And Now the Bad News – It Takes an Hour a Day to Lose Weight

Only a week ago I was writing that, if you found half-an-hour a day too much to devote to exercise, you could replace it with 10 minute of intense, vigorous exercise.  And next day I read in the Journal of the American Medical Association that women need an hour of moderate exercise a day to maintain a healthy weight!  This escalation comes from Boston researchers, who followed 34,000 healthy women for an average of 13 years.

At baseline, the women’s average age was 54.  Physical activity and body weight was reported after 3, 6, 8, 10, 12, and 13 years.  There w as no attempt to influence diet.  The participants were classified as spending less than 7½, 7½ to less than 21, and 21 or more MET hours (metabolic-equivalent-task hours) a week of activity at each 2- to 3-year interval.  (7½ MET hours is equivalent to up to 150 minutes of moderately intense physical activity, i.e. a half-hour, 5 days a week.)   

The women gained an average of 5.7 pounds during the study.  Those who exercised the most (i.e. 21+ MET hours or 420+ minutes a week) gained significantly less weight than those who exercised less than 420 minutes a week.  Over a 3-year period, all the women exercising less than 420 minutes weekly gained an additional ¼ pound, on average, over those doing 420 minutes a week.

To make matters worse, although physical activity was shown to be associated with less weight gain, this wasn’t the case for women with a body mass index (BMI) over 25;  for those women with a BMI above 25 (i.e. designated “overweight”, according to current thinking), exercise had no effect on weight control.

In this study, women on a usual diet who were successful in maintaining normal weight (or gaining fewer than 5½ pounds over 13 years) averaged an hour a day of moderate exercise 6 days a week.  So what’s to be done if this is an impossible task?  Change to a more prudent diet, and/or adapt periodic high-intensity bouts within your workout regime.  Just don’t abandon exercise completely – diet alone probably won’t do it.