If you’ve been following #fitspo, it might seem like working out on an empty stomach is the new workout. But does it deserve this spotlight? Don’t you need that hearty meal to really push through?

The truth of fasted cardio is complicated. While it may work for some bodies and lifestyles, it’s not necessarily for everyone. Here are the pros and cons to know.

“Fasted cardio” means working out when you’re no longer digesting food. So, your tummy’s empty. Zilch. No food inside. How long it takes to digest food will depend on what you’ve eaten.

Most of the time, you’ll reach this state first thing in the morning, but it can also happen at later hours if you practice intermittent fasting.

Fasted cardio fans say it’s an amazing way to accelerate fat loss — but this hasn’t really been proven.

The idea behind fasted cardio goes like this: If you fast before you work out, your body’s glucose supply (its main energy source) will be lower. This could encourage your body to burn stored fat for fuel instead.

But is that actually the case? The research is mixed.

A 2018 review of several studies found that fasted exercise did lead to a metabolic boost after the workout was over. However, the researchers also noted that eating before the workout enhanced performance.

A 2016 review of several studies concluded that cardio performed in a fasted state leads to a higher fat burn than exercise done in a “fed” state.

So, if fat-burning is your priority, you might want to try fasted cardio. However, if you’re looking to set a personal best, it’s prob going to be better to fuel up. Focus on finding what works best for your body and keep in mind that any form of cardio can help you burn calories.

While fasted cardio might lead to a temporary fat-burn boost, some research suggests that it doesn’t make a difference in overall weight loss.

May not make a real difference for weight loss

In a small 2014 study, 20 female participants were split into two groups. One group performed 1 hour of fasted cardio, and the other did 1 hour of non-fasted cardio. Both groups worked out 3 days per week for 4 weeks while following a calorie-restricted diet.

While both groups showed significant weight loss, there was no notable difference in either weight loss or body size change between the two.

So, what’s up with that 2016 review that said fasted cardio led to greater fat burn? Well, that review was aimed at confirming the relationship, not questioning it. That means the researchers included studies that supported a connection and left out those that didn’t.

Remember, even though many studies suggest that fasted cardio provides a fat-burning boost, this is a complicated process, and we need more larger, comprehensive studies to fully understand the potential connection.

Could reduce your results

Fasted cardio also might hinder muscle building. If your body doesn’t have enough carbs to use for energy, it kick-starts the gluconeogenesis process. That’s how it converts other compounds (like protein) into fuel. But protein is also important for building muscle, so you could be working against your #gains.

Remember how studies found that fasted cardio can hinder performance? That’s especially true if you’re doing a higher-intensity workout. If you don’t have enough energy stores to make it through your workout, you can’t get the full benefits of your exercise.

The benefits of fasted cardio are debatable, but it’s generally safe for most peeps to try when doing light or moderate workouts of up to 30 mins.

However, if you plan to do a long, high intensity workout, fasted cardio may not be the safest choice. You could experience low blood sugar or dehydration, which can cause dizziness, lightheadedness, or even fainting.

It’s probably best to avoid fasted cardio if:

  • you have a medical condition affected by low blood sugar
  • you have high blood pressure
  • you’re pregnant
  • you’re new to cardio or to working out

If you’re still onboard the fasted-cardio train, keep these tips in mind to do it as safely as possible:

  • Hydrate, hydrate, hydrate. Sure, you’re not eating before your workout — but no one said anything about not drinking! Knocking back some water before and after your cardio sesh will help your bod regulate its temperature, lubricate your joints, and give you the energy you need to make it through.
  • Take it slow. Start with 10 minutes of moderate-intensity exercise (think walking or jogging or cycling slowly) and see how you feel. If your body gives you the green light, you can gradually work your way up to 30 mins or so.
  • Fuel up when you’re done. Afterward, it’s time to break your fast! Nourish your body with a balanced meal or a protein– and carb-packed snack.

Pairing regular exercise with a nutritious diet is a great way to lose weight sustainably. Here are a few ways to help maintain a moderate weight — no fasting required:

  • Hit up some HIIT. A 2018 research analysis suggests that high intensity interval training (HIIT) could help you get that belly fat burn. We need more research to know for sure, but the current studies are promising.
  • Run, don’t walk. Though walking, biking, and hiking are excellent workouts, running seems to remain the reigning cardio queen when it comes to calories burned.
  • Combine cardio with strength training. Building muscle boosts your resting metabolic rate, which can lead to greater calorie and fat burn over time. (That includes when you’re just sitting on the couch.) So if you want to reap the biggest benefits from your workouts, try a combo of cardio and strength training.

Cardio can be beneficial for reaching a healthy-for-you weight, but that doesn’t mean it has to be fasted cardio.

The research on the benefits of fasted cardio is far from conclusive, but this practice doesn’t appear to impact weight loss. It may even have a negative effect on performance or muscle growth, So take it slow and assess your body’s unique needs before trying.

If you’re not sure whether it’s right for you, reach out to a fitness professional or your doctor for personalized advice.