The article in the August 17th 2009 issue of TIME magazine entitled “The Myth About Exercise” is filled with inaccuracies and irrational conclusions. It misquotes medical research to paint a picture of exercise that is simply wrong.
Play Podcast 140
I’ll start with a brief discussion of some of the medical articles that were used by the author of the TIME article. I did my own review of the medical research and I conducted interviews with Dr. Timothy Church who is cited in the TIME article and Dr. Mark Pereira of the University of Minnesota School of Public Health.
To make an argument that exercise may cause weight gain the author of the TIME article cherry picked bits of data from several respectable medical studies about weight loss. The TIME article is a frustrating example of how the mainstream media can completely confuse and distort the facts about an issue. Whether the misinformation about exercise in the TIME article is a consequence of incompetence or intentional creation of controversy where none exists is not clear. People who read the article could use it as an excuse to not exercise.
The TIME article attempts to make the point that more people are exercising at the same time that more people are becoming obese. To make this argument the author picked a single data point from a study called the Minnesota Heart Survey (MHS) published in the journal Medicine and Science in Sports and Exercise in October 2006. TIME states that data from the MHS indicate that the number of people who say they exercise increased from 47% in 1980 to 57% in 2000. During the same time period there was an explosion in the percentage of Americans who are obese. Therefore, the TIME article concludes, exercise must be making us fat.
This is an absolutely stunning oversimplification and misrepresentation of data. Let’s begin with the fact that the MHS was restricted to people living in the Minneapolis – St. Paul metropolitan area and the obesity rates that are quoted are from data based on the whole country. So, it’s very possible that the people doing more exercise and the people getting fat are not the same people. To conflate two data points from unrelated groups is just irrational.
But it gets worse. What the MHS actually found was that between 1980 – 2000 the percentage of people who exercised varied dramatically based how the survey questions were asked. The TIME article cherry picked the most impressive number to make it appear as though we are in the middle of an epidemic of over exercising. We aren’t. In the MHS there was a tendency for all of the study population to gain weight between 1980 and 2000. However, the authors of the MHS clearly point out that the people who exercised the most were the people who gained the least amount of weight. The MHS actually concludes that exercise is an important part of the solution to the obesity epidemic. The TIME magazine article took the MHS that demonstrated the benefit of exercise for weight control and used it to make the argument that exercise is not helpful for weight control, and might even cause us to gain weight.
Dr. Timothy Church appears prominently in the TIME article – including a large photograph of him and his lab. Dr. Church is a medical researcher at the Pennington Biomedical Research Center in Louisiana. He and his colleagues conducted a study in which they took just over 400 postmenopausal, overweight or obese, sedentary women and looked at the health effects of different doses of exercise. It was an ingenious study because rather than ask the women how much they exercised Dr. Church put them through a supervised exercise program using carefully controlled intensity levels and durations. The training period lasted 6 months. The women were divided into 4 groups that included a control group who did not exercise and 3 exercise groups that did differing amounts of exercise. The exercise groups were created based on the current exercise recommendations, which are 30 minutes per day five days a week. In Dr. Church’s study there was a group of women who were exercised for 70 minutes a week, a group who exercised for 136 minutes per week, and a final group that exercised for 194 minutes per week. These duration groups correlated roughly to 50%, 100%, and 150% of the current exercise recommendations thus giving the different “doses” of exercise. The exercise sessions alternated between treadmill walking and stationary bicycling. The exercise intensity was controlled at 50% of the individual participant’s maximum oxygen consumption. This is an intensity that Dr. Church describes as moderate enough that most people can do it. A variety of physiological parameters were collected on the women during the study including baseline fitness levels and fitness levels after the exercise training ended.
The women were told that this was not a weight loss study and that they should not change their diet. Dr. Church did have the women keep records of what they ate, but the study was focused on exercise and the methods of tracking food consumption were kept simple.
Dr. Church was able to make predictions on how much weight the women would lose based on how many calories he calculated they were burning with their exercise. Again, it is important to appreciate that this study carefully controlled the duration and intensity of the exercise and the exercise was done under direct supervision. Using simple math Dr. Church estimated how much weight should be lost using the value of 3500 calories per pound of fat. So, if a woman expended 7000 calories with exercise she would be expected to lose 2 pounds. Expending 7000 calories is something that accumulated over several weeks of exercise.
Over the 6 months of the study the 2 exercise groups of shorter duration, corresponding to 50% and 100% of current exercise recommendations, lost slightly more weight than Dr. Church calculated they would. The group of women who did the most exercise, corresponding to 150% of current exercise recommendations, lost only half as much weight, on average, as Dr. Church calculated they should. Dr. Church points out that within this group there was a wide variation with some women losing more weight and about a quarter of the women losing no weight. The women who didn’t lose as much weight as predicted were called “compensators” by Dr. Church and he speculates that they may have been rewarding themselves with extra food for their exercise. Dr. Church believes that the women may have overestimated how many calories they were burning through exercise and underestimated how many calories were in the food they were eating leading them to lose less weight than expected.
Dr. Church is quick to make two very important points: 1. All three study groups did demonstrate weight loss in response to exercise. 2. His study was not designed to investigate the phenomenon of compensation and therefore he can only guess as to why some of the women didn’t lose as much weight as anticipated – but they did lose weight!
Another very important finding from Dr. Church’s study was that the improvement in measured aerobic fitness in the study women was dose dependent. The more exercise the women did, the more fit they became based on carefully measured maximum oxygen consumption. This aspect of the study is discussed in detail in an interview with Dr. Church in Fitness Rocks podcast 073.
The TIME article used Dr. Church’s research to make the argument that exercise makes us hungry and so we won’t lose weight by exercising, and might even gain weight. But, I repeat, all three exercise groups in Dr. Church’s study lost weight in response to exercise. The group that exercised the most did not lose as much weight as expected – but they did lose weight!
Fitness Rocks Podcast 140 has a telephone interview with Dr. Church that I think you will find very interesting.
Have a great workout.
Monte
References:
Article by Dr. Timothy Church regarding exercise dose and weight loss
National Weight Control Registry Research Findings
Effect of Exercise in 24-Month Weight Loss in Women
Related posts:
Welcome back. I just caught your podcast this morning while working out. I thought I’d dip into an old one of yours and found this new one.
You are always the welcome voice of scientific reason on these issues. I don’t think anyone else summarizes, synthesizes, mixes, combines and interviews key figures on exercise and health as well as you do. And with no conflicts of interest.
As you’ve spoken before on disease compression, lowering the cost of chronic disease, and lowering the cost of health care, these points need to be taken into account in the upcoming health care reform debate.
And of course they are vital to all of us as individuals.
Good to see a new episode from your voice of fact, research and reason. Since 2007 I’ve listened to all the episodes, followed the recommendations you make based on the medical research, and I’m pleased with the results. At some point I’ll go through and listen to the episodes again, but if there are new ones from time to time, so much the better. Thanks!
Dr. Monte,
I wanted to thank you for posting this excellent rebuttal to the Time Magazine article. I actually assigned that article to my Exercise Physiology class to read last week, and we had an excellent discussion of its shortcomings. Given the level of student interest, I’m assigning them to listen to this podcast episode as a way of demonstrating that you can’t believe everything you read in a popular media article.
Great Work!
Pete