Junkfood Science: The exercise diet that wasn’t

July 31, 2008

The exercise diet that wasn’t

“Step it up ladies,” we’ve been hearing this week. Research from the University of Pittsburg was reported as showing that it takes an hour a day of exercise for overweight women to get in shape and keep the weight off. According to the media, a new study published in Archives of Internal Medicine found “it only takes one hour of exercise a day to maintain a steady weight loss and keep those unwanted extra pounds off.”

Did reporters read the same study I did? Or, did they take their lead from a press release and fill in the rest with what’s popularly believed fat women should do?

The objective of this study, led by John M. Jakicic, Ph.D., associate professor and Director of the Physical Activity and Weight Management Research Center at the University of Pittsburgh, was to answer the debate about “the amount of physical activity that will facilitate weight loss maintenance.”

It found that no amount or intensity of exercise worked to maintain weight loss. Instead, it demonstrated that exercise was mostly unrelated to weight loss and that cutting calories will result in a temporary weight loss for about 6 months and then, even with continued caloric restrictions and exercise, the inevitable and expected weight gain trajectory ensues.

The study’s actual findings are considerably different from what we’ve been hearing in the news, but won’t be at all surprising to JFS readers or obesity experts, as they’re nearly identical to nearly every other weight loss study published over the past half century. Let’s take a look.


This two-year intervention trial had recruited 201 physically and psychologically healthy women, with an average age of 37 years and body mass index of 32.6. This registered trial [ID # NCT00006315] ran from December 1, 1999 to January 31, 2003. The interim results after the first year had been published in 2003 in the Journal of the American Medical Association and this paper is reporting the final results.

The women participants had been randomly assigned to one of four exercise groups — combinations of intensity and durations: Vigorous intensity/High duration (VH), Vigorous intensity/Moderate duration (VM), Moderate intensity/High duration (MH); and Moderate/Moderate (MM) — to burn an estimated 1,000 to 2,000 kcal/week. They’d been taught the prescribed exercise regimens and to monitor their pulse to reach their age-predicted maximal heart rates, and provided with home treadmills.

The weight loss program also included fat-restricted, very low-calorie diets aiming for between 1,200 and 1,500 kcal/day, which the researchers monitored using food frequency questionnaires; group meetings (weekly x 6 months; bimonthly x 6 months; and monthly x 6 months); telephone calls one to two times per month; and questionnaires to assess other leisure-time physical activity.

Nearly 85% of the women (170) completed the two-year weight loss study. The authors reported only the results of those who completed the study. [In other words, they didn’t skew the results by including those who dropped out and carry forward their weight losses.] Compliance with the group meetings and phone follow-ups was similar among all of the intervention groups: nearly 80% during the first six months and over the course of the study dropped to 67%.


Over the first six months, all of the groups lost weight, 8.3% to 10.8% of their body weight. There was no statistical difference in weight losses among the various exercise groups, however, and the average weight losses differed by a mere 4.84 pounds. The groups exercising the longest (regardless of intensity) lost slightly more than those exercising for half as long each week.

But wait: before you conclude that the nominal larger weight losses were because of exercise, the groups differed in their caloric intakes (1,454 to 1,551 kcal/day). Those women had also cut their average daily calories by about 97 kcal/day more than the other groups. If you believe that 3,500 kcal = 1 pound, this calorie reduction alone would account for a 5-pound weight loss. Nearly exactly the difference seen.

Thereafter, every intervention group steadily gained weight and the upward trajectories showed no signs of leveling off when the trial was stopped at the end of two years. Does this look like weight maintenance to you?

Like all weight loss studies, the familiar rebounding wasn’t because the women were pigging out and cheating on their diets. They all continued to restrict their calories to 1,454-1,689 kcal/day through the end of the trial — eating 350 to 642 kcal less per day than they had been eating while weight stable before the start of the trial. While all of the groups slipped in their exercise regimens over the two years, they also continued to exercise considerably more (about 2-5 times) than they had been at the start of the study.

If you believe the calorie theory, just considering the continued calorie restrictions, then there should have been humongous total weight losses and a dramatic difference of 60 pounds of weight lost between the groups at the end of two years.

Instead, after two years of dieting and exercise, not only were all of the women gaining weight (already nearly half of their weight loss back), but the average weight losses differed among the different regimens by less than 1 ounce per week: 6.38 pounds total at the two year mark. This, too, was not statistically significant, nor was the difference in regain trajectory patterns clinically meaningful.

In other words, weight loss was no more successful with more or less exercise. There was no statistical difference.

And again, in a secondary analysis, those “most successful losers” on the lower end of the rebound trajectories after two years, were also the women most cutting their calories - to increasingly extreme levels, down to 1,365 kcal/day, as well as exercising nearly 6 hours a week. Their calorie restrictions alone during those final 18 months, based on 3,500 kcal = 1 pound, theoretically would have resulted in the loss of another 95 pounds (1.3 pounds/week). But, of course, they were still gaining.

Once again, as the body of evidence has continued to show, regardless of the contrivance to cut calories, most everyone will lose a degree of weight temporarily, then homeostatic metabolic adjustments kick in to return body weights to their genetically-determined setpoint range. [Nor is there any support for healthfulness of starvation-level diets and extreme measures used by anorectics to a maintain weights appreciably lower than what is natural for them.]

Even the most rigidly-followed diets among the most motivated people in the real world will result in weight loss for about 6 months and then regain. It’s only the rate and trajectory of the regains that vary, not the fact of regain. As the FTC’s expert panel and every expert review of the evidence has concluded, weight regain is the rule and virtually everyone regains all of their weight by 5 years. While it is well acknowledged among obesity researchers that for a diet study to credibly demonstrate effectiveness or evaluate health outcomes, it must follow people for at least five years until weights have stabilized, this is another one that stopped well before that.

How many more decades of these studies will there need to be before people realize that weight loss interventions don’t work? While people can repeatedly lose and gain a small percentage of their weight, most yo-yoing a dozen or so pounds, the natural diversities of our sizes are not determined by calories in and calories out.

As professor and Jakicic and colleagues noted in their concluding comments:

Analysis based on randomized group assignment did not indicate a favorable contribution of exercise to weight loss maintenance... However, the greater magnitude of weight loss achieved in the present study may be a result of a greater emphasis on reduction in energy intake along with the inclusion of physical activity... This study demonstrates the difficulty in sustaining weight loss of 10% or more of initial body weight...

However, relatively high levels of physical activity appear to contribute to sustained weight loss.

The study’s conclusion — that exercising 275 minutes/week is beneficial for weight loss, and that “interventions to facilitate this level of physical activity are needed” — are a disconnect, given what the evidence actually showed. Yet this study is precisely what the evidence looks like behind the government’s 2005 Dietary Guidelines calling for an hour exercise a day for weight management.

In fact, according to Dr. Jakicic’s university webpage, his line of prior research showing “that approximately 60 minutes a day of moderate intensity is necessary to enhance long-term weight loss and prevent weight regain...has significantly influenced the physical recommendations included in the 2005 Dietary Guidelines for Americans, which supports this level of physical activity for weight control.”

But how many people actually read the research behind guidelines? Or, has everyone chosen to believe that government public health guidelines are based on something like... evidence?

© 2008 Sandy Szwarc. All rights reserved.


No media story reported the financial disclosure, although it was noted in both the journal article and press release: “Dr. Jakicic is on the Scientific Advisory Board for BodyMedia Inc. and the Calorie Control Council.” BodyMedia makes wearable body monitoring devices that, according to its website:

Our innovative products and patented technologies provide accurate and actionable information about the health and behaviors of people outside of the traditional clinical setting... all taking a more proactive role...through the tracking and management of day-to-day behavior modification...

As the urgency of global health issues such as obesity, diabetes, and cardiovascular disease continues to grow...BodyMedia is responding to these trends and problems by creating state-of-the-art solutions that make it easy for patients and practitioners to track a person's total energy expenditure, duration of physical activity, nutrition, and sleep.

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