Exercise may be needed for dietary restriction benefits

Friday, July 6, 2012. In the July 3, 2012 issue of the journal Cell Metabolism, scientists at the Buck Institute for Research on Aging report the outcome of experiments that suggest that it may be necessary to be physically active in order to derive maximum benefit from dietary restriction (DR). Significant restriction of the intake of a particular nutrient or total calories has extended the life span of numerous species in laboratory experiments; however, researchers are still clarifying the mechanisms involved in the technique.

In research involving fruit flies, Pankaj Kapahi, PhD and colleagues observed that the insects became more physically active when their protein source was restricted. The increased physical activity observed in the dietary-restricted flies was associated with greater fat synthesis and breakdown. When fat synthesis in muscle tissue was blocked, so was the life-extending benefit of dietary restriction. And in flies whose motion was limited, the extended life span that normally results from a restricted diet did not occur. "Ours is the first study to suggest that for dietary restriction to enhance lifespan, you need increased fat turnover in the muscle and an associated increase in physical activity," Dr Kapahi announced. "Furthermore, it also suggests that dietary changes may enhance motivation to exercise and help derive maximal benefits of exercise."

In flies genetically engineered to overexpress the hormone AKH, metabolism and activity levels were enhanced and lifespan was extended, even without dietary restriction. "Our data suggests that DR may induce changes in muscle similar to those observed under endurance exercise and that molecules like AKH could serve as potential mimetics for DR that enhance activity and healthspan," remarked lead author and Buck Institute staff scientist Subhash D. Katewa, PhD. "A better understanding of the dynamics of fat metabolism is needed in order to clarify its role in aging and disease. These current results suggest that enhanced fat metabolism could help slow aging and the onset of age-related disease."

"Dietary restriction is known to enhance spontaneous movement in a variety of species including primates, however this is the first examination of whether enhanced physical activity is necessary for its beneficial effects," Dr Kapahi added. "This study establishes a link between DR-mediated metabolic activity in muscle, increased movement and the benefits derived from restricting nutrients. Our work argues that simply restricting nutrients without physical activity may not be beneficial in humans."

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