Yes, you can lose weight with exercise alone. It’s actually a myth that you cannot lose weight with only exercise and no change to your diet. Losing weight happens when you create a calorie deficit.

I’m a former certified personal trainer, and many times, I have read articles stating that you cannot lose weight with just exercise. This is incorrect.

A calorie deficit can be created by just exercise, thereby causing weight loss. Look at this in reverse: a slender person who eats quite a bit, but hits the gym 90 minutes every day, and on weekends, goes on 40 mile mountain bike rides.

If this person were to quit exercising, yet not change his eating habits, he’d gain weight.

He then moves to another town, 15 pounds overweight, still not exercising, and asks a fitness professional if he can get slim by just exercise alone.

Chances are that the fitness professional, or even a physician, would say, “No, you cannot lose weight with just exercise.”

This person then resumes exercise, and the weight comes off. The general consensus is that exercise alone will result in some weight loss, but not all the pounds that a person wishes to lose. But this is false. It depends on how much weight the person needs to lose.

Let’s take a sedentary person, who eats 2,000 calories a day, and is 10 pounds overweight, who decides to take up strength training three times a week for 45 minutes and cardio training three times a week for 45 minutes.

If he works out with gusto, they will certainly lose all of those 10 pounds, and maybe even a few bonus pounds of fat.

It isn’t just the calorie deficit created by new physical activity that matters here. It’s the faster resting metabolic rate that results from exercise, especially bouts of intense activity several times a week.

So if you burn an extra 300 calories a day strength training, your caloric deficit will be more than 300 calories a day, because strength training, especially if it’s intense, will cause you to burn more calories per hour even when you are at rest. This is called the after-burn effect.

Over time, a lot of fat can be lost, if the person goes from completely sedentary to very active, engaging in hormonal exercise and HIIT training.

The result will be many more calories burned every day, which will lead to pounds lost.

However, fat loss will be expedited if a person indeed changes their eating habits, and especially if their original eating habits consisted of huge quantities of food; this creates more room for a larger daily caloric deficit.

Bottom line: 1) You can lose weight with exercise alone; 2) Exercise alone may cause all the weight you want to lose to disappear, depending on how much you wish to lose, and how you work out; 3) The more weight you have to lose, the more you’ll need to change your eating habits to get the job done.

Lorra Garrick is a former personal trainer certified by the American Council on Exercise. At Bally Total Fitness she trained clients of all ages for fat loss, muscle building, fitness and improved health.