To examine whole body protein turnover and muscle protein fractional synthesis rate (MPS) following ingestions of protein in mixed meals at two doses of protein and two intake patterns, 20 healthy older adult subjects (52-75 yr) participated in one of four groups in a randomized clinical trial: a level of protein intake of 0.8 g (1RDA) or 1.5 g·kg Ϫ1 ·day Ϫ1 (ϳ2RDA) with uneven (U: 15/20/65%) or even distribution (E: 33/33/33%) patterns of intake for breakfast, lunch, and dinner over the day (1RDA-U, 1RDA-E, 2RDA-U, or 2RDA-E). Subjects were studied with primed continuous infusions of L-[ 2 H5]phenylalanine and L-[ 2 H2]tyrosine on day 4 following 3 days of diet habituation. Whole body protein kinetics [protein synthesis (PS), breakdown, and net balance (NB)] were expressed as changes from the fasted to the fed states. Positive NB was achieved at both protein levels, but NB was greater in 2RDA vs. 1RDA (94.8 Ϯ 6.0 vs. 58.9 Ϯ 4.9 g protein/750 min; P ϭ 0.0001), without effects of distribution on NB. The greater NB was due to the higher PS with 2RDA vs. 1RDA (15.4 Ϯ 4.8 vs. Ϫ18.0 Ϯ 8.4 g protein/750 min; P ϭ 0.0018). Consistent with PS, MPS was greater with 2RDA vs. 1RDA, regardless of distribution patterns. In conclusion, whole body net protein balance was greater with protein intake above recommended dietary allowance (0.8 g protein·kg Ϫ1 ·day Ϫ1 ) in the context of mixed meals, without demonstrated effects of protein intake pattern, primarily through higher rates of protein synthesis at whole body and muscle levels. sarcopenia; essential amino acids; protein turnover; stable isotope tracers IT IS WELL ESTABLISHED THAT protein or amino acid ingestion (AA) stimulates protein synthesis (PS), for which essential amino acids (EAA) are mainly responsible (31, 33). There is a potential decline in muscle protein synthetic efficiency with an advancing age when a small amount of EEAs are ingested (14), but a larger intake of EAAs (i.e., 15 g in the form of beef) resulted in a similar stimulation of muscle protein synthesis (MPS) in young and old adults (27). Previous studies have shown that ingestion of ϳ20 -35 g of high-quality protein results in a near-maximal stimulation of MPS (18, 28). More specifically, Moore et al. (17) have shown in a breakpoint analysis using published fractional synthesis rate data from their laboratories that the minimum amount of protein intake per meal to achieve a maximal fractional synthesis rate is 0.40 g/kg body wt for healthy older (71 Ϯ 1 yr) and 0.24 g/kg body wt for healthy younger (22 Ϯ 4 yr) individuals. According to these data, the daily protein intake required to maximally stimulate the 24-h integrated MPS response for older individuals should be higher than 1.2 g·kg Ϫ1 ·day Ϫ1 . However, the recommended dietary allowance (RDA) for protein is 0.8 g protein·kg Ϫ1 ·day Ϫ1 regardless of age in adults despite the demonstrated anabolic resistance with an advancing age. Individuals typically consume the majority of protein intake (and daily calories) with the dinner meal. The amount o...

We have determined whole body protein kinetics, i.e., protein synthesis (PS), breakdown (PB), and net balance (NB) in human subjects in the fasted state and following ingestion of ϳ40 g [moderate protein (MP)], which has been reported to maximize the protein synthetic response or ϳ70 g [higher protein (HP)] protein, more representative of the amount of protein in the dinner of an average American diet. Twenty-three healthy young adults who had performed prior resistance exercise (X-MP or X-HP) or time-matched resting (R-MP or R-HP) were studied during a primed continuous infusion of]phenylalanine and L-[ 2 H2]tyrosine. Subjects were randomly assigned into an exercise (X, n ϭ 12) or resting (R, n ϭ 11) group, and each group was studied at the two levels of dietary protein intake in random order. PS, PB, and NB were expressed as increases above the basal, fasting values (mg·kg lean body mass Ϫ1 ·min Ϫ1 ). Exercise did not significantly affect protein kinetics and blood chemistry. Feeding resulted in positive NB at both levels of protein intake: NB was greater in response to the meal containing HP vs. MP (P Ͻ 0.00001). The greater NB with HP was achieved primarily through a greater reduction in PB and to a lesser extent stimulation of protein synthesis (for all, P Ͻ 0.0001). HP resulted in greater plasma essential amino acid responses (P Ͻ 0.01) vs. MP, with no differences in insulin and glucose responses. In conclusion, whole body net protein balance improves with greater protein intake above that previously suggested to maximally stimulating muscle protein synthesis because of a simultaneous reduction in protein breakdown. essential amino acids; optimal protein intake; protein turnover; stable isotope tracers.THE PRINCIPAL NUTRITIONAL goal of a protein-rich meal is to induce an anabolic state in which protein synthesis exceeds breakdown. Several recent studies, including our own (25), indicate that the maximum acute stimulation of muscle protein synthesis (MPS) occurs with ingestion of ϳ 20 -35 g of high-quality protein (20,25,31) or more specifically 0.24 g·kg body wt Ϫ1 ·meal Ϫ1 in healthy young adults (19). The maximal dose in terms of stimulation of MPS is less than that typically consumed with the dinner meal in the average American diet, which generates a hypothesis that distributing the amount of protein intake throughout the day can more effectively stimulate anabolic response. However, the assertion that there is limited effectiveness of the conventional protein intake with dinner is based on incomplete assessment of the metabolic response of muscle protein. Importantly, the extent of muscle protein anabolism (the anabolic response) is not simply the response of MPS but rather the net balance between the response of protein synthesis and protein breakdown. We recently demonstrated the potential importance of suppression of protein breakdown in response to dietary intake of meals containing two levels of protein totaling either 0.8 or 1.5 g protein·kg Ϫ1 ·day Ϫ1 . We found that at both levels of dietary p...

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To determine if age-associated vascular dysfunction in older adults with heart failure (HF) is due to insufficient synthesis of nitric oxide (NO), we performed two separate studies: 1) a kinetic study with a stable isotope tracer method to determine in vivo kinetics of NO metabolism, and 2) a vascular function study using a plethysmography method to determine reactive hyperemic forearm blood flow (RH-FBF) in older and young adults in the fasted state and in response to citrulline ingestion. In the fasted state, NO synthesis (per kg body wt) was ∼ 50% lower in older vs. young adults and was related to a decreased rate of appearance of the NO precursor arginine. Citrulline ingestion (3 g) stimulated de novo arginine synthesis in both older [6.88 ± 0.83 to 35.40 ± 4.90 μmol · kg body wt(-1) · h(-1)] and to a greater extent in young adults (12.02 ± 1.01 to 66.26 ± 4.79 μmol · kg body wt(-1) · h(-1)). NO synthesis rate increased correspondingly in older (0.17 ± 0.01 to 2.12 ± 0.36 μmol · kg body wt(-1) · h(-1)) and to a greater extent in young adults (0.36 ± 0.04 to 3.57 ± 0.47 μmol · kg body wt(-1) · h(-1)). Consistent with the kinetic data, RH-FBF in the fasted state was ∼ 40% reduced in older vs. young adults. However, citrulline ingestion (10 g) failed to increase RH-FBF in either older or young adults. In conclusion, citrulline ingestion improved impaired NO synthesis in older HF adults but not RH-FBF, suggesting that factors other than NO synthesis play a role in the impaired RH-FBF in older HF adults, and/or it may require a longer duration of supplementation to be effective in improving RH-FBF.

BACKGROUND:Inadequate hydration in the elderly is associated with increased morbidity and mortality. However, few studies have addressed the knowledge of elderly individuals regarding hydration in health and disease. Gaps in health literacy have been identified as a critical component in health maintenance, and promoting health literacy should improve outcomes related to hydration associated illnesses in the elderly.METHODS:We administered an anonymous survey to community-dwelling elderly (n = 170) to gauge their hydration knowledge.RESULTS:About 56% of respondents reported consuming >6 glasses of fluid/day, whereas 9% reported drinking ≤3 glasses. About 60% of respondents overestimated the amount of fluid loss at which moderately severe dehydration symptoms occur, and 60% did not know fever can cause dehydration. Roughly 1/3 were not aware that fluid overload occurs in heart failure (35%) or kidney failure (32%). A majority of respondents were not aware that improper hydration or changes in hydration status can result in confusion, seizures, or death.CONCLUSIONS:Overall, our study demonstrated that there were significant deficiencies in hydration health literacy among elderly. Appropriate education and attention to hydration may improve quality of life, reduce hospitalizations and the economic burden related to hydration-associated morbidity and mortality.