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Male Wistar rats were maintained on four dietary regimens: fed ad libitum throughout life (A); fed intermittently either during the first year of life and ad libitum thereafter (RA) or vice versa (AR); and fed intermittently throughout life (R). Low body weights, low amounts of body components (protein, fat, moisture, and ash), and long life spans were observed in R. AR and RA lost or gained body weight, respectively, after dietary transfer and lived longer than A. Maximum body weight and the age at which it was attained were correlated positively with life span in A. Predicted mature body weight was correlated negatively with life span in R. RA and AR differed in growth and body composition, but their life spans were similar and intermediate to those of A and R. Increases in life span were obtained by intermittent feeding during all or part of the life span, but growth and body composition data did not consistently explain the mechanism of this effect.

Effects of ad libitum and restricted (50% of ad libitum) feeding on performance of female broilers were assessed in a 68-week experiment. The treatments imposed were AA, fed ad libitum throughout; RR, fed restricted amounts of feed throughout; RA restricted through 24 weeks of age and ad libitum thereafter; and AR, fed ad libitum through 24 weeks and restricted thereafter. Average age at first egg was delayed by 17 days in RA hens compared with AA hens. Average body weight at first egg was 3.9 kg for RA birds and 4.5 kg for AA birds. Peak production was higher for RA birds (71 vs. 59%), but age at peak production was similar for both AA and RA hens. Through 68 weeks, AR birds produced 50% more eggs than AA birds (159 vs. 106). Cumulative number of eggs produced for RR and AR birds were 37 and 47, respectively. Mortality was similar for RR, RA, and AR birds but was approximately fourfold greater in AA birds. At 68 weeks of age, live body, carcass, abdominal fat pad, and estimated fat-free carcass weights were similar for AA and RA birds. Although abdominal fat as a percent of carcass weight was similar for AR and RR birds, average live weight, carcass weight, and fat-free carcass weight were higher for AR than RR birds at 68 weeks.

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The influence of diet and feed restriction on kidney function was studied in aging male albino rats. Rats were fed either a commercial feed (LB) or a modified human diet (MHD) from weaning until sacrifice at either 12 or 24 mo. of age. Restricted rats were fed for only 15 out of each 48 hours. Feed restriction during either the first, the second, or both years of life was beneficial in delaying age-associated changes in kidney function as indicated by decreased proteinuria, increased in vitro transport of paraaminohippuric acid, and reduced incidence and severity of renal lesions. Urinary creatinine and blood urea nitrogen levels were also favorably influenced by restriction. Most parameters were modified by diet as well as by restriction, with MHD being generally associated with improved kidney function. Improvement in kidney function may have been more related to a reduction in protein intake than to a reduction in caloric intake as a whole.

This study examined the effects of diet restriction and exercise training during aging on adipocyte size and number in male Wistar rats. An average of 30 weanling rats each were assigned to one of four experimental groups: ad libitum access to food, nonexercised; diet restricted, nonexercised; ad libitum access to food, exercised; diet restricted, exercised. Diet-restricted groups were allowed free access to food every other day, and, over the course of the study, they consumed 18-25% less than the groups allowed ad libitum access. Exercise training consisted of swimming on alternate days for up to 3 h per exercise period. Fat cell size, number and fat depot mass were determined in the inguinal, epididymal and perirenal fat depots at 12 mo of age and every 4 mo thereafter until 28 mo of age. Fat cell number was not influenced by age, exercise or food restriction in the epididymal or perirenal fat depots. Inguinal cell number was lower (P < 0.05) in the diet-restricted, exercised group at all ages compared with all other treatments. Dietary restriction and exercise training significantly decreased fat depot mass and fat cell size, with dietary restriction having the greatest effect. A bimodal distribution of adipocytes was observed in the epididymal, perirenal and inguinal depots of animals allowed ad libitum access to food. The presence of a large population of small fat cells (< 35 microns) indicated that even in the very aged animal there was the propensity for large variations in fat pad mass. The influence of diet restriction, exercise and aging on adipocyte cell size was highly variable and these effects were dependent on adipose tissue depot location.

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