Should I Work Out On An Empty Stomach?
Working out on an empty stomach, or ‘fasted cardio’, may work for some people, but it isn’t for everyone.
A common question I get asked is whether intermittent fasting might help them you results faster. For anyone who has tried intermittent fasting, you’ve probably done a cardio workout on an empty stomach, and you might already have an opinion about it!
- What Is Fasted Cardio?
- When To Workout On An Empty Stomach
- Pros & Cons of Fasted Cardio
- How Does Our Body Burn Fat
- Should I Do Fasted Cardio?
To help you to decide if you want to try fasted cardio, here are the pros and cons of working out in a fasted state, and whether fasting can make your cardio more effective.
What is fasted cardio?
Fasted cardio is exercise that you do when your body is in a fasted state. You enter a ‘fasted state’ when your body is no longer processing food, around 3-6 hours after eating.
When you do fasted cardio, you are working out on an empty stomach. Your levels of insulin (the hormone that is produced in the body when you eat) are low or at your baseline level.
When insulin levels are low, there isn’t readily available energy in the form of glucose in your bloodstream.
When you do fasted cardio, your body must rely on stored energy such as glycogen and fat to fuel muscle movement.
Fasted cardio doesn’t just have to be done first thing, it can be done at any time of day when your body is in a fasted state.
When to workout 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!
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.
Pros and cons of fasted workouts
There are both cons and benefits to working out on an empty stomach.
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 fuel
- Increase in the hormones that encourage the use of energy stored as fat
- Increased 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!
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 LISS for those following my programs in the Sweat app) 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.
Try fasted cardio and see if it works for you!
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.
Do you prefer to have a snack first or workout on an empty stomach? Let me know in the comments below!
* Disclaimer: This blog post is not intended to replace the advice of a medical professional. The above information should not be used to diagnose, treat, or prevent any disease or medical condition. Please consult your doctor before making any changes to your diet, sleep methods, daily activity, or fitness routine. Sweat assumes no responsibility for any personal injury or damage sustained by any recommendations, opinions, or advice given in this article.