Eat less, live longer?
We have known for a long time that prolonged calorie restriction increases longevity in laboratory mice and rats. These rodents-on-diet also were found to have fewer age-related chronic illnesses. Sound good? You bet. But we are not talking about a eating a few less pellets of food here and there. These experiments involved decreasing the animals’ calorie intake by 30% or more.
Until recently, we suspected, but were not sure whether nutritionally adequate calorie restriction would have similar effects in humans. Studies of some highly motivated individuals who voluntarily consumed a nutritionally balanced, but severely calorie-restricted diet have demonstrated significant reductions in cardiovascular risk factors (blood pressure, markers of inflammation, fasting insulin and glucose levels). It is of note that these same risk factors are elevated in overweight and obese individuals who manifest insulin resistance, glucose intolerance, and Type 2 diabetes.
A recent paper published in the Journal of the American Medical Association ((JAMA, April 5, 2006, 295(13), 1577)) by Leonie Heilbronn and colleagues, reported on the results of a 6-month study of the impact of calorie restriction on biomarkers of longevity. Over the short run, it is impossible to determine if human lifespan is increased because of the long duration of human lives. It will take decades to see such an effect. However, measuring biomarkers, such as fasting insulin, core body temperature, and looking at changes in damage to our genetic material (DNA) is a scientifically legitimate, albeit indirect, way of determining if calorie restriction is likely to have beneficial effects on human longevity.
The JAMA study is a high quality design -- participants were randomized into one of three treatment groups or a control (or comparison) group. Twelve normal weight people were assigned to a group that consumed 25% fewer calories than they usually ate to maintain their weight. Another 12 were assigned to a diet that was reduced by 12.5%, but they also had to exercise 12.5% above their resting level of calorie expenditure. The 12 people in the final treatment group ate a very low calorie diet of 890 kcal per day. For the control group, their diet was business as usual.
It should not be a surprise that all of the people in the treatment groups lost weight – about 10% for the calorie restriction and calorie restriction with exercise groups and 14% for the very low calorie group. This compared to a 1% loss in the control group.
Interestingly, all of the treatment groups demonstrated reductions in 2 biomarkers of longevity: fasting insulin level and core body temperature. Further, also reduced their metabolic rates beyond the level expected from just losing weight. They also lowered their levels of thyroid hormone and oxidative damage to their DNA. These changes are similar to changes seen in experiments of calorie restriction and longevity in short-lived laboratory animals, like rodents.
While this study does not prove that calorie restriction increases longevity, taken together with the piles of evidence that overweight and obesity in individuals with insulin resistance develop chronic illnesses that shorten life and reduce its quality, this study supports the concept that eating less may be associated with longer lives….here, here, it’s one more reason to lose weight.