The Facts on Fasted Weight Training

Many people believe that a fasted workout, which means exercising on an empty stomach, is beneficial for maximum fat loss—so if you want to lose fat, you should exercise in a fasted state. This can be especially relevant for those who choose an intermittent fasting eating pattern.

There is some truth to the idea that fasted workouts burn fat, but the reality is a little more nuanced. There are both benefits and drawbacks to fasted workouts and weight training.

What Is a Fasted Workout?

A fasted workout is one you do at least four to six hours after eating. Your body has had time to digest and metabolize most of what you ate at your last meal so fat will serve as your body's fuel source rather than glucose.

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. Glucose comes from all of the macronutrients, but mostly from carbohydrates. When blood glucose levels subside, the body burns fat to preserve the glucose stored in muscle and the liver. This helps maintain an optimum blood glucose level.

Fasted weight training aims to take advantage of the way the body burns fuel for energy in order to optimize the amount of fat burned during an exercise session. Some believe you can burn more fat by exercising on an empty stomach. Others believe that some pre-workout nutrition makes your weight training session more effective because your body has more energy.

Benefits of Fasted Weight Training

Fasted weight training increases insulin sensitivity and growth hormone production, which can escalate fat loss. This supports the argument that fasted workouts result in more fat loss.

The advice to train in a fasted state is a strategy to increase fat burning with the hope of using some stored fat.

Drawbacks of Fasted Workouts

The intensity of your exercise affects whether your body uses fat or glucose as fuel. Heavy weight lifting 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 for all energy demands, not just those of your workout. You may burn extra fat during a fasted workout session, but it is not likely to be enough to burn a lot of stored fat when considered overall.

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

Best Pre-Workout Fuel

The best strategy for burning maximum fat is to eat two hours before exercising. 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 a small sports drink during your workout. (Eating too much before a workout can lead to stomach upset.)

A mix of carbohydrates and protein is an excellent choice before weight training. The carbohydrate gives your body fuel to enhance performance and the protein helps your body build muscle during recovery.

By eating a small snack prior to a workout, you can still encourage the fat-burning process without depriving your body of necessary fuel. You also need calories, protein, and carbohydrates after your workout to help your muscles recover and get stronger.

A Word from Verywell

There are pros and cons to fasted weight training, so consider your unique situation to determine which option is best for you. Think about your goals, and see how you feel when you do fasted workouts instead of pre-fueling with a light snack.

Fitness is a journey, so as long as it is healthy for you, experiment with different fuel levels before weight training. Or do a period of fasted workouts followed by a period of training with a pre-workout snack.

If you have any concerns about how you should fuel your workouts, speak with a healthcare professional. They can help guide you to the best solution for your health and fitness goals.