When trying to lose weight/fat, one of the first things that people think to do is cardio. A quick search online will return a lot of different results that will tell you to do a specific type of cardio to lose the most weight. Of all the different types of cardio, one that has been gaining popularity recently is fasted cardio. Some people will tell you that fasted cardio is amazing and better than fed cardio, while others do not like doing cardio on an empty stomach. So, will fasted cardio really help you lose more weight than fed cardio?
What Is Fasted Cardio?
Fasted cardio, as the name implies, is cardio that is done before you have eaten any calories during the day, usually in the morning. Since your body does not have any food or calories in it and it has been in a fasted state for a couple hours, people think that your body will go to the fat stores in the body and begin burning them for fuel. During fed cardio, which is done after you have consumed some calories, your body will burn the calories that you consumed for energy. This has led people to believe that fasted cardio will cause them to burn more fat, which will lead to a greater fat loss. In theory, this does sound logical, but does it actually work.
Research on Fasted Cardio
Unfortunately, the saying “If it sounds too good to be true, it probably is” applies here. Studies have been done that show that fasted cardio does not have any substantial benefits over fed cardio, and some studies even showed that in certain situations fed cardio was more beneficial than fasted.
One study that looked at changes in body composition from fasted cardio vs. fed cardio showed that the changes were similar in fasted and fed cardio. This study used 20 young, healthy females who were broken into two groups, a fasted and a fed group. Both groups were given a diet plan that was customized so that each person was in approximately a 500 calorie deficit and both groups performed 60 minutes of steady state cardio for the study. One group drank a shake containing 40 grams of carbs, 20 grams of protein, and 0.5 grams of fat before they performed the cardio and the other group drank the shake after their cardio (3).
The study lasted for four weeks, and afterwards the testers concluded that neither fasted nor fed cardio led to a more significant change in weight, BMI, body fat percentage, waist circumference, fat mass, and fat free (lean) mass. Of course, further, longer and more accurate testing needs to be done to properly solidify these claims, but in the short run it appears that there is not enough evidence to support the claim that fasted cardio is better for weight loss (3).
Another study looked at how eating carbohydrates can help you exercise longer. The study took 10 trained cyclists and put them through two training sessions, one where they remained fasted, and one where they were given a glucose (sugar) solution soon after they began exercising. When given the glucose solution, 7 out of 10 cyclists were able to train longer than when they were given a placebo solution that did not contain glucose (2).
Another, similar study was done using 7 trained cyclists who were given a flavored water solution during one exercise and a glucose polymer solution another time. The study found that when the cyclists were fed carbohydrates, on average, they were able to exercise for an hour longer than when they were given the placebo. The testers also commented that during the initial duration of both trials, the cyclist’s bodies used their muscle glycogen stores at similar rates, meaning that fasted cardio does not necessarily break down more muscle than fed cardio. However, the study also found that during the extra hour of exercise after being fed, the cyclists bodies also did not use much of their stored muscle glycogen, and they burned carbs at a similar rate as the first part of the exercise (1).
What’s My Point?
I did not do this research or write this article to bash fasted cardio and to tell you that it does not work. Actually, the tests showed that fasted cardio does work (3). The point that I was trying to make was that, contrary to what you might hear, fasted cardio does not make you lose more fat than fed cardio. As the mentioned studies showed, the amount of fat loss was similar between the fasted and the fed group and that the breakdown of carbohydrates and muscle glycogen was similar as well. So, both types of cardio are effective ways to burn more calories and fasted cardio does not necessarily burn more muscle than fed cardio. But, after eating carbohydrates, studies show that you can work out longer without compromising muscle, leading to a higher calorie expenditure.
Basically, there is no difference between fasted vs fed cardio, only cardio that you complete or do not complete. If you feel more comfortable eating a little bit of food before you exercise, then do that. The research shows that you will not be compromising your weight loss because you ate before working out. But, if you prefer to wake up early and to exercise and get your cardio done first thing in the morning before you eat, go for it. Currently, science has not conclusively shown that either option provide a significant benefit or downside as compared to the other.
To lose weight, for most people, it can be simplified to calories in versus calories out. If you are burning more calories than you are consuming, then you will eventually lose weight, period. So, do whatever works best for your life and your routine. There is no one singular magical food or exercise you can use that will “melt” away your fat. The most important part of losing weight is being consistent with your diet and exercise to ensure that, at the end of the week, you have burned more calories than you consumed. You can get to this result however you would like, fasted cardio, fed cardio, HIIT, steady state, no cardio, whatever. As long as you can be consistent and maintain your plan, then choose whatever works best for you.