As I was leaving the gym today, my friend Tiffany asked me what I thought about running on an empty stomach in the morning. If she had asked me this same question a year ago, I would have probably told her that it was a bad idea. However, I’ve been hearing and reading a lot about intermittent fasting and the benefits of working out on an empty stomach. I told her to go for it. But her question did get me thinking more about this unconventional approach to eating.
Question: What is intermittent fasting? What are the benefits and it is good for runners?
Intermittent fasting is simply alternating periods of fasting with periods of non-fasting. There are many different approaches to IF, including:
1) skipping a meal
2) Eating only within a certain time window (for example, eating for only 8 hours during the day and fast the other 16)
3) the 48 hour fast which alternates 24 hours of fasting with 24 hours of non-fasting
4) eat early in the morning and late in the evening but fast throughout the rest of the day
5) do not eat several hours before bed, fast throughout the night, and then workout before eating breakfast
All my life, I have always been told to eat first thing in the morning to kick start my metabolism. And more importantly, to continue eating several meals throughout the day, as this will prevent a drop in blood sugar and keep me mentally focused for the day. So why in the world would I want to try intermittent fasting?
As humans, are bodies are only able to store a limited amount of glycogen, about 500 grams. On the other hand, it can store tens of thousands of calories of fat. The reason so many people experiment with intermittent fasting is because, teaching your body to burn fat as opposed to glycogen will give it an almost unlimited supply of energy (great for endurance) and make your body a lot leaner. I was recently listening to a podcast and the speaker compared the body using glycogen as fuel to a fuel truck running out of gas on the side of the road. The truck’s gas tank can only hold a limited amount of fuel, and even though the truck is carrying a large supply of gas, it can not access it. I really liked that analogy.
By experimenting with intermittent fasting, not only are you teaching your body to burn fat for fuel, but you are also learning a thing or two about self control. As one study put it, it is essential to fitness and good health to experience intentional hunger, become accustomed to the feeling, and not freak out. You gain more control of your own body. Some of other benefits of intermittent fasting are reduced blood lipids, blood pressure, markers of inflammation, oxidative stress, and cancer. There is also increased cell turnover and repair, fat burning, growth hormone release, and metabolic rate. Intermittent fasting also helps to improve appetite control, blood sugar control, cardiovascular function, and neuronal plasticity.
It was difficult to find a lot scientific evidence on intermittent fasting and running, mainly because this topic is still so new. I did find, however, one study that looked at the blood sugar levels in two different runners, one who fasted for 23 hours and the other who did not. After the 23 hours, both runners completed a 90 minute run at 70-75% of VO2 max. What the researchers found was that the two runners had the exact same blood sugar levels! This completely blew my mind, because I would have never expected that. The body really is amazing at maintaining homeostasis.
Ben Greenfield, who is top triathlete and nutrition expert, often discusses intermittent fasting for athletes on his podcasts. He recommends not eating a few hours before bed and then working out first thing in the morning, before eating breakfast. This is an easy way to incorporate a 12-14 hour fast into the day. Ben Greenfield, along with everything else that I read today, put a strong emphasis on eating high quality, unprocessed, nutrient dense foods along with lots of good quality proteins. If you are going to be doing this to your body, it’s super important to make sure it gets the right stuff when you are eating.
Currently, with my schedule I can not work out first thing in the morning. However, summer break is quickly approaching and I look forward to experimenting with intermittent fasting during the summer. In reading at a lot of the anecdotal evidence, IF seems to help people really lean out, lose weight, and have more energy. And when I was looking for a picture to include with this post, Google Images just kept giving me pictures of really ripped people. I think I might like this…
Happy Trails and Happy Running,