Many long distance runners perform at least some of their long runs in a fasted state (for example before breakfast, without taking anything), hoping that this will teach their bodies to become more effective at using fats for energy production. Even though it is not sure that it helps on race day, studies have shown indeed that you become better at burning fats if you train your body to do so.
The next question is then: would it help you to lose weight? In other words: would you lose more fatty tissue when you exercise in a fasted state than after a meal? Brad Schoenfeld and his colleagues have investigated this and concluded that it does not seem to make a difference. They published their study in the Journal of the International Society of Sports Nutrition in November 2014.
They divided 24 young female volunteers in two groups. One group exercised in a fasted state and the other after consuming a meal replacement shake. They all worked out on a treadmill three times a week at 70% of their maximal heart rate and followed the same diet with the aim to slim down. The women who started by exercising had their shake immediately after the workout.
After four weeks, all the women had lost weight, but there were no differences between the groups concerning amount of weight lost, waist line, lean or fat mass.
The researchers therefore concluded that it does not matter whether you exercise before or after a meal.
Schoenfeld explains the findings by citing previous research showing that our bodies change what they use as fuel, depending on what is available. If you burn more fats for a while, you will use more carbohydrates later in the day, and you have therefore to look at much longer periods than just a few hours.
You might understand their findings better if you think about the First Law of Thermodynamics, which states that energy does not get destroyed or created, but only changes from one form into another. What matter is therefore to get rid of the excess energy, whatever the form it is in.
A study with a negative result?
It is true that reading a study with a negative result is always slightly disappointing, and that is why in the past they did not get published. It is great that this now changing, because it might avoid repeating the same studies over and over again and it might also help us (I hope!) to avoid doing useless things.
Disclaimer: this article is for general information only, and does not replace medical or coaching advice. It cannot be used to guide treatment or training. If you have any concerns or questions, you should talk to a qualified health provider.
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