Can You Do HIIT on an Empty Stomach

Can You Do HIIT on an Empty Stomach

If you’ve come across this article, chances are you’ve looked into the benefits of cardio or training on an empty stomach (or fasted to be more technical). The basic concept is that by doing cardio or training in a fasted state, you’ll force the body to use stored body fat as a source of energy and can therefore utilize this for fat loss. 

This form of fasted training, however, is typically done with low-moderate intensity exercises like walking, jogging, or swimming. High-Intensity Steady State Training (HIIT) is a much more demanding form of training and requires much more energy to train optimally. With that said, can you do HIIT on an empty stomach?

As HIIT is such a demanding form of exercise you should not do HIIT on an empty stomach. You need a sufficient amount of energy available for HIIT training so not only will you fatigue significantly quicker doing HIIT on an empty stomach but you will also start to break down muscle mass for energy. 

In this article, we’ll cover the myth of benefiting from fasted HIIT for fat loss and whether or not you should do HIIT on an empty stomach as there may be some benefit to it…

Can You Do HIIT on an Empty Stomach

Firstly, it’s worth mentioning from a lifestyle perspective you definitely can do HIIT on an empty stomach. If for example, you work a demanding job, don’t finish until late evening most days, and have other commitments outside of work like family then getting to the gym first thing in the morning might be the only way that you can stick to a training routine. 

If you’re anything like me, you’ll find it’s not easy to consume a big meal first thing in the morning so training fasted is just an easier option. It’s also worth pointing out that the effectiveness of doing HIIT on an empty stomach will depend on the type of HIIT you’re engaging in. 

HIIT cardio, for example, will be much easier to do on an empty stomach than a HIIT weight training session. By easier, I also don’t mean that HIIT cardio on an empty stomach will be easy so don’t get confused by the terminology.

Therefore, the only time I’d recommend HIIT on an empty stomach is if you plan on doing cardio and need to do it fasted as a preference. When it comes to performance, body composition, or workout effectiveness though, you shouldn’t do HIIT on an empty stomach. 

Is It Ok to Do HIIT Fasted

Fasted and an empty stomach is two different things. Training fasted is a very intentional form of exercise with the sole purpose of utilizing stored body fat as an energy source through fat oxidation. I alluded to this earlier but fasted training is not ideal when it comes to HIIT because the energy requirements for HIIT are so high that it will become detrimental from a performance perspective. 

When something is a low energy output like LISS cardio, the research shows a significant benefit to fasted cardio as you utilize fat stores for energy without fatiguing nearly as much as you would with intense exercise. 

This is also strictly the case when looking at cardio only. When it comes to training with weights, the energy requirements for HIIT are even higher and you’ll start to break down muscle tissue for a source of energy (which is far from preferential). 

With an empty stomach, however, you can still have optimal glycogen stores to support a workout. Therefore, when looking to do HIIT on an empty stomach, you are less limited by the time of day that you can train and also by the energy demands placed on the body.

With HIIT, however, it would be less of a recommendation to do this fasted, especially if your HIIT involves weight training.

When doing HIIT fasted, your ability to perform will be significantly impacted and you won’t be able to perform a HIIT session for an extended duration of time. You can do HIIT fasted for convenience but the benefit in terms of energy output won’t be as much as if you have a pre-workout meal before it. 

Should You Eat Before or After HIIT

If you are considering HIIT on an empty stomach, there are two factors that you’ll need to take into consideration:

  1. Fueling before the HIIT session
  2. Refuelling after the HIIT session

I touched on this earlier but fueling before a HIIT session can have two schools of thought. The reason to do HIIT when fasted (or on an empty stomach) is to utilize your stored body fat for energy in order to improve body composition. 

In terms of effective exercise though, HIIT training can burn more calories than LISS but when considering both in a fasted state, the difference in fat cells being metabolized for energy is negligible. When given a choice, it would make more sense to do LISS in a fasted state as you also need to consider workout performance and effectiveness. 

It’s worth saying that there are no performance-based benefits to fasted HIIT and if anything, you’ll suffer a negative performance output with fasted HIIT. This is mainly due to the intensity of exercise requiring a much greater energy reserve to be readily available. The energy demands are also the main reason why I recommend doing HIIT after weights as well.

In order to see the greatest benefit for HIIT, you should therefore eat beforehand. 

You should eat 45-60 minutes before a HIIT workout. It’s important to eat a meal before HIIT to provide your body with the energy required for an intense workout and to also prevent muscle loss. You should also eat a meal 45-60 minutes after a HIIT workout to refuel and start the recovery process. 

It’s easy to get caught up in diet or training theory (or research in many cases) and focus on very microelements that are only really beneficial for elite-level athletes (which is usually why these studies are done initially). 

As a slightly relevant example, a calorie deficit and energy balance are the two most important factors when looking to lose body fat. Combined, they make up 80-90% of your progress/results and should be the primary focus. The same is true with HIIT training. 

Trying to maximise fat loss by doing HIIT on an empty stomach or in a fasted state to burn more body fat will be counterproductive at a point. Sure, it may marginally burn more body fat but you’ll also have a worse training session, potentially cause muscle degradation and spike cortisol (the stress hormone) to higher levels than normal.

Therefore, you should eat before HIIT to properly fuel your training session and also afterwards to refuel and aid recovery. Training fasted has its place and benefits but unfortunately, these do not transfer well to HIIT. 

Final Thoughts

There are two reasons why you’d want to do HIIT on an empty stomach. Convenience, maybe when training first thing in the morning or for fat loss benefits from increased fat oxidation. With both methods, it’s important to note that doing HIIT on an empty stomach is not optimal for performance or body composition. 

HIIT workouts by the very name are intense, this means you need a stored supply of energy in order to perform them at an effective level. Without a meal in the hours leading up to a HIIT session, you’re far more likely to fatigue quicker, utilize muscle tissue for energy (leading to muscle loss), and negatively impact recovery due to raised cortisol and muscle damage. 

Therefore, doing HIIT on an empty stomach is not a recommended strategy as the drawbacks of using this method far outweigh any minor benefit you will receive in terms of fat oxidation.

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