Should You Eat Before Your Morning Workout?

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Exercising first thing in the morning is a reality for many people. I know from first hand experience. As a parent early mornings are the only time that I can reliably carve out for myself in the day.

But is it a good idea to exercise on an empty stomach after an overnight fast? Or should you eat?

Like most things with nutrition, it depends. Your goals and how you tolerate food while exercising are major factors to consider.

First, let’s revisit the major energy sources in the body.

Carbohydrates. This is your muscles preferred source of energy. Muscle glycogen can start to run out in approximately 45 minutes of exercise, but of course there is variation between individuals and intensity level is a major factor too.

Fat. Everyone’s got it (even very lean people) and it is a very concentrated source of energy that can sustain you for a long time. Your body will look to fats as an energy source when you have used up your muscle glycogen.

Protein. Amino acids are what proteins are made of and these are the building blocks for muscle. Your body doesn’t really like using protein for energy, but it will when it is running low on other fuel sources.

Unlike shifting gears in a car, your body doesn’t use just one energy source at a time. Your metabolism is so much more sophisticated than that. While your body does often use one fuel source predominantly (often carbohydrates), it is also using other fuel sources (fat and protein) at the same time, but to a lesser degree.

When it comes to eating for sport, food is really only helping you if it’s digested and absorbed.
— Lindsay Van der Meer

So What Does This Mean for Morning Workouts?

Exercising first thing in the morning without eating does encourage your body to rely more on stored energy (including your body’s fat stores) as a fuel source than if you ate something before. However, you may be able to exercise for longer and at a higher intensity if you have something to eat before. If you are exercising with a weight loss or a performance goal, this is something to consider.

There may also be benefits to exercising early without eating. Early morning exercise on an empty stomach means that while your stored energy in your muscles (called your muscle glycogen) should be normal, the stored energy in your liver (called you liver glycogen) will be low because your body has been using this as energy while you sleep. This is probably the most common way to ‘train low’.

What Does Training Low Do?

Training low increases your ability to use fats as an exercise fuel source. It’s not that surprising really, because if you don’t give your body something to fuel your workout (a small snack before your workout), it’s going to use something in your body as fuel instead. So while training low can make your body can become more efficient at using fats as a fuel source, the evidence is still mixed on whether or not this actually means you’ll be able to perform better. For more on this and the concept of ‘metabolic flexibility’ check out my prior post on carbohydrates and performance.

Takeaway

You may be able to exercise for longer and at a higher intensity if you have something to eat beforehand. If you are training for an event and have a performance goal in mind, eating a small carbohydrate rich snack before early morning exercise can help you reach it. You may also feel better during your workouts, which helps you enjoy your activity more and can be a great confidence boost. If you’re skeptical, give it a try and see how it works for you.

When it comes to eating for sport, food is really only helping you if it’s digested and absorbed. Otherwise, it’s just sitting in your stomach drawing blood away from your muscles and making you feel sluggish. So if you choose to eat shortly before a morning workout, choose something small, rich in carbohydrate, and without a lot of fibre, fat or protein (which empty slower from the stomach) such as ½ a banana, a small glass of juice or your favourite sports drink.

References:

Burke, L. (2015). Nutrition for recovery after training and competition. In Burke, L. & Deakin, V. (5th Eds), Clinical sports nutrition (pp 420 - 462). Sydney, NSW: McGraw-Hill

Jeukendrup, A. E. (2017). Periodized Nutrition for Athletes. Sports Med 47(Suppl 1); S51-S63.