By Julie Redfern, R.D., L.D.N.
Is it possible to live a good deal longer by eating a good deal less? Proponents of a strict dietary regimen called calorie restriction (CR) claim that it can extend your life and prevent diseases associated with aging. The diet consists of eating a very low-calorie but nutritionally balanced diet that meets 100% of vitamin, mineral, protein and essential fat needs. But can such a lifestyle, which means a dramatic change in eating habits for most Americans, be the "fountain of youth" its followers claim?
CR gained momentum in the 1930s after studies on mice showed that reducing their normal food intake by about 40% increased their maximum life span by 30% to 40%. Since then, research on worms and monkeys has shown that CR works in other species.
In humans, CR has been shown to improve markers of cardiovascular aging in overweight people. According to a 2006 study reported in the Journal of the American Medical Association, calorie restriction reduces certain biomarkers of aging and disease, such as lower body temperature and fasting insulin level. The subjects who participated in the six-month study were all overweight. They cut their daily calories by 25% either through diet alone or through diet and exercise. Their core body temperatures and fasting insulin levels fell. These findings suggest that calorie restriction may help prolong life by preventing diseases and aging in overweight people. Whether people who have normal body weight can show similar improvements has not been proven.
The mechanisms behind CR are still theoretical. New research is casting doubt on the theory that CR slows aging by reducing free radicals and oxidative damage. Instead, CR may redirect energy away from growth and reproduction toward cell maintenance, repair and protection. Another theory is that CR may shift the body into preservation mode where damage is more efficiently corrected. Based on this theory, CR is not recommended for those younger than 18 or for pregnant women.
Scientists question if CR is really applicable to humans. Here's why:
Low-calorie diets are difficult to adhere to, especially given the need to insure adequate intake of essential vitamins and minerals. The potential physical and psychological side effects may outweigh the still unproven promises of longevity. However, CR supports age-old advice to eat nutritious foods in modest amounts and maintain a healthy weight as the best protection against premature death and disease.
Julie Redfern, R.D., L.D.N., is a registered dietitian and manager of the Nutrition Consultation Services at Brigham and Women's Hospital. She specializes in nutrition counseling for the obstetrics and gynecology department. She is a graduate of the University of Vermont and completed her dietetic internship at the University of Cincinnati Medical Center.
Jaimie Winkler is a dietetic intern at the Brigham and Women's Hospital. She completed her BS in nutrition at West Chester University and a BA in History/journalism at the University of Michigan.