Fight The Bonk: Endurance Athletes and Fasting

A friend of mine, who is Muslim, is a runner, and has said before that she plans her running year around religious fasting holidays. Ditto my friend who is Greek Orthodox. I’ve never specifically made a point to not be in training during Yom Kippur (a major Jewish holiday involving 25 hours of abstaining from all food and water) though it has always seemed to work out that way. But this year, as I meshed together my training schedule and the holiday calendar, I realized I was going to be fasting forty-eight hours before my long run, which, if you ask me, has bonk written all over it. (Luckily, it’s a long training run and not, say a race. However, the Chicago Marathon is this weekend, so I’m sure a few other folks are wondering about all of this, too.)

Anyway, I’m one to try and troubleshoot my way out of tough spots and figure out a win-win situation. So, that’s what I did.

Obligatory disclaimer: Now, before we begin, let us not launch into a debate of fast or not to fast, as it is purely a matter of personal choice. Whether you, reader dear, are pro-fasting, anti-fasting, or altogether indifferent to fasting is perfectly valid and reasonable, as are your personal feelings about the nature of human beings and the universe. I’m only offering options and information for those who do observe fasts, or for people who coach people who fast, in order to help people out. Also, due to the nature of my experience and the information I was able to find, this focuses more on a one-day-only fast. I would love to hear from people who observe multi-day fasts about the ways they maintain their fitness and health during said periods. Lastly, while I welcome all comments, we’re just going to examine the aspects of fasting which might concern an athlete.

Capisci? Great. Let’s begin.

First, it’s important to understand the physical processes the body undergoes at various stages of fasting. The good news is that, to the best of my knowledge, there isn’t any fast that involves running around and expending a lot of our energy reserves, so at the very least, our exertion levels during a fast will be very low. “Fasting done for one day is not likely to do any harm for healthy individuals like athletes,” says Talli van Sunder, DPT of Being Healthy TV. In this post series, Modern Forager explains the physiological processes involved with fasting in great detail over six posts. But, the short version goes like this:

Food contains glucose, in some form or another. As we digest food, some of this glucose is stored in our muscles and liver as glycogen while the rest of it fuels our brain cells and intestinal absortion cells (erythrocytes). So, if we go about 6-ish hours (give or take two hours either way) without giving our bodies more glucose (via eating), that glycogen store in the liver is called upon, at which point said glycogen is converted right back into glucose to fuel our bodies. Got it? Good. So, this glycogen store can last about 12-ish hours before the body looks to the muscles’ stored supply of glycogen for fuel and can go a day or so in that manner. But, to protect its muscles from being damaged, the body, smart little machine that it is, steps in and makes a temporary switch, leaving the glycogen in the muscles alone after a point and focusing on fueling off of our stores fat cells instead. Blood glucose, then glycogen stores, then stored fat.

As most of you are aware, the literal definition of “bonk” is the point when glycogen reserves in the liver and muscles become depleted, totally derailing an athlete mid-event. So, you can see where fasting and endurance sports might potentially be at odds. The body’s search for fuel reserves inside the body is to keep us alive and functioning until we find more food, not, say, for running a race.

That said, step one is to prepare. Let’s take a look at things athletes can do to prepare for a fast in the days and hours beforehand. First, it’s always important to hydrate, but it’s very, very important to hydrate pre-fast, with water, of course, but also, just before the fast begins is a great time to hydrate with an electrolyte-replacement sports drink (Be mindful of the sugar hidden in some sports drinks, though). Placing our bodies in top-form before a fast will only help us both through the fast, and after. Planning far ahead is a good move, too. Say, ten or so days ahead, and work to get your blood sugars regulated and not spiking in either direction by eating quality, low glycemic index whole foods of complex carbohydrates and proteins while paying attention to eating at regular and slightly shorter intervals to keep blood sugar levels on an even keel. Coach Adam from Racing With Purpose adds an excellent point, too, that:

“…nutritional addictions take between four and 10 days to overcome from an irritability and blood sugar/insulin standpoint, and the two Jewish holidays are so conveniently spaced to fit this. …as endurance athletes one of our main objectives is to regulate our blood sugar and insulin response to optimize the use of fuel and avoid both spikes and crashes of energy levels…  If you withdraw off of these [foods and habits that de-regulate blood sugar levels], your cravings are eliminated and your blood sugar is moderated before you begin your fast, life gets a whole lot easier on Yom Kippur and for a lot longer afterwards. Consider this your pre-fast taper.”

During the fast, taking an easy walk mid-day isn’t an awful ideal, either, to slightly raise insulin levels. No hoofing it, of course, but a gentle stroll and stretch can boost the system significantly. Keyword, though, is gentle. And, gently tweak your workout schedule if need be as well, not only to avoid exercise during the fast period, but first before or after as well.

Then, after the fasting period, it’s important to consider the best ways an athlete can help his/her body return to training, both nutritionally (ie, what type of nutrition is most important and urgent at the end of a fast?) and physically  (what body processes are the most compromised during a fast? In what ways should an athlete coming off a fast try to be the most productive? In which ways should s/he give it a little time?).

The first order of business at the end of a fast is, of course, eating. It is super-important though, to not over-eat when breaking-fast, with the ideal scenario being a small meal to break the fast, followed by a healthy snack before going to bed. And, what you eat is important, too. van Sunder says of fasting, “The important thing for athletes is to drink and eat a healthy meal before hand and do the same afterward….eat a healthy meal that is easy to digest. Protein is harder to digest than carbohydrates.”

Iin my experience, eating a very healthy, low-glycemic carbohydrate with a lean protein first upon ending a fast is the best way for me to ease out of fasting, as a straight high-glycemic carb tends to make my body react with a burst of insulin and a sudden jittery, high. And, that’s not what I’m going for at all. Even-keeled is the name of the game to fight off this potential bonk. And, of course, go back to hydrating immediately, too– water, of course, and also electrolyte-replacement drinks (remember, sports drinks can suffice for electrolytes, but some of them have as much sugar as a can of coke, so watch it) or juice, and I like to add a banana, or at least part of a banana, a short time after breaking fast to get my potassium levels back up to par, while continuing to hydrate throughout the night. Then, as mentioned above, add a small, healthy snack shortly before going to bed, keeping the blood sugar as leveled out as possible.

The following morning, eat a good-sized, healthy breakfast, and keep up the hydration. To run that day, pay close attention to how you feel. Perhaps bring along an extra gel or GU or Shot Blok, just in case a little reinforcement is needed. And do the carbohydrate + protein post-run meal after that is customary (I know we all have our post-run to-go meal.)

This sounds like a lot of information to process at once, but once you do it once, it’s an easy routine. And the ability to not miss a beat in either area of our lives is worth the extra effort. But again, this really only troubleshoots a one-day fast period; I would love to hear comments, experiences or insights from folks who observe longer fasting periods.

One Response

  1. Thanks for a thorough and thoughtful post about fasting. I’ve often wondered about fasting during a training cycle, but never did the research!

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