Calorie deficit explained: Is it a safe, sustainable approach to weight loss? - Harvard Health

Reducing calorie intake has extended lifespan in animals including mice, rhesus monkeys, and fruit flies. In some studies, the animals also remained healthier for longer. But severe calorie restriction can come with serious costs. Mice placed on a diet with 40% fewer calories, for instance, become more vulnerable to infections, reproduce less successfully, and show impaired growth. That has left scientists with a difficult question: Could humans gain some of the longevity benefits of calorie restriction without experiencing those harmful effects? A new study, published in Nature Aging, points to a possible answer involving an immune protein called complement component 3 (C3).

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