Does exercise help you lose weight? What the science really says

At a glance:‍

• Exercise alone usually produces modest weight loss
• Exercise improves heart, metabolic, mental, and physical health
• Strength training helps preserve muscle, especially during weight loss
• Exercise is key for keeping weight off long-term

If you’ve started exercising to lose weight, the number on the scale may not change as quickly as you expect. That can feel frustrating, but it doesn’t mean your workouts are failing.

In June 2026, the American Heart Association released a major scientific statement published in Circulation, confirming what many people experience firsthand: exercise alone is unlikely to produce substantial weight loss for most adults. But exercise remains one of the most important tools for improving heart health, metabolic health, muscle mass, mood, energy, and long-term weight maintenance.

In other words, exercise may not be a quick fix for weight loss, but it is central to lasting health.

Can exercise alone lead to weight loss?

The AHA statement reinforces a critical distinction:

• Exercise alone rarely delivers clinically significant weight loss, unless performed at exceptionally high volumes
• Exercise is one of the most powerful tools we have to improve cardiometabolic health, regardless of whether the scale moves

People can increase activity, burn significant calories, and still see minimal movement on the scale, which can feel frustrating. But weight is only part of the picture.
When you’re physically active, not only do you get fitter and stronger, it also improves blood pressure, insulin sensitivity, lipid profiles, and cardiovascular function. These are the markers that directly influence the risk of heart disease, stroke and some cancers, while improving longevity. What’s more, exercise provides other life-enhancing benefits, such as increased brain power, more resilience, stress reduction, and greater levels of happiness too.

Why does exercise not always change the number on the scale?

One of the clearest demonstrations comes from a controlled exercise trial involving participants from Midwest Universities. The JAMA-published Midwest Exercise Trial, took 131 sedentary, overweight students and split them into two groups. Both groups kept their diets the same. Group One maintained a sedentary lifestyle. Group Two added exercise to their weekly routine for 16 months –  mainly walking and jogging, with the option of doing some cycling and elliptical training. They started with 20-minute sessions, five days a week, gradually building the duration to 45-minute sessions. They also progressively increased intensity from 60% of their maximum heart rate at the start, to 75% at the six-month mark. This resulted in Group Two burning upwards of 400 calories per session – that’s 2,000 extra calories across a week for a total of 69 weeks.

At the end of the study, fitness improved (a 20 percent increase for guys and 16 percent for girls), body fat reduced (an average of 2.9kg for the males and 4.4kg in the female group), yet weight loss was modest – and in some cases, non-existent.

I know this sounds surprising …  “If they burnt upwards of 2,000 extra calories per week for 16 months without changing their diet, what did it do if it didn’t reduce their body mass?”

The underlying driver is what researchers describe as constrained energy expenditure. This is where the body adapts to increased activity by adjusting energy use elsewhere, protecting total daily energy output. It is a survival mechanism, not a flaw.

What is constrained energy expenditure?

Constrained energy expenditure is the theory that the body actively regulates how much energy it uses each day. Evolutionary anthropologist Herman Pontzer explains it well in his book Burn, which explores the inner workings of the body and throws traditional weight loss mythology on its head. He illustrates that as we evolved in our hunter-gatherer past, we became experts at controlling how much energy we spend on a daily basis – meaning we do everything we can to keep it constant.

Being a hunter-gatherer, as you can imagine, demands a very active lifestyle. For example, in the Hadza tribe in Tanzania, men will typically walk around 8.5 miles a day in search of game, while women will walk around 5 miles. In order to survive that lifestyle, the body must be able to control energy output so that we don’t overspend in our search for calories from food. Unfortunately for us, this can work against us during exercise.

To illustrate how entrenched this constrained energy effect is, Lara Dugas and colleagues compared the daily energy expenditure of people with sedentary occupations in industrialized countries with that of more active people living in developing countries. Once the measures were controlled for body weight (the heavier you are, the more energy you burn), the study, published in the American Journal of Clinical Nutrition, found the average office worker in New York burned the same amount as an active individual in Nigeria or a hunter gatherer in Tanzania. We conserve energy as if our lives depend on it, because for a long time, they did.

Why exercise still matters for weight loss

While exercise is not a shortcut to rapid weight loss, it is a regulator of how the body functions, adapts, and stays healthy. And importantly, it reshapes how energy is used across the system, reducing inflammation, improving hormonal balance, and dampening chronic stress responses.

What actually drives long-term weight loss success

If weight loss is the goal, the most effective approach is to balance energy usage with diet. Reducing the amount of calories we ingest and improving the quality of food we eat has a far greater effect on our body mass than exercise alone.

• Nutrition has the strongest influence on creating an energy deficit
• Exercise improves adherence, health outcomes, and long-term maintenance

How exercise supports people using GLP-1 medications

There’s no doubt that GLP-1 medications can provide significant weight loss results. For many people, they provide a breakthrough after years of struggling. But, a report led by Gillian L. Hatfield, PhD, Associate Professor at the University of the Fraser Valley, Canada, shows GLP-1 medications also introduce a new challenge that is often overlooked. Weight loss via GLP-1s is not purely fat loss. A 2024 study, published in Circulation, indicates that 20 to 50 percent of weight lost can come from lean mass, including muscle and bone. This has serious implications, as loss of muscle reduces metabolic rate and functional strength, and bone density loss increases long-term health risks. This is where exercise, particularly resistance training, matters more than ever.

How exercise enhances long-term weight loss results

Physical activity is a core pillar within a broader system. I exercise six days a week and will continue to do so because it provides so many physical, mental, and emotional benefits. And although exercise doesn’t significantly alter the amount of energy you burn each day, it drastically changes the way you spend your calories.

When energy is scarce – like when we burn extra during exercise – non-essential metabolic processes reduce. The first of these is inflammation. Acute bursts of inflammation are an essential part of our repair and immunity response. However, prolonged chronic inflammatory responses contribute to allergies, arthritis, arterial diseases, and other metabolic disorders. Exercise means we have less energy to spend on overzealous, harmful, inflammatory processes, and that is a huge win.

Secondly, spending energy on exercise dampens overactive stress responses. Again, a short burst of stress hormones during a crisis is good, but prolonged over-production is harmful. Some reproductive hormonal activity can also be suppressed. That might not sound like a good idea – but too much activity in these areas is thought to contribute to reproductive cancers such as prostate and breast cancer.

Thirdly, numerous investigations have demonstrated that being sedentary causes us significant harm. The amount of time we spend sitting each day is a strong predictor of heart disease, diabetes, cancer and a range of other serious health problems. Although exercise alone may not result in significant weight loss, it definitely reduces the impact of our sedentary lifestyles.

And finally, people who lose weight through dieting are far more likely to keep it off if they exercise. This is highlighted by one study on obese policemen. For two months, some followed dietary restrictions alone, some diet plus exercise. At the end of the study, there was no difference in the amount of weight lost across the groups (as we should now expect). But once the intervention was over, only those who exercised maintained their weight loss.

What we know is that exercise changes motivation. When people move beyond scale-driven goals and start to value strength, energy, and how they feel, consistency improves. And consistency is what ultimately delivers long-term, life-changing results.

What type of exercise is best for long-term weight management?

While cardio, HIIT, and strength training all support weight loss, the best type of workout depends on the individual. The best workout is one you’ll actually do. Rather than choose workouts based on weight loss potential, it is better to select workouts based on enjoyment, as this is a more effective motivator which leads to more exercise, more often, and for a longer-term – and that’s when the real benefits kick in.

Key takeaways:

Exercise will not transform your body overnight. But over time, it will transform how your body functions, feels, and performs.

Exercise is not a quick fix for weight loss. It is far more valuable.

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Weight loss truths, grounded in evidence

• Exercise alone rarely produces significant weight loss, but is essential for health
• The biggest benefits of exercise extend far beyond the scale – the improved cardiometabolic risk factors result in greater longevity.
• GLP-1 medications can accelerate weight loss, but increase the risk of muscle loss without exercise
• Resistance training is critical to preserve lean mass and protect long-term outcomes
• Exercise is one of the strongest predictors of sustained weight loss maintenance
• Exercise is a catalyst for better mood, resilience, and daily energy

The best exercise approach to support weight loss

1. Focus on consistency over calorie burn
2. Combine cardio and strength training across the week
3. Use resistance training to protect muscle and bone
4. Track health, energy, strength, and fitness markers, not just weight
5. Pair regular exercise with balanced nutrition for best results

Find a LES MILLS class near you. Use the LES MILLS+ app to access at-home workouts and explore science-backed training plans designed for results.

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About the author‍

Bryce Hastings is the Head of Research and Technical Advisor at Les Mills International, where he leads research that shapes how millions of people train. Working alongside internationally renowned research partners, Bryce bridges the gap between the lab and the gym floor, ensuring every LES MILLS™ program is safe, effective, and powered by science. He has developed numerous research programs and co-authored reports across a range of fitness and scientific publications. A certified Physical Therapist since 1986, Bryce’s academic work is supported by extensive hands-on experience. He holds an Advanced Diploma in Manipulative Therapy and a Master of Philosophy from Auckland University of Technology, where he is currently undertaking a doctorate.

FAQs

Can you lose weight with exercise alone?

Exercise alone can support weight loss, but it usually produces modest results unless training volume is very high (which is unachievable for many). For most people, meaningful weight loss is more likely when regular exercise is paired with nutrition changes that create a sustainable calorie deficit. The major benefit of exercise is that it improves health, fitness, muscle, energy, and long-term weight maintenance.

Why am I exercising but not losing weight?

You may be getting fitter and healthier even if the scale is not moving. Exercise can improve cardiovascular fitness, insulin sensitivity, blood pressure, mood, strength, and body composition. Weight can also be affected by muscle gain, fluid changes, food intake, hormones, and the body’s ability to adapt energy use. The scale is only one measure of progress.

Is diet or exercise more important for weight loss?

Nutrition usually has the biggest impact on weight loss because it directly influences calorie intake. Exercise plays a different, but important, role. It supports heart health, metabolic health, muscle maintenance, mood, motivation, and the ability to keep weight off long-term. The most effective approach combines balanced nutrition with regular physical activity.

Does strength training help with weight loss?

Yes. Strength training helps preserve and build lean muscle, which is especially important during weight loss. While it may not always produce fast changes on the scale, it can improve body composition, strength, bone health, and metabolic function. It also helps protect against muscle loss when calorie intake is reduced.

Should I exercise while taking GLP-1 medication?

Regular physical activity is an important part of a healthy approach while using GLP-1 medication, especially resistance training. GLP-1 medications can lead to significant weight loss, but some of that weight may come from lean mass, including muscle and bone. Regular strength training, aerobic exercise, and adequate nutrition can help support muscle, mobility, and long-term health. Anyone taking medication should follow guidance from their healthcare provider.

How does exercise help keep weight off?

Exercise helps maintain weight loss by improving fitness, preserving muscle, supporting metabolic health, and reinforcing healthy habits. It can also improve mood, energy, confidence, and motivation, which makes long-term consistency easier. Research suggests people who stay active after losing weight are more likely to maintain their results.

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