Starting in the 1930s, a number of studies in laboratory animals have concluded that a reduced calorie diet, which delivers sufficient vital nutrients, results in a longer life and delays age-related diseases. Because of these findings in animals, many people have voluntarily adopted calorie-reduced diets in the hope of increasing longevity and improving health.
A new study has shown, however, that a nutritious low calorie diet may be less effective at prolonging life in humans. In many species, reduced function mutations in the insulin / insulin-like growth factor 1 (IGF-1) signalling pathway increase maximal healthy lifespan. Although calorie restriction in rodents decreases serum concentrations of IGF-1 by around 40%, with an accompanying beneficial effect on life span, the long term effects of calorie restriction on circulating IGF-1 levels in humans was not known.
The new study has shown that, in humans, long term calorie restriction with adequate nutrients does not lead to similar changes in IGF-1 levels. By contrast, reduced protein intake did lead to a significant reduction in circulating IGF-1. These data suggest that reduced protein intake rather than just reduced calorie intake may be important to improve health and delay ageing in humans.