Contact:
Dr. Christopher Bell, University of Colorado at Boulder, 
(303) 492-4568 or cbell@spot.colorado.edu 
 

DECREASE IN EXERCISE (EVEN WITH DECREASE IN CALORIES) CAUSES DECREASE IN RESTING METABOLIC RATE IN ACTIVE OLDER ADULTS

Our bodies burn the majority of calories doing relatively nothing, simply sitting still, breathing, even sleeping.  Unfortunately, this resting metabolic rate decreases progressively with age.  An earlier study by Dr. Christopher Bell, University of Colorado, and colleagues found that older people who exercise habitually have a higher resting metabolic rate than their counterparts who are sedentary, even after adjusting for weight and relative amounts of fatty tissue versus muscle mass.   That was the good news.  Now, in a new study first reported at Experimental Biology 2001, Dr. Bell reports the bad: regularly exercising older adults who slow down their exercise (energy output) can't make up for it by reducing their calories (energy input) accordingly.  In the resulting reduced energy flux, their resting metabolic rate will steadily decline.  The researchers took two healthy male and two healthy female older adults, aged between 62 and 67 years, who exercised regularly and had a body fat percentage of 25 percent or less.  Using careful baseline measures of calories taken in and energy expended, the researchers restricted the subjects' exercise by the equivalent of 400 calories a day.  They then restricted their caloric intake by approximately the same amount.  Theoretically, this should have equaled things out and resting metabolic rate should have stayed the same.  But in these active older adults, the resting  metabolic rate declined significantly in less than a week, from an average of 1,248 calories on day one to an average of 1,155 calories on day five.  Dr. Bell says the study is further evidence of the importance of exercise for older people.  Declines in the resting metabolic rate increase the challenge of weight maintenance and likely contribute to the high prevalence of age-associated obesity and its subsequent increased risks of cardiovascular disease and metabolic diseases like diabetes. Furthermore, older people who grow sedentary and thus must continually restrict their calorie intake in order to maintain weight control may eventually limit their ability to achieve recommended daily allowance of vitamins and nutrients.