Biomedical subjects

V R Young

Publications and source records attributed to V R Young.

At least 145 records · Page 8Linked to original sources

PubMed1990

Nutritional implications of microparticulated protein.

Recent technological developments have permitted the large-scale preparation of ingredients enriched with microparticulated proteins (MPP) that can be used to replace much or essentially all of the fat in a variety of traditional, full-fat foods. These include ice cream, salad dressings, mayonnaise and cheese spreads. In this paper we consider the nutritional implications of MPP, beginning with an assessment of the need for a fat-substitute and then the potential impact of MPP on the fat content of applicable foods and on the diet as a whole. Under projected conditions of maximum use of these MPP-containing foods by the consumer, the mean reduction in the fat content of the "current U.S. diet" would be about 14%. Although not dramatic, this represents a significant move in the direction of dietary changes that have been recommended by national and international authorities concerned with diet-health relationships. The risk/benefit ratio associated with inclusion of MPP in the diet is considered to be very high. This new development by the food industry is of considerable scientific interest and of potential practical importance for the nutrition and well-being of our society.

Dietary Fats↗

PubMed1990

Amino acids and proteins in relation to the nutrition of elderly people.

In this short review some aspects of body protein and amino acid metabolism during ageing in human subjects have been explored. The picture that emerges is a progressive diminution of total body protein with ageing, due largely to a decline in the size of the skeletal muscle mass. These changes are accompanied by a shift in the overall pattern of whole body protein synthesis and breakdown, with muscle mass estimated to account for about 30% of whole body protein turnover in the young adult, as compared with a lower value of 20% or less in the elderly subject. The metabolic significance and possible functional implications of this alteration in the quantitative contribution by muscle to whole body amino acid and protein dynamics have been considered. The determination of requirements for individual essential amino acids and for total protein has been discussed, and it is evident that the data are limited and often contradictory. However, elderly individuals are more likely to be influenced by various biological, environmental and social factors, the effects of which would be generally to increase protein needs above those for younger adults. Thus, in practice, the protein needs of elderly people are probably higher than for the young. The decline in energy intake, together with its possible consequences for reduced dietary protein utilization, will also tend to increase the protein need of elderly subjects, compared with that for physically more active young adults. Until more data become available, it is recommended for food planning purposes that an appropriate protein allowance could be 12-14% of the total energy intake, for mixed protein sources characteristic of the diets of industrialized countries or the more affluent sectors of populations in developing countries. Energy intake should be at a level that meets the estimates proposed by FAO/WHO/UNU for older persons. Tentative recommendations are made herein that intakes of specific indispensable (essential) amino acids, per unit of protein need, should be similar to those for the young school-age child and they should be higher than those currently judged by international authorities (i.e. FAO/WHO/UNU) to be sufficient for maintenance of protein nutritional status in the adult. In view of (i) the increasing proportion of older individuals within technically advanced populations together with the need of this group for health care and (ii) the important role played by diet and food habits in health maintenance, and in the aetiology or progression of degenerative disease, it is vitally necessary to improve upon the current state of knowledge concerning protein and amino acid metabolism and nutrition during the later phases of our lives.

Adult↗

PubMed1990

Mechanisms and nutritional significance of metabolic responses to altered intakes of protein and amino acids, with reference to nutritional adaptation in humans.

Altered intakes of protein and amino acids modulate the rates of the major systems (protein synthesis, protein degradation, and amino acid oxidation) responsible for the maintenance of organ and whole-body protein and amino acid homeostasis. The cellular mechanisms responsible for such changes at low intakes are discussed. For oxidation amino acid availability is a primary determinant and protein synthesis is affected particularly at the initiation phase. Much remains to be learned about amino acid-dependent changes in mRNA synthesis, processing, turnover, and translation. The relationships between protein and amino acid intake and components of whole-body protein and amino acid kinetics are considered with reference to nutritional adaptation and accommodation. The limit of adaptation to protein intake cannot be lowered substantially beyond that for healthy adults whose habitual protein intake is generous. Metabolic control theory should be considered in the interpretation of results of studies dealing with amino acid requirement estimations.

Adaptation, Physiological↗

PubMed1990

Use of p-aminobenzoic acid to monitor compliance with prescribed dietary regimens during metabolic balance studies in man.

A new method is described for simultaneously monitoring compliance with prescribed-diet and urine-collection regimens during metabolic balance studies. It involves incorporation of the potassium salt of p-aminobenzoic acid (PABA) into provided foods and measurement of its extent of recovery in urine. A validation study was conducted in 10 healthy adults. During three consecutive 24-h periods, subjects consumed four foods per day that had each been supplemented with 72.0 mg PABA and also made complete urine collections. An additional 24-h urine collection was made by each subject for determination of baseline PABA excretion. The PABA was easily incorporated into the test foods and was not detected by taste. The recovery of the PABA in urine, determined by colorimetric assay, was 98.7 +/- 3.7% (means +/- SD) of intake. Thus, in metabolic studies for greater than or equal to 3 d, PABA can be used to provide a sensitive index of dietary compliance.

4-Aminobenzoic Acid↗

PubMed1990

The selenite-exchangeable metabolic pool in humans: a new concept for the assessment of selenium status.

An in vivo isotope-dilution approach is considered for assessment of selenium status in human subjects. The approach depends upon the dilution of a single dose of the stable isotope 74SeO3(2-) in the selenite-exchangeable metabolic pool. Data from six metabolic protocols, conducted with healthy North American males, are presented in order to analyze characteristics of this pool. Pool size (WSe-EMP) correlated positively with daily selenium intake in subjects consuming diets of known and variable selenium content. When subjects were given a selenium-adequate or -restricted diet for 30 d, WSe-EMP,7d decreased from 4.49 +/- 0.28 to 3.76 +/- 0.22 mg (p less than 0.05). The corresponding 24-h urinary selenium concentration dropped from 0.556 +/- 0.035 to 0.341 +/- 0.058 mumol/d (means +/- 1 SEM). Route of administration (iv vs po) had no apparent effect on WSe-EMP. In subjects of similar selenium status, the WSe-EMP was reproducible within the expected uncertainties of the method. This approach may be suitable for assessment of selenium status for a wide range of chronic intakes.

Adult↗

PubMed1990

Plasma proline kinetics and concentrations in young men in response to dietary proline deprivation.

This study examined plasma proline concentration flux, oxidation, and endogenous biosynthesis in five healthy young men given three isocaloric, isonitrogenous diets for 1 wk [a complete egg-pattern amino acid diet (diet 1), an amino acid mixture devoid of proline (diet 2), and a diet composed solely of indispensable amino acids (diet 3)]. At the end of each dietary period, a 360-min postabsorptive, primed, continuous stable-isotope-tracer infusion of L-[1-13C]proline and L-[methyl-2H3]leucine was performed in all subjects. Plasma proline concentrations declined by 22% on diet 2 (p less than 0.02) and by 29% on diet 3 (p less than 0.01). No statistically significant (p greater than 0.2) changes were observed for proline oxidation, endogenous biosynthesis, or flux. The data suggest that the absence of proline in the human diet does not trigger changes in proline dynamics during the postabsorptive state. The metabolic significance of the reduction of plasma proline concentrations requires elucidation.

Adult↗

PubMed1990

High-carbohydrate, high-fiber diets increase peripheral insulin sensitivity in healthy young and old adults.

To examine extra-alimentary effects of high-carbohydrate, high-fiber (HCF) diets, insulin-mediated glucose disposal employing the euglycemic clamp and hepatic glucose output (HGO) employing [6,6-2H2]glucose were measured in 12 healthy young and old individuals before and after 21-28 d of an HCF diet. Diet lowered fasting concentrations of glucose from 5.3 +/- 0.2 to 5.1 +/- 0.1 mmol/L (p less than 0.01) and insulin from 66.0 +/- 7.9 to 49.5 +/- 5.7 pmol/L (p less than 0.01). Fasting serum cholesterol decreased from 5.17 +/- 0.18 to 3.80 +/- 0.20 mmol/L (p less than 0.01) in young individuals and from 6.15 +/- 0.52 to 4.99 +/- 0.49 mmol/L (p less than 0.01) in elderly individuals. Fasting serum triglyceride concentrations, basal HGO, and insulin suppression of HGO were unchanged by the diet. Glucose disposal rates increased from 18.87 +/- 1.66 before 23.87 +/- 2.78 mumol.kg-1.min-1 after the diet (p less than 0.02). Therefore, HCF diets may improve carbohydrate economy by enhanced peripheral sensitivity to insulin.

Adult↗

PubMed1990

Assessment of protein nutritional status.

An evaluation of protein status can be approached by use of anthropometric, clinical, and biochemical data, either singly or in combination, and further aided with dietary data. Each of these approaches has advantages and limitations. Biochemical evaluation has the potential of being the most objective and quantitative. Indicators that have been or might be used include plasma hormone responses to reduced protein intake, plasma levels of specific proteins or specific amino acids, urinary excretion of specific amino acids and other nitrogen-containing compounds, anthropometric and physical measurements of body muscle mass, and functional tests of muscle strength. Several measurements can be combined to produce nutritional indices of broader potential value. The importance of concomitant infection and inflammation, with its many effects on protein metabolism, cannot be ignored in making these assessments. Unfortunately, no single test or group of tests can be recommended at this time as a routine and reliable indicator of protein status. Nonetheless, our increasing knowledge of the metabolism and functions of proteins, together with the recent use of noninvasive stable isotope techniques and of sophisticated physicochemical measurements, provides encouragement that more appropriate indicators are in the offing.

Amino Acids↗

PubMed1990

Plasma amino acid kinetics during acute states of glucagon deficiency and excess in healthy adults.

The effects of glucagon deficiency and excess on plasma leucine, lysine, and alanine were examined in six healthy young adult men, with primed continuous infusions of L-[1-13C]- or L-[5,5,5-2H3]leucine, L-[alpha-15N]-lysine, and L-[3-13C]alanine for 150 min before and during 210 min of either a glucagon-deficient euglycemic state (experiment 1), a basal glucagon state (experiment 2), or a glucagon-excess state (experiment 3). Steady-state plasma hormone levels were achieved by infusion of somatostatin (250 micrograms/h) and insulin (0.07 mU.kg-1.min-1), without (experiment 1) or with an infusion of glucagon at 0.7 ng.kg-1.min-1 (experiment 2) or 2.5 ng.kg-1.min-1 (experiment 3). Plasma branched-chain amino acid (AA) concentrations did not change with altered glucagon status, whereas significant differences were observed for plasma lysine, alanine, glycine, serine, threonine, proline, tyrosine, citrulline, and ornithine levels (0.05 greater than P greater than 0.001). Plasma leucine, lysine, and alanine fluxes and the rate of de novo alanine synthesis showed no significant changes with either glucagon deficiency or excess. These findings lead to the conclusion that glucagon-induced alterations in plasma AA profiles are not due to changes in the rate of appearance of AA from peripheral tissues but rather a consequence of changes in the fate of AA within the splanchnic region.

Adult↗

PubMed1990

[1-13C; methyl-2H3]methionine kinetics in humans: methionine conservation and cystine sparing.

Methionine (Met) conservation in healthy young adult men (4/diet group) was explored by supplying one of the following three L-amino acid based diets: 1) adequate Met but no cystine; 2) neither Met nor cystine; or 3) no Met but cystine supplementation. After 5 days, subjects received a continuous intravenous infusion of L-[1-13C; methyl-2H3]Met for 5 h while the diet was given as small isocaloric isonitrogenous meals. Estimates were made of rates of Met incorporation into protein synthesis (S) and release from body proteins (B), transmethylation (TM), remethylation of homocysteine (RM), and transsulfuration (TS). For the adequate Met diet, the rates were S = 24 +/- 2, B = 18 +/- 1, TM = 12.4 +/- 1.7, RM = 4.7 +/- 1.1, and TS = 7.6 +/- 0.6 (SE) mumol.kg-1.h-1. The sulfur amino acid-devoid diet significantly (P less than 0.05) reduced S, TM, RM, and TS. Supplementation of this diet with cystine reduced Met oxidation (P = 0.05). Therefore, two loci are quantitatively important regulatory points in Met conservation in vivo: 1) the distribution of Met between the pathways of protein anabolism and TM (Met locus) and 2) the distribution of homocysteine between RM and TS (homocysteine locus).

Adult↗

PubMed1990

Quantitative role of splanchnic region in leucine metabolism: L-[1-13C,15N]leucine and substrate balance studies.

The role of the splanchnic region (Sp) in whole body leucine metabolism was assessed in six chronically catheterized fasting mongrel dogs and in eight dogs during constant enteral feeding of a complete amino acid solution (0.24 g.kg-1.h-1). We used primed continuous intravenous infusions of L-[1-13C,15N]leucine and L-[1-14C]leucine and measurements of arteriovenous isotope and leucine balance across the gut, liver, and Sp. In the fasted condition, 3.5% of arterial leucine supply was oxidized in the Sp, accounting for 13% of total body leucine oxidation, with 10% by liver. With amino acid feeding 1) leucine carbon and nitrogen fluxes and oxidation were increased (P less than 0.01) at the whole body level; 2) the percent of whole body leucine oxidation occurring in the Sp and liver increased (P less than 0.01) to 41 and 27%, respectively; 3) fractional metabolic utilization of leucine delivered to the Sp was reduced (P less than 0.01) from 47 to 35%; 4) the deamination rate of leucine in the gut was increased (P less than 0.05), along with an increased reamination rate of alpha-ketoisocaproic acid in the Sp (P less than 0.05). These findings reveal that the Sp accounts for a small fraction of whole body leucine oxidation during the fasting condition, but it plays a quantitatively important role in total body leucine oxidation during amino acid feeding; the gut and liver play cooperative roles in controlling leucine supply to peripheral tissues.

Animals↗

PubMed1990

Insulin- and thyroid hormone-independent adaptation of myofibrillar proteolysis to glucocorticoids.

Myofibrillar protein breakdown in skeletal muscle progresses through two distinct phases in response to chronic glucocorticoid administration in the rat, i.e., an early phase lasting 4-5 days, during which proteolysis increases followed by a later phase during which proteolysis decreases. The possible involvement of insulin and the iodothyronines in this phenomenon has now been examined. Diabetic, thyroidectomized, and normal rats were treated with corticosteroid for 10-11 days, and at timed intervals muscle proteolysis was evaluated by measuring the release of 3-methyl-L-histidine (3-MH) and tyrosine from the perfused hindquarter as well as the excretion of 3-MH in the urine. Corticosterone (CTC) administration to normal rats increased plasma insulin, whereas plasma 3,5,3'-triiodothyronine responded with an early rise followed by a fall after 4-5 days. However, the biphasic response of myofibrillar proteolysis to chronic glucocorticoid treatment was not abolished in CTC-treated diabetic or thyroidectomized rats. CTC treatment increased release of tyrosine by perfused muscle of diabetic rats but, unlike 3-MH release, did not diminish later. Thus the adaptation of myofibrillar proteolysis to chronic glucocorticoid treatment appears to be independent of insulin and thyroid hormones. However, insulin may play a role in curtailing glucocorticoid-induced breakdown of nonmyofibrillar proteins.

Animals↗

PubMed1990

Energy expenditure and subsequent nutrient intakes in overfed young men.

We investigated the mechanisms of body weight regulation in young men of normal body weight leading unrestricted lives. Changes in total and resting energy expenditure, body composition, and subsequent voluntary nutrient intakes in response to overeating by 4,230 +/- 115 (SE) kJ/day (1,011 +/- 27 kcal/day) for 21 days were measured in seven subjects consuming a typical diet. On average, 85-90% of the excess energy intake was deposited (with 87% of this amount in fat and 13% in protein on average). There was no detectable difference between individuals in susceptibility to energy deposition. The resting metabolic rate, averaged for fasting and fed states, increased during overfeeding (mean +/- SE, 628 +/- 197 kJ/day, P less than 0.01), but at least some of this amount was obligatory expenditure associated with nutrient assimilation. No significant increase in energy expenditure for physical activity or thermoregulation resulted from overfeeding. Thus energy expenditure did not substantially adapt to increased energy intake. However, significant decreases in voluntary energy intake (1,991 +/- 824 kJ/day, P less than 0.05) and fat intake (48 +/- 11 g/day, P less than 0.01) followed overeating, indicating that adaptive changes in nutrient intakes can contribute significantly to body weight regulation after overeating.

Adult↗

PubMed1990

Adaptation to low-protein diets in renal failure: leucine turnover and nitrogen balance.

In normal subjects, short to intermediate responses to dietary protein restriction include decreased amino acid oxidation and protein degradation plus increased utilization of amino acids for protein synthesis; these responses are activated to improve amino acid utilization and nitrogen balance. To assess whether chronic renal failure (CRF) impairs the adaptive responses to a low-protein diet, we measured nitrogen balance and the kinetics of infused L-(15N,1-13C)leucine during fasting and feeding. In six adult CRF and four control (C) subjects, 0.6 (LP) and 1.0 (HP) g protein kg-1 day-1 diets were compared. LP reduced feeding stimulated oxidation of leucine by 26% in CRF and 33% in C (P = NS). During fasting, oxidation was unaffected by diet or CRF. For both groups, feeding suppressed protein degradation to the same extent; leucine incorporation into protein did not change. Nitrogen balance during the two diets was the same with C and CRF, as was protein balance estimated from results of measured leucine kinetics. Thus, patients with CRF can activate appropriate adaptive responses to LP inasmuch as reduced amino acid oxidation occurring with feeding and estimates of protein balance did not differ from control.

Adaptation, Physiological↗

PubMed1990

Protein and amino acid metabolism with reference to aging and the elderly.

In this short review, selected aspects of body protein and amino-acid metabolism during aging in human subjects have been explored. There is a progressive diminution of total body protein with aging, due largely to a loss of skeletal muscle protein. These changes are accompanied by a shift in the overall pattern of whole body protein synthesis and breakdown, with muscle mass estimated to account for about 30 percent of whole body protein turnover in the young adult, as compared with a lower value of 20 percent or less in elderly subjects. There is no evidence that the loss of muscle protein is related to a reduced "amino acid tolerance" to insulin, since leucine-insulin metabolic relationships appear to remain intact during advancing adult age. However, because skeletal muscle mass plays an important role in the response to body protein and amino-acid metabolism to stress, such as that due to infection or trauma, this decline in the contribution of muscle to total body protein metabolism might be a factor responsible for the reduced ability of older people to withstand such unfavorable circumstances. Recent observations on the importance of muscle as a source of glutamine that is essential for immune cell function support this contention. The dietary requirements for individual essential and for total protein are limited and often contradictory (see, for example, Young, et al, 1982). However, elderly individuals are more likely to be affected by various biological, environmental and social factors, which would generally increase protein and amino acid needs above those for younger adults. Thus, in practice, the protein needs in the elderly are likely to be higher than those in the young. The decline in energy intake, together with its possible consequences for reducing the efficiency of dietary protein utilization, also will tend to increase the protein need for elderly subjects, relative to that for physically more active young adults. Until more data become available, it is recommended, for food planning purposes, that an appropriate protein allowance would be about 15 percent of the total energy intake, for mixed food protein sources characteristic of the diets of industrialized countries. Epidemiological surveys of the protein nutritional status of healthy, free living elderly subjects and of institutionalized individuals without clinically apparent terminal or wasting illness are consistent with this recommendation.

Aged↗

PubMed1989

Experimental selenium restriction in healthy adult humans: changes in selenium metabolism studied with stable-isotope methodology.

Mechanisms responsible for selenium homeostasis were investigated in healthy adult men receiving diets adequate or low in Se (eight subjects per group). The appearance of a stable isotope of Se, 74Se, in plasma, urine, and feces was measured after oral administration of 74Se-selenite. One group received a restricted level of Se (18 +/- 1 micrograms/d) for 30 d, which resulted in a decrease in urinary, fecal, and plasma Se content compared with the group that consumed 119 +/- 1 micrograms/d. Low Se intake also resulted in decreased urinary 74Se excretion (27.2 +/- 1.4% vs 32.5 +/- 2.3% of the absorbed dose for the adequate intake), increased body retention of 74Se (74.8 +/- 3.1% vs 67.6 +/- 3.8% of the absorbed dose for the adequate group), and a contracted selenite-exchangeable metabolic pool (Se-EMP) (9782 micrograms for adequate Se and 6314 micrograms for the low-Se group; p less than or equal to 0.05). Measurement of Se-EMP may provide an additional and sensitive approach for assessing Se nutriture in human subjects.

Absorption↗

PubMed1989

Ascorbic acid-selenite interactions in humans studied with an oral dose of 74SeO3(2-).

The interaction between dietary ascorbic acid at extremes of ascorbic acid intake and selenium in young adult male humans was investigated with a stable-isotope approach using 74Se-selenite. Measurements were made of 74Se in plasma, urine, and feces with neutron-activation analysis after oral administration of 74SeO3(2-). Urine excretion and total body retention of isotope and the selenite-exchangeable metabolic pool (Se-EMP) were calculated. Limiting dietary ascorbic acid to about 20 mg/d appeared to reduce the time-related retention of absorbed selenite and the size of Se-EMP. Compared with a diet providing 1 g ascorbic acid/d the low ascorbic acid intake was associated with a lower fractional absorption of the isotope, a reduced retention of the label, and a smaller Se-EMP. These data and those previously obtained in subjects with more usual ascorbic acid intakes point to a possible important role for ascorbic acid in the maintenance of Se homeostasis.

Absorption↗

PubMed1989

A theoretical basis for increasing current estimates of the amino acid requirements in adult man, with experimental support.

Estimates of the minimum (obligatory) rates of loss of indispensable acids via irreversible oxidation in healthy young adults are predicted from published data for obligatory nitrogen losses and from published values for whole-body protein turnover and the efficiency of amino acid recycling. The estimates obtained by these two different approaches are consistent and equal to or in most cases considerably higher than current values for the upper range of the individual amino acid requirements in healthy adults. From these estimates of the obligatory, or minimum, rates of amino acid oxidation, the minimum requirements for indispensable amino acids are predicted. These are about two to three times higher than current requirement figures. Experimental support for these higher requirement figures is presented, based on published 13C-labeled amino acid tracer studies. When these revised estimates are expressed per unit of protein need, the amino acid pattern is similar to the 1985 Food and Agriculture Organization/World Health Organization/United Nations University amino acid scoring pattern for the preschool child (aged 2-5 y).

Adult↗