Your intention when you lose weight is to drop fat, not lean muscle tissue. Certain types of exercise expend more energy than other types, improving your capacity for burning more calories and therefore more fat.
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You can't really directly measure the number of fat grams burned through cardio; cardio burns calories, which helps deplete your fat stores. And, exactly how many calories you burn in a workout depends on the intensity, your size, your body composition, your metabolism and your genetics.
Fat vs. Calories
The intensity of cardiovascular exercise determines how many calories you burn from fat and how many you burn from carbohydrates. In general, a lower intensity exercise tends to burn a greater percentage of fat calories, but fewer total calories overall. For weight loss, focus on total calories burned rather than a special "fat-burning" zone.
A low-intensity cardio workout that raises your heart rate to 50 to 70 percent of your maximum heart rate gets approximately 60 percent of its fuel from fat. When you work at 70 to 75 percent of your maximum heart rate, roughly 50 percent of the calories used for fuel come from fat.
Even higher intensity cardiovascular exercise burns a lower percentage of calories from fat — anywhere from 5 to 35 percent from fat. However, because you burn more calories overall, you may burn an equal amount of fat during higher intensity exercise.
For example, if you burn 100 calories in a workout at a low intensity, 60 calories came from fat. But, if you burn 250 calories in a workout at a higher intensity, up to 75 calories may have come from fat — even though it burned a lower percentage of fat calories.
Read more: The Burn Fat Faster Workout
What It All Means for Weight Loss
If you're truly concerned with determining fat grams burned, consider the following equations. To burn 1 gram of fat, you need to burn 9 calories from fat. Since moderate-intensity exercise, such as walking, hiking, dancing or moderate bicycling, burns roughly 140 to 185 calories in 30 minutes, you can estimate that 50 to 60 percent of those calories comes from fat.
That translates to 70 to 111 calories burned from fat. At nine calories per gram, you burn approximately 7.8 to 12.3 g of fat in 30 minutes, or two times that amount in 60 minutes. This is an extremely rough estimation, however.
Although you may have heard a great deal about the fat-burning zone — then supposed level of exercise intensity that burns the most fat — the number of fat grams you burn or the percentage of fat you burn during exercise is not the key to losing weight or fat with exercise.
The key is to burn more calories than you take in. As long as you're not severely limiting your caloric intake below 1,200 calories per day for women or below 1,800 for men, and causing your metabolism to rebel and slow down, you'll lose fat if you create a calorie deficit. Watch what you eat, particularly the number of total calories and the overall quality of your food and beverage choices.
Read more: The Best Fat Burning Exercise Machines