Many studies show that exercise alone won’t help you shed the extra pounds, but a few studies suggest that it works for some people.
Like 2017 and 2018, pollsters have again found that losing weight is the top New Year’s resolution for 2019.
Many people turn to exercise to help them achieve their goal—which is why you see a spike in gym memberships in January.
But can you lose weight just by exercising more?
Research on the matter is mixed.
Here’s a quick overview to help you decide if you should focus on diet or exercise to shed a few extra pounds.
A July 2018 review of previous research, published in Progress in Cardiovascular Diseases, breaks down what you might expect to lose initially with different types of exercise:
- Resistance training only: 0 to 1 percent weight loss
- Aerobic exercise only: 0 to 3 percent weight loss
- Aerobic and resistance training: 0 to 3 percent weight loss
- Diet (aka caloric restriction) combined with aerobic exercise: 5 to 15 percent weight loss
For a 160-pound person, a 3 percent weight loss comes out to about 4.8 pounds.
This is better than nothing. But clinical guidelines recommend that people who are overweight or obese lose at least 5 percent in order to see improvements in risk factors like lipid levels and insulin sensitivity.
In most of the studies reviewed, doing exercise by itself falls short of this. But it can work with “high volumes of aerobic exercise training,” write the authors of the paper.
Intense Exercise Can Promote Weight Loss
Joseph E. Donnelly, professor of medicine and director of the Center for Physical Activity and Weight Management at the University of Kansas Medical Center, is an author of several of the studies in the 2018 review. He’s also a big proponent of exercise for weight loss.
“If you can get people to exercise at a certain level, you can produce 5 to 7 percent weight loss in almost anybody, and that is clinically significant,” said Donnelly.
In one of his studies, young adults did five aerobic workouts per week for 10 months.
They were divided into two groups: burning either 400 calories or 600 calories per workout. There was also a control group of people not assigned to exercise.
By the end of the study, people in the 400 calories group lost an average of 4.3 percent of their weight, and those in the 600 calories group lost an average of 5.7 percent.
Women and men lost about the same amount of weight. However, some people lost more weight and some less.
To put this in perspective, in order to burn 400 calories, a 160-pound person would need to do one hour of water aerobics. To burn 600 calories, they’d have to run at 5 miles per hour for an hour.
The average daily intake is 1,600 to 2,400 calories for adult women and 2,000 to 3,000 calories for adult men.
It’s not surprising that people in Donnelly’s study lost weight—they were burning an extra 2,000 to 3,000 calories per week.
This amount of exercise essentially burns off an entire day’s worth of food each week.
Exercise Doesn’t Always Lead to Weight Loss
Weight loss studies in the laboratory aren’t the same as what happens in the real world, though, so there’s no guarantee that you’ll lose weight with exercise.
There are also other factors that can affect how much weight you lose, such as sex, body size, exercise type, and metabolic changes.
To turn exercise into weight loss, you have to stick with it—which is also true of dietary changes.
This isn’t always easy in the modern world.
“When it comes to physical activity and nutrition, people do what they have to do,” said Donnelly. “When you no longer have to be physically active, the environment is perfectly set up to gain weight.”
Throughout much of our day, we have easy access to high-calorie foods, as well as cars, elevators, and televisions to keep us sedentary.
To lose weight with exercise, you have to work out continuously at a moderate or vigorous intensity.
In the lab, researchers use high-tech tools to make sure people burn a certain number of calories.
Outside the lab—and in physical activity guidelines—we generally use hours to track exercise because it’s easier.
But people often overestimate how hard they’re exercising—so your hour-long workout might only include 30 to 40 minutes of real effort if even that.
There’s also the danger that you’ll undo all your hard work by indulging in a high-calorie treat after your workout—like a handful of chocolate chip cookies or a sugar-loaded coffee drink.
This kind of dietary compensation, though, isn’t a given.
In Donnelly’s study, people in the 400-calorie group didn’t eat more than people in the control group. The 600-calorie group ate slightly more, but not enough to counter the weight loss.
“If you do extreme amounts of exercise, you’re going to start to eat more, but you won’t eat more than the energy that you expend,” said Donnelly. “And that’s why you can lose weight when you exercise.”
It’s not surprising that combining exercise and dietary restriction leads to greater weight loss—you’re burning more calories and at the same time reducing your intake.
So should you focus on diet or exercise … or both?
One study found that people who focused on both in the beginning did a better job of meeting their physical activity and diet goals over the long run.
However, people who started with only diet had trouble meeting their physical activity goals later on.
The real goal of any program is keeping the weight off in the long term.
For this, exercise can play an important role—for some people.
One weight loss study found that 38.8 percent of people who maintained their weight loss after 4 years were still doing at least 150 minutes per week of moderate-to-vigorous exercise.
Of course, that means some people were able to keep the weight off even with less exercise.
Not everyone will be able to do five 600-calorie workouts per week. Some people may have physical limitations such as arthritis or a super busy work or home schedule.
So you have to find what works for you and what you will stick with.
Right now, there’s no magic formula for how much to focus on exercise versus diet.
But an online tool provided by the National Institute of Diabetes and Digestive and Kidney Diseases could help. It lets people customize their exercise and diet to reach their desired weight loss goals.
Before you choose diet over exercise, keep in mind that regular physical activity has many other health benefits beyond weight loss—including improving mood, boosting energy, and reducing the risk of stroke, type 2 diabetes, depression, and other diseases.
“If you exercise and don’t lose weight, just keep going,” said Donnelly, “because you get all sorts of health benefits regardless of the weight.”
Shawn Radcliffe is a freelance health and science writer. This article was first published on Healthline.