Scientists already have evidence which suggest that prolonged calorie restriction increases maximum life span in rodents and researchers at Louisiana State University in Baton Rouge were interested to see whether prolonged calorie restriction affected the biomarkers of longevity in humans.

Dr. Eric Ravussin, and his team enrolled 48 healthy overweight but not obese, men and women in a 6-month trial in order to look at the effects of calorie reduction.

The men and women were assigned to one of four groups: a control group, which followed a normal diet; a calorie restriction group, which received 25 percent less calories than the daily requirement; a third group, which exercised and reduced calorie intakes (12.5 percent calorie restriction and 12.5 percent increase in energy expenditure); or a group that received a very low calorie diet, starting with 890 kcal a day and then increased to maintain a 15 percent weight loss.

The researchers found that after 6 months, while patients in the control group lost about 1 percent of their weight, both calorie restriction groups lost approximately 10 percent of their weight with or without exercise, while those on the very low-calorie diet lost nearly 14 percent of their weight.

The researchers also found lower blood levels of insulin after fasting and a lower body temperature in all participants who undertook a restricted calorie regimen.

Body temperature and blood insulin levels are considered markers of longevity and it has been shown both in animals and humans that those with lower body temperature tend to live longer, as do those with lower fasting insulin levels.

It was also found that less DNA damage seemed to occur in patients with lower calorie intakes.

The researchers say the findings suggest that prolonged calorie restriction in humans supports the theory that metabolic rate is reduced beyond the level expected from reduced metabolic body mass.

But they believe studies of longer duration are needed to determine if calorie restriction attenuates the aging process in humans.

Goals for the intervention groups included a 15 lb weight loss (95 percent of participants were overweight or obese), 3 hours per week of moderate physical activity, daily sodium intakes of no more than 2300 milligrams (1 tsp salt), and limits of one alcoholic drink per day for women, and two per day for men. Those also following the DASH diet were asked to increase their consumption of fruits and vegetables to 9-12 servings per day, consume 2-3 servings of low-fat dairy products, and keep total fat to no more than 25 percent of total daily calories. To keep track, participants kept food diaries, monitored calories and sodium intakes, and recorded minutes of physical activity.

More than one-third of participants had high blood pressure at the beginning of the study. Of these, 62 percent in the intervention group with DASH, and 60 percent in the intervention group without DASH successfully had their blood pressure under control after 18 months (that is, their blood pressure levels were no longer considered high). Comparatively, only 37 percent of the control group with hypertension at the study's start had their blood pressure under control at the end of the study.

"These rates of hypertension control produced by the two interventions are even better than the 50 percent control rates typically found when single drug therapy is used to control high blood pressure," said William M. Vollmer, Ph.D., a study investigator from Kaiser Permanente Center for Health Research.

Compared with the control group, one or both intervention groups had:

Greater weight loss: 5.9 lb in the DASH group and 4.8 lb in the group without DASH. Greater improvement in fitness: 2 beats per minute lower heart rate for the DASH group and 1 beat per minute lower heart rate for those without DASH. (The greater the reduction in heart rate, the greater the improvement in fitness.) Greater sodium reduction: 354 milligrams for those on the DASH eating plan and 384 milligrams without DASH (about 1/6 tsp less salt). Greater reductions in calorie intake: the intervention groups reduced their daily intake by 95 (DASH) and 130 calories (without DASH).

In addition, 25 percent of intervention group participants met the weight loss goal. The group following DASH also achieved increased fruit, vegetable, dairy, fiber and mineral intakes and decreased fat intake.

The 6-months results of PREMIER results were reported in April 2003 in the Journal of the American Medical Association.

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