April 19, 2004 -- Severely restricting calories has been shown to slow aging and prolong life in mice and rats. Now early research hints that the same just might be true in humans.
In the small study comparing people who practice calorie restriction as a lifestyle with those who ate a more typical Western diet, the calorie-restricted group had dramatically reduced risks of heart disease and diabetes. Researchers reported that their risk factors were so low they were comparable to those of people who were much younger.
"It is clear that calorie restriction has a powerful protective effect against diseases associated with aging," researcher John O. Holloszy, MD, says. "We don't yet know if these people will live longer, but we known that their risk for these diseases is very low."
The study included 18 people who belong to an organization called the Calorie Restriction Optimal Nutrition Society. The group advocates consuming between 10% and 25% fewer calories than is considered normal while being careful to maintain proper nutrition. Men in the group typically eat fewer than 2,000 calories a day and women eat fewer than 1,500.
The findings are published in the April 27 issue of the Proceedings of the National Academy of Sciences.
Eighteen study participants -- including three women -- on calorie restriction had been following the diet for as little as three years and as long as 15, and their daily intake of calories ranged from about 1,100 to 1,950, depending on height, weight, and gender. They were compared with 18 age- and sex-matched people who ate a typical American diet, consuming between 1,975 and 3,550 calories per day.
To examine heart disease risk, the leading cause of death in the U.S., researchers examined heart disease risk factors such as blood pressure and cholesterol. They also measured blood sugar and insulin levels in the blood to evaluate diabetes risk, one of the most significant heart disease risk factors.
The average blood pressure in the normal diet group was 130/80, which is considered above normal. Last year, researchers linked blood pressure over 120/80, called prehypertension, to an increase in heart disease and stroke. Doctors recommend a healthy diet and exercise to treat prehypertension. A blood pressure of 140/90 is officially considered high.
By contrast, the average blood pressure in the calorie-restriction group was 100/60, which is more typical for a 10-year-old.
Body mass index (BMI), an indicator of body fat, was much lower in the calorie-restriction group. At 19.5 the calorie-restriction group had a normal BMI compared with a BMI of 26 in the normal diet group. A BMI of 25 and up is considered overweight. Total body fat was 7% in the calorie-restriction group -- considered on par with serious athletes -- compared with 22% for the normal diet group.
Cholesterol was also much better in the calorie-restriction group with total cholesterol of 158 vs. 205 in the normal diet group. Blood sugar and insulin levels were also improved in the calorie-restriction group.
Restriction Diet Not for Everyone
While the findings are intriguing, Holloszy tells WebMD that the message is not that everyone would be better off following a calorie-restriction diet.
"This is an extreme diet that takes tremendous motivation," he says. "There are very few people who could stay on it very long. I think the message for everyone else is that moderate calorie restriction to lower body mass is still beneficial."
Brian Delaney, who is president of the calorie-restriction group, agrees that the diet is not for everyone, or even most people. He says the organization now has about 900 members.
Khurram Hashmi, 36, tells WebMD that he began following the diet a little more than four years ago. He is around 6 feet tall, weighs 117 pounds, and eats about 1,900 calories a day. He says he ate fewer calories for a while, but was losing too much weight.
Delaney says he also eats around 1,900 calories a day, which is about 600 less than what is considered normal for an average-sized man.
"I think everyone should do what they need to do to have a great life," Delaney says. "Some of the most productive people in history were gluttons who died young. So for people who would be miserable doing this and who wouldn't be productive, I say why do it? But for those who want to try it there is no question that it prevents disease."
American Heart Association nutrition expert Robert Eckel, MD, says the study offers some of the first evidence that the longevity benefits found in the animal studies may also apply to humans. But he agrees that very few people could stick to a diet that so severely restricts calories.
"We have trouble getting people to lose 5 to 10 pounds," the University of Colorado Health Sciences Center professor tells WebMD. "I can't imagine telling them to restrict their calories by 30% or so for the rest of their lives. That is an unrealistic message. But benefit can clearly be derived by maintaining a healthy body weight, and that is not an unrealistic goal."