Fasted Weight Training Workouts

Many people believe that a fasted workout (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 burns fat, but the reality is a little more nuanced. There are both benefits and drawbacks to this practice.

What Is a Fasted Workout?

A fasted workout is a workout you do in a fasted state (at least four to six hours after eating). When fasted, your body has had time to digest and metabolize a good proportion of what you ate at your 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. 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 Workouts

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.

The advice to train in a fasted state is a strategy to increase fat burning, with the hope of using some stored fat. For those who practice intermittent fasting, training on an empty stomach can be more convenient because you may have more time available in your schedule during your fasting period.

Drawbacks of Fasted Workouts

The intensity of the exercise you are doing 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 burn a lot of stored fat when considered overall.

When you exercise too intensely in a fasted state, your muscles can degrade. This is 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, 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.)

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

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 some 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 training on an empty stomach, 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 exercise 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.