There are many books out there which tell you that working out on an empty stomach will help you lose weight, and then there are books which disagree with them. Some say that it is a never ending debate. There are also people who believe that it is a matter of personal choice. Few say that, it depends on your body type. I say, working out on an empty stomach is bad. What Happens During Exercise? Does exercising on an empty stomach burn more fat? Before I answer this, I would tell you what happens in your body during exercise. When you exercise, you make your muscles active. These muscles need constant supply of energy. This energy is provided by adenosine triphosphate (ATP). The main source of ATP is glucose, which is generally obtained from carbohydrates. In the absence of the primary source, ATP is generated from protein and fat. If you do not have enough energy, you will be exhausted in no time. Does Exercising on an Empty Stomach Maximize Fat Burning? Now, that you know what happens internally during exercise, you might be able to guess the answer to the above question. Yes, exercising on an empty stomach burns more fat. This is due to the fact that, during exercise, your muscles search a source of ATP. When it does not find enough sources of ATP, it starts utilizing the protein and fat from your body as a source of ATP, thereby burning them. Is Exercising on an Empty Stomach Good or is it Bad? The problem in exercising on an empty stomach is that, the protein which is utilized to generate ATP is taken from the muscles, which leads to the loss of muscle mass. You cannot restrict protein from your muscles from getting utilized, in the absence of carbohydrates. Thus, you cannot subject your body to just burning your fat. People who exercise generally focus on preservation and growth of muscles but working out on an empty stomach will lead to the loss of muscle mass. Those who exercise in the morning on an empty stomach are most prone to the loss of muscle mass. This is due to the fact that during the morning hours, the catabolic conditions are higher. Catabolic activity leads to the breakdown of complex molecules like proteins into simpler ones. This leads to muscle wasting, which is bad for the overall health. So Finally What Should I Do? Exercising on an empty stomach is not bad, if your prime focus is to lose weight, regardless of the muscle loss. If you want to lose weight by preserving your muscles, I suggest you to eat something before you exercise. Be careful that you do not eat so much that it makes you feel lethargic. If you are planning to foray into body building, then you should never think about exercising on an empty stomach. So, the books that say that you will lose weight if you workout on an empty stomach are right, but these books often do not tell you that you will also end up losing your muscle mass. Getting instant and sufficient energy during your workout is essential. You do not want to drop down on the floor while working out, right? Carbohydrates can provide ATP at a relatively faster rate when compared to proteins or fats, since carbohydrates are simpler molecules. Some of the people who had started working out on an empty stomach to lose weight faster, despite having a habit of not exercising on an empty stomach, have complained that they are facing the problem of acidity. So, be aware of the after effects of working out on an empty stomach. On a personal note, I would like to say that, do not follow any weight loss or body building tips blindly, you should research on the side effects that these tips might have. It is your body, do the best for it.