Could eating less help you live a longer, healthier life? If you're a lab animal, the answer is probably "yes". The answer is less certain for us humans.

The idea of calorie restriction (also known as "CR") as a way of living longer has been around for a long time. Researchers studying mice back in the 1930's discovered that lowering the mice's calories lengthened their lives. But would the same thing happen in humans? Two decades ago, some researchers started studying calorie restriction in monkeys since monkeys are much more like humans than mice. 

The Study Results             The results of this ongoing study in monkeys were published in the July 10 edition of Sciencemagazine.  For 20 years, the researchers fed half of the monkeys a healthy diet that gave the monkeys all the food they wanted to eat. They fed the other half a healthy diet with one difference - the diet was 30% lower in calories. So basically, it was the same food just calorie restricted versus "all you can eat". Here's what they found:

  • Over the 20-year period, 50% of the monkeys on the regular diet died. Only 20% of the monkeys on the lower calorie diet died.
  • The monkeys on the lower calorie diet were less likely to get diabetes, cancer, heart disease than the monkeys on the regular diet.
  • The brains of the calorie-restricted monkeys showed fewer signs of shrinking then the brains of the monkeys on the regular diet.

How Does It Work?            Researchers aren't sure why calorie restriction lengthens life. Most do not think the weight loss is the reason. In fact, when researchers lower animals' calories too quickly, they live shorter than expected lives. Only when the calories are dropped slowly, over a long time, do animals live longer. There is another possible reason caloric restriction works. Many researchers think that when we eat less food we produce fewer dangerous by-products of processing that food for energy.

Should You Restrict Your Calories?     So should we recommend calorie restriction for people who want to live longer and lower their chances of getting certain diseases? We still don't know for sure if people who restrict their calories will get the same results that the monkeys did. But some people are already trying it. You can see how they're doing it at the Calorie Restriction Society's 

But before you drastically cut back on your calories, keep a few things in mind:

  • You may be very hungry.Calorie restricted diets are usually 20% to 30% lower in calories than your current needs. So if you need 2000 calories, you would want to drop your calories down to 1400 to 1600 calories a day over time
  • Calorie restriction could cause an eating disorder.Cutting back on the amount of your food could lead to an eating disorder in some people because of the extreme focus on food.
  • You have to eat very nutritious food to avoid malnutrition. You have to eat much less food but still get all the right nutrients. That does not leave much room for chocolate chip cookies or French fries!
  • It's a major lifestyle change. You may find that you spend a lot more time making your meals. It could also have an undesirable effect on your social life if you and your friends like to go out to eat a lot.
  • You may lose too much weight. Although weight loss is not the goal of caloric restriction, many people do lose quite a bit of weight. For some, the change in their appearance may be positive. But if you're already thin, losing weight may not be a good look for you.
  • CR could be bad for your bones. Losing too much weight can lower your bone density and can contribute to osteoporosis.

All that said, the benefits of CR could be great - if you do it right! You may lower your chances of getting heart disease, diabetes, or certain cancers. You might even keep your brain in better health. So if you would like to try CR, I recommend meeting with a registered dietitian who can help you design a nutritious plan that will lower your calories gradually. You can find a dietitian in your area by visiting the American Dietetic Association's website:

Beth Kitchin, MS, RD
Assistant Professor
UAB Department of Nutrition Sciences

Source: Colman RJ, Anderson RM, Johnson SC, et al. Caloric restriction delays disease onset and mortality in rhesus monkeys. Science 325, 201 (2009).