Researchers caution that not many studies have examined humans who are practicing intermittent fasting or caloric restriction. But the little evidence that exists is favorable.
A study published last week in the Proceedings of the National Academy of Sciences found that reducing calories 30% per day increased the memory function of elderly men and women. The study was performed at the Salk Institute in La Jolla.
University of Utah scientists looked at health data from members of the Church of Jesus Christ of Latter-day Saints, who have lower rates of heart disease than most Americans. Mormons typically don't smoke or drink alcohol, and some abstain from food on the first Sunday of every month. After controlling for several factors that protect against heart disease, the researchers found that only fasting made a significant difference in lowering the risk of heart disease. Among 448 people surveyed, intermittent fasting was associated with more than a 40% reduction in heart disease risk. Fasting was also linked to a lower incidence of diabetes. The study was published in October in the American Journal of Cardiology.
Another study showed that asthma patients who fasted had fewer symptoms, better airway function and a decrease in the markers of inflammation in the blood than those who didn't fast or restrict calories. The study was conducted because being overweight is known to worsen asthma symptoms. The study was published in 2007 in the journal Free Radical Biology & Medicine.
"They complied with the diet pretty well," Mattson says. "If people know that tomorrow they can eat whatever they want, today they can eat less."
The National Institutes of Health is now supporting calorie-restriction research at three medical centers. At one study site, Washington University in St. Louis, Dr. Luigi Fontana is following the largest group to date of people who practice caloric restriction or intermittent fasting. So far his research shows that such people are not malnourished and have excellent cardiovascular health.
"Eating less is important because 65% of the American population is overweight," Fontana says. "But another question is: If you are already lean, should you change your diet to improve your health and possibly extend your life span?"
That ultimately may be the strongest selling point of a reduced-calorie lifestyle.
(For first-person accounts, see accompanying article.)
"It does demand more than some other diets," says Joseph Cordell, a St. Louis lawyer who limits his intake to 1,800 to 1,900 calories a day.
"But surely the payoff is dramatically better than anything else. I feel so much better and have more energy. And there is this prospect of living so much longer than you otherwise would."
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Daily calorie consumption has increased among American adults, from an average of 2,234 per day in 1970 to an average of 2,757 in 2003, according to the U.S. Department of Agriculture. The number of calories needed each day to maintain weight varies according to age, gender and activity level. A calorie calculator to individualize your intake can be found on the USDA website MyPyramid.gov.
Here are some general calorie consumption recommendations from the USDA:
* Active females ages 19-30: 2,400
* Active females ages 31-50: 2,200
* Active females ages 51 and older: 2,200
* Active males ages 19-30: 3,000
* Active males ages 31-50: 3,000
* Active males ages 51 and older: 2,800
* Sedentary females ages 19-30: 2,000
* Sedentary females ages 31-50: 1,800
* Sedentary females ages 51 and older: 1,600
* Sedentary males ages 19-30: 2,400
* Sedentary males ages 31-50: 2,200
* Sedentary males ages 51 and older: 2,000
Active is defined as a lifestyle that includes physical activity equivalent to walking more than three miles a day at three to four miles per hour in addition to the light physical activity associated with typical day-to-day life.
-- Shari Roan