Fasted cardio has become a popular practice among fitness folks looking to shed unwanted body fat. Research is fairly convincing that performing cardio in the morning before eating can, for some, help burn more body fat (up to 20%) and *may* help target fat loss in problem areas like the abdomen and thighs for those with already low body fat percentages. So should you try it? That depends.
How Fasted Cardio Works
Assuming you aren't a sleep eater your body fasts overnight. If you perform cardio in this fasted state your body is more likely to conserve its carbohydrates and use fat stores for fuel. Unfortunately, your body could also burn more amino acids too which could compromise muscle building. To minimize the affects of fasted cardio on muscle growth it's recommended to eat or drink a meal with fast digesting protein directly after. So if your main goal is fat loss, fasted cardio could be an effective tool. If your main goal is to build muscle, it may not be. However, I do know several bodybuilders who use fasted cardio before competition to "cut" and it works for them. Others prefer HIIT or long slow duration. Since every person is unique with unique bodies, lifestyles, goals, diets and fitness programs there is no one definitive "best" approach.
What About HIIT?
Fasted cardio may not work for your lifestyle. Some people simply HATE working out in the morning or have jobs/lives that make it impossible to workout in the morning. Others feel weak and sick if they exercise without food in their system and that could be dangerous. If that's the case for you, fasted cardio is out. Consider integrating High Intensity Interval Training (HIIT) into your workouts. Whether performed in a fasted state or un-fasted state research is pretty convincing that HIIT workouts burn up to twice as much fat as steady state cardio in far less time. I personally do fasted HIIT workouts 1-2x/week and that works well for me.
Targeting Stubborn Areas?
This article suggests fasted cardio can work well for men with body fat in the low single digits (~5-6%) and women in the low teens (~13-24%) who are looking to target fat loss in problem areas like the lower back and thighs. The author states "Over the years, I found that once people drop the majority of their total body fat, fasted cardio seems to work well on resistant or stubborn areas. Although there's no direct data to reference, it might be that when a person only has a small amount of fat lingering in hard-to-attack areas, exercising in a fasted state could spark those resistant fat cells to release stored fat so it can be burned for fuel."