Eat Less, Live Longer?

Summarized by Robert W. Griffith, MD
September 25, 2006

Summary

In a 6-month volunteer study of three methods of calorie restriction, different biological markers of longevity were changed by all three methods in favor of prolonging lifespan.

Introduction

Numerous rodent studies have shown that prolonged calorie restriction increases their lifespan. Of course, there's a big advantage of rodent studies - their lifespan is short enough for one to be able to measure it easily, compared with doing studies in humans. But there are 'markers' that can serve as fairly reliable surrogates for lifespan, which we can measure in man. This consideration led to the conduct of a study of calorie restriction in human volunteers, the results of which are published in the Journal of the American Medical Association, and which we summarize here.

What was done

Healthy, sedentary volunteers were sought to participate in a study of calorie restriction at the Pennington Biomedical Research Center, Baton Rouge, Louisiana. They had to be younger than 50 (men) or 45 (women), and overweight but not obese; i.e. their baseline body mass index (BMI) had to be between 25 and 29.9.

A total of 600 people were screened, resulting in selection of 48 individuals. These were then randomly assigned to one of 4 groups:

• controls - weight maintenance diet
• calorie restriction - 25% of baseline energy requirements
• calorie restriction with exercise - 12.5% calorie restriction plus 12.5% increase in energy expenditure by planned exercise
• very low calorie diet - 890 calories a day until 15% weight reduction, then weight maintenance diet

The subjects' energy requirements at baseline were calculated from their measured energy expenditure. Menus were designed for each subject within 100 calories of the individual's target intake. All food was provided by the research center - initially for full consumption at the center, later allowing one meal a day and snacks as take-out.

Cognitive behavior techniques were used to help adherence to diets and exercise programs. The latter involved walking, running, or cycling on 3-5 days a week.

The main measurements recorded were related to longevity - fasting insulin level, core body temperature, dehydroepiandrosterone sulfate (DHEAS) level, thyroxine and tri-iodothyronine (T4 & T3), and blood glucose. The carbonyl content of proteins and DNA fragmentation were estimated as indicators of free radical damage.

Metabolic tests were done at baseline, and at 3 and 6 months. They comprised body weight, body composition, sedentary 24-hour energy expenditure, and sleeping energy expenditure.

What was found

Below are the significant changes seen in the three intervention groups after 6 months:

There were no significant differences found in the other tests listed in the study design, above.

What these findings mean

There was a clear reduction in two of the three previously-reported markers of longevity - fasting insulin level and core body temperature - with all three reduced calorie intake diets. And the decrease in energy was greater than that expected from the loss of body weight and fat mass. This suggests that metabolic adaptation had occurred; the reduction in thyroid tests supports this idea. Finally, the reduction in DNA fragmentation reflects lessened DNA damage, presumably through lower free radical intake in the food.

These findings, taken together, show that reduced calorie intake achieved by different means produces changes in recognized indicators of longevity, suggestive of prolongation of lifespan. However, they are, after all, only pointers obtained after 6 months. Much longer studies need to be done to confirm that the changes produced by this approach continue to be beneficial, and not harmful in the long term. Meanwhile, it wouldn't hurt most people to eat fewer calories, provided they make sure they eat the right sort of food. And they probably would live longer - any degree of overweight is associated with increased mortality¹.

Source

• Effect of 6-month calorie restriction on biomarkers of longevity, metabolic adaptation, and oxidative stress in overweight individuals. A randomized controlled trial. LK. Heilbronn , L. de Jonge, JP. DeLany ,  et al., JAMA, 2006, vol. 295, pp. 1539 --1548

Footnotes
1. Adams KF, Schatzkin A, Harris TB, et al. Overweight, obesity, and mortality in a large prospective cohort of persons 50 to 71 years old. N Engl J Med 2006;355:763-778

Related Links
The Calorie Restriction Society
The Longevity Meme
Quality Counts: Calorie Restriction