Fasted vs Fed Cardio For Fat Loss, Which One Is Better?
The Idea behind fasted cardio for fat loss
So you may ask yourself why people are performing cardiovascular exercise after an overnight fast, waiting until after the exercise bout to consume breakfast?
The basic premise for this practice is that low levels of glycogen (and/or glycogen depletion during the exercise bout itself) and insulin, shift energy utilisation away from carbohydrate for fuel, thereby allowing greater mobilisation of stored fat that can be used for fuel (fat oxidation).
Even though this has been a trending topic in the fitness industry this notion of ‘fasted cardio’ has been practised for decades in weight making sports such as boxing but research has only scratched the surface in understanding the physiology and biochemistry behind this matter.
Furthermore…….
Fasted cardio in the morning is effective because as you sleep and fast overnight your body conserves its precious carb stores and leans toward mobilizing fat for fuel. The story doesn’t end here, however. Your body also breaks down amino acids into glucose overnight, so fasted cardio mobilizes more fat and potentially more amino acids for fuel, which isn’t ideal if building muscle is your primary goal. This isn’t a huge problem as long as you consume a fast-digesting protein like whey, along with some slow-digesting casein, after your cardio.
What does science say?
Acute effects of fasted vs. fed exercise on fat oxidation
During the exercise bout
Results from several acute studies (Spriet & Watt, 2003; Horowitz et al., 1999) support the idea that exercise in a fed state can result in a decrease in fat oxidation during the exercise bout due to a reduced entry of long chain fatty acids into the mitochondria.
However……..
Despite the evidence above, we can’t unequivocally say that fasted cardio is best for burning fat. Many studies on fasted or fed cardio focus solely on how many calories are burned during exercise. This is problematic because the real benefits of exercise, particularly high-intensity cardio and lifting, come after training. High-intensity training burns more calories and fat after a workout than low-intensity cardio. With high-intensity interval training (HIIT), you burn calories for the rest of the day, even when you’re not doing anything.
What I recommend….
For certain people at specific time’s fasted cardio can work well for men with body fat in the low single digits (5-6 percent) and females with body fat in the low teens (13-14 percent), especially if they have specific problem areas like the lower back or thighs.
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.
All in all my take home message would simply be to perform the type of cardio that you prefer and be consistent with it on a regular basis, but of course ensure you are doing weight training also!