A study published in the March, 2006 issue of Antioxidants and Redox Signaling found that animals whose calories were restricted by just 8 percent and who engaged in light exercise experienced an increased average life span and a reduction in the cellular damage that occurs with aging. Although restricting calories by 20 to 40 percent has been well established as a method to increase life span, most humans find it difficult to duplicate this degree of dietary restriction.

Scientists at the University of Florida's Institute on Aging in Gainesville compared four groups of rats: old rats who had received a diet that allowed them to eat all they wanted, old rats who received a diet that contained 8 percent fewer calories than the unlimited diet, old rats who received the 8% calorie restricted diet plus access to an exercise wheel, and young rats on non-restricted diets. (An 8 percent reduction is the human equivalent of a few hundred calories.)

When rats on non-restricted diets were compared, levels of reactive oxygen species and peroxynitrite were higher in the older animals, while the antioxidant glutathione was lower. The calorie restricted groups lived longer on average than rats allowed to eat as much as they desired. By evaluating damage to liver RNA and DNA, the team found more age-asociated damage to RNA than DNA in the non-restricted older rats, suggesting that RNA could be useful as an aging biomarker.

Senior author and University of Florida College of Medicine associate professor of aging and geriatric research Christiaan Leeuwenburgh, PhD, stated, "This finding suggests that even slight moderation in intake of calories and a moderate exercise program is beneficial to a key organ such as the liver, which shows significant signs of dysfunction in the aging process."