If you google “fasted cardio” right now, you’ll get results ranging from “The best way to lose stubborn belly fat!” to “Fasted cardio will kill your gains!” Clearly this is a controversial subject in the fitness world, so today we’re going to add our opinion to the pile.
Fasted cardio is typically performed in the morning, shortly after waking up, and on an empty stomach. It would be low intensity, steady-state cardio, vs high intensity training or interval training. On its face, fasted cardio sounds like a pretty solid premise: without fuel from food, the body needs to get energy from somewhere. We hope that somewhere will be our fat reserves. Low intensity cardio primarily uses energy from fat reserves (vs. stored glycogen from carbohydrate), so that checks one more box. Plus, insulin is low after a long fast (like overnight), and we burn fat faster when insulin is low. Clearly this is an effective method, right?
It turns out that may not be the case. In 2014, Brad Schoenfeld and Alan Aragon performed a study on looking at the effectiveness of fasted vs. fed cardio on a group of healthy young females. Both groups followed a precise diet and exercise routine, including morning cardio. The experimental group did their morning cardio on an empty stomach, while the control group did theirs after consuming a protein shake. To keep their caloric intake equal, the experimental group consumed the same protein shake after completing their cardio workout. Their findings? Both groups lost a significant amount of weight, but there was no statistically significant difference between the two groups.
Basically, this study confirms something we all already know. Eating a calorie-controlled diet while exercising leads to significant weight loss. Fasted cardio may be more applicable to experienced athletes and bodybuilders, as fat utilization during low-intensity cardio is a training adaptation (you get better at it with practice). For now, stick to the basics and be consistent with your nutrition and training routine. That will get you the best results. They may not be quick, but they will be sustainable, and that’s what will matter most in the long run.