Issue 140 Item 7 Fat Mass, Not Caloric Intake Linked to Longevity

Study shows an 18% increase in usual lifespan by reducing fat mass. While caloric restriction has been shown to increase lifespan, findings from a new animal study suggest that it is fat mass rather than caloric intake per se that determines longevity.

Because leanness and caloric intake are interrelated, it has been difficult to determine the relative importance of each in enhancing longevity, Dr. C. Ronald Kahn and colleagues, from Harvard Medical School in Boston, point out in the January 24th issue of Science.

To address this point, the researchers created a strain of mice that lack insulin receptors in their fat cells. This alteration causes the animals to have reduced fat mass and protects them from age-related obesity. However, their food intake remains normal.

The researchers found that the experimental mice had a mean lifespan that was about 134 days longer than control littermates. This represents an 18% increase in their usual lifespan.

In addition to sorting out the effects of leanness and caloric intake on longevity, the findings also have therapeutic implications. "Perhaps one day if we are able to find a drug to reduce or block insulin action in fat cells in humans, we might be able to prevent obesity, as well as type 2 diabetes and other metabolic diseases," Dr. Kahn said in a statement. "And who knows, they might also live longer." Science 2003;299:572-574.