Adults may be able to delay age-associated diseases by restricting the amount of calories they consume, according to a new study being presented Sunday, June 3, at The Endocrine Society’s 89th Annual Meeting in Toronto.

The study, in adults ages 25 to 50, evaluated the effect of six months of calorie restriction on levels of growth hormone in the body. Growth hormone not only is responsible for growth in childhood, it also plays an important role in maintaining normal health in adults. With aging, levels of growth hormone decline.

“Our results indicate that short-term calorie restriction in humans can increase growth hormone production, which is opposite to the changes reported with aging,” said study presenter Leanne Redman, PhD, clinical fellow at Pennington Biomedical Research Center, Baton Rouge, La. “However, the form of calorie restriction is important.”

Redman defined calorie restriction as a low-calorie diet that maintains proper nutrition. She and her group studied three different dietary interventions in 43 healthy men and women who were slightly overweight. One group ate a diet that restricted by 25 percent the number of calories needed daily to maintain their weight (called daily energy requirement). Another group ate a diet that restricted their calories by 12.5 percent, and they did aerobic exercise five days a week, which burned another 12.5 percent of calories. The third intervention restricted calories the most. This group drank low-calorie shakes totaling 900 calories a day for eight to 11 weeks, until they lost 15 percent of their weight. After that, they ate a diet that provided their daily energy requirement. Members of a control group ate 100 percent of their calorie needs.

Only two interventions significantly raised levels of growth hormone and a hormone that partners with it, immunoglobulin factor-1. Compared with controls, the group that had the greatest calorie restriction (low-calorie shakes) had the greatest increase in levels of these hormones. Both hormones also markedly increased in the group that combined exercise and calorie restriction.

Animal research shows that calorie restriction delays age-related diseases and increases longevity. “Whether this kind of intervention can extend lifespan in humans remains to be determined,” Redman said. She receives funding through Australia’s National Health and Medical Research Council.

This trial is the first phase of a two-year study sponsored by the National Institute on Aging, called CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy). For more information, visit www.calerie.org.

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