Exercising on an empty stomach may not appeal to everyone, but it seems to have some positive effects on fat burning. If you don't load up on carbohydrates for quick energy before a workout, it makes sense that you would be pulling energy from your fat stores. Still, the approach is a little controversial and the jury is still out on whether it actually benefits athletic performance.
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Train Low, Compete High
The term "train low, compete high" refers to the idea of doing some workouts in a carbohydrate-depleted state, then racing or competing with a full supply of carbohydrates. Initial research claims that this technique enhances fat-burning and other metabolic responses. While you will go further and faster by drawing on readily available carbohydrates, the theory behind training low is to stress your body to the point it becomes stronger. Fourteen cyclists in New Zealand trained for four weeks, half before breakfast and the other half after breakfast for five mornings a week. The group that trained before breakfast increased the amount of carbohydrate they stored in their muscles by 54.7 percent, while the after breakfast group only increased that amount by 2.9 percent, according to the website Natural Society.
Muscle biopsies were tested in a study from the University of Birmingham in Great Britain, reported in the November 2010 issue of "Medicine and Science in Sports and Exercise." The study showed that "training low" caused the body to burn fat rather than carbohydrates. However, a test of performance in a 60-minute cycling time trial did not show that performance improved compared to the control group. Still, athletes such as Frank Shorter, the 1972 Olympic marathon champion, and Tour de France winner Miguel Indurain, are two well-known people who indulged in long, difficult training sessions in a carbohydrate-depleted state.
Fasting Exercise and High-Fat Diet
A study published in the November 2010 "Journal of Physiology" found that exercising before breakfast has a protective effect on a bad diet. Twenty-eight healthy, active young men in Belgium ate a diet of 50 percent fat and 30 percent more calories than usual. One group did not exercise at all while the other two groups did exhaustive exercise four times a week. One group ate a high-carbohydrate breakfast and additional carbs during their workouts. The second group worked out on an empty stomach and drank only water during training, then ate the same high amount of calories later. Six weeks later the non-exercise group had gained an average of 6 lbs., developed insulin resistance and begun storing extra fat. Those who ate breakfast gained half as much weight as the non-exercisers, but had also become more insulin-resistant and fat-storing. The group that exercised prior to breakfast gained almost no weight, had no insulin-resistance and burned the fat they were ingesting more efficiently.
Disadvantages of Empty Stomach Exercising
Obviously, you cannot train as hard or fast without having more fuel to rely on. It is possible that you could increase your risk of illness or injury by exercising in a depleted state. Exercise on an empty stomach can increase the production of the stress hormone cortisol, which can lead to the breakdown of muscle tissue. To make the best use of the concept of exercising on an empty stomach, you might consider "training low" at times to help your endurance, but switching over to fueled training before a competition or race.