There is ample evidence from experiments in mice and rats that, if you substantially reduce their intake of calories, they will live longer. Take a rat or mouse and reduce its caloric intake to 40% of the usual laboratory diet. Of course, in this experimental design, while you reduce calories, you give the animals the normal amounts of vitamins, minerals and other nutrients that are vital to their health and well-being. These mice live on average about 50% longer than mice given a usual laboratory diet. But the caloric restricted rodents mature slower, take more time to go through puberty and reproduce later. Roy Walford and his colleagues went one step further and gave mice normal calories as they matured but then switched to caloric restriction in early adulthood. These animals lived 40% longer than animals given the usual laboratory diet. In addition, the caloric restricted animals were healthier with fewer cancers and other diseases ¹.

Weight and longevity

There are many scientists who would like to extrapolate these experimental results to human beings. Dr. Walford has written The 120 Year Diet, a book that calls for a reduction in human calorie consumption, which Dr. Walford believes will substantially increase human lifespan. He has reduced his own caloric intake by 1/3. Is he right?

He is certainly right for rodents! There have been human populations subjected to near starvation through famine and war. However, these groups never received the normal amounts of vitamins, minerals and nutrients. Therefore, there are no human studies done the same way that the mouse studies were done (except for Dr. Walford, and we're not sure that he'll make it to age 120).

There are two ongoing studies of caloric restricted primates that suggest that restriction of calories may reduce the risk of certain diseases such as diabetes ². However, these studies have not lasted long enough to demonstrate any significant increase in life expectancy.

For humans, all we have are the weights, heights and age at death of millions of individuals that have been compiled over the years by insurance companies. If you look at this incredible data base, it is clear that the longest lived group are those in the middle weight categories and that those who were at the two extremes, the very underweight and the very overweight, had the shortest time on this planet. So, at least for now, if you're a rodent, severely limit your calories. For us primates, there's no compelling evidence to support serious fasting right now. There's also no evidence that the caloric restricted mice thought the extra years were worth the substantial caloric restriction they suffered.

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