Exercise is a very important part of living a healthy lifestyle and is recommended to many of our patients as it promotes weight loss, preserves your muscle mass, and improves your mood. But is it true that working out on an empty stomach can help you burn fat faster? In this blog, I am going to talk about the science behind this thought and provide you with my opinion on whether you should engage in fasted vs fed cardio.
So what exactly is fasted vs fed cardio?
Fasted vs. fed cardio is an idea that you will lose more body fat and more weight when you either eat before or after your workout. Fasted being you workout in the morning before eating breakfast and fed being you eat a light snack before working out.
To clarify, in order to engage in a fasted workout, you have to exercise in the morning after an overnight fast (or period of not eating).
Some studies predict that during fasted cardio, you are likely to burn 20% more calories than you otherwise would if you had eaten. This theory has to do with the way the body metabolizes fat and carbs. It is important to note that this theory will only be accurate if you maintain consistency in your workout intensity and how many calories you are consuming.
Let’s dive into the science a little.
The Science
We all know that your weight is, in general, predicted based on the balance between your food intake and your energy expenditure—how much you eat versus how much you move. So, it makes sense that the fewer calories you consume, the more weight you will end of losing. A similar process happens in your body when you workout on an empty stomach. As we have explained in a previous blog, carbs are used as the body’s source of fuel. When your body’s insulin (sugar) levels are low—as a result of not eating carbs for a long period of time—the body will turn towards your stored fat for energy. This is known as fat oxidation or the burning of fat for energy.
In summary, insulin inhibits the breakdown of fats for energy. When we eat before working out, our insulin levels will rise and therefore our body will turn towards carbohydrates as our source of energy.
So this is where the idea that “fasted cardio will result in greater weight/fat loss” comes from
Challenging the Science
As with every good research conducted, there is evidence out there that challenges this thought. The contradictory theory is that fat oxidation was not much higher for individuals who performed fasted cardio as opposed to fed cardio.
Therefore, this would suggest that there really was no difference in fat loss when working out before or after eating.
Similarly, it is important to look into fat oxidation over a longer period of time—not just when you are working out—as your body burns energy throughout the day. And there have been studies that point to evidence that fat oxidation is higher post-workout when you engage in fed cardio versus fasted cardio.
This suggests that you are likely to burn more fat longer term when you eat before working out.