Dietary protein requirements of younger and older adults.

BACKGROUND: For older men and women, the Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for protein are not known with confidence. Data from the limited research studies available suggest that the EAR and RDA might be greater than the assumed 0.66 and 0.80 g protein x kg body wt(-1) x d(-1), respectively. OBJECTIVE: This study assessed the effect of age on the EAR and RDA for protein. DESIGN: Twenty-three younger (age: 21-46 y; 11 men, 12 women) and 19 older (age: 63-81 y; 8 men, 11 women) persons completed three 18-d trials with protein intakes of 0.50, 0.75, and 1.00 g protein x kg body wt(-1) x d(-1). Nitrogen balance was determined by using data from total nitrogen analyses of duplicate food composites and complete urine and feces collections from days 14 to 17 of each trial. Each subject's protein requirement was estimated by using linear regression of protein intake and nitrogen balance data from all 3 trials and inverse prediction. RESULTS: The mean (+/- SD) protein requirement was not different between the younger and older subjects: 0.61 +/- 0.14 compared with 0.58 +/- 0.12 g protein x kg body wt(-1) . d(-1). On the basis of individual requirement estimates from the younger and older subjects combined (2.5% trimming from each tail and variation estimated by the bootstrap), an adequate protein allowance for these subjects was calculated to be 0.85 +/- 0.21 g protein x kg body wt(-1) x d(-1). CONCLUSIONS: These short-term nitrogen balance results suggest that the requirement for total dietary protein is not different for healthy older adults than for younger adults and that the allowance estimate does not differ statistically from the RDA.

Nutrient ingestion, protein intake, and sex, but not age, affect the albumin synthesis rate in humans.

The aim of this study was to assess the effects of nutrient ingestion, dietary protein intake, age, and sex on the fractional synthesis rate (FSR) of albumin. Thirty-six healthy free-living individuals (8 females and 10 males aged 21-43 y and 9 females and 9 males aged 63-79 y) completed three 18-d periods of controlled feeding with protein intakes of 125% (P125, 1.00 g protein x kg(-1) x d(-1)), 94% (P94, 0.75 g protein x kg(-1) x d(-1)), and 63% (P63, 0.50 g protein x kg(-1) x d(-1)) of the recommended dietary allowance. On d 12 of each trial, postabsorptive (PA) serum albumin concentration was determined and PA and postprandial (PP) albumin FSR were estimated from the rate of l-[1- 13C] leucine incorporation into plasma albumin during an 8-h infusion. There were no age-related differences in PA and PP albumin FSR. Albumin FSR was higher PP than PA (P < 0.0001), and the increase in albumin FSR from PA to PP was smaller as dietary protein intake decreased from P125 to P94 and P63 (P < 0.05). Independent of protein intake, males had a higher albumin FSR (P < 0.05) and a greater increase in albumin FSR with feeding (P < 0.05). There was no age or dietary protein effect on serum albumin concentrations, but males had higher albumin concentrations than females (P < 0.0001). These results show that older persons are responsive to nutrient ingestion and dietary protein-related changes in albumin FSR. The greater albumin synthesis rate in males might contribute to a higher albumin concentration set point.

Inadequate dietary protein increases hunger and desire to eat in younger and older men.

Many older people experience changes in appetite and consume marginal or inadequate dietary protein. This study was designed to examine the appetitive responses to habitual protein intakes that span the range of adequacy in younger and older men. Twenty-two men (12 younger, aged 21-43 y and 10 older, aged 63-79 y) completed, in random order, three 18-d trials that involved consumption of individualized, isoenergetic menus providing 1.00, 0.75, and 0.50 g protein . kg BW(-1). d(-1), which were 125% (trial P125), 94% (trial P94), and 63% (trial P63) of the Recommended Dietary Allowance for protein. Near the end of each trial, the subjects recorded appetitive sensations hourly throughout one day using a visual analogue scale. Independent of age, ratings of hunger were lower for P125 (1.3 +/- 0.5 cm) than P94 (1.8 +/- 0.8 cm) and P63 (1.8 +/- 0.6 cm) (P = 0.037), and desire to eat was lower during the P125 trial (1.4 +/- 0.5 cm), compared with the P63 trial (2.1 +/- 0.7 cm) (P = 0.003), and P94 (1.8 +/- 0.7 cm) was not different when compared with P63 and P125. Protein intake did not influence fullness. These results show that younger and older men who consume inadequate protein experience appetite changes that may promote increased food intake.

Inadequate protein intake affects skeletal muscle transcript profiles in older humans.

BACKGROUND: Inadequate dietary protein intake causes adverse changes in the morphology and function of skeletal muscle. These changes may be reflected in early alterations in muscle messenger RNA levels. OBJECTIVE: This study assessed whether inadequate protein intake differentially affects skeletal muscle transcript concentrations and expression profiles in older adults. DESIGN: Twenty-one older men and women (aged 55-80 y) consumed controlled diets that provided 1.2 g protein x kg(-1) x d(-1) (adequate protein) for 1 wk and then were randomly assigned to consume either 0.5 g protein x kg(-1) x d(-1) [inadequate protein (IP) group; n=11] or 1.2 g protein x kg(-1) x d(-1) (control group; n=10) for a second week. RNA was isolated from fasting-state vastus lateralis biopsy samples obtained at the end of each period, and transcript levels in the IP group were measured by using microarray analysis. Changes in selected transcript levels were confirmed by real-time polymerase chain reaction in both groups. RESULTS: Analysis of variance showed 529 differentially expressed transcripts (P<0.05) after inadequate protein intake. Using the false discovery rate (FDR) correction to adjust for multiple comparisons, we observed that 85 transcripts were differentially expressed: 54 were up-regulated and 31 were down-regulated. The differentially expressed transcripts were in functional classes for immune, inflammatory, and stress responses (predominantly up-regulated); contraction, movement, and development (up-regulated); extracellular connective tissue (up-regulated); energy metabolism (down-regulated); protein synthesis (down-regulated); and proliferation (down-regulated). Diet-related differences in the expression of 9 transcripts were cross-validated by using real-time polymerase chain reaction. CONCLUSION: The results document changes in skeletal muscle transcript levels induced by short-term inadequate protein intakes in older humans that might precede adverse metabolic, functional, and structural events, including muscle wasting.

Higher protein intake preserves lean mass and satiety with weight loss in pre-obese and obese women.

OBJECTIVE: To examine the effects of dietary protein and obesity classification on energy-restriction-induced changes in weight, body composition, appetite, mood, and cardiovascular and kidney health. RESEARCH METHODS AND PROCEDURES: Forty-six women, ages 28 to 80, BMI 26 to 37 kg/m(2), followed a 12-week 750-kcal/d energy-deficit diet containing higher protein (HP, 30% protein) or normal protein (NP, 18% protein) and were retrospectively subgrouped according to obesity classification [pre-obese (POB), BMI = 26 to 29.9 kg/m(2); obese (OB), BMI = 30 to 37 kg/m(2)). RESULTS: All subjects lost weight, fat mass, and lean body mass (LBM; p < 0.001). With comparable weight loss, LBM losses were less in HP vs. NP (-1.5 +/- 0.3 vs. -2.8 +/- 0.5 kg; p < 0.05) and POB vs. OB (-1.2 +/- 0.3 vs. -2.9 +/- 0.4 kg; p < 0.005). The main effects of protein and obesity on LBM changes were independent and additive; POB-HP lost less LBM vs. OB-NP (p < 0.05). The energy-restriction-induced decline in satiety was less pronounced in HP vs. NP (p < 0.005). Perceived pleasure increased with HP and decreased with NP (p < 0.05). Lipid-lipoprotein profile and blood pressure improved and kidney function minimally changed with energy restriction (p < 0.05), independently of protein intake. DISCUSSION: Consuming a higher-protein diet and accomplishing weight loss before becoming obese help women preserve LBM. Use of a higher-protein diet also improves perceptions of satiety and pleasure during energy restriction.

Water balance, hydration status, and fat-free mass hydration in younger and older adults.

BACKGROUND: Older adults are at increased risk of dehydration, yet water balance is understudied in this population. OBJECTIVE: This controlled diet study assessed the effect of age on water input, output, and balance in healthy adults. Hydration status (plasma osmolality and urine specific gravity) and body composition were also measured. DESIGN: Eleven men and 14 women aged 23-46 y and 10 men and 11 women aged 63-81 y were subjects. Water balance was assessed during days 7-10 of three 18-d controlled feeding trials with protein intakes of 0.50, 0.75, and 1.00 g . kg(-1) . d(-1). Total water input included water from the provided foods and beverages, ad libitum intake, and metabolic production. Water output included the losses in urine and stool and the insensible losses from respiration and nonsweating perspiration. RESULTS: Ad libitum water consumption, total water intake, water output through urine, total water output, and net water balance were not different in the older subjects than in the younger subjects. Markers of hydration status were within the range of clinical normalcy for all groups. Total body water (TBW) was not significantly different, fat-free mass (FFM) was significantly lower (P < 0.05), and FFM hydration (TBW:FFM) was significantly higher (P < 0.05) in the older subjects than in the younger subjects. Dietary protein intake did not influence any of these results. CONCLUSIONS: These results show that healthy older adults maintain water input, output, and balance comparable to those of younger adults and have no apparent changes in hydration status. The results support that the hydration of FFM is increased in older men and women.

Short-term low-protein intake does not increase serum parathyroid hormone concentration in humans.

We investigated whether inadequate dietary protein would result in increased serum parathyroid hormone (PTH) concentration, consistent with secondary hyperparathyroidism. Data from 2 controlled feeding studies were utilized. In study 1, 26 healthy women (15 young, 21-46 y, and 11 elderly, 70-81 y) consumed for 12 d each in separate trials 3 levels of protein, 1.00, 0.75, and 0.50 g protein/(kg. d). Blood was drawn from fasting subjects on d 12 of each trial. In study 2, 24 persons (54-80 y) were fed diets with either 1.20 g protein/(kg. d) for 2 wk (HPro, n = 11, 6 men, 5 women) or 1.2 g protein/(kg. d) for 1 wk and then 0.50 g protein/(kg. d) for a 2nd week (IPro, n = 13, 6 men, 7 women). Blood was obtained from fasting subjects after wk 1 and 2. Consistent with altered protein metabolism, urinary total nitrogen excretion and blood urea nitrogen fell progressively with decreasing protein intake in study 1; in study 2, the values decreased from wk 1 to 2 in the IPro group only. Serum intact PTH concentrations did not differ among the 3 protein intakes in study 1, or between the HPro and IPro groups in study 2. These findings do not support the hypothesis that the short-term ingestion of inadequate dietary protein increases serum PTH concentration.

3-Hydroxypropionic acid and methylcitric acid are not reliable indicators of marginal biotin deficiency in humans.

In two studies comprising 10 and 11 subjects, respectively, marginal biotin deficiency was induced experimentally by an egg-white diet in healthy men and women. The following urinary organic acids were assessed for their usefulness in detecting marginal biotin status: 1) 3-hydroxypropionic acid and methylcitric acid, organic acids that reflect decreased activity of the biotin-dependent enzyme propionyl-CoA carboxylase and 2) methylcrotonylglycine and isovalerylglycine, organic acids that reflect decreased activity of methylcrotonyl-CoA carboxylase. Mean 3-hydroxypropionic acid excretion rates remained normal during biotin depletion in both studies. By the end of the depletion period, 3-hydroxypropionic acid excretion identified only 5 of 21 marginally deficient subjects. Mean methylcitric acid excretion increased (P < 0.0001) in the first study but not in the second. Mean methylcrotonylglycine excretion increased in each study (P < 0.004 and P < 0.05, respectively); methylcrotonylglycine excretion identified 13 of 21 marginally deficient subjects. Mean isovalerylglycine excretion increased only in the first study (P = 0.006) and identified only 6 of 21 deficient subjects. We conclude that none of these organic acids is as sensitive an indicator of marginal biotin deficiency as 3-hydroxyisovaleric acid, which reflects decreased methylcrotonyl-CoA carboxylase.

Indicators of marginal biotin deficiency and repletion in humans: validation of 3-hydroxyisovaleric acid excretion and a leucine challenge.

BACKGROUND: The results of clinical studies have provided evidence that marginal biotin deficiency is more common than was previously thought. A previous study of 10 subjects showed that the urinary excretion of biotin and 3-hydroxyisovaleric acid (3HIA) are early and sensitive indicators of marginal biotin deficiency. OBJECTIVE: Marginal biotin deficiency was experimentally induced and corrected to assess the utility of 3 indicators of biotin status: urinary excretion of biotin and 3HIA and the increase in 3HIA excretion after leucine loading. DESIGN: Eleven healthy adults consumed an egg white diet for 28 d. Blood and 24-h urine samples were collected before the start of the diet and twice weekly thereafter. In 5 subjects, an oral leucine challenge was performed weekly for 4 wk. After depletion, biotin status was restored with a general diet with or without a supplement containing 80 micro g biotin. Urinary excretion of biotin, bisnorbiotin, and biotin sulfoxides was determined by avidin-binding assay after HPLC. Excretion of 3HIA, an indicator of reduced activity of the biotin-dependent enzyme methylcrotonyl-CoA carboxylase (EC 6.4.1.4), was measured by gas chromatography-mass spectrometry. RESULTS: 3HIA excretion increased significantly with time on the egg white diet (P < 0.0001), as did 3HIA excretion in response to the leucine challenge (P < 0.002); the excretion of both biotin and bisnorbiotin decreased significantly with time (P < 0.0001). In most subjects, biotin status returned to normal after 1 wk of a general diet. CONCLUSIONS: Excretion of 3HIA and of biotin are early and sensitive indicators of biotin deficiency. 3HIA excretion after a leucine challenge is at least as sensitive.

Lymphocyte propionyl-CoA carboxylase and accumulation of odd-chain fatty acid in plasma and erythrocytes are useful indicators of marginal biotin deficiency small star, filled.

BACKGROUND: Recent studies indicate marginal biotin deficiency is more common than previously thought. That conclusion's validity rests on two indicators of biotin status that depend on renal function.OBJECTIVE: Assessing the validity of two indicators of biotin status that do not depend upon renal function: 1) activity of the biotin-dependent enzyme propionyl-CoA carboxylase (PCC) in lymphocytes and 2) accumulation of odd-chain fatty acids in the lipids of plasma and erythrocytes.DESIGN: Marginal biotin deficiency was induced in 11 healthy adults by egg-white feeding for 28 days. Blood and 24-h urine samples were collected before commencing the diet and twice weekly thereafter. After depletion, biotin status was restored with a general diet with or without 80 &mgr;g/day or 328 nmol/day biotin supplement. Activity of PCC was determined by an optimized NaH 14CO(3) incorporation assay. Fatty acid composition was determined by gas chromatography.RESULTS: With time on the egg-white diet, lymphocyte PCC activity decreased significantly (P <0.0001); C15:0 and C17:0 content increased significantly in the lipids of plasma and erythrocytes (P <0.015). In eight of 11 subjects, lymphocyte PCC activity returned to normal within three weeks of resuming general diets with or without biotin supplement. With repletion, C15:0 and C17:0 in plasma lipids decreased (P <0.02), but odd-chain content of erythrocytes did not decrease significantly.CONCLUSIONS: Lymphocyte PCC activity is an early and sensitive indicator of marginal biotin deficiency. Odd-chain fatty acids accumulate in blood lipids more gradually during marginal deficiency and return to normal more gradually after biotin repletion.