays (3). The reported biological variations for tHcy under fasting or otherwise standardized conditions include 20–34% interindividual variation (CVg) and 7–11% (with a single extreme of 15–17%) intraindividual variation (CVi) (4)(5)(6)(7)(8)(9). Because of the short-term influence of meals, e.g., protein, on CVi (10), it is generally recommended that blood samples be collected under fasting or otherwise meal-standardized conditions. The influence of protein intake on between-day CVi is, however, unknown. The necessity for fasting has been questioned because fasting and nonfasting tHcy concentrations and reference values, as well as fasting and postprandial short-term CVi and CVg values, are similar (11)(12). We investigated whether tHcy concentrations and variations under nonfasting conditions differ from those under fasting conditions. For this we calculated tHcy biological variation from samples taken at different clock times during a single day and during 3 weeks. We studied 16 apparently healthy individuals [8 men and 8 women; median (range) age, 44 (25–58) years]. Our study design is illustrated in Fig. 1A⇓ . Six blood samples were taken from all participants on Monday of week 1. A standardized breakfast (0815 in the morning) and lunch (1215) and a dinner (1730–1800) of unrestricted composition and quantity were provided during the day. Participants documented food and beverage intake on Monday and …

Calculated nitrogen balance in hemodialysis patients: Influence of protein intake

Optimal nutrient intake is important in the maintenance of a positive nitrogen balance in hemodialysis (HD) patients. The objectives of this study were (1) to assess the influence of two levels of protein intakes on nitrogen balance in stable adult HD patients, and (2) to identify a minimum level of protein intake that would result in a negative nitrogen balance, so that preliminary recommendations may be made in Indian patients on maintenance HD (MHD). Stable, adult, nondiabetic MHD patients were recruited after informed consent into a cross over trial with a high-protein (HP) diet [1.2 g/kg ideal body weight (IBW)/day), followed by a low-protein (LP) diet (0.6 g/kg IBW/day] after appropriate periods of equilibration; for both diets, 50% of protein was of high biological value, and calorie intake was 35 kCal/kg IBW/day. Duplicate meals and residues were weighed, homogenized, and stored at -20 degrees C for analysis of dietary N by the Kjeldahl method, used to check the consistency of the N content of the diet supplied. Pre- and post- (30-minute equilibrated) blood urea samples were drawn, and details of weights and other HD parameters were recorded. Interdialytic urine collections for urea were obtained. N input came from dietary protein calculated as 16% of the weight of biological protein; N output was calculated using blood-side urea measurements and urinary urea excretion and was the sum of urea N (UN) and nonurea N (NUN) losses (assumed to be equal to 0.031 g N/kg/day). Fifteen patients were recruited. Twelve patients completed both limbs of the study. The mean age was 30.3 +/- 12.7 years. The body mass index was 18.9 +/- 2.4. Serum albumin was 3.8 +/- 0.35 g/dL, and Kt/V (equilibrated) was 1.17 +/- 0.3 g/dL. Protein consumed was 1.06 +/- 0.18 g/kg IBW/day in the HP limb versus 0.61 +/- 0.1 g/kg IBW/day in the LP limb (P = 0.000). Energy intake was 33 +/- 6.5 vs. 32.8 +/- 6. 7 kCal/kg IBW/day, respectively (P = 0.8). The normalized protein N appearance (nPNA) was 0.88 +/- 0.2 g/kg/day in the HP limb versus 0. 78 +/- 0.2 g/kg/day in the LP limb (P = 0.02). Dietary N was 73.5 +/- 15.3 g in the HP week and 42.5 +/- 7.5 g in the LP week (P = 0. 000). The difference between this and the sum of (UN + NUN) losses over the week was 29 +/- 13.2 g versus 1.2 +/- 8.1 g, respectively (P = 0.001), showing a strong, uniformly positive nitrogen balance with HP diet and neutral to negative nitrogen balance with LP diet. The ratio of dietary protein intake (DPI) to nPNA was significantly lower (anabolic) in the HP limb (0.7 +/- 0.2 vs. 1.12 +/- 0.3, P = 0. 000). On a scatter plot of nPNA to DPI, a catabolic relationship was demonstrated below a DPI of 0.75 g/kg/day (95% CI, 0.65 to 0.85 g/kg/day). A DPI of approximately 1.1 g/kg/day produces a positive nitrogen balance and 0.6 g/kg/day a neutral to negative nitrogen balance, demonstrating protein anabolism as a function of protein intake. It is suggested that a protein intake of 0.85 g/kg/day should be considered unsafe. These conclusions apply in stable nondiabetic adult HD patients in the setting of adequate dialysis and adequate calorie intake.

Metabolic Demands for Amino Acids and the Human Dietary Requirement: Revisited

In 1988, Millward and Rivers reappraised existing metabolic models for amino acid requirements. The metabolic demand for amino acids was reviewed in relation to both obligatory metabolic consumption and adaptive pathways of amino acid oxidation. The obligatory demand pattern was deemed unknowable from first principles except that the level of one amino acid would be similar to its concentration in an amount of tissue protein equivalent to the obligatory nitrogen loss. The adaptive demand pattern was predicted to vary in relation to the amount and the periodicity of food protein intake that influenced the amplitude of the diurnal cycle of gains and losses. A regulatory influence of protein intake on anabolism, the anabolic drive, was identified in animal studies; benefit appeared to derive from intakes in excess of the minimum for balance, which could facilitate definition of an optimal requirement. The inherent and design-related limitations of both nitrogen and stable isotope balance studies of requirement were recognized as a major problem in identifying secure values for indispensable amino acid requirements. A decade of research of increasing methodological sophistication has generated much new information, confirming the adaptive diurnal model of balance regulation and allowing development of the anabolic drive into a general protein-stat theory for coordinated control of growth and maintenance of the lean body mass. However, notwithstanding several new estimates of amino acid requirement values, definition of a widely accepted human amino acid requirement pattern remains unresolved. Although a case can be made for an adjusted 1985 FAO adult requirement pattern being a reasonable estimate of the obligatory indispensable amino acid requirements for human maintenance, the problems posed by adaptation, methodological inadequacies and lack of independent measures of adequacy mean that assessment of the adequacy of the human diet to satisfy amino acid needs remains inherently difficult.

Influence of protein intake on whole body and splanchnic leucine kinetics in humans.

The influence of the protein content of the meal on protein turnover was investigated in the splanchnic bed and in the remaining parts of the body in humans. Two groups of five subjects consumed every 20 min a liquid formula providing either 1.5 g protein x kg(-1) x day(-1) (P) or no protein (PF). L-[1-(13)C]leucine and L-[5,5,5-(2)H3]leucine were administered by vein and gut, respectively. An open two-pool model was developed to calculate leucine kinetics in both compartments, with the assumption that the enrichment of the tracers incorporated into very low density lipoprotein apolipoprotein B100 at isotopic steady state could reflect the leucine labeling in the splanchnic region. Nonsplanchnic uptake and release of leucine were not significantly different in the two groups. Within the splanchnic area, leucine uptake was 2.1 times higher in the P than in the PF group (P < 0.01), whereas leucine release was reduced but not significantly (-19%) in the P group compared with the PF group. Moreover, data derived from this model showed that protein intake induced an increase in whole body protein synthesis and no change in whole body protein breakdown. Albumin synthesis, as well as its contribution to whole body protein synthesis, was significantly enhanced by protein intake.

The influence of protein intake on water balance, flow rate and apparent digestibilty of nutrients at the distal ileum in growing pigs

Two experiments were carried out with castrated male pigs to determine the effect of protein intake on water balance and N output via urine. In Expt. 1, the appearance of N and water in urine was determined with the balance technique at mean live weights of 45.5 and 68.5 kg when pigs were fed different amounts of dietary protein. In Expt. 2, the ileal digestibility of amino acids in two different diets (a semi-synthetic and a barley-based diet) was measured in relation to water intake and N-output in urine and faeces. A higher daily protein intake increased water consumption by pigs ( P < 0.05) in Expts. 1 and 2, with a corresponding higher volume of daily urine excretion (Expt. 1 ). In addition, higher concentrations of urinary urea- and ammonia-N were observed. Furthermore, a high protein level in the diet resulted in a significantly higher flow rate of digesta at the distal ileum compared to the low protein diet. Ileal digesta contained higher amounts of nutrients (water and amino acids) and higher concentrations of urea and ammonia originated from dietary protein. The apparent digestibility coefficients of amino acids at the distal ileum and apparent faecal digestibility of nutrients were comparable with literature values. Deux expériences ont été réalisées sur des porcs mâles castrés afin de déterminer l'influence du niveau de consommation de protéines sur le bilan hydrique et 1 ⨴ crétion urinaire d'N. Dans l'expérience 1, l'apparition d'N et d'eau dans l'urine était déterminée par la technique des bilans aux poids moyens de 45,5 et 68,5 kg en fonction de l'apport de protéines alimentaires. Dans l'expérience 2, la digestibilité iléale des acides aminés de deux régimes différent (un régime semi-synthétique et un régime à base d'orge) était mesurée en relation avec la consommation d'eau et l'excrétion d'N dans l'urine et les fèces. Une consommation journalière plus élevée de protéines augmentait la consommation d'eau des porcs ( P < 0.05) dans les expériences 1 et 2, l'excrétion quotidienne correspondante d'urine étant plus importante (expérience 1). De plus, des concentrations supérieures d'N sous forme d'urée et d'ammoniauq étaient observées dans l'urine. En comparaison du faible taux de protéines, une teneur élevée en protéines du régime augmentait également la vitesse du transit digestif de façon sigificative. Le digesta iléal contenait de plus grandes quantités de nutriments (eau et acides aminés) et présentait des teneurs supérieures en urée et en ammoniaque provenant des protéines alimentaires. Les coefficients de digestibilité apparente des acides aminés au niveau de l'iléon distal et la digestibilité fécale apparente des nutriments étaient comparables aux valeurs de la bibliographie. In zwei Bilanzversuchen mit männlichen, kastrierten Schweinen wurde in Expt. 1 bei einer Lebendmasse von 45,5 und 68,5 kg der Einfluβ des Rohproteingehaltes der Diät auf die Wasserbilanz sowie die Höhe der N-Exkretion über den Harn gemessen. Während in Expt. 2 — hier kamen eine semi-synthetische sowie eine Gerstenmonodiät zum Einsatz — die scheinbare ileale Verdaulichkeit der Aminosäuren bestimmt wurde. Zudem wurde die Wasseraufnahme pro Tier und Tag sowie die N -Exkretion über Harn und Kot erfaβt. Die höhere Proteinaufnahme führte in beiden Experimenten zu einem höheren Wasserkonsum der Tiere ( P < 0.005), womit eine erhöhte tägliche Harnexkretion einherging. Darüber hinaus wurde eine höhere Harnstoff-N- und NH 3 -N-Exkretion beobachtet. Fernerhin führt ein höherer Proteinlevel in der Diät zu signifikant höheren Digestafluβraten am distalen Ileum. Daneben enthät die Ileumdigesta höhere Nährstoffmengen (Wasser und Aminosäuren) und weist höhere Harnstoff- und NH 3 -N-Mengen auf.

The Influence of Protein Intake on Vitamin B-6 Metabolism Differs in Young and Elderly Humans

AbstractVitamin B-6 metabolism was studied as a function of dietary protein intake. Subjects were 29 young adults (29 ± 1 y old) and 26 elderly adults (70 ± 1 y old) who consumed standardized diets containing 12% (Diet A) and 21% (Diet B) of total energy as protein for 3 wk each, according to a randomized crossover design. Vitamin B-6 intake for young and elderly subjects was 1.52 ± 0.08 mg/d (21.74 ± 0.45 µg/g protein) and 1.47 ± 0.05 mg/d (23.81 ± 0.08 µg/g protein), respectively, during consumption of Diet A and 1.79 ± 0.07 mg/d (14.49 ± 0.11 µg/g protein) and 1.73 ± 0.05 mg/d (16.24 ± 0.06 µg/g protein) during consumption of Diet B. Plasma pyridoxal phosphate (PLP), pyridoxal and total vitamin B-6 concentrations were significantly lower in the elderly subjects compared with the young adult subjects during both diet periods. In the elderly subjects, PLP was significantly higher during Diet B consumption (Diet A: 27 ± 3 nmol/L; Diet B: 32 ± 3 nmol/L), whereas the level of protein intake had no significant effect on plasma PLP in the young adults (Diet A: 47 ± 6 nmol/L; Diet B: 45 ± 5 nmol/L). Plasma pyridoxal and plasma total vitamin B-6 concentrations were not influenced by the amount of protein intake in young and elderly subjects. Relative urinary pyridoxic acid excretion did not differ significantly between diet periods in the elderly subjects (Diet A: 37 ± 3%; Diet B: 43 ± 3%), whereas pyridoxic acid excretion was lower in young adults when Diet B was consumed (Diet A: 46 ± 3%; Diet B: 38 ± 2%; P < 0.001). The results of this study suggest an age-dependent difference in the protein intake-related vitamin B-6 needs, whereby elderly subjects apparently need less vitamin B-6 at a higher protein intake as compared with young adults

Calciuria and aminoaciduria in very low birth weight infants fed a high-mineral premature formula with varying levels of protein

To assess the influence of protein intake on renal excretion of calcium and amino acids and on bone mineralization in preterm infants, we randomly selected within weight group strata 27 infants who weighed <1500 gm at birth (nine per group) to be fed a high-mineral (calcium, 940 mg/L; phosphorus, 470 mg/L) premature formula with one of the following protein contents: formula A, 3.0 gm/100 kcal; formula B, 2.7 gm/100 kcal; and formula C, 2.2 gm/100 kcal. Mean (±SD) daily weight gain was greater in infants receiving the higher protein intakes for the first 30 days (formula A, 24.8 ± 5.1 gm; formula B, 20.5 ± 3.8 gm; formula C, 16.2 ± 5.9 gm [analysis of variance: p < 0.01; C < A, p <0.05]). Bone mineral content did not differ at any time point, and all groups had a high prevalence of generalized aminoaciduria (4 weeks: formula A, 56%; formula B, 71%; formula C, 75%). Urinary calcium corrected for creatinine (in milligrams per milligram) increased as protein content decreased (2 weeks: formula A, 0.16 ± 0.10; formula B, 0.20 ± 0.13; formula C, 0.44 ± 0.33 [C > A, C > B, p < 0.05]; 4 weeks: formula A, 0.23 ± 0.15; formula B, 0.34 ± 0.17; formula C, 0.49 ± 0.22 [C > A, p < 0.01]). We conclude that the high mineral content and other components of premature formulas result in a higher growth rate and may increase protein requirements. Failure to meet protein requirements may result in underutilization of absorbed calcium and increased renal excretion of calcium. In preterm infants, higher protein intake probably supports rather than jeopardizes bone mineral accretion, and reduces rather then increases calciuria. (J PEDIATR 1994;125:288-94)

Nitrogen homeostasis in man: influence of protein intake on the amplitude of diurnal cycling of body nitrogen.

1. The diurnal nature of nitrogen (N) homoeostasis was investigated in adults fed increasing protein intakes. N balance was estimated during a 48 h period of consecutive 12 h periods of feeding hourly meals and fasting, after 12 days of adaptation to diets containing 0.36 +/- 0.01, 0.77 +/- 0.03, 1.59 +/- 0.08 and 2.31 +/- 0.65 g of protein day-1 kg-1. N losses were determined from measured urinary N excretion corrected for changes in the body urea pool, and estimated faecal and miscellaneous losses. [13C]Leucine and [2H5]phenylalanine balances were measured during a primed, continuous infusion of the two amino acids during the fasting and feeding phase on the second day. 2. Increasing fasting N losses were observed (47 +/- 7, 60 +/- 6, 95 +/- 15 and 140 +/- 36 mg day-1 kg-1) on the four intakes, with corresponding increasing fed gains of 8.2 +/- 3.9, 40.2 +/- 7.1, 112 +/- 24 and 180 +/- 56 mg day-1 kg-1. 3. Increasing fed-state amino acid gains with increasing protein intake were observed with both [13C]leucine and [2H5]phenylalanine, whereas increasing fasting amino acid losses were confirmed with [13C]leucine. 4. The N equivalent of the leucine oxidation rate was mostly in the range of 10-50% lower than expected from the N excretion rates. This may reflect the timing of the amino acid balance measurements and non-uniform rates of gain and loss throughout the diurnal cycle. 5. We conclude on the basis of both N and amino acid balances that the amplitude of the diurnal cycling of body protein N in human adults increases with increasing dietary protein intake. Thus one component of the protein requirement for N balance reflects a demand for repletion of fasting losses which increases with increasing habitual protein intake.

Influence of protein intake associated with coconut or salmon oils on lipid fatty acid composition of liver and VLDL in the rat

Influence of protein intake associated with coconut or salmon oils on lipid fatty acid composition of liver and VLDL in the rat