The Underappreciated Role of Physical Activity in the Battle Against Obesity—Part 3: Adults and the Relationship Between Physical Activity and Adiposity.

by Kenneth W. Krause.

[Notable New Media]

Kenneth W. Krause is a contributing editor and “Science Watch” columnist for the Skeptical Inquirer. Formerly a contributing editor and books columnist for the Humanist, Kenneth contributes frequently to Skeptic as well. He can be contracted at

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Is physical activity, including structured exercise, an effective strategy in the battle against overweight and obesity? Some have recently suggested that successful weight loss and weight maintenance are the results of improved diet alone.

In part one of this article, I reviewed evidence suggesting that, despite popular media misinformation, most people who maintain weight loss do so through a combination of diet and physical activity. Nor does it appear true, as many have reported, that exercisers completely compensate for energy expenditure through increased sedentary time or energy intake.  In part two, I examined evidence showing that both moderate-to-vigorous physical activity and television viewing time significantly affect adiposity in children.

The National Academies’ Institute of Medicine recently gathered preeminent experts in several relevant fields to summarize the current science exploring “the impact of physical activity in the prevention and treatment of overweight and obesity” (IOM 2015). Here, I discuss the panel’s conclusions relating specifically to adults.

Robert Ross, professor in the School of Kinesiology and Health Studies at Queen’s University, Kingston, Ontario, Canada, presented the most credible evidence on the subject from randomized controlled trials. Before doing so, however, he distinguished between efficacy trials, which ask what happens physiologically when adults actually do exercise, and effectiveness trials, which investigate instead what occurs in terms of behavior change when adults are in one way or another encouraged to exercise.

In terms of efficacy trials, Ross described the results of his own extensive work. First, he found that when previously active male and female participants increased their exercise time and caloric intake, they either did not gain weight or found it challenging to avoid weight loss (Ross et al. 2000, 2004).  As such, exercise appears at the very least to prevent weight gain, even when accompanied by an increase in consumption.

Second, in a study of 300 mostly inactive obese adults who were asked to maintain caloric intake but to add five days of supervised exercise per week for six months, Ross’s team observed an impressive loss of body weight along with decreased waist circumference among all treatment groups (which varied in terms of exercise amount and intensity) (Ross et al 2015). Importantly, they revealed as well that participants did not compensate for elevated energy expenditure through increased sedentary time.

Such results appear to bode very well for those committed to an intelligent and consistent exercise program. “I just don’t think there is any ambiguity here,” Ross commented.  Even for the obese, unless one eats more, an increase in exercise will translate to lost weight.

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But what happens in terms of behavior change when people are simply asked to lose weight? The results of effectiveness trials are encouraging, but, sadly, less than spectacular.  For example, in a systematic review of nine diet and exercise trials including 1595 women and 375 men and involving a variety of behavior change strategies, investigators found a significant but modest difference in weight gain in only five trials, largely due to gain among control group members (Lombard et al. 2009).

In another diet and exercise trial incorporating three distinct interventions—one clinic-based, one correspondence-based, and one informational only (the control group)—researchers discovered trends among women toward weight gain in the informational and correspondence groups, and toward gain prevention only in the clinic group (Levine et al. 2007).  According to Ross, most prevention effectiveness trials have demonstrated success in achieving a similarly modest yet significant goal, but of course have been unable to distinguish between the effects of improved diet and increased exercise.  Higher quality trials have yet to be conducted.

From these results, researchers including Ross have concluded that prevention of weight gain, rather than substantial weight loss, appears to be the most achievable goal. Which might seem intuitive, given that overweight and obesity renders effective exercise a much more difficult, though certainly not impossible, prospect.  On the other hand, a commitment to weight gain prevention requires considerable foresight and, at least during the earliest stages, an apparently rare ability to decline immediate gratification in exchange for future health and performance benefits.

But the evidence is clear: exercise works.  Less plain is why that message has failed to fully penetrate developed societies, certain regions of the United States in particular.  Perhaps the answer should be obvious.  The goal of the popular media is seldom to enlighten, after all, and much less to encourage discipline.  Their primary aim, rather, is almost always to manipulate and indulge consumer emotions.  Arguably, it’s a wonder anyone ever succeeds in his or her battle against an unhealthy bulge.

In any case, evidence of “don’t” is not evidence of “can’t,” and the fact that some do succeed tends to show that many more can. Consistent with the evidence presented here, and as I have frequently argued in the past, true success for the obese and overweight is entirely attainable.  But it surely requires extraordinary candor, personal growth beyond the typical, and, in most if not all instances, substantial modifications to life priorities.


IOM (Institute of Medicine). 2015. Physical activity: moving toward obesity solutions: workshop summary. Washington, D.C.: The National Academies Press.

Levine, M.D., M.L. Klem, M.A. Kalarchian, et al. 2007. Weight gain prevention among women. Obesity 15(5):1267-1277.

Lombard, C.B., A.A. Deeks, and H.J. Teede. 2009. A systematic review of interventions aimed at the prevention of weight gain in adults. Public Health Nutrition 12(11):2236-2246.

Ross, R., D. Dagnone, P.J. Jones, et al. 2000. Reduction in obesity and related comorbidity conditions after diet-induced weight loss or exercise-induced weight loss in men: A randomized controlled trial. Annals of Internal Medicine 133(2):92-103.

Ross, R., I. Janssen, J. Dawson, et al. 2004. Exercise-induced reduction in obesity and insulin resistance in women: A randomized controlled trial. Obesity Research 12(5):7898798.

Ross, R., R. Hudson, P.J. Stotz, et al. 2015. Effects of exercise amount and intensity on abdominal obesity and glucose tolerance in obese adults: A randomized controlled trial. Annals of Internal Medicine 162(5):325-334.



2 thoughts on “The Underappreciated Role of Physical Activity in the Battle Against Obesity—Part 3: Adults and the Relationship Between Physical Activity and Adiposity.

  1. Brad

    Yeah, little penetration indeed. You look around and have to wonder, what in the world are people thinking? Thanks again, Kenneth.


  2. Shelly

    People think they can have it both ways. Some can, some can’t. That’s just life. But you’re right, Ken, people have to make choices. One might think that health and liveliness would be the clear winner. But apparently not!



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