Exercise for Weight Loss: The Lie That Won’t Die

The Ghost of a FleaSometimes an idea firmly plants itself in the popular imagination. Once there, it takes root and persists like a weed. It simply will not die. So it is with the idea that exercise is an excellent tool for weight loss.

This is a lie that won’t die.

A Nice Little Study

Gretchen Reynolds at the New York Times accidentally demonstrated this week how hardy this lie is. She found a good study of the physiological response to two different regimens of exercise versus a sedentary control group. It was a small RCT with just 52 subjects in total. Only 44 subjects completed the study, which lasted 12 weeks.

Despite the small numbers, the researchers did find some differences between the groups. They found that fat mass decreased more in the group that exercised six times per week, than it did in either the twice weekly exercise or sedentary control group. They also found interesting patterns in energy compensation among the three groups. Leptin seemed to predict how much a person would compensate for the energy they used for exercise.

A False Promise

However, there’s a catch. Between the three groups, the researchers found no difference in the amount of weight lost or gained. None. Deep inside the study, the authors note this:

“The increases in total body weight of the control group (0.40 ± 0.99 kg and 0.78% ± 1.19%) were not significantly different from either exercise group.”

Despite that finding, the researchers put Exercise for Weight Loss right up front in the title of their study. Reynolds took it a bit further in her article for the Times. The headline exclaimed:

To Lose Weight With Exercise, Aim for 300 Minutes a Week

This is the lie that won’t die. Exercise is a great way to improve your health. It’s a lousy way to lose weight. You can’t outrun a bad diet.

Click here for the study and here for the reporting by Reynolds. For an excellent Twitter thread by Yoni Freedhoff, dissecting this study, click here.

The Ghost of a Flea, miniature painting by William Blake / WikiArt

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December x, 2020

One Response to “Exercise for Weight Loss: The Lie That Won’t Die”

  1. December 12, 2020 at 2:37 pm, mary pittaway said:

    Thanks for this short but sweet reminder of what we learned years ago.