Dietary restriction studies in humans: focusing on obesity, forgetting longevity.

Dietary restriction (DR: food restriction without malnutrition) is often considered as a nearly universal means to extend longevity in animal species and we could make the hypothesis that DR could increase longevity in humans. Some authors support the opinion that DR has already increased longevity in Okinawa inhabitants, and thus that DR can increase longevity in humans. The purpose of this article is to stress that no data on humans with a normal body mass index (neither overweight nor obese) indicate that DR can increase life span and health span, particularly because the results observed in Okinawa inhabitants can probably be considered as showing mainly deleterious effects of malnutrition rather than positive effects of DR. Since DR does not appear to increase human life span, studies testing for the effect of DR in humans should focus on the health effects of a mild DR in overweight and obese people, rather than in normal-weight people.