Is it true that not eating before a morning workout enables you to burn more fat?
This is an extremely common fat burning strategy used by fitness enthusiasts who perform cardiovascular exercise early in the morning on an empty stomach. This strategy was popularized by Bill Phillips in his book, “Body for Life”. According to Phillips, performing 20 minutes of intense aerobic exercise after an overnight fast has greater effects on fat loss than performing an entire hour of cardio in the postprandial (after eating) state. The rationale for this theory is that more fat will be utilized for fuel if little glycogen (energy from carbohydrates) is present. While this theory sounds enticing, it is not supported by the scientific literature nor have I seen it be effective in practical application.
According to the research:
1) There is no evidence of improved fat oxidation associated with exercise in a pre-fasted state.
2) Consumption of food before training increases the thermic effect of exercise, creating a higher calorie burning advantage during and post-exercise as compared to pre-exercise fasting.
3) Body fat deposition and subsequent utilization as fuel is highly individualized and dependent on numerous other factors, such as hormonal profiles, age, subcutaneous vs. adipose fat mass, exercise duration, training age, etc.
4) It has been suggested that exercising in a fasted state could have an impact on proteolysis – meaning, the amount of muscle mass that we maintain and/or use as fuel. Performing cardiovascular exercise while fasting might not be advisable for those seeking to maximize muscle mass.
5) Finally, studies show that a pre-exercise meal allows an individual to train more intensely compared with exercise while fasting. The net result is that a greater number of calories are burned both during and after physical activity, heightening fat loss.
The research does not support training early in the morning on an empty stomach as being more effective than consuming a pre-exercise meal. Moreover, in clinical practice, I have seen this strategy negatively affect one’s training intensity, mental focus, blood sugar management, and long-term improvement compared to those that eat before they train on the morning.
Reference: National Strength and Conditioning Journal. Volume 33. Number 1. February 2011. Pgs 23-24.