Fasted cardio is basically doing cardio on an empty stomach. This means that doing your workout first thing in the morning without any breakfast or snacks would count as fasted cardio. There are many people who swear by it and I personally prefer to workout first thing in the morning without food as I also do intermitted fasting.
The idea of fasted cardio is often popular with those who are looking forward to lose weight. It is believed that you can make your body use the fat stored in your system to be burned out by cardio as you didn’t eat anything for a while, therefore there’s no stored carbs for your body to burn. This requires your digestive system to no longer process food, this happens around 4 to 6 hours after eating or first thing in the morning after sleeping.
Officially, there still isn’t many science based studies to back up the claim that by doing fasted cardio you’ll be able to burn more fat that you are storing in the body. There has been a meta-analysis though, it included 96 participants who showed that fasted cardio has led to a change in body mass. Small studies have suggested that you might be able to burn up to 20% more fat. However, there are also studies that suggested people are able to do aerobic workouts for longer after eating.
As long as you’re doing it safe, it’s totally fine to do fasted cardio. Try to start out small, if you’ve never tried fasted cardio, you might not want to do it cold turkey. Instead, you might start of by eating something light for pre-workout such as a banana, apple or even an egg. If you feel great, then you might want to continue without food next. Don’t forget to drink water before you workout though! Water is 0 calories and therefore doesn’t impact you much in the digestive tract.
In the end, everybody’s body is different. Ultimately the key is to improve your workout, gain muscles, lose fat etc. You should choose what works best for yourself, whether it be fasted cardio or fed cardio. If you’re trying to lose weight, the when you eat is a lot less important that what you eat.