Marginal protein intake results in reduced plasma IGF-I levels and skeletal muscle fiber atrophy in elderly women.

We investigated the effects of dietary protein on plasma IGF-I levels and muscle fiber cross-sectional area (CSA). Twelve healthy elderly women were randomly assigned to a weight-maintaining diet containing either 1.47 (marginal) or 2.94 (adequate) g protein/kg body cell mass (BCM)/d, (0.45 and 0.92 g/kg body weight/d, respectively) for 10wks. Plasma IGF-I levels and muscle fiber areas and distributions were evaluated at baseline and 10wks. After 10wks, both IGF-I and type I fiber CSA had declined significantly in subjects fed the marginal diet (30.1+/-2.1% and 32.7+/-7.9%, respectively) while they increased in those fed the adequate diet (19.5+/-7.0% and 22.3+/-7.5%, for IGF-I and type I CSA, respectively). The change in IGF-I was the only significantly associated with the change in type I fiber CSA (r2=0.70; p<0.03). These findings show that marginal dietary protein intakes will result in losses of muscle mass in the elderly and suggest a role for plasma IGF-I as a biochemical marker for the histological changes in skeletal muscle.

High-intensity strength training of patients enrolled in an outpatient cardiac rehabilitation program.

PURPOSE: This randomized controlled study assessed whether adding a program of high-intensity strength training (80% of maximum) to an outpatient cardiac rehabilitation program would be a safe and effective means of improving muscle strength and body composition. METHODS: Thirty-eight cardiac patient volunteers (29 men and 9 women) were randomized to either high-intensity strength training or flexibility training added concurrently to a 12-week outpatient cardiac rehabilitation aerobic exercise program. Muscle strength, local muscle endurance, joint flexibility, maximum treadmill tolerance time, and body composition were measured before and after completion of the training. RESULTS: The strength-trained patients (n = 18) had greater increases in mean strength (90 +/- 19% versus 9 +/- 4%, P < 0.0001) and local muscle endurance (20 versus 6 times, P < 0.0001), and decreases in mean perceived exertion for lifting the initial one repetition maximum load (11 +/- 1 versus 15 +/- 1, P < 0.0001) when compared with flexibility-trained patients (n = 16). The strength group lost more body fat (2.8 +/- 2.0 versus 1.3 +/- 2.0 kg, P < 0.01), tended to gain more lean tissue (1.5 +/- 2.3 versus 0.5 +/- 1.2 kg, P < 0.10), and had greater improvements in treadmill time (2.3 +/- 1.3 versus 1.2 +/- 1.0 minute, P < 0.02) than did the flexibility group. Improvements in joint flexibility were similar for each group. None of the subjects had evidence of cardiac ischemia or arrhythmia during the training sessions. CONCLUSIONS: Medically supervised high-intensity strength training is well tolerated when added to the aerobic training of cardiac rehabilitation programs and allows patients to aggressively gain the strength and endurance they will need to complete daily living tasks at lower perceived efforts. Strength training also reduces cardiac risk factors by improving body composition and maximum treadmill exercise time.

Effects of high-intensity strength training on quality-of-life parameters in cardiac rehabilitation patients.

Cardiac rehabilitation programs have not consistently been shown to improve the psychological well being of their patients. In our study of 38 cardiac patients (29 men and 9 women), a variety of quality-of-life parameters were assessed before and after they completed either 12 weeks of high-intensity strength training or flexibility training added to their outpatient cardiac rehabilitation aerobic exercise program. The strength-trained patients increased their self-efficacy scores for lifting (29% vs 4%, p <0.05), push-ups (65% vs. 17%, p <0.01), climbing (36% vs 0%, p <0.001), and jogging (100% vs -9%, p <0.001), when compared with the flexibility-trained patients. The strength group also had greater improvements in Profile of Mood States dimensions: total mood disturbance (123% vs 18%, p <0.05), depression/dejection (73% vs 15%, p <0.05), and fatigue/inertia (42% vs 3% p <0.05), than did the flexibility group. The Medical Outcome Survey Short Form 36 role emotional health domain scores were significantly improved in the strength group when compared with the flexibility group (64% vs 0%, p <0.05), and the role limitation scores improved in both groups. Increases in strength were associated with enhanced self efficacy and improved mood and well-being scores (n = 34, r = 0.30 to 0.53, p <0.05). High-intensity strength training added to a cardiac rehabilitation program of selected patients leads to improvements in quality-of-life parameters. These data, in conjunction with improvements in strength, strongly support the value of adding high-intensity strength training to cardiac rehabilitation programs.

Conditions altering plasma concentrations of urea cycle and other amino acids in elderly human subjects.

OBJECTIVE: Describe plasma amino acid concentrations and total urinary amino acid excretion in subjects from an elderly female population. SUBJECTS: Fasting plasma samples, complete 24-hour urine samples, and 3-day diet records were obtained from 96 healthy postmenopausal women in one study and fasting plasma samples were obtained from an additional 44 subjects in 3 separate studies. In one study, nonfasting plasma samples were also collected. The subjects ranged in age from 49 to 80 years of age. Samples were obtained to allow the evaluation of the effects of fasting vs. nonfasting, normal vs. Alzheimers subjects, and level of protein intake effects. MEASURES OF OUTCOME: Heparinized plasma samples were deproteinized with a 5-sulfosalicylic acid solution and centrifuged at 14,900 x g. Deproteinized plasma and urine samples were analyzed for free amino acids on a Beckman System 6300 analyzer using a postcolumn reaction with ninhydrin to quantitate the amino acids. RESULTS AND CONCLUSIONS: It is concluded that: 1) From fasting plasma samples, 1 or 2 sampling days are sufficient to establish a characteristic concentration for most plasma amino acids. 2) Fasting amino acid concentrations do not reflect levels of dietary protein intake when dietary amino acid composition is similar. Shifts in fasting amino acid concentrations would be more indicative of changes in relative amounts of amino acids absorbed rather than level of dietary protein per se. 3) Totals of fasting plasma concentrations of arginine, citrulline and ornithine were relatively constant, but fluctuations occurred in the ratio of ornithine to arginine in the different populations; and 4) Patients with Alzheimers disease exhibited altered plasma ornithine and arginine concentrations relative to active or sedentary controls.

Elderly women accommodate to a low-protein diet with losses of body cell mass, muscle function, and immune response.

A 9-wk study of adaptation to marginal protein intakes was conducted in 12 elderly women. Subjects were randomly assigned to two groups fed a weight-maintenance diet containing either 1.47 (low) or 2.94 (adequate) g protein.kg body cell mass-1.d-1 (0.45 and 0.92 g.kg body wt-1.d-1, respectively). Mean nitrogen balance in the low-protein group remained negative throughout the study. These subjects experienced significant losses in lean tissue, immune response, and muscle function. The adequate-protein group was in nitrogen balance throughout the study, without changes in lean tissue, and with improvements in immune response, serum immunoglobulins, albumin, total protein values, and muscle function. Thus, elderly women fed the low-protein diet accommodated to the diet by compromising functional capacity, whereas those fed the adequate diet maintained functional capacity.

Protein turnover and energy metabolism of elderly women fed a low-protein diet.

The metabolic mechanisms of accommodation to a low-protein diet in elderly women were studied. Diets containing 1.47 (low) or 2.94 (adequate) g protein.kg body cell mass-1.d-1 (0.45 or 0.92 g.kg body weight-1.d-1, respectively) were fed for 10 wk. Fed state leucine kinetics, fasted and fed metabolic rate, and acute-phase responses to a bout of exercise were measured. Leucine uptake into protein, breakdown, and acute-phase responses were not significantly different within or between diet groups. In the low-protein group, leucine flux and oxidation were lower after 3 wk and oxidation continued to decrease throughout the 10-wk study. When expressed per body cell mass, metabolic rate increased over time in the low-protein group only. Leucine oxidation was a more sensitive index of the adequacy of protein intake than synthesis, flux, metabolic rate, or acute-phase response.

Effects of resistance training and dietary protein intake on protein metabolism in older adults.

Nitrogen (N) balance, fed-state leucine kinetics, and urinary 3-methylhistidine (3-MeH) excretion were examined in 12 men and women, aged 56-80 yr, before and during 12 wk of resistance training (RT). Subjects were randomized to groups that consumed diets providing either 0.80 +/- 0.02 g protein.kg-1.day-1 (lower protein, LP) or 1.62 +/- 0.02 g protein.kg-1.day-1 (higher protein, HP). At baseline, mean N balance was negative for LP (-4.6 +/- 3.4 mg N.kg-1.day-1) and positive for HP (13.6 +/- 1.0 mg N.kg-1.day-1). N retention increased similarly in LP and HP at the 11th wk of RT by 12.8 and 12.7 mg N.kg-1.day-1, respectively. Thus LP had an increased efficiency of N retention. LP had decreased leucine flux (P < 0.001), oxidation (P < 0.001), and uptake for protein synthesis (P < 0.02), relative to HP, both at baseline and after RT. Leucine flux increased with RT in both diet groups (P < 0.05) and was associated mainly with an increase in protein synthesis in LP (91% of change in flux) and an increase in oxidation in HP (72% of change in flux; RT-diet interaction, P < 0.05). RT increased actomyosin protein breakdown (increased 3-MeH-to-creatinine ratio, P < 0.01). Diet-related differences in protein metabolism did not influence body composition changes with RT. These data show that the efficiency of N retention and protein utilization during RT is higher in older subjects who consume 0.8 vs. 1.6 g protein.kg-1.day-1 dietary protein.

Increased protein requirements in elderly people: new data and retrospective reassessments.

Dietary protein requirements of elderly people were determined by short-term nitrogen-balance techniques and using calculations recommended by the 1985 Joint FAO/WHO/UNU Expert Consultation. Twelve men and women aged 56-80 y were randomly assigned to groups that consumed either 0.80 +/- 0.01 or 1.62 +/- 0.02 g protein.kg-1.d-1 (mean +/- SEM). Net nitrogen balance was negative for the lower-protein group (-4.6 +/- 3.4 mg N.kg-1.d-1) and positive for the higher-protein group (13.6 +/- 1.0 mg N.kg-1.d-1); the intake required for nitrogen equilibrium was estimated to be 1.00 g.kg-1.d-1. Nitrogen-balance data from three previous protein requirement studies in elderly people were recalculated by using the same balance formula and combined with the current study data to provide an overall weighted mean protein requirement estimate of 0.91 +/- 0.043 g.kg-1.d-1. Together, the current and retrospective nitrogen-balance data suggest that the mean protein requirement in elderly adults is considerably greater than the 0.60 g.kg-1.d-1 established by the 1985 Joint FAO/WHO/UNU Expert Consultation. A safe protein intake for elderly adults would be 1.0-1.25 g.kg-1.d-1 of high-quality protein.

Increased energy requirements and changes in body composition with resistance training in older adults.

Body composition and the components of energy metabolism were examined in 12 men and women, aged 56-80 y, before and after 12 wk of resistance training. Subjects were randomly assigned to groups that consumed diets that providing either 0.8 or 1.6 g protein.kg-1.d-1 and adequate total energy to maintain baseline body weight. Fat mass decreased 1.8 +/- 0.4 kg (P < 0.001) and fat-free mass (FFM) increased 1.4 +/- 0.4 kg (P < 0.01) in these weight-stable subjects. The increase in FFM was associated with a 1.6 +/- 0.4 kg increase in total body water (P < 0.01) but no significant change in either protein plus mineral mass or body cell mass. With resistance training, the mean energy intake required for body weight maintenance increased by approximately 15%. Increased energy expenditure included increased resting metabolic rate (P < 0.02) and the energy cost of resistance exercise. Dietary protein intake did not influence these results. Resistance training is an effective way to increase energy requirements, decrease body-fat mass, and maintain metabolically active tissue mass in healthy older people and may be useful as an adjunct to weight-control programs for older adults.

Hepatic synthesis and urinary excretion of alpha2u-globulin by male rats: diurnal rhythm and response to fasting and refeeding.

The urine of sexually mature male rats contains a protein of hepatic origin, alpha2u-globulin, not found in the urine of immature or female rats; output of this protein is greatly reduced by fasting. We have examined the effects of feeding and of fasting for various lengths of time on urinary output and hepatic synthesis of alpha2u-globulin. Rats eating ad libitum showed diurnal rhythms of urinary alpha2u-globulin excretion reaching maxima between 2000 and 0800 hours, thus coinciding with the daily feeding period of the rat. Fasting for 12 hours extinguished this diurnal rhythm. When fasting was prolonged up to 36 hours, urinary excretion of alpha2u-globulin was reduced to very low levels. Hepatic synthesis of alpha2u-globulin under these nutritional conditions was investigated by incubating liver polyribosomes with [3H]leucine and a preparation of soluble enzymes for protein synthesis and separating the labeled alpha2u-globulin peptides by immunoprecipitation followed by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. By this technique, it was shown that only membrane-bound ribosomes in the livers of mature male rats make this protein. Semi-quantitative measurement suggested that the proportion of liver polyribosomes synthesizing alpha2u-globulin was unchanged after 12 hours of fasting, but was reduced after 24 and 36 hours of fasting. It is proposed that the diurnal rhythm in alpha2u-globulin output in the urine represents translational control of its synthesis in the liver, whereas the more extensive reduction with prolonged fasting is partly due to a selective reduction in transcription of the messenger RNA for this protein.