Working out on an empty stomach in order to lose weight?
Is training on an empty stomach the solution to losing weight effectively? First of all, we would lose fat because the body would not draw from our food, but from our fat. That’s what you might think at first glance. Let’s demystify it, step by step.
By using the energy provided by food, we can become fitter and stronger, faster. People who are in better physical condition are more motivated to move, and each session can be performed at a higher level of intensity. The result is a more significant energy expenditure, which enables us to lose more weight in the long term.
Working out on an empty stomach to burn fat?
So where does the popular belief that working out on an empty stomach helps burning fat comes from? On the one hand, while fasting, we often see the weight on the balance decrease quickly. However, this phenomenon only happens on the short term. Indeed, fasting essentially makes us lose water, not fat. Without food, the body draws first on sugar reserves (glycogen), a process that results in an important loss of water.
On the other hand, some people believe that by not eating prior to effort, the body will be forced to draw on fat reserves. Even though this argument makes senses and has been demonstrated by some studies (1-2), fasting is still not effective to lose fat on the long term. By consuming less energy before the effort, we spend less during and after as well. Indeed, European researchers (2) compared the effects of fasting against a breakfast eaten 40 minutes prior to effort. They found that working out on an empty stomach results in a lowered metabolism for the next 24 hours. They also observed that the body ends up using less fat as energy throughout the day. In summary, on top of burning less calories during the day, the energy spent does not come from fat as much as it should.
Finally, skipping a meal can harm appetite control. Then, the body has a hard time recognizing satiety signals. For more information, see the article Will Skipping a Meal Make You Fat?
Working out on an empty stomach is not the solution to lose weight efficiently. Under these conditions, you will have less energy for your workout and in the end, you will spend less calories.
1. Achten J et Jeukendrup AE (2004). Optimizing fat oxidation through exercise and diet. Nutrition. 20(7-8):716-27.
2. Paoli A et al. (2011). Exercising fasting or fed to enhance fat loss? Influence of food intake on respiratory ratio and excess postexercise oxygen consumption after a bout of endurance training. Int J Sport Nutr Exerc Metab. 21(1):48-54.
3. Stevenson EJ et al. (2009). Fat oxidation during exercise and satiety during recovery are increased following a low-glycemic index breakfast in sedentary women. J Nutr. 139(5):890-7.