On the surface, it seems to make sense. Exercise first thing in the morning on an empty stomach and your body should burn more fat. After all, without food intake for eight to 12 hours, you’re in a fasted state. With glycogen stores depleted and low morning insulin levels, your body has to turn to other energy sources to power through your workout, and it’s more likely to turn to fat for fuel.
Fasted cardio is a technique that has been around for years in the bodybuilding community, and one that’s gaining popularity among regular gym goers and even endurance athletes. But will forgoing your morning oatmeal really lead to a leaner body and better athletic performance?
Here’s the skinny on sweating it out sans food and whether or not it is suitable for your body and fitness goals.
The Fast Track to Fat Loss?
Early morning, un-fueled workouts are a common protocol among bodybuilders, especially in preparation for competition when they need to lean out as much as possible before they walk on stage. Some celebrities also turn to this technique to get ready for their close-up, whether that’s a photo shoot or red carpet event.
“Is fasted cardio a good way to burn fat? The answer is yes and the answer is also no,” says Jay Cardiello, a NSCA and ISSA-certified strength and conditioning specialist and fitness expert who has worked with celebrities such as Jennifer Lopez, Curtis “50 Cent” Jackson and Sofia Vergara. “It’s effective, but it’s not sustainable,” he says.
Some studies have found that exercising in a fasted state can burn almost 20 percent more fat compared to exercising with fuel in the tank. Why? Once we eat, insulin (which regulates the breakdown of fat) increases in our body. And, according to some research, higher insulin levels have been shown to suppress fat metabolism by up to 22 percent.
However, research has demonstrated that fasted cardio does not increase fat burning over a 24-hour period. While your muscles adapt to using more fat when you exercise, you don’t actually lose more fat overall on the days that you exercise compared to days that you don’t. Another study suggests that ingesting carbs before working out increases the post-exercise “afterburn” effect more than the fasted state. That means more calories burned throughout the day, not just during your sweat session.
While more research is needed, if you’re curious about running on empty, be sure not to go it alone. Cardiello has employed the fasted cardio method with clients for a short period of time and within a controlled environment. He advises that fasted cardio “shouldn’t be used unless you are being looked after by a nutritionist, professional strength training coach and a medical professional.” For example, 50 Cent used fasted cardio to prepare for an album cover photo shoot. Cardiello closely monitored the rapper’s fitness and nutrition throughout this period to ensure that he was healthy and safe.
Glycogen-Depleted Workouts: The New Face of Fasted Cardio
Beyond bodybuilding and celeb weight loss, endurance athletes have started to turn to “glycogen-depleted workouts,” too. The hope is to teach their body to adapt to low blood sugar levels by burning fat and, as a result, prevent “bonking” during a race. Occasional early morning exercise without fuel has been shown to increase VO2 max and the concentration of glycogen found in muscles when at rest. Fasted runs may have their ups, but keep in mind that while these workouts can adapt the body to more efficiently burn fat as fuel, they didn’t help athletes lose weight or improve their aerobic conditioning or endurance during the studies. Plus, runners still need to practice fueling during workouts to properly prepare for taking in nutrition on race day — particularly if you’re going the 13.1-distance or more.
