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Should I Wait To Eat After Exercise?

The Consequences Of Not Eating After High-Intensity Training

February 19th, 2012

By , CISSN, Clinical Nutrition Writer

Question: Is it better to eat directly after high intensity interval training (HIIT), or wait for two hours? I read that eating after exercise reduces human growth hormone and can reduce the effect of my training.

There is a lot of confusion around exercise and eating schedules. In this case, the confusion is in regards to the effect human growth hormone (hGH) has on your body. After any exercise, but especially high intensity exercise, hGH levels are significantly elevated. The problem is that eating directly following exercise appears to lower hGH levels.

Since hGH is important for muscular growth, it seems as if this is the last thing you'd want to happen after resistance training or HIIT. After all, you've just devoted time to increasing your fitness so you want that training to be as effective as possible, right?

To understand why the answer is actually "yes, you should eat directly after exercise", we need to better understand why our body is releasing so much hGH in the first place. To understand this, we also need to bring a couple other hormones into the discussion.

    1. Insulin 2. Cortisol

Insulin's Role In Exercise

Insulin is our "too much sugar" hormone. Our blood likes to have a very specific amount of sugar in it--too much is toxic, too little is dangerous. When our blood sugar increases, such as after a meal, insulin is released to clear the excess sugar away. For a healthy individual with no insulin resistance, most of that sugar gets escorted into the muscles where it is stored as glycogen (glycogen is a type of starch our body stores).

If the amount of sugar is too much for our muscles to use, or the individual is insulin resistant, then more sugar gets stored as fat instead. From our body's perspective, it's better to store sugar as fat than have it floating around in the blood.

During high-intensity exercise, our body has extremely high requirements for carbohydrates. This is because only carbohydrates can be burned anaerobically (without oxygen). To deal with the increased demand for carbohydrates, our body releases the muscle glycogen it has stored. Unfortunately, during high-intensity intervals, we blow through that stored glycogen extremely quickly. Suddenly, our body needs to create more sugar so our blood sugar doesn't drop too much.

Cortisol and Human Growth Hormone: Fuel-Making Tag Team

When this happens, insulin production nearly ceases and many more hormones come into play instead. These include adrenaline, glucagon, cortisol, and hGH, but we'll focus primarily on cortisol and hGH. Cortisol and hGH work in tandem to create new sugar for our brain and body to run on.

Cortisol starts the job by breaking down our muscles in order to release amino acids. These amino acids flow in the blood all the way to the liver, where hGH sends a signal to turn them into more sugar in a process called "gluconeogenesis". Literally, this means "new sugar creation".

Because our body has no way to turn fat into sugar, and because our brain can only run on sugar, our muscles become a form of fuel reserve. When blood sugar drops, cortisol and hGH help our body turn our muscles into fuel so our brain can keep running and exercise can continue. In this case, hGH is actually not building muscle, it's creating fuel. In fact, during exercise that is hGH's primary function: telling the liver to create more sugar.

What About After Exercise?

It's true that if you eat directly after exercise, hGH levels drop. Let's consider why, though.

During exercise, hGH is released because our body has run out of carbohydrates. It needs a way to turn our muscles into sugar, and cortisol and hGH fulfill that need. If you don't eat after exercise, then your body continues to run in "low blood sugar" mode and it continues to pump out cortisol and hGH to turn your muscles into sugar. What the elevated levels of hGH after exercise literally mean is that your body is continuing to break down muscle--clearly, this is not what we need or want!

If, on the other hand, you eat directly after exercise, you introduce fuel back into the bloodstream. Your body recognizes that it has fuel once more and that cortisol and hGH are no longer needed. Insulin is released so that your muscles can take all that sugar and turn it into glycogen, preparing you for next time. Insulin also helps your muscles take in more protein so that all the muscle you've turned into sugar can be restored.

So yes, if you eat directly after exercise hGH levels will drop, but this is actually a good thing. Unlike when we sleep, the time we have the greatest growth-inducing release of hGH, hGH release during exercise does not cause muscular growth. In fact, it is a sign of muscular breakdown.

After Exercise, Insulin Is Better Than Growth Hormone For Muscle Growth

Don't get discouraged by muscular breakdown, it is a necessary part of exercise. However, we do want to do everything we can to control and limit muscle breakdown after exercise ceases. Part of this control is eating as soon as we can after exercise, which sends a very loud signal to the body to stop stripping our muscle and start rebuilding it. Insulin is a great "building" hormone, provided our muscles need the energy. Right after high-intensity exercise they definitely need it, and insulin will help you build more muscle.

If you participate in resistance training or HIIT, you will do yourself a favor by eating within thirty minutes of finishing. The best way to accomplish this is to plan your exercise right before one of your meals. For example, you could do 15-20 minutes of burst training and then eat lunch during your lunch break. If you prefer working out first thing in the morning, wait until after training to have your breakfast (preferably a protein shake!). If this is you, drink a cup of fruit juice before you exercise so your energy stays high throughout your exercise.

Remember that the goal of HIIT is to increase your after exercise calorie burn. The number of calories you burn during the session is minimal compared to how many you will burn over the next six hours. You're going to burn the same amount of fat regardless of whether you starve yourself or not, but if you eat right after exercise then you can ensure you're not also burning muscle!

Take Home Points:

    Human Growth Hormone does not significantly encourage muscle growth during or immediately after exercise.
    Human growth hormones primary effect during exercise is to work with cortisol to turn muscle into sugar.
    Waiting to eat after exercise causes your body to continue breaking down muscle. This increases recovery time and decreases fitness gains.
    Eating right after exercise stops muscle breakdown and encourages muscle growth.
    Waiting to eat will not significantly increase the amount of fat burned from HIIT.
    For maximum effect, plan your HIIT before a major meal. This way you take advantage of eating right after exercise without unduly increasing the amount of calories you consume every day.
    Make sure you eat a healthy meal after exercise with low-glycemic carbs, lots of protein, and some healthy fats. Large, high-sugar meals will spike blood sugar and cause fat storage, not muscle growth.

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