Should I Work Out On An Empty Stomach?

For anyone who finds that the best time of day to work out is first thing in the morning, it’s likely that you do your workout before breakfast!  

Whether you are doing cardio or weights training, you probably want to know whether working out on an empty stomach can get you faster results or lose fat faster.

Some of us can eat before a workout and feel amazing, whereas others might feel nauseous or uncomfortable when they work out after eating. 

Let’s take a look at why you might consider trying fasted cardio. 

Benefits of fasted cardio 

Fasted cardio is sometimes recommended to improve fat oxidation (fat-burning), encouraging your body to rely on stored energy, rather than energy from recently digested food, as fuel. 

Your blood glucose and glycogen, a carbohydrate in the muscles, is often depleted after sleep. 

When there is less energy available in the bloodstream from a recent meal, your body may burn more fat during exercise. 

Here’s what happens in your body when you workout on an empty stomach: 

Adipose cells are broken down (lipolysis)

Fat released from cells is burned as fuelIncrease in the hormones that encourage the use of energy stored as fatIncreased blood flow to the abdomen

Facilitation of breakdown of adipose tissue stored around the abdomen.

So you can see that fasted cardio potentially has benefits when your goal is to shift stubborn fat. 

When fasted cardio isn’t best

If your blood glucose and glycogen are completely depleted then this can sometimes result in muscle tissue being used up for energy. 

This is something we DO NOT want, as muscle is what gives you definition, shape and tone! Usually, if you were at this stage, you wouldn’t be feeling that great either. 

However, this situation would be an extreme one most of us have a meal a few hours before getting to sleep and with the busy lives we lead, we may not always get the recommended 8 hours of sleep. This means that the likelihood of completely depleting your blood glucose and glycogen stores while sleeping is pretty slim. 

While some people may find they still have sufficient energy to workout when fasted, others might feel too depleted. In this case, attempting to work out fasted might not be the best idea. Instead, try having a light pre-workout snack. 

When you should eat before a workout

If you are doing a high-intensity workout, it can help to have a light snack first. Having a snack before you exercise can also mean you’ll be less likely to overeat after your workout!

As a general rule, I don't recommend having a large meal within an hour of starting your workout. If you are hungry, try eating a piece of fruit or a few nuts! If you train with me on a Saturday morning, something like a boiled egg with be just perfect as we usually train more intense like just body weight HIIT.

These foods are easy to digest, and then you can have a larger meal or snack after your workout. 

If you are a night owl who prefers to train after dinner, allow a couple of hours for digestion, or break your evening meal into two smaller meals, before and after your workout. 

How does our body burn fat?

Fat is stored in special tissue called adipose tissue, in various locations throughout the body. In order for fat to be burned (i.e. used for energy), it must first be released from the adipose tissue. 

To do this, a process called ‘lipolysis’ causes fat to be converted to triglycerides and released into the bloodstream. This process is kickstarted in the first few minutes of your workout!

Once the fatty acids (triglycerides) are in your bloodstream, they are delivered to your muscles, where they will be oxidised (burned) for energy. The important thing to remember is that oxygen MUST be present in order for fat to be broken down.

Lipolysis is not the step that determines your body’s fat-burning ability. Rather, it’s how much oxygen is available to turn fat into useable energy. 

This means that to effectively burn fat during fasted cardio, there needs to be plenty of oxygen available.

What type of exercise is best on an empty stomach?

Aerobic exercise like low-intensity cardio (that’s like a power brisk walk or light steady state jog) is better for burning fat. 

This is because when you exercise at a high intensity, there isn’t enough oxygen present to metabolise stored energy, and your body uses an alternative ‘anaerobic’ energy production process that doesn’t require oxygen. 

Should I do fasted cardio?

To get the most out of your workouts, you should do whatever feels best for you. Whether this means eating a pre-workout snack to give you the motivation and energy for exercise or exercising on an empty stomach, when you do what feels best, you’ll be more likely to train consistently!

At the end of the day, training done consistently is going to give you better results than whether you eat before a workout or not. 

Something you should be aware of is that if you’ve eaten a large meal before your workout, a portion of your blood is potentially being diverted away from your working muscles to the digestive system to help process your food. 

As a result of this, there is less oxygen available to your muscles. You might feel sluggish and your body’s fat-burning capacity could be reduced. 

At the end of the day, no amount of ‘fitness hacks’ like fasted cardio can get you the results that you will get if you simply train consistently over time and follow a healthy lifestyle!

Lasting results need to be sustainable over time and form a natural part of your life. 

Some people love fasted cardio and they find it is the best way for them to train. 

However, if you need to have a snack in order to find the motivation to workout, go for it! This isn’t going to stop you from reaching your goals faster if it’s what works best for you.