Should I eat before or after exercise?

As a nutritionist, two of the most common questions I’m asked is ‘what should I eat before I exercise?’ and ‘should I exercise on an empty stomach if I want to lose weight?’

Here, I’ll combat the myths so you’ll be better equipped to maximise your workout, and reach your goals.

To eat or not to eat

When deciding whether to eat before your workout, it’s important to think about:

1. How long are you planning to exercise for? and

2. What are your goals of your workout?

If you’re planning to exercise for more than an hour, then it’s a good idea to have something quick and easy to digest before your workout. Not only to give you enough energy to get through your workout and prevent light headedness and low blood sugar, but also to help you perform at your best. The second, more important question is ‘what am I aiming to achieve from my workout?’ If the answer is ‘a personal best in a deadlift or a 5km run’ then you’ll be better equipped to do this if you’ve had some fuel before your workout. However, if your goal, as with many people, is either to lose weight or to build endurance to train for an event then it may be that you will benefit more from training in a fasted state.

Why exercise fasted? 

Evidence shows that when you exercise in a fasted state (usually having not eaten or consumed any calories for at least 8 hours), there are many positive effects on the way your body uses fuel. For example, when you’re fasted, as there are no sugar reserves and fat is used as the main fuel. Not only does this mean that you’ll be using up excess fat stores, but there’s also evidence to suggest that it makes you more efficient at using fat for fuel in the future, even when carbohydrate is available. This is why endurance athletes often train in a fasted state as when they then consume carbohydrate before their important races, they’re more efficient.

Another benefit of fasted exercise is clear when you look at the behaviour of hormones in the body. Fasting is one of the best ways to increase the amount of the body’s Growth Hormone. This hormone helps to build muscle, burn fat and also improve exercise performance. Similarly, testosterone, the sex hormone linked to muscle growth and fat use is shown to increase in fasted exercise.

So are there any flipsides to working out on an empty stomach?

Unfortunately yes. When you’re relying solely on fat as an energy source, high-intensity sessions in particular will feel a lot harder and you may struggle to complete them. Training fasted can also lead to an increased breakdown of muscle protein so if gaining strength and muscle is your goal then this probably isn’t best for you. In addition to this, fasted training puts a lot of pressure on the immune system and your risk of illness and infection may increase. For this reason, it’s recommended that if you choose to train fasted, you mix up your training sessions and don’t always workout in a fasted state. You’ll also need to pay extra attention to your diet and ensure you’re getting enough antioxidant nutrients to keep immunity high, as well as maximising sleep and minimising stress.

So the choice is yours, but remember to keep it varied and always drink plenty of fluid before and after a workout to stay hydrated.

Written by Ruth Tongue
(MSc Nutrition)