Fat and carbohydrate metabolism during exercise in elderly and young subjects

Abstract

We evaluated the effect of aging on fat and carbohydrate metabolism during moderate intensity exercise. Glycerol, free fatty acid (FFA), and glucose rate of appearance (Ra) in plasma and substrate oxidation were determined during 60 min of cycle ergometer exercise in six elderly (73 +/- 2 yr) and six young adults (26 +/- 2 yr) matched by gender and lean body mass. The elderly group was studied during exercise performed at 56 +/- 3% of maximum oxygen uptake, whereas the young adults were studied during exercise performed at the same absolute and at a similar relative intensity as the elderly subjects. Mean fat oxidation during exercise was 25-35% lower in the elderly subjects than in the young adults exercising at either the same absolute or similar relative intensities (P < 0.05). Mean carbohydrate oxidation in the elderly group was 35% higher than the young adults exercising at the same absolute intensity (P < 0.001) but 40% lower than the young adults exercising at the same relative intensity (P < 0.001). Average FFA Ra in the elderly subjects was 85% higher than in the young adults exercising at the same absolute intensity (P < 0.05) but 35% lower than the young adults exercising at a similar relative intensity (P < 0.05). We conclude that fat oxidation is decreased while carbohydrate oxidation is increased during moderate intensity exercise in elderly men and women. The shift in substrate oxidation was caused by age-related changes in skeletal muscle respiratory capacity because lipolytic rates and FFA availability were not rate limiting in the older subjects.

Lipid metabolism in the elderly

“…Sial et al (1996) found that during exercise of the same caloric expenditure, older individuals oxidized less fat than younger individuals. The difference in fat oxidation between the age groups was not due to differences in energy needs since, by design, the energy expended during exercise was similar in both groups.…”

“…For example, under resting conditions, free fatty acid rate of appearance is greater in older men and women despite reduced resting energy expenditure (Bonadonna et al, 1994;Toth et al, 1996). Moreover, during exercise of the same caloric expenditure, the rate of appearance of free fatty acid was greater in older compared to younger individuals (Sial et al, 1996). Finally, following a brief fast, the rate of appearance of palmitate was 26% higher in older compared to younger individuals when expressed relative to lean body mass, the metabolically-active component of body mass.…”

“…Studies by Sial et al (1996) showed that the lipolytic response to exercise was reduced with age. During 60 minutes of submaximal exercise (50% of VO 2 max), the rate of appearance of free fatty acids was lower in older compared to younger individuals.…”

“…In contrast, age is associated with a reduction in fat oxidation during exercise (Sial et al, 1996) and in the postprandial state (Roberts et al, 1996). Sial et al (1996) found that during exercise of the same caloric expenditure, older individuals oxidized less fat than younger individuals.…”

“…Aging is associated with reduced fat oxidation at rest (Nagy et al, 1996), following a meal (Roberts et al, 1996) and during exercise (Sial et al, 1996). The age-related reduction in fat oxidation, therefore, may promote the accumulation of total and central body fat.…”