Weight Training on an Empty Stomach for Fat Loss

woman raising kettlebell over her head in an empty gym
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Many people believe that weight training on an empty stomach is beneficial for maximum fat loss, so if you want to lose fat, you should exercise in a fasted state. But is this just trainer-speak, or is there science to back up the assertion?

When you are in a "fasted state" (four to six hours after eating), your body has had time to digest and metabolize a good proportion of what you ate at the last meal. That means your body's fuel preference will change from glucose to fat.

Hormones like insulin and glucagon change in relation to the amount of glucose in the blood and liver. When blood glucose is high, the body uses glucose for fuel. When blood glucose subsides, the body burns fat to preserve the glucose stored in muscle and the liver. This helps maintain an optimum blood glucose level.

In the fasted state, insulin sensitivity increases and so does production of growth hormone. Both of these can boost fat loss, which supports the argument that fasted exercise results in more fat loss.

Drawbacks of Fasted Training

The advice to train in a fasted state is a strategy to increase fat burning, with the hope of using some stored fat. However, the intensity of the exercise you are doing also affects whether your body uses fat or glucose as energy fuel. Heavy lifts or fast running will use stored muscle glucose (glycogen) more than fat, whether or not you are doing these tough workouts on an empty stomach.

In addition, how much fat and glucose is used as fuel is prioritized over 24 hours in relation to all energy demands, not just those of your workout. You may burn some extra fat during a fasted exercise session, but it is not likely to be enough to mobilize stubborn stored fat when considered overall.

When you exercise too intensely in a fasted state, your muscles can degrade. This is because your system pulls apart amino acids to help preserve critical blood glucose. Chronic low blood glucose and rising cortisol (stress hormone) levels can depress the immune system.

Another risk of fasted exercise: You may experience a strong tendency to overeat after exercise, which could negate any fat-burning advantage.

Pre-Workout Fuel

The best strategy for burning maximum fat and losing weight, if that's your aim, is to eat two hours before weight training or other exercise. If you wake early and like to exercise first thing, have a pre-workout snack, like a piece of toast with honey or an energy bar. Or have a diluted glass of juice or small sports drink during your workout. (Eating too much before a workout can lead to stomach upset.)

This way, you can still encourage the fat-burning process without depriving your body of necessary fuel. And while it's important not to overeat after exercise, you do need some calories, protein, and carbohydrates after your workout to help your muscles recover and get stronger.

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4 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  4. Academy of Nutrition and Dietetics. Timing your pre- and post-workout nutrition.