San Diego Sports Medicine Doctor | San Diego's Coastal Sports & Wellness

Sure that’s a controversial headline, much like Time’s recent article entitled “Why Exercising Won’t Make You Thin” talks about why exercising most days of the week may not make you any thinner, The magazine article author, John Cloud, cites his own battle with a bulging stomach despite a well-prescribed exercise program at his local gym, and suggests that exercise really may not be worth doing for weight loss because of the extra calories that some people eat after they exercise.

Its an unfortunate misrepresentation of some good research by some talented scientists.

I’ll be spending the week picking apart the problems with the Time Magazine article, simply because it ignores a large body or research out there.

In the first section of the Time article, Mr. Cloud references a recent research study published by scientists at Louisiana State University and The Cooper Institute (Dr Kenneth Cooper is the physician that coined the term “aerobics” back in the 1960′s). You can get a copy of the article here. The study looked at the effected of different weekly amounts of moderate exercise (cycling or treadmill) on weight loss and waist size in fairly inactive, older, post-menopausal women (average age of 57 with an average weight of 185 lbs and a body fat percentage of almost 29%)

The reality of this exercise study is that the researchers found that all three exercise groups lost weight. Interestingly, the group that exercised the most, did not lose weight at the researchers’ predicted rate – however, that group still lost weight. Here’s a look at the data from the first two exercise groups (4KKW and 8 KKW) below. These two exercise amounts are equal to 72 minutes (4 KKW group) and 134 minutes (8 KKW group) of exercise per week based on current national exercise duration recommendations by organizations like the American College of Sports Medicine.

The data from these two exercise groups actual show that both groups loss more weight than predicted by the researchers, and the 8 KKW group lost more weight that the 4 KKW group, as seen in the two graphs below:

The researchers did find that the 12 KKW group (exercising at 194 minutes per week) did not lose as much weight as predicted based on their exercise calorie expenditure. Looking at the data on the graph below, it seems that the 12 KKW group had a much slower rate of weight loss that the other two groups even in the first 4 weeks of the study. Why is that slower rate of weight loss in the first 4 weeks significant? It’s based on the study design. Since the researchers started with an older group of subjects, they started each group out at 72 minutes of exercise per week for the first week. The two middle and higher exercise groups then had roughly 18 minutes of exercise added to their weekly exercise time until they reached the maximum exercise duration for each group. So the 8 KKW and 12 KKW groups would have been increasing their exercise durations at the same pace for weeks 2 through 4 (where the 8 KKW group would stay at the 134 minutes and the 12 KKW group would continue to add time each week until they reached the 194 minutes of weekly exercise at week 8 of the study.

To their credit, the researchers acknowledge that the point of their study was to determine whether or not there was a linear dose (or time)-dependent relationship between the amount of weekly exercise and the amount of weight loss by their test subjects. They also clearly state during their discussion of their findings that:

Our findings should not be interpreted as suggesting that lower doses of exercise are more effective in producing weight loss than higher doses. We emphasize that DREW was not a weight loss study and it was not designed to examine the nuances of exercise induced weight loss.

The authors of the research paper also note the a good portion of the 12 KKW (higher duration exercise group) continued to loss weight at the predicted rate (27% of the 12 KKW participants according the the data). So the reality is that while a subgroup of the higher amount of weekly exercise group didn’t lose weight at the predicted rate, another group did match the predicted weight loss.

One reason suggested for the lack of weight loss in the higher time-duration exercisers from the Time article was the possibility that the high exercise-time group were less activity during their non-exercise time away from the research lab. A credible reason, except that the researchers controlled for this variable by having all groups wear pedometers, including the control group that did not exercise at all. What kind of difference did they find in the outside activity levels between all groups?

None. That’s right. All four groups (the non-exercising control group and the three exercise groups) had roughly the same activity levels outside of the research lab when they were performing their exercises for the study. So the high exercise group didn’t go home and lay around on the couch after their workouts, or limit their walking or other activities any more that the other groups.

Further studies have also demonstrated that people that have lost a substantial amount of weight (think the Biggest Loser) usually exercise 45 minutes a day in order to maintain their weight loss. Exercising 45 minutes a day for 4 days a week would put that prior weight loss group at roughly the 8 KKW group exercise duration.