Working Out on an Empty Stomach: Good or Bad?

Food and nutrition

Published on 1 November 2018
by Isabelle Huot

Working out on an empty stomach (to “train low”) is preferred by many. The theory suggests that training in a glycogen-depleted state before and during a workout session promotes weight loss.


Studies show that having a high-carb meal or snack before a workout allows the body to use the carbs as its primary source of energy. This means that fats provide less of the energy needed for physical activity. But do you burn fewer calories?


When you don’t eat before a workout, your body uses its fat reserves at first, but it burns fewer calories in the hours that follow. When you eat before a workout, you burn fewer calories during the activity, but more in the hours that follow. In both cases, the number of calories burned in a day is quite similar.


Working out on an empty stomach can affect athletic performance and increase muscle fatigue. Working out without energy reserves increases the perception of effort, making it difficult to work out for as long and at as high an intensity. Energy levels are easier to maintain if you’ve eaten before your workout. 


Those who are more sensitive and who experience digestive issues during physical activity should have a lighter pre-workout meal. Liquids, such as smoothies or a small glass of juice, are often easier to digest. When you return from your workout, you can supplement your breakfast with complex carbohydrates (grains) and protein (eggs, cottage cheese, nut butter, milk, etc.).

Isabelle Huot
Doctor in nutrition