When it comes to exercise, the focus for many people is to burn fat. There's a lot of talk about the "fat burning zone" and questions regarding what the best exercise or intensity is to maximize the burning of fat. The best way to understand this concept is to explore how fuel is used for energy production and intensity of activity.
The average person uses about 60% fat (as free fatty acids) and 40% carbohydrate (as glycogen/glucose) for each calorie used to perform essential body functions for living, aka known as basal metabolism. Although the primary fuel is fat, the effort level is low and therefore, not a lot is expended in this area. When a person increases their level of activity, the cells begin to use more carbohydrate than fat for each calorie expended. As activity becomes more intense, less total fat is burned, but more total calories overall are expended. At relatively low intensities (50% VO2 max) of exercise, both fat and carbohydrate are used at a slow rate of 3-5 calories per minute. At higher intensities, the rate of energy expenditure increases to 7-9 calories per minute, but the shift to increased carbohydrate usage also occurs. This shift is due to the availability of oxygen. As exercise intensity increases, less oxygen is available and to metabolize fat, cells require adequate amounts of oxygen.
We will continue to explore more about this topic in tomorrow's health tip.