Calorie restriction (CR), or caloric restriction, is a dietary regimen that is based on low calorie intake. “Low” can be defined relative to the subject’s previous intake before intentionally restricting calories, or relative to an average person of similar body type.
CR has been shown to work in a variety of species, among them yeast, fish, rodents and dogs to decelerate the biological aging process, resulting in longer maintenance of youthful health and an increase in both median and maximum lifespan. However, no clinical trial has been performed involving humans.
Two trials have been performed involving primates, both of which did not demonstrate an increase in lifespan. The first study, which began in in 1987 , was of rhesus monkeys and was conducted by the National Institute on Aging (Mattison, 2012). The results were published in August 2012 and although the researchers found evidence of health benefits, they did not find an increased median lifespan. b Some lab test results improved, but only in monkeys put on the diet when they were old. The causes of death — cancer, heart disease — were the same in both the underfed and the normally fed monkeys.
Lab test results showed lower levels of cholesterol and blood sugar in the male monkeys that started eating 30 percent fewer calories in old age, but not in the females. Males and females that were put on the diet when they were old had lower levels of triglycerides, which are linked to heart disease risk. Monkeys put on the diet when they were young or middle-aged did not get the same benefits, though they had less cancer.
The second study by the University of Wisconsin began in 1989 is still ongoing and the research on maximum life span in that study is still ongoing. Overall studies have shown both positive and negative effects. Fore example, calorie restriction can lead to loss of muscle mass and strength and reduced bone mineral density (Morley, et al. 2010). This is to be expected as part of the weight loss that accompanies CR. Some specialists say that minor mineral losses can be minimized with regular physical activity and vitamin D and calcium supplements.
Some of the positive effects of CR that have been noted in research include a reduction in atherosclerosis risk factors (Fontana, 2004) and improved memory (Witte et al., 2009). CR has many of the same issues associated with fasting. Just like fasting, supervision can be an important component.