Saturday, July 02, 2016

Exercise, weight loss, and the food environment

A clear and effective video from Vox explains why exercise is not directly a cure for overweight. The video's message -- rightly -- is that we should pay close attention to food intake and the quality of the food environment.

The video does note that physical activity has strong direct effects on health. Nonetheless, I would have emphasized the benefits of physical activity even more strongly than the video does.

My first reason for giving physical activity yet more credit is a bit geeky. Much of the research literature uses regression models where a weight measure is the outcome variable and physical activity or exercise is the main explanatory variable. To make sure the analysis really reflects the "effect" of exercise, the studies include additional control variables such as food intake and general health. Yet, when we step up our physical activity, we may experience improvements in health, mood, and feelings of self-efficacy. Including explanatory variables for food intake and health status may risk "over-controlling" for other factors. We may eat healthier when our mood is good. We may avoid periods of poor health and inactivity that lead to weight gain. Perhaps stepping up our physical activity deserves some of the credit for improvements in weight that are being picked up by the control variables.

My second reason for giving physical activity yet more credit is more superficial. For some people who seek to lose weight, the ultimate goal is to look better. I have mixed feelings about whether this is good psychology, but it does seem to be common. Stepping up physical activity may affect posture, muscle tone, and confidence, making people look better in ways that the scale may not register.

But the video certainly is right that researchers in recent years have become more careful about not over-promising physical activity as a complete weight loss program on its own.

 

2 comments:

Anonymous said...

I am shocked, pleasantly so, to find you and I agree on something for once.

Physical exercise is just plain common sense. It is not harmful or unnatural, as demonstrated by the obligatory segment in the video worshiping the hunter-gatherer. I sense the major reason hunter-gatherers are seldom obese is because, instead of being awash in a cornucopia of luscious nuts, berries and succulent grubs for the taking, they are usually pretty hungry as they expend most all of their time evading predators and groveling about for any morsel of digestible food they might salvage from competing species. Yes, a truly blissful all-natural existence as foodie purists like to imagine it.

Anyway, you may want to reconsider your position on physical exercise because you and I are just plain wrong about it. You see, Marion Nestle, who is comfortably seated in an endowed chair and you're not plus she blogs more regularly than you do - almost daily, emphatically disagrees with us on this crucial point. Nestle abhors physical exercise and will tolerate no mention of it. She has even savaged the FLOTUS for daring to endorse physical exercise.

http://www.foodpolitics.com/2011/12/lets-move-campaign-gives-up-on-healthy-diets-for-kids/

http://www.foodpolitics.com/2011/12/white-house-insists-eat-better-is-still-part-of-lets-move/

Nestle takes herself seriously in this business of seeing sugar prioritized to the exclusion of all else, so much so she may be compelled to send someone around to kick your ass (if she weren't 100% opposed to physical exertion she would do it herself, but exhilarating and rejuvenating as it might feel she then would appear a hypocrite). Just a neighborly heads up so you don't get crossways of prevailing food politics around here. Don't make the mistake of thinking just because you are fit and trained you can outrun the long arm of your more lethargic superiors in the food policing business.

Parke Wilde said...

Anonymous, you've got the personalities in this debate all mixed up.

Leading researchers who prioritize sugar and simple carbohydrates (not quite to the exclusion of all else, but very heavily) are Gary Taubes, Robert Lustig, and to some extent David Ludwig. Nobody -- just nobody -- puts Marion Nestle in this camp.

Marion Nestle instead emphasizes (a) total food energy (as in her book title, Why Calories Count) and (b) basic quality of the diet.

See Nestle's new post today summarizing the most recent evidence supported by Gary Taubes' organization.

If you value evidence as much as you say, consider sharing your thoughts in this forum. Consider whether you want to spend your time on paranoid rants about the Food Police or on wrestling with the evidence.