Some fitness professionals say exercising at a low intensity is best for fat burning. Others disagree. Which is it? Should you exercise at a low intensity or high intensity to maximize fat loss?

During aerobic activity, your body uses two kinds of stored energy for fuel: fat and carbohydrates/sugar. The intensity of your exercise session determines how much of each energy source is utilized.

Many people believe that a long duration of low- to moderate-intensity exercise is the best way to lose fat. That’s because at an easy pace, working at 60% of maximum heart rate, approximately 50% of the calories you burn come from fat. If you exercise at a higher intensity, say 80% of heart rate max., only 40% of calories you burn come from fat. The majority (60%) come from sugars.

Lower intensity exercise burns more fat calories than higher intensity activities. The more intensely you exercise, the more carbohydrates (and the less fat calories) you’ll expend. But if you’re ready to conclude that lower intensity exercise is the way to go for optimal fat loss, hold on.

When your goal is fat loss, you have to look at the total number of calories you expend during an exercise session. Low-intensity activity burns less overall calories than high-intensity exercise. Let’s say you walk at an easy pace for 45 minutes. You would burn far less calories than if you ran at a higher intensity for that same duration. Burning a greater percentage of fat as fuel does not mean greater fat loss. To make the most of your fat loss program, focus on the total amount of calories you burn in a session, not the percentage of fat versus sugars.

Since high-intensity exercise burns more calories in a shorter period than low-intensity activity, it’s very time-efficient. But is higher intensity exercise always the best choice? No. If you’re just starting an exercise program and your goal is fat loss, it wouldn’t be wise to jump into a high-intensity exercise routine. If you don’t injure yourself first, you’re bound to feel so uncomfortable and discouraged that you quit your program fairly quickly. For beginners to exercise who are interested in fat loss, stick with low to moderate intensity. Give yourself time to improve your fitness level and gradually increase the intensity of your workouts.