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Clever genetic detective work may have found out the reason why a near-starvation diet prolongs the life of many animals. Ronald Kahn at Harvard Medical School in Boston, US, and his colleagues have been able to extend the lifespan of mice by 18 per cent by blocking the rodents increase of fat in specific cells. This suggests that thinnessand not necessarily dietpromotes long life in calorie restricted animals. Its very cool work, says aging researcher Cynthia Kenyon of the University of California, San Francisco. These mice eat all they want, lose weight and live longer. Its like heaven. Calorie restriction dramatically extends the lifespan of organisms as different as worms and rodents. Whether this works in humans is still unknown, partly because few people are willing to submit to such a strict diet. But many researchers hope they will be able to trigger the same effect with a drug once they understand how less food leads to a longer life. One theory is that eating less reduces the increase of harmful things that can damage cells. But Kahns team wondered whether the animals simply benefit by becoming thin. To find out, they used biology tricks to disrupt the insulin receptor gene in lab micebut only in their fat cells. Since insulin is needed to help fat cells store fat, these animals were protected against becoming fat, explains Kahn. This slight genetic change in a single tissue had dramatic effects. By three months of age, Kahns modified mice had up to 70 per cent less body fat than normal control mice, despite the fact that they ate 55 per cent more food per gram of body weight. | 
