Reducing calorie intake provides health benefits to all people regardless of their current health status, a new study found

Cutting calories by 15% for two years can slow the metabolic process that leads to aging and protect against age-related diseases, new US study found, CNN reports.

After just one year on a reduced-calorie diet, study participants saw their metabolic rates drop significantly.

"Reducing calorie intake provides health benefits to all people regardless of their current health status," said Leanne M. Redman, lead author of the study and an associate professor at Pennington Biomedical Research Center at Louisiana State University.

After pilot studies, the National Institute on Aging committed to funding larger phase two CALERIE studies at three universities: Pennington in Baton Rouge, Washington University in St. Louis and Tufts University in Boston.

Reducing calories

At Pennington, Redman and her colleagues focused on reducing calories by 25% through diet alone. Women between 25 and 45 and men between 25 and 50 were recruited; about half were normal weight and the other half overweight but not obese. Each participant was also given a scale. Instead of calculating daily calories and slashing them by 25%, weight loss was used to estimate the total reduction in calories for each participant over time.

The results

However, the participants did not hit the 25% reduction as anticipated, Redman said: "People achieved 15% calorie restriction, actual, over the two years." No matter the results from this lesser calorie restriction amount were "pretty remarkable," she said.

For example, participants lost an average of about 20 pounds each by the end of the first year and maintained that loss during the second year.

Not only did calorie restriction slow the metabolism of participants, lower levels of oxidative damage were seen when measured by a compound in urine. Calorie restriction, then, mimicked some of the healthy aging signposts seen in long-lived individuals, Redman said.

The "big breakthrough" with this study is that it is the first randomized controlled trial of calorie restriction in humans, said biologist John R. Speakman of the University of Aberdeen in Scotland and the Chinese Academy of Sciences in Beijing.

Exactly how calorie restriction prevents aging, Speakman said "is the million-dollar question." The research supports two theories of longer life: the "rate of living" (lower metabolism) and reduced oxidative damage.