Does exercising on an empty stomach maximize fat burning?

Originally Published: April 15, 2005 - Last Updated / Reviewed On: April 20, 2012
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Dear Alice,

I have recently learned that in order to burn fat as a fuel, your body requires carbohydrate. Up until this point I had been doing cardio training first thing in the morning on an empty stomach, as I had read that this is optimum for fat burning. However, now I have a small carbohydrate snack before I train in order to prevent my body using lean muscle tissue as a fuel. Today I have again read in another book that training on an empty stomach first thing in the morning burns the most fat. I am a little confused over the best thing to do! I train with weights twice a week and do cardio three times per week. I do want to maintain my lean muscle, but am looking to reduce my body fat.

Dear Reader,

First things first: Great job staying active! Now, on to your very interesting (and slightly complicated) question. As you have already noticed, there are many schools of thought on the issue of maximizing fat loss. Do you exercise on an empty stomach or do you make sure and eat a little something before your morning run? Sifting through all this information can indeed be confusing. Let’s get to the bottom of the issue.

The latest research seems to indicate the following: If you will be exercising longer than 30 minutes, eat a light snack in the morning before you run. It’s a good idea if that snack contains some carbohydrates and some protein (i.e. a banana with peanut butter). This allows your body to use the carbohydrates to help burn fat in your body and the protein will keep you going past that 30 minute mark. However, if your aerobic workouts are less than 30 minutes, exercising on an empty stomach may indeed be the most beneficial for fat-burning.

Carbohydrates are the easiest for your body to burn — they require the least amount of oxygen. Fat, the body’s long–term energy storage mechanism, takes more oxygen. If no carbohydrate is present (i.e. an empty stomach), your body will burn fat for energy. But your body will also start burning protein. Herein lies the catch to performing aerobic exercise on an empty stomach: You may experience some muscle loss, especially if your work out is 30 minutes or longer. Here are a few more things to consider:

  • Not eating before a workout may cause you to fatigue faster, thereby shortening or lowering the intensity of your workout.
  • Exercising on an empty stomach can decrease blood sugar levels, which may make you hungrier and more prone to overeat at your next meal.

Lastly, individual bodies with different metabolisms do this sugar-protein-fat dance slightly differently. For example, certain types of health conditions, such as diabetes and low blood pressure, necessitate eating before exercising, as a cardio workout on an empty stomach could cause other health problems. Medical conditions aside, some people are more prone to muscle loss than others, and some will burn fat more quickly or easily than others. Additionally, the altitude at which you work out makes a difference. People exercising at higher altitudes have less oxygen at their disposal, so running at a slower pace, which will lower your heart rate, will help you burn more fat. Many trainers say that to maximize fat burning, you should do your cardio workout at a level that allows you just enough breath to hold a conversation.

Columbia students interested in more physical activity information can by sign up for Columbia's CU Move motivational emails. You can also visit the CU Move webpage for other physical activity related information. Best of luck to you on your morning workouts!

Alice