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PubMed2004

Lowering dietary protein to U.S. Recommended dietary allowance levels reduces urinary calcium excretion and bone resorption in young women.

High-protein diets increase calciuria. No previous studies have examined the ad libitum U.S. diet's effect on calciuria or bone resorption.Thirty-nine healthy, premenopausal women consuming ad libitum diets [mean, 1.1 g/kg protein, 819 mg (20.5 mmol) Ca, 1152 mg (37 mmol) P, 129 mmol Na] were switched to isocaloric diets containing the U.S. recommended dietary allowance (RDA) of protein (0.8 g/kg) and similar amounts of calcium, phosphorus, and sodium. Bone resorption and related endpoints were assessed before and 1 wk after the switch. As dietary protein changed from ad libitum to RDA levels, mean urine nitrogen decreased 26% (2.4 g/d; P < 0.001) and mean blood urea nitrogen decreased 15% (1.9 mg/dl; P < 0.001). Mean urine pH increased from 6.3 to 6.8 (P < 0.001), and net renal acid excretion (NRAE = urine ammonium plus titratable acids minus bicarbonate) decreased 68% (21.4 mEq/d; P < 0.001). Mean urinary calcium decreased 32% [42 mg (1 mmol)/d; P < 0.001], and bone resorption urine N-telopeptides) decreased 17% (74 micromol bovine collagen equivalents/d; P < 0.001). Mean serum calcium, PTH, and 1,25 dihydroxy vitamin D remained unchanged. In this 2-wk study, decreasing dietary protein from ad libitum to RDA levels decreased NRAE, calciuria and estimates of bone resorption, suggesting that decreased U.S. protein consumption might reduce bone loss. Inasmuch as other dietary modifications, such as increasing vegetable and fruit intake, can result in sustained reductions in NRAE without reducing protein intake, the advisability of reducing protein intake for skeletal protection from acid attack requires further investigation.

Acids↗
PubMed1985

Physiological and morphological responses of the rat kidney to reduced dietary protein.

Renal physiological and morphological adjustments to a reduced protein diet were studied in young Munich-Wistar rats. Two groups of animals were used for the correlative physiological-morphological studies: normal protein (NP, 24% dietary protein) rats and reduced protein (LP, 8% dietary protein) rats. Both groups were fed their respective diets for 4-5 wk and had free access to drinking water. Physiological measurements of GFR and urea clearance were made on five animals from each group. These data showed that the changes in renal function specifically and almost exclusively affected the handling of urea. There was no difference in GFR between the NP and LP rats. Urea clearance was substantially reduced in LP rats. Morphological analyses were made on perfusion-fixed kidneys of five animals from each group. Selected slices were examined and photographed by light and electron microscopy. These data showed no difference in size and number of elements within the vascular bundles but showed significantly smaller lumina of the thin limbs of the short-looped nephrons and a significant thinning of the wall of the thin descending limbs of the long-looped nephrons. These morphological changes may in part be responsible for the observed physiological adjustments to a reduced protein diet. An additional group of rats (6 NP and 5 LP, all dehydrated) were analyzed for distribution of solutes within the inner medulla. The data showed that the concentration of urea, but not that of Na+, was reduced at the papillary tip in LP rats.

Adaptation, Physiological↗
PubMed1990

[Study on the pathogenetic factors of the progression of renal insufficiency, with special reference to the effects of dietary protein intake].

The effects of dietary protein intake on the progression of renal insufficiency were studied in daunomycin (DMC) induced nephrotic rats (DMC rats) and also patients with chronic renal diseases. In the first study, the author examined which treatment among enalapril (E) and indomethacin (I) and dietary protein restriction was the most effective to prevent proteinuria and glomerulosclerosis, and then the effect of dietary protein restriction on renal content of malondialdehyde (MDA) and superoxide dismutase (SOD) in DMC rats. These rats were divided into four groups as follows: group PL and group PH were isocaloric diets containing either 5% or 24% protein, respectively and group PE and PI were given orally E (100 mg/l drinking water) or I (50 mg/l drinking water) with diets of 24% protein, respectively. In group PL, urinary protein excretion (U-Protein) rates and renal damage index were significantly lower than those in other three groups. In group PE, renal damage index was significantly improved although U-Protein showed no reduction in contrast with these in group PH. Renal MDA in group PL was lower than that in group PH was significantly lower than that in group PL. In this study dietary protein restriction was the most effective treatment for the prevention of progressive renal insufficiency. In the second study, patients with chronic renal diseases were divided into two groups according to their Ccr: group I; Ccr greater than or equal to 60 ml/min, group II; Ccr less than 60 ml/min. All patients orally received diets of high protein (1.4 g/kgBW) and subsequently of low protein (0.7 g/kgBW). Ccr, U-Protein, serum MDA and serum SOD were estimated at the end of each dietary period. In group I, Ccr was significantly lower on low protein diet than that on high protein diet, although these were no significant changes in Ccr in group II. The low protein diet caused a significant decrease in U-Protein in both groups. Serum MDA in group I was significantly lower on low protein diet than that on high protein diet, but not in group II. Serum SOD activity showed no changes. It is suggested that dietary protein restriction might reduce oxidant stress to the kidney, in addition to renal hemodynamic changes induced by prostaglandin and renin-angiotensin system, resulting in the prevent of progress of renal insufficiency.

Adolescent↗
PubMed1992

Suppression of muscle protein turnover and amino acid degradation by dietary protein deficiency.

To define the adaptations that conserve amino acids and muscle protein when dietary protein intake is inadequate, rats (60-70 g final wt) were fed a normal or protein-deficient (PD) diet (18 or 1% lactalbumin), and their muscles were studied in vitro. After 7 days on the PD diet, both protein degradation and synthesis fell 30-40% in skeletal muscles and atria. This fall in proteolysis did not result from reduced amino acid supply to the muscle and preceded any clear decrease in plasma amino acids. Oxidation of branched-chain amino acids, glutamine and alanine synthesis, and uptake of alpha-aminoisobutyrate also fell by 30-50% in muscles and adipose tissue of PD rats. After 1 day on the PD diet, muscle protein synthesis and amino acid uptake decreased by 25-40%, and after 3 days proteolysis and leucine oxidation fell 30-45%. Upon refeeding with the normal diet, protein synthesis also rose more rapidly (+30% by 1 day) than proteolysis, which increased significantly after 3 days (+60%). These different time courses suggest distinct endocrine signals for these responses. The high rate of protein synthesis and low rate of proteolysis during the first 3 days of refeeding a normal diet to PD rats contributes to the rapid weight gain ("catch-up growth") of such animals.

Alanine↗
PubMedDate not supplied

mRNA expression of renal urea transporters in normal and Brattleboro rats: effect of dietary protein intake.

Differences in dietary protein level induce differences in fractional excretion of urea, in arginine vasopressin (AVP) plasma level, and in urine concentrating activity (in which intervene the renal urea transporters (UT)). The abundance of mRNA for UT-A1 (of the inner medullary collecting duct, IMCD) UT-A2 (of the descending thin limb) and UT-B1 (of descending vasa recta) was determined by Northern analysis of total RNA extracted from medullary subregions of Sprague-Dawley rats fed for 1 week, a low, normal, or high protein diet. The implication of AVP was then examined by studying AVP-deprived (Brattleboro) rats. Our results show that none of these transporters is affected by the level of protein intake, except UT-A1 that is reduced in terminal IMCD by low protein diet in the absence of AVP (Brattleboro rats). These data suggest that (1) the previously reported effect of kidney medulla hypertonicity on UT-A2 and UT-B1 mRNA expression is somehow obliterated by protein intake deficiency or excess, and (2) AVP influences the mRNA abundance of the UT-A1 of the terminal IMCD during protein deficiency.

Animals↗
PubMed1996

Whole-body protein turnover in the fed state is reduced in response to dietary protein restriction in lactating women.

We examined the adaptive responses of body protein metabolism in the fed state to dietary protein restriction in lactating women to determine whether rates of body protein degradation and synthesis were lower than those of nonlactating women. Thirteen healthy women (five lactating, four nonlactating postpartum, four nulliparous) aged 28-32 y were given protein intakes of 1.5, 0.4, and 1.0 g.kg-1.d-1 over three consecutive 3-d periods, respectively. At the end of each period, while in the fed state, subjects received orally a single bolus dose of [1-13C]leucine. A 24-h urine collection was obtained simultaneously. Whole-body protein metabolism was characterized by using the end product model based on nitrogen excretion and leucine catabolism. Nitrogen flux and rates of protein degradation and synthesis in the fed state were significantly lower at a dietary protein intake of 1.0 g.kg-1.d-1 in lactating women than in their nonlactating postpartum counterparts. Net protein retention in the fed state was significantly higher at a dietary protein intake of 1.0 g.kg-1.d-1 in lactating than in nonlactatating postpartum and nulliparous women because of the relatively greater reduction in protein degradation than in protein synthesis. These studies suggest that lactating women rapidly adapt to dietary protein restriction by down-regulating protein metabolism, and that 13C-labeled amino acid tracers in combination with urinary nitrogen excretion serve as useful metabolic markers for the adequacy of the dietary protein content of lactating women.

Adult↗
PubMed1992

[Blood glucose, insulin, GH, and amino acids in rats receiving 3 levels of dietary proteins].

The effect of dietary protein content on the variations in plasma insulin, GH, glucose and both gluconeogenic and branched-chain amino acids (BCAA) levels, was studied in Wistar rats. For 21 days animals consumed ad libitum diets containing 4% (LP group) 10% (MP group) or 20% (HP group) protein. Body weight gain and plasma concentrations of the glucose, insulin and both the insulin/glucose (I/G) and insulin/GH (I/GH) ratios varied directly with the protein content of the diet. In contrast the relationships between dietary protein content and GH levels, were inverse. These results indicate that an increase of energy yielding nutrients availability and an decrease of tissue sensitivity to insulin was produced as the protein content of the diet was increased. The increase of plasma aspartate, serine, histidine and alanine levels on LP group suggest a low gluconeogenic process, and the higher rate of BCAA on HP group against to MP and LP groups can be related to a lower tissue uptake. Both effects can be mediated by the tissular sensitivity to insulin.

Amino Acids↗
PubMed1990

Dietary protein and nitrogen balance in lactating and nonlactating women.

Adaptive responses of body protein metabolism to dietary protein intakes of 1.0 g.kg body wt-1.d-1 were determined by nitrogen balance and urinary 3-methylhistidine excretion in lactating and nonlactating women. Despite higher energy intakes (p less than 0.04), lactating women had lower nitrogen balances compared with nonlactating postpartum and nulliparous women (p less than 0.001). Nitrogen losses in milk did not account entirely for these differences. Nitrogen balance showed linear (p less than 0.04) and quadratic (p less than 0.03) trends over time postpartum among the lactating women. Urinary 3-methylhistidine excretion also was reduced (p less than 0.05) in lactating compared with nonlactating women. These observations suggest that protein intakes of 1.0 g.kg body wt-1.d-1 in lactating women are associated with adaptive responses that promote the conservation of skeletal muscle protein stores and that currently recommended dietary protein allowances may be insufficient to meet the nutritional needs of well-nourished lactating women.

Adaptation, Physiological↗
PubMed1979

Diurnal variations in plasma concentrations of tryptophan, tryosine, and other neutral amino acids: effect of dietary protein intake.

The effect of dietary protein content on the diurnal variations in plasma neutral amino acid levels was studied in normal human subjects. For three consecutive 5-day periods, subjects consumed diets containing 0, 75, or 150 g of egg protein per day. Blood samples were drawn at 4-hr intervals on the 4th and 5th days of each period. Consumption of the protein-free diet caused plasma concentrations of all amino acids studied to fall in the late morning and afternoon, while the 150-g protein diet elicited increases in these levels during the daytime. Ingestion of the diet containing 75 g of egg protein tended to diminish the amplitudes of the daily rhythms in plasma amino acid levels, but most amino acids still exhibited small but significant elevations late in the evening. At all times of day, plasma concentrations of the large neutral amino acids studied (i.e., aromatic and branched-chain amino acids, and methionine) varied directly with the protein content of the diet. In contrast, the relationships between dietary protein content and the plasma concentrations of glycine and alanine, two small neutral amino acids, were inverse. The ratios of plasma tryptophan, tyrosine, and phenylalanine levels to the sum of the concentrations of other large neutral amino acids tended to fall as the protein content of the diet was increased. The corresponding ratio for valine increased as protein was added to the diet, while the leucine and isoleucine ratios were not correlated with dietary protein content. Since diet-induced changes in plasma trypotphan and tyrosine ratios in animals are known to cause parallel alterations in brain tryptophan and tyrosine levels, and thus in the rates of brain serotonin and catecholamine synthesis, our data suggest that ingestion of carbohydrates and protein may also normally affected brain monoamine synthesis in humans.

Adult↗
PubMed1998

Enhanced preference for a protein-containing diet in response to dietary protein restriction.

Rats were maintained for 10 days on either a protein-free or a nutritionally complete maintenance diet, and they were also given access to protein-rich and carbohydrate-rich test diets during separate daily 2-h test sessions. In Experiment 1, rats maintained on the protein-free diet gradually and selectively increased their intake of the protein test diet, and eventually derived 16% of their daily energy intake from the protein test diet. Rats maintained on a nutritionally complete diet ate similar amounts of the two test diets even when their total caloric intake was matched to that of rats maintained on the protein-free diet. In Experiment 2, rats that developed a preference for the protein test diet while maintained on a protein-free diet were given Purina Chow for 25 days to allow them to recover from their protein deficiency. When these rats were later returned to the protein-free diet for 10 days, their preference for the protein test diet was immediate and sustained. However, if they were maintained on the nutritionally complete diet after the 25-day recovery period, they initially preferred the protein test diet, but this preference diminished over days. Results of these studies are consistent with other findings showing that rats can learn to compensate for macronutrient deficiencies by using oral-sensory cues. In particular, the rats' diet selection was consistent with their having learned a preference for the cues paired with dietary protein.

Animal Nutritional Physiological Phenomena↗
PubMed2000

Effects of age on the feeding response to moderately low dietary protein in rats.

Moderately low levels of dietary protein are associated with increased food intake and body fat. We propose that the generation of this feeding signal is dependent on the level of dietary protein relative to the protein requirement of the animal, that is, that protein-dependent feeding is maximized when the level of dietary protein is around the animal's protein requirement. One of the factors that affects an animal's protein requirement is age. We predict that young, growing animals are more responsive to a moderately low level of dietary protein than are mature animals. The feeding response to moderately low dietary protein (10% casein) was determined in young ( approximately 190 g) and more mature ( approximately 340 g) Sprague-Dawley rats for 12 days. As an index of amino acid deamination, serum urea nitrogen concentrations were determined, as was the in vitro release of neuropeptide Y (NPY) from hypothalamic tissue containing the paraventricular nucleus. Young rats were more responsive to the feeding effects of moderately low dietary protein than mature animals. In young rats, cumulative food intake was inversely correlated with serum urea nitrogen concentration. No correlation was found in mature animals. Although the amount of NPY remaining in hypothalamic tissue after incubation was significantly greater (p = 0.04) in young rats fed 10% casein as compared with rats fed the standard 20% casein diet, no dietary difference in K(+)-stimulated NPY release was observed. We hypothesize that the signal for low-protein-induced hyperphagia is a reduction in a compound whose production is coupled to the level of amino acid deamination in the brain.

Aging↗
PubMed1984

Diurnal variations in plasma concentrations of basic and neutral amino acids and in red cell concentrations of aspartate and glutamate: effects of dietary protein intake.

The effects of dietary protein content on diurnal variations in plasma concentrations of neutral and basic amino acids, and on red blood cell levels of acidic amino acids, were studied in seven normal humans. The subjects consumed, on three consecutive 3-day periods, diets containing 0, 75, or 150 g of egg protein per day; blood was collected at 4-h intervals on the 2nd and 3rd days of each diet. For each of the large neutral amino acids (LNAA; isoleucine, leucine, tyrosine, phenylalanine, methionine, valine, and tryptophan) significant correlations were observed between its plasma levels and the protein content of the diet; highest levels were noted after consumption of the 150-g protein diet, and lowest values after the O-g protein diet. For each LNAA, except tryptophan, "fed" values (ie, those at 3 PM and 7 PM) were decreased relative to "fasting" values (those at 3 AM and 7 AM) after consumption of the O-g protein-free diet, but increased after consumption of the 150-g protein diet. Threonine, serine, and proline behaved like the LNAA: in contrast, glycine and alanine rose after protein-free meals and fell with the high-protein diet. The basic amino acids, lysine, arginine, and histidine tended to respond like the LNAA to variations in dietary protein content. Red blood cell concentrations of glutamate tended to vary inversely with the protein content of the diet, while no relationship was noted between red blood cell aspartate and dietary protein content. Food-induced changes in plasma LNAA have been found to affect brain levels of amino acids that are neurotransmitter precursors, as well as the syntheses of the transmitters themselves.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

The effect of dietary protein and sulfur amino acids on hepatic glutathione concentration and glutathione-dependent enzyme activities in the rat.

Hepatic glutathione concentration and glutathione-dependent enzymes, glutathione S-transferase, glutathione peroxidase, and glutathione reductase, are important for protection against toxic compounds. Rats were fed diets containing 4, 7.5, 15, or 45% protein for 2 weeks. Glutathione and cysteine concentrations in rats fed the 4 and 7.5% protein diets were significantly lower (p less than 0.05) than in rats fed the 15 and 45% protein diets. Glutathione S-transferase activity increased with increasing dietary protein. Glutathione peroxidase activity was significantly lower (p less than 0.05) in rats fed 4 and 7.5% protein compared with rats fed 15 and 45% protein, whereas the activity of glutathione reductase was higher in rats fed 4 and 7.5% protein then in rats fed 15 or 45% protein. Dietary sulfur amino acids alone could account for the increase in glutathione concentration resulting from the increase in dietary protein from 7.5 to 15%. The limited availability of glutathione in animals fed the low protein diets could reduce the potential for detoxification of xenobiotics.

Amino Acids, Sulfur↗