A very common believe that people have is that low intensity exercise is the best way to lose body weight, especially body fat.
The misconception is in fact because of the energy exchange ratio (RER), whereby below the value of 0.86, a higher percentage of fat is being burned for fuel. Thus, people think that by exercising at low intensity more fat will be burned for fuel and fat stores would selectively increase. However, this notion has never been proven in the laboratory.
Scientists at the University of Wisconsin, La Crosse, had subjects perform two 30-minute bouts of exercise: relatively low intensity bout (RER: 0.88) and a relatively high intensity bout (RER: 0.93) (Porcari, 1994)
The results, illustrated in the chart below, show that for the low-intensity exercise, subjects burned a total of 240 calorie, with 96 of those calories (41%) coming from fat. During high intensity bout, total of 450 calories were burned, with 108 calories (24%) coming from fat.
Therefore, during the low-intensity bout, there was a higher percentage of calories coming from fat, BUT the total number of fat calories was LESS than during the high intensity trial. It is important for us to remember that the total number of calories burned is what contributes to the weight loss, regardless of the source of the calories.
*Reference: ACE’s Essentials of Exercise Science for Fitness Professionals
