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Exercise tunes your appetite
Appetite and satiety
The calorie burn itself is modest. One finding from Herman Pontzer's work is that 100 calories burned through exercise comes with a 28-calorie reduction in basal metabolic rate, leaving a net of 72. Among people who lose weight and keep it off for years, over 70% exercise regularly, while fewer than 30% of those who regain do. That is a correlation, and it doesn't prove causation.
The Bengali workers
Controlled trials of adding exercise typically find people eat less rather than more, though averages hide individuals, and some people do report being hungrier. A classic 1950s study of Bengali workers tracked what people ate across four levels of job activity: sedentary, lightly active, moderately active, and heavily active, with no intervention. Intake followed a J-shaped curve. Sedentary workers ate more than lightly or moderately active ones, and from light to heavy activity, intake rose almost exactly in step with the energy burned.
Beyond weight
Exercise also improves insulin sensitivity and inflammation independent of any change in body weight. The research on blood sugar driving appetite isn't compelling, and the appetite effect is probably mostly at the brain level.
How does exercise change appetite hormones?
Exercise acutely changes gut hormones that signal fullness. Studies led by David Broom at Loughborough University found that running lowered the hunger hormone acylated ghrelin during and after exercise, and raised the fullness hormones PYY and GLP-1. Those shifts were temporary, lasting around the exercise session and a short window after it. They fit reports that hard exercise often suppresses appetite for a while.
Why doesn't daily energy burn rise one-for-one?
Herman Pontzer and colleagues proposed the constrained energy model. In a 2016 paper in Current Biology covering more than 300 adults, they found that total daily energy expenditure rose with physical activity only up to a moderate level, then plateaued. The body appears to trim spending on other processes as activity climbs.
Who studied Bengali workers in the 1950s?
Jean Mayer, a French-born physiologist at Harvard, led the research in the mid-1950s at jute mills in West Bengal. He measured the food intake and body weight of workers whose jobs ranged from sedentary to very heavy. Below a threshold of activity, intake did not fall in proportion, and weight crept up. Mayer called that range the sedentary zone.
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