At what intensity is fat the predominant fuel source for the body?

Fat serves as the predominant fuel source for the body during moderate-intensity exercise due to several physiological factors. At this level of exertion, the body efficiently utilizes fatty acids as they can provide a significant amount of ATP (energy) while allowing for a sustainable energy output over a longer period. This intensity strikes a balance between aerobic and anaerobic metabolism, promoting the utilization of fat stores without the onset of fatigue that often accompanies higher intensities.

During low-intensity exercise, while fat may still be used as a fuel source, the metabolic rate is generally low, and the absolute energy expenditure is not high enough to classify fat as the predominant fuel. Conversely, high-intensity exercise shifts the body’s reliance more towards carbohydrates for quick energy due to the anaerobic nature of such activities. Resting metabolism also predominantly uses fats for energy, but it does not align with the concept of active exercise, where we can observe the transition and preference for fuel sources based on intensity.

Thus, during moderate exercise, the body effectively taps into its fat reserves, making it the optimal intensity for fat metabolism.