I get asked this question a lot, and I never used to really know the answer. But after studying nutrition and from my own personal experiences, I have learned a lot about this topic! So should you exercise on an empty stomach? Here is the answer.

How Your Body Burns Fat 

Your body uses energy in two ways: aerobically (with oxygen) and anaerobically (without oxygen).

Anaerobic exercise is exercise that is high intensity and shorter in duration (i.e. HIIT, crossfit, weights). This type of exercise will burn stored carbohydrates and creatine phosphate.

Aerobic exercise is exercise that is lower intensity and because of this, you can sustain it for much longer (i.e. walking, jogging). This type of exercise will burn stored carbohydrates and FAT.

I have explained this more in another blog post here.

Low Intensity Exercise

When you are doing low intensity exercise such as walking, your body is burning carbohydrates and fat. If you do not eat beforehand, you will likely have less stored carbohydrates to burn, and you will burn up more fat. The same thing will happen if you are eating a very low carbohydrate diet – you won’t have much stored carbohydrate, and you will end up burning more fat.

I recommend that if you are doing low intensity exercise, you do it first thing in the morning on an empty stomach. 

beginner's guide to running

Moderate Intensity Exercise

Depending on your fitness level, you will either use the aerobic or anaerobic pathway for moderate intensity exercise (such as light running, light resistance training, etc). If you are fit, you will most likely use the aerobic pathway and burn stored fat. If you are not fit, you will use the anaerobic pathway and won’t burn fat.

A fit person should be able to do this type of exercise on an empty stomach, but will find it more difficult because of the lack of stored carbohydrates for energy. If you find this type of exercise too difficult, I would eat something small and high in carbohydrates before your workout, such as a banana. If it’s first thing in the morning, allow at least 30 minutes. If it’s in the afternoon, eat it 1-2 hours prior to exercise. If you can handle it and want to burn lots of fat, don’t eat before.

If you do not have a high fitness level, I would recommend eating before this type of exercise, otherwise you will not have the energy to complete it. As I recommended above, eat a banana or piece of fruit.


High Intensity Or Long Duration Exercise (>2 hours)

This type of exercise (HIIT, heavy weight lifting, crossfit) will use up stored carbohydrates and creatine phosphate. It will be hard to do if you do not eat before hand, and if you are very low in carbohydrates, you may use up protein / muscle as fuel (which you don’t really want).

If you do this type of exercise first thing in the morning, I would recommend eating something small and high in carbohydrates (such as fruit) prior to this workout. If you are exercising in the afternoon, I would recommend eating something high in carbohydrates and moderate in protein around 2 hours before. Some examples include yoghurt and berries, healthy sports bar or a piece of toast with eggs.

should you exercise on an empty stomach

Rachael is an Australian born certified personal trainer and nutritionist who holds a Bachelor degree in Science.

After struggling for years to find an exercise and diet program that is tailored to women striving for lean and toned body with no bulk she designed her Lean Legs Program. This program is tailored to each body type and focused on helping women get toned but feminine bodies, without getting bulky.

Her mission is to empower women and help them stay in shape in a healthy and balanced way.

4 Responses

  1. Hi Rachel
    Hope your well first time I am leaving a comment. Legs is something I have always struggled with. I am a slim build but never seem to get my legs to look slimmer. I run about 4 times a week for atleast 40min if not more. Still not seeing a difference, im always active but still don’t get it. could you give any advice? many thanks :) xxxxxx

    1. Hi Maria, walking is actually better for slimming down your legs, believe it or not! So I would try to do as much walking as you can (every day if possible). With the running, just do it 2-3 times per week for a maximum of 20-30 minutes, and try to run a bit faster. If you do this, I’m sure you will get results! xx

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