Exercise and Weight Loss

Quick Intro

Exercise helps with weight, but on its own the effect is usually modest. Trials of exercise without changes to eating show small average weight loss, partly because the body makes up for some of the energy used. Exercise seems to matter more for keeping weight off after a loss, and its benefits for health, mood and daily life come whether or not the scale moves.

This article explains what exercise does for weight, why the effect is smaller than many people expect and why it is still worth doing. Food plays a large part in weight, and that is outside the scope of this article; a registered dietitian or doctor can give personal advice.

What the Research Shows

When people take up regular exercise without deliberately changing how they eat, they lose some weight on average, but usually less than they hoped. Results vary a lot between people: some lose a fair amount, some lose little or none and a few gain a little, often as muscle.

This can be disappointing if weight loss was the main reason for starting, but it does not mean the exercise is failing. It means weight is a poor way to judge it.

Why the Effect Is Smaller Than Expected

A few things reduce the effect of exercise on the scale:

The body makes up for some of the energy used. After exercise, many people eat a little more without noticing, and some move a little less for the rest of the day. Over long studies, this making up can cancel out a large share of the energy burned.
Daily energy use may not rise as much as expected. One line of research suggests the body adjusts other processes so that total daily energy use rises less than the exercise alone would suggest at high activity levels. This idea is debated, and the size of the effect is not settled.
Exercise burns less than people think. A typical session uses a moderate amount of energy, which a snack can replace. Calorie figures shown by machines and trackers are rough estimates that can be far off.
Muscle and water can rise. New training can add some muscle and stored water, which offsets fat loss on the scale, especially early on.

Where Exercise Does Help

Exercise still makes a real difference in several ways:

Keeping weight off. People who keep weight off after losing it tend to be regularly active, and guidance suggests regular activity helps prevent regain, although the exact amount needed is uncertain.
Waist and organ fat. Regular aerobic exercise reduces waist size and fat stored around the organs, the kind most linked to health risk, even when body weight changes little.
Body composition. Strength training builds muscle, so the share of the body that is fat can fall even if weight stays the same.
Health at any weight. Fit people in larger bodies have health risks similar to fit people of normal weight. Getting fitter lowers risk whether or not you lose weight.

A Better Way to Think About It

Weight is one measure, and a noisy one. If you exercise mainly to change your weight, the slow pace can make it feel pointless. If you exercise to feel better, sleep better, get stronger and stay capable, you will see results within weeks, and any weight change becomes a side effect.

Better measures of progress include how daily tasks feel, how your clothes fit, your waist measurement and what you can do in a session. Why the scale is a poor measure of progress and how to tell you are getting fitter cover these.

What Kind of Exercise Helps Most

There is no single best kind. A mix works well:

Regular aerobic activity, such as Brisk Walking, cycling or swimming, which reduces waist and organ fat.
Strength training two or three times a week, such as Bodyweight Squats, Dumbbell Rows and Glute Bridges, which builds muscle and supports long-term body composition.
More movement through the day, such as walking and taking stairs, which adds up and is easy to keep.

Combining aerobic and strength work tends to give better results than either alone.

FAQ

Why am I gaining weight since I started exercising?

Early in training the body often stores more water and energy in the muscles, and some people eat a little more without noticing. Small early gains are common and usually not fat.

Is cardio or strength better for weight loss?

Both help in different ways. Aerobic exercise reduces waist and organ fat, and strength training builds muscle. A mix of both works well.

How much exercise do I need to lose weight?

There is no exact amount, and results vary widely between people. Regular activity helps most with keeping weight off over time.

Can I exercise off a bad diet?

Usually not. A session uses less energy than most people think, and food plays a large part in weight. For personal advice on eating, speak to a registered dietitian or doctor.