Why exercise alone won’t help you lose weight

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Why exercise alone won’t help you lose weight

Published: 24 Apr. 2025, 00:05

Audio report: written by reporters, read by AI

Jung Jae-hoon

The author is a pharmacist and food writer.

When people notice they've gained weight, their first instinct is often to hit the gym. They take to the treadmill or stationary bike with determination, sweating through high-intensity workouts in hopes of burning off extra calories. But despite all that effort, the weight often lingers. That’s because the human body is remarkably strict about managing its daily calorie budget.

Participants run on indoor marathon treadmills during the “Speed Race 8.4” competition hosted by the Seoul Metropolitan Government at Jangchung Gymnasium in Seoul on June 29, 2024. [YONHAP]

A revealing 2012 study compared the energy expenditure of the Hadza, a hunter-gatherer tribe in Tanzania, with that of sedentary Westerners. At first glance, the difference between a population that hunts and forages daily and another that spends much of its time sitting at desks seems obvious. Surely the Hadza must burn far more calories, right? Surprisingly, the study showed otherwise. Male Hadza adults burned about 2,600 kilocalories a day, and the women around 1,900 — figures not unlike those of adults in cities across the United States and Europe.

Animal studies support these findings. Mice given unlimited access to a running wheel appeared to burn more calories through exercise. But total daily energy expenditure remained mostly unchanged, as the mice compensated by being less active in other ways. The body, it seems, adjusts. When you burn 300 calories on a spin bike, your metabolism doesn’t treat it as “extra” effort. Instead, it reallocates energy, much like someone sticking to a strict $20 daily allowance who spends $14 on a movie ticket and tightens their belt for the rest of the day.

Wild animals rarely move more than necessary. Colobus monkeys, for instance, spend nearly half their waking hours at rest. Michael L. Power, a researcher at the Smithsonian National Zoo, wrote in his book The Evolution of Obesity that humans are likely the only species that exercises purely for health reasons. In the wild, survival often favors energy conservation over exertion.

None of this is to say exercise isn’t important. It plays a key role in cardiovascular health, mental well-being, and physical strength. But when it comes to shedding pounds, it cannot shoulder the responsibility alone. The more crucial factor is food intake. That doesn’t mean following extreme diets. A modest adjustment — like skipping or lightening a meal after overeating — can make a difference. Though some fret over skipping a meal, it's worth remembering that eating three square meals a day is a relatively modern habit. Larger animals, including humans, are generally better at enduring short-term hunger than smaller ones.

To lose weight, you need to eat less. But to live well, you need to move. Exercise remains a uniquely human endeavor — one that reflects our will not just to survive, but to thrive. Let’s embrace that, and move like humans do.

Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.