Calorie-Restricted Diets (Science Review)

N.B. This science review was originally published in Optimyz Magazine in March 2012 by Mandy Wintink, PhD

Restrict Calories to Prolong Life

Calorie-restricted diets are known scientifically to offer a variety of health benefits, including lowered metabolic rate, which lowers reactive oxygen species and the rate of oxidative damage to vital tissues. Lowering metabolic rate decreases the biological rate of aging and extends life expectancy. Calorie restriction (CR) is so compelling that there is a society named after it, which exists to support people’s efforts for longevity and good health through CR. CR also improves markers of age-related diseases (e.g., insulin resistance for diabetes), lowers obesity rates, alter neuroendocrine activity, and reduce cancer rates.

CR has been studied extensively in non-humans and to a limited extent in obese individuals as a non-pharmacological treatment for obesity and diabetes. A multi-centre study funded by the National Institute of Aging is currently underway examining the benefits in obese, mildly overweight, and normal-weight individuals. The study is called the Comprehensive Assessment of Long-Term Effects of Reducing Intake Energy, or CALERIE, study.

A few results from this very comprehensive study are already available, for example, 6 months of a 25% CR diet increased anti-oxidant levels such as glutatione in overweight individuals. It also lowered levels of fasting glucose, of total cholesterol, of core body temperature (a marker of metabolic rate), of body weight, and of fat, all correlates of longevity and reduced incidence of obesity and diabetes. The diet also reduced DNA damage, all within the first 6 months. Full results won’t be available until after 2 years of such diet. Also important, is that this study will be the first to study the long-term effects of CR diets in healthy, non-obese individuals. Individuals of the CR Society may be happy to hear the results because as of right now their efforts are theoretically motivated, but with a theory that warrants the good science soon to be available.

CR also offers benefits with cancer prevention. In an article published in February of 2011, the authors summarized many studies showing that CR protects cells through reducing stress-induced damage, keeping inflammation down and regulated, regulating the immune responses, and ensuring adequate metabolism and energy expenditure. CR also enhances DNA repair, while preventing its damage, and ramps up the clean-up process when damage does occur. CR’s protection likely involves regulating gene expression in tumor-suppressor genes (a process I described 2 issues ago on epigenetics), among a host of other biochemical processes.

Fasting - no calorie intake - also produces changes that offer protection to cells and is currently being investigated as a potential clinical intervention in cancer, partially because there is little to no weight loss with fasting but some of the health benefits are achieved. The benefits appear to be meditated though a differential stress resistance. Normal cells respond to fasting by inducing a variety of mechanisms to protect cells from damage. Cancer cells do not appear to have this ability because of changes in gene expression that effectively ward off the protective effects allowing for their own death and thus reduces tumor growth. This idea was reviewed in the scientific journal, Oncogene, in July 2011, and also as a more lay version in the February 8th issue of Scientific American, suggesting that 5 days of fasting around chemotherapy may optimize the treatment.

Whether CR, fasting, or some other diet is your diet of choice, one thing seems clear. High-caloric intake is not healthy. Many evolutionary scientists believe that our bodies adapted to a food-shortage environment. The problem is that we are actually living in a food-abundant environment, at least that’s true for many of us who live in developed countries. CR appears to offer health benefits because it is capitalizing on a system that is geared to work well under food-restricted circumstances. That being said, these same bodies probably also evolved to be less sedentary that we typically are. Exercise and physical activity are also important elements of healthy living. However, exercise does not appear to extend life expectancy in the way that CR does.

One final thing to keep in mind is that the benefits of CR have been studied while maintaining proper nutrition. CR does not imply starvation!