Is a low-calorie diet the secret to longevity?

Madelyn Fernstrom, Ph.D., CNS TODAY diet and nutrition editor • Profile • E-mail

We all know that cutting back on calories promotes weight loss, but does it also promote longevity? Several thousand Americans seem to think so. Their beliefs are based on animal studies, such as those involving rodents and monkeys, done as far back as the 1930s. The experiments show that eating 25 to 40 percent fewer calories every day can extend animals’ lifespan by up to 50 percent. The idea of living longer depending on what you eat, or don’t eat, is an exciting one, so I wanted to share what we know about this diet.

What is a restricted-calorie diet?
The restricted-calorie diet limits the total calories a person consumes, while retaining a balance of nutrients, in the belief that that will slow down the aging process and reduce the risk of developing diseases associated with aging. This diet, which takes a lot of focus and discipline, is not a weight-loss plan, although, of course, that is one of its side effects.

While considered by some to be “extreme,” people who follow a restricted-calorie diet don’t have eating disorders. They eat a balance of nutrient-rich foods and don’t restrict specific foods. While skipping meals is not unheard of as part of a restricted-calorie diet, extended fasting and irregular eating habits that is common with people who have eating disorders are not.

How many calories do you have to cut?
Calories are typically cut anywhere from 25 percent up to 40 percent. The founder of the movement, the late Dr. Roy Walford, advocated reducing daily calories over time to achieve a target body weight that is somewhere between 10 and 25 percent less than your weight when you were in your late teens or early 20s (assuming that you were not overweight or obese at that age). Dr. Walford thought that this would be a healthy adult weight, since it’s before most people assume a more sedentary lifestyle and their metabolic rates start to slow down.

Confused? Let’s do the math. If you’re a 5’ 5” woman weighing 145 pounds, that puts your BMI at 24, which is considered to be healthy by the latest U.S. health standards. To maintain that weight, you need to eat around 2,200 calories a day. If you switch to a restricted-calorie plan, you’re looking at about 1,600 calories a day. The assumption is these calories will include foods that have maximum nutritional power, ranging from protein, to fat, to vitamins and minerals.

It’s pretty easy to get an idea of how much you can eat if you’re interested in this diet. Here’s how to calculate your daily calories on the restricted-calorie diet:

1. Multiply your present weight by 15. This gives you a reasonable idea of the total number of calories you need to maintain your present weight.
2. Now divide this number by four. This is the number of calories you need to cut out every day to comply with the restricted-calorie plan.

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