When aerobic activity is used for weight loss, all attempts should focus on the caloric expenditure, even though training in “the fat burning zone” is often recommended by some professionals to encourage weight loss. Low and low-moderate intensity training do yield a higher percentage of calories metabolized from fat compared to moderate high intensity, but… again these training intensities do not measure up when total caloric expenditure is compared.
Example based on a 150lb person:
3 mph walking 30 min 117 kcal expended 64 fat kcal expended
6mph running 30 min 357 kcal expended 117 fat kcal expended
As you can see, the elevated intensity not only burned more than two times the calories, but also utilized more fat during the exercise bout, even though the percentage of calories burned from fat was higher with the lower intensity exercise. In fact the amount of calories expended from fat while running equated to the total calories burned while walking. In addition, higher intensities increase post-exercise metabolism further contributing to weight loss potential.
Info thanks to the National Council of Strength and Fitness
Lisa Hansen - Seattle Personal Trainer 