Before answering this, I will point out that many people have very passionate opinions on this question. Similarly, many athletes have a system of pre-workout nutrition that works well for them.
In short, the answer to when and what an athlete should eat depends on your own personal goals. In this article we will explore some of the pros, cons, and myths around working out on an empty stomach.
Pro: You can lean out quickly
If one of your fitness goals is to lose weight and lean out, you should probably experiment with intermittent fasting. Intermittent fasting involves not eating for 16-20 hours in a row. There are many documented health benefits to an occasional intermittent fast including increased fat burning, shifting to fat as your primary source of fuel, normalizing insulin sensitivity, and lowering triglycerides. Working out on an empty stomach has many of the same effects. Because the body has no readily available blood glucose, it will tap into the next ready available source of fuel – adipose tissue (fat).
Pro: Increased levels of human growth hormone
Working out while fasted can increase human growth hormone by 1,300 percent. Coupled with the high intensity nature of CrossFit workouts, these hormone changes can accelerate strength and conditioning gains as well as causing lean muscle growth and decreased fat storage.
Myth: Working out on an empty stomach causes the body to burn muscle for fuel.
When the body is in a fasted state and blood sugar is low, the body releases a hormone called glucagon, which begins to breakdown fat for energy. The biggest threat to muscle is performing long moderate intensity workouts such as jogging on a treadmill. These types of exercises cause losses in muscle mass and the release or dangerous stress hormones such as cortisol. It would take well over 24 hours of fasting before the body goes into starvation mode and taps into muscle for fuel. Doing CrossFit on empty will not induce muscle loss unless you are already starving yourself for an extended period of time.
Con: Decreased intensity during workouts
Since an empty stomach involves low blood sugar, the body will not have a readily available source of carbohydrates to tap for quick energy. This lack of quick energy can lead to feelings of sluggishness and decreased intensity. The CrossFit training guide explicitly states that intensity is the most important variable in our daily training. A decrease in intensity – meaning decreased loads, duration, or reps – would likely trump all of the benefits listed above.
The bottom line: Your particular goals should guide you in the decision to workout on an empty stomach or not. It is not dangerous or unhealthy to do so, …just keep in mind the trade off in performance you may experience. There is no right or wrong answer to this question. For many, whether or not to eat before a workout is a personal preference.
Personally, I have experimented with working out on empty and had great success. That being said, I would never work out on empty during a competition or a day that I wanted to have my absolute best performance.
Part of CrossFit is constantly varying our workouts and I would encourage everybody to experiment with varying your pre-workout eating habits (again, depending on your goals) to find out what works best for you.
Do you have any experience working out on an empty stomach? Do you prefer it? Let us know on the community page what your pre-workout nutrition rituals are.