Biomedical subjects

A Taveroff

Publications and source records attributed to A Taveroff.

9 recordsLinked to original sources

PubMed1998

Dietary protein restriction alters glucose but not protein metabolism in non-insulin-dependent diabetes mellitus.

We determined whether a customary diet high or low in protein (1) influences postabsorptive amino acid catabolism, nitrogen (N) balance, and hepatic glucose output (HGO) in normal subjects or patients with non-insulin-dependent diabetes mellitus (NIDDM) or (2) alters blood glucose levels in NIDDM. Eight normal young adults and five obese middle-aged persons with NIDDM consumed low-protein (0.8 g/kg lean body mass [LBM]) or high-protein (3.0 g/kg LBM) diets at maintenance energy for consecutive 7-day periods. Fasting and average blood glucose and N balance were measured daily. The level of dietary protein had no effect on the basal plasma leucine rate of appearance (Ra) or urinary 3-methylhistidine excretion in either subject group. Basal leucine oxidation (and by inference, whole-body amino acid catabolism) was reduced on the low-protein diet but basal HGO was not, and although exogenous glucose effectively suppressed HGO, it did not reduce leucine oxidation with either diet. After adaptation to the low-protein diet, N balance in both the normal and NIDDM subjects was close to zero. The low-protein diet reduced the fasting and daily blood glucose of the diabetic subjects by approximately 2 mmol/L (P < .05). We conclude that physiologic variation in dietary protein does not affect basal whole-body protein turnover or HGO in either normal young adults or obese middle-aged NIDDM subjects. However, protein restriction to the level of the average daily requirement significantly reduces postabsorptive and average daily blood glucose concentrations in persons with NIDDM.

Adult↗

PubMed1997

Metabolic adaptation to protein restriction in insulin-dependent diabetes mellitus.

Eight normal subjects, four subjects with intensively treated insulin-dependent diabetes mellitus (IDDM), and six subjects with conventionally treated IDDM consumed a test meal of 0.5 g protein and 10 kcal per kg body weight, first while adapted to a conventional diet high in protein, and then again after 5 days of dietary protein restriction. Metabolic N balance (N consumed minus urea production) and net protein utilization were measured over the 9 h after consumption of the test meal, as was recovery in urea of 15N from a tracer dose of [15N]alanine included in each test meal. After the first test meal, N balance and net protein utilization were similar and close to zero for all groups. After the second test meal, N balance and net protein utilization became positive for all groups (P < 0.05) but significantly less so (P < 0.05) for the conventionally treated than for the normal and intensively treated diabetic subjects. 15N recovery in urea was reduced for all groups after the second test meal (P < 0.05) but probably less effectively (P < 0.09) for the conventionally treated diabetic subjects. Metabolic adaptation to protein restriction may be less effective than normal in conventionally treated IDDM.

Adaptation, Physiological↗

PubMed1997

Effects of leucine on whole body leucine, valine, and threonine metabolism in humans.

We tested whether expansion of the plasma leucine pool distorts leucine or valine tracer kinetics, causing errors in the derived values of whole body proteolysis. Seven normal adults received a 10-h primed-continuous tracer infusion of L-[5,5,5-2H3]leucine, L-[(1-13)C]valine, and L-[(1-13)C]threonine, during the final 7 h of which L-leucine was infused at a rate that more than tripled the plasma leucine concentration. Leucine, valine, and threonine rates of appearance were converted to a common value of whole body proteolysis on the basis of their concentrations in body proteins. The conversion of labeled leucine and valine to their corresponding branched-chain alpha-keto and alpha-hydroxy acids was also monitored. Before the unlabeled leucine infusion, postabsorptive whole body proteolysis was estimated similarly by the three tracers (approximately 180 mg protein.kg-1.h-1. The leucine infusion reduced proteolysis by an average of 21% (P < 0.006), as estimated by use of valine or threonine kinetics, and by 10% by use of leucine kinetics (P < 0.02). No delay in the conversion of valine to alpha-ketoisovalerate occurred during the leucine infusion. Thus all three tracers indicated similar postabsorptive rates of whole body proteolysis and a reduction of proteolysis during leucine administration, although the magnitude of the effect was underestimated with use of the leucine tracer.

Adult↗

PubMed1994

Are leucine turnover measurements valid in the intravenously fed state?

We tested whether the primary or reciprocal pool models for whole-body leucine kinetics accurately depict human adaptation to protein deficiency and repletion in the fed state by comparing model-derived leucine oxidation with urea appearance calculated from urinary urea excretion and changes in the body urea pool. Five normal men consumed a control diet providing maintenance energy and 80 g protein/d for 5 days; this was followed by 7 days of an isoenergetic protein-free diet, and finally by a return to the original control diet for 5 days. At the end of each dietary period, urea appearance and leucine oxidation were measured during a 4-hour intravenous infusion of crystalline amino acids providing a total N to leucine N ratio similar to that in mixed body proteins. Primary pool-derived fed-state leucine oxidation decreased after adaptation to protein deficiency and remained low during refeeding (18.6 +/- 1.2, 13.2 +/- 1.1, and 15.0 +/- 1.8 mumol.kg-1.h-1, respectively, P < .01), in agreement with the physiologic prediction. A similar pattern occurred with the reciprocal pool model (24.4 +/- 2.7, 17.3 +/- 2.0, and 20.3 +/- 2.7 mumol.kg-1.h-1, P < .01) as well as with urea N appearance (3.06 +/- 0.32, 2.34 +/- 0.24, and 2.38 +/- 0.26 mmol N.kg-1.4 h-1, P < .05). Despite these relative agreements, absolute rates of whole-body amino acid oxidation were 25% (reciprocal pool model) to 43% (primary pool model) lower than when estimated from urea N appearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1994

Effects of dietary protein restriction on glucose and insulin metabolism in normal and diabetic humans.

We determined whether the amount of protein in the diet can affect insulin requirements in subjects with diabetes mellitus and glucose metabolism in normal subjects. Seven normal-weight volunteers with uncomplicated, intensively controlled, type I (insulin-dependent) diabetes and 12 similar nondiabetic subjects were studied on a metabolic ward before and after consuming a maintenance-energy but protein-free diet for 10 days. Blood glucose levels of diabetic subjects were measured seven times daily in response to insulin administration by continuous subcutaneous infusion. The plasma glucose appearance rate (Ra) was measured in seven normal subjects and all diabetic subjects using a primed-continuous infusion of D-[6,6-2H2]glucose. After adaptation to the protein-restricted diet, diabetic subjects experienced a 30% decrease in average preprandial and average daily blood glucose concentrations (P < .01); this occurred despite a concurrent 25% decrease in both basal and bolus insulin dosages (P < .001). Protein restriction decreased the postabsorptive glucose Ra (P < .05) and insulin concentrations (P < .01) of normal subjects by 20%, and increased their fasting glucagon concentrations by 24% (P < .01). We conclude that severe protein restriction decreases insulin requirements in type I diabetes and fasting hepatic glucose output and basal insulin levels in normal subjects. This effect appears to be mediated in part by decreased hepatic gluconeogenesis, but a contributory influence of increased insulin sensitivity is not ruled out.

Adult↗

PubMed1994

Mechanism governing short-term fed-state adaptation to dietary protein restriction.

The mechanism governing short-term adaptation to dietary protein restriction was investigated in nine normal adults by measuring their metabolic response to a standard mixed meal, first while they were adapted to a conventional, high-protein diet (day 1) and then again after they had eaten two low-protein meals (day 2). Urea appearance (measured as the sum of its urinary excretion and the change in body urea pool size), body retention of 15N-alanine included in each test meal, and whole-body protein turnover were calculated over the 9 hours following meal consumption on each day. Postprandial urea nitrogen appearance was 5.05 +/- 0.26 g/9 h on day 1 and decreased to 4.16 +/- 0.31 on day 2 (P < .05). Whole-body N flux (Q), protein synthesis (S), and protein breakdown (B) all decreased significantly on day 2 as assessed using either urea or ammonium end-product enrichments; however, recovery of 15N in the test meal as 15N-urea was similar on both days, approximately 22%. It is concluded that short-term metabolic adaptation occurs within two meals of reduced protein intake. The mechanism appears not to involve selectively an increased "first-pass" retention of dietary amino acids, but rather a general reduction in fed-state whole-body protein breakdown.

Adaptation, Physiological↗

PubMed1993

Alpha-keto and alpha-hydroxy branched-chain acid interrelationships in normal humans.

Plasma concentrations of the branched-chain amino acids leucine, isoleucine and valine, and those of leucine's and isoleucine's transamination products alpha-ketoisocaproic acid (KICA) and alpha-keto-beta-methylvaleric acid (KMVA), respectively, are known to increase after a protein meal or during extended fasting, but little or no increase in the concentration of valine's transamination product, alpha-ketoisovaleric acid (KIVA), has been observed under these conditions. To determine whether this could be explained by the conversion of KIVA to its alpha-hydroxy analogue, we measured the plasma concentrations of KICA, KMVA and KIVA, as well as their alpha-hydroxy analogues [alpha-hydroxyisocaproic acid (HICA), alpha-hydroxy-beta-methylvaleric acid (HMVA) and alpha-hydroxyisovaleric acid (HIVA)], in normal volunteers immediately after a protein meal or during a 60-h fast. We also determined the oxidoreduction equilibrium constants for HIVA/KIVA and HICA/KICA and their extent of plasma protein binding. In subjects in the postabsorptive state, the plasma concentrations of KICA and KMVA were 100 times those of HICA and HMVA, whereas that of KIVA was only twice that of HIVA. Shortly after a protein meal, KICA and KMVA concentrations increased significantly by 30 and 60%, respectively, whereas that of KIVA decreased by 25% (P < 0.05). HICA, HMVA and HIVA concentrations did not change. During prolonged fasting the plasma concentrations of all six metabolites increased gradually. The high plasma keto/hydroxy acid ratios were not related to their K(eq), which favored alpha-hydroxy analogue formation. The reduction of the branched-chain alpha-keto acids to their alpha-hydroxy analogues seems to take place too slowly to attain thermodynamic equilibrium.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Reducing parenteral energy and protein intake improves metabolic homeostasis after bone marrow transplantation.

The purpose of this prospective study was to compare the metabolic effects of reducing parenteral energy and protein intake in bone-marrow-transplant (BMT) patients from 150% (hi-TPN group) to 100% (lo-TPN group) basal energy expenditure. Cytotoxic therapy was given on days 1-5, BMT on day 6, and TPN beginning on days 6 or 7. The lo-TPN group exhibited higher serum albumin (38 +/- 0.4 vs 32 +/- 0.4 g/L, P less than 0.01) but similar nitrogen balance (-83 +/- 8 vs -86 +/- 8 mg.kg-1.d-1, P greater than 0.05). Serum Na+ remained greater than 134 +/- 1 mmol/L in the lo-TPN group but fell to 127 +/- 1 mmol/L in the hi-TPN group (P less than 0.001) despite similar Na+ intakes and balances. Serum K+ remained less than 4.4 +/- 0.2 mmol/L in the lo-TPN group but rose to 5.1 +/- 0.1 mmol/L in the hi-TPN group (P less than 0.01) despite similar K+ intakes and balances. Delivering TPN at lower-than-normal rates after BMT appears to minimize Na+ and K+ disturbances and improve serum albumin concentrations without having any adverse effect on nitrogen balance.

Analysis of Variance↗

PubMed1988

Evolutionary traits in human milk proteins.

Human milk has the lowest concentration of protein of any mammalian species. Since the rate of growth of the offspring is negatively related to the protein content of the milk, the time required to double the birth weight is greater in the infant than in any other mammal in which it has been measured. Similarly, in weaned animals, a low protein diet increases the time required to reach maximal growth, senescence and natural death. Human milk protein has the highest whey protein to casein ratio than the milk of any other mammalian species. Our previous experiments have shown that mice fed a 20% whey protein diet exhibit increased resistance to Streptococcus pneumoniae and a humoral immune response significantly higher than that of mice fed most of the commercially available animal and plant proteins in nutritionally similar and adequate formula diets. Other studies have demonstrated that mean and maximal longevity of hamsters fed a 20% whey protein diet is increased in comparison with those fed commercial laboratory feed or a supplemented casein diet of similar nutritional efficiency. Thus, the low protein content and the prevalence of whey protein, which are characteristic features of human milk, are both associated with slow body growth and increased longevity. For human infants, mother's milk is the first and, for most, the only food ingested for a considerable period of time. We, therefore, propose that a trace of Nature's design for the offspring and the evolution of the species can be found in mother's milk.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗