Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Benefits From Calorie Restriction Not Yet Proven Long Term

Dear Doctor: Some studies suggest that long-term calorie restriction can lengthen lifespan; others say it won't. Which should we believe?

Dear Reader: This is a perplexing question. We need energy to live, and the food we eat provides that energy. Obviously, gluttony can lead to dire health consequences, including Type 2 diabetes, obesity and high blood pressure, but less obvious is the case for decreasing caloric intake to below normal levels in order to improve health.

The benefit of calorie restriction was first seen in laboratory rats in the 1930s. Subsequent studies have shown that a 30 to 60 percent reduction in calories in mice and rats led to an increase in both the average and maximal lifespan of the rodents.

Of note, researchers found equal improvement in average lifespan among rodents that exercised to keep the weight down, but no improvement in maximal lifespan. In other words, if the maximal age of a rat is 2 1/2 years, the maximum age would increase to 3 years by calorie restriction, but would stay at 2 1/2 years by exercise.

Calorie restriction has shown benefits in chickens, spiders and even single-celled organisms.

The reason may lie in the reduction of the metabolic rate that occurs with calorie restriction. In reducing the metabolic rate, the body temperature decreases, as does the formation rate of damaging oxidative chemicals. These oxidative chemicals damage DNA, cell membranes and the protein within cells, and may be one of the reasons that bodies age. Also, calorie restriction leads to a decrease in blood sugar and body insulin levels.

As for whether the physical benefits of calorie restriction apply to humans, a 2016 study in non-obese males and females compared those who maintained their normal diets to those who had a 25 percent decrease in their caloric intake. The subjects were followed for 24 months. The calorie restriction group lost almost 16 pounds more than the control group. Further, people's moods improved significantly in the calorie restriction group, as did reported improvements in quality of life, sleep and sexual function.

When it comes to calorie restriction and longevity, note that in Okinawa, Japan, calorie intake is 17 percent less in adults and 36 percent less in children when compared to the rest of Japan. The rate of death from heart attacks, strokes and cancer is 31 to 41 percent less than the national average. This doesn't prove cause and effect, but it does suggest the need for additional research.

Clearly, calorie restriction seems to have benefits, but proving those benefits over the long term in our not-so-steady human lives? That's not easy. Certainly, however, in our world of plenty, we need to be mindful of the amounts that we eat.

(Send your questions to, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)