Fresh, Small-Batch Nutrition for Better Health & Performance

An Introduction to Intermittent Fasting for Endurance Athletes

Food Clock

by Brian Maslach

I can recall hearing about fasting almost as early as when I first became interested in nutrition, but until a couple years ago I was skeptical there was a place for it amongst endurance athletes. You see, prior to my experimenting with Intermittent Fasting (IF) I was that type who would always wake up ravenous. If I didn't eat within 30 minutes of getting out of bed my thoughts would be solely focussed on finding food as quickly as possible. I would also experience a similar scenario if I went more than a few hours without food during the day. For someone who loves food, this was great from the standpoint that I'd get to eat again, but also made me feel like a slave to eating. "Hangry" was an all-to-common state for me. Unfortunately, this feeding schedule was reinforced by the often-touted concept that we should eat every 3 hours for optimal health and performance.

Thus, the freedom from having to eat every few hours is what initially intrigued me most about the prospect of fasting. Although, for the longest time I couldn't grasp how an active person who go so long without food. The thought of doing so would nearly make me lightheaded from low blood sugar. Nonetheless, I remained fascinated by stories of people who'd go extended periods without food.

More recently I began hearing about Intermittent Fasting and it piqued my attention. If you're not familiar Intermittent Fasting (often referred to as IF) it involves going for 16 hours periods, or longer, without eating. In many ways, it's the opposite end of the spectrum from eating 5 small meals a day. After some trial and error I've found it to be a simple and effective way to improve my body composition and endurance.

The longer breaks from eating allow your digestive system more downtime and for me this has translated into less bloating and gas (fun topic!). The constant barrage of food I used to consume seemed to be a never-ending source of inflammation. I tried all sorts of "diets" to help lessen this, and while some helped, nothing has made as big of a difference than simply allowing my digestive system more downtime.

An even bigger benefit in my eyes, however, is improved insulin sensitivity. I've written about insulin sensitivity a few times and consider it to be the crucial factor in getting and staying lean, as well as performing well throughout long workouts and races. Simply put, being more insulin sensitive means the body is more effective at releasing the optimal amount of this hormone to regulate blood sugar without storing excess in fat cells. Diet and exercise are the most effective natural means to improve insulin sensitivity, and Intermittent Fasting is the most powerful change I've found with the way I eat. I consider it one more way to train my body to perform better.

So what do I do? While some people practice Intermittent Fasting daily, I've found that a once or twice per week approach works best for me. I have difficulty consuming enough calories when doing it more often and my performance begins to suffer. Friday is my main day for Intermittent Fasting, but I'll sometimes do it on Mondays as well if I haven't put myself in too big of a caloric deficit over the weekend. I picked these days as they are often active-recovery or rest days for me. I was initially concerned that my performance would decline the day after Intermittent Fasting, but to my surprise I found that I have better endurance on Saturday after eating this way on Friday.

Costco Pizza

Yeah, I've been known to occasionally break fasts with pizza. Don't hate!

One of the most attractive things about IF is its' simplicity. I don't like overcomplicated training or nutrition as I've found such plans are most often not worth the effort. With IF the main thing is to allow at least 16 hours between meals. This means that if I eat dinner at 8pm (early for me), I won't eat again until noon (or later) the next day.

I didn't start Intermittent Fasting this way, however. Had I tried to go so long without food I probably would have been arrested for assaulting someone. Rather, I challenged myself to go a little longer each time before breaking my mini fast. After a few months I was able to get to late afternoon before eating. Unless I'm traveling, I don't usually push myself that long anymore. I simply go as long as I comfortably can before breaking the fast. If my body tells me I need to eat before noon, I will. If I find that I'm doing fine and don't feel the need to eat, I'll wait until I feel the need to do so. Listening to one's body is key.

I don't drink juices or protein drinks while fasting, either. I've tried each at different times and don't think they helped. They seem counterproductive to what I want to accomplish. I will, however, drink coffee and plenty of water (without getting crazy). I'll usually start the day with my bastardization of Bulletproof Coffee, which is a tablespoon of butter and a tablespoon of virgin coconut oil blended at high speed with hot coffee. Other days I'll stick to an Americano or pour-over coffee with a little butter and coconut oil stirred in for taste and less hassle. The coffee/butter/coconut oil blend does seem to even out the caffeine response for me, which is great since I am sensitive to stimulants.

When breaking my fast I'll eat as healthy as I can within reason. What does this mean? Since I'm eating less often, my appetite is larger and I'll allow myself leeway. While I don't follow a specific diet, my normal eating pattern most closely resembles the Mediterranean Diet. I'll focus on getting lean(er) protein sources, vegetables, fruits, and some grains, but I may allow myself an indulgence (or two). Intermittent Fasting isn't about consuming fewer calories to lose weight - at least it's not for me. I practice it to train my body to go longer without food, and the health benefits this brings.

Anything else? Well, I do find that I'll get chilled quicker in cool environments, so I'll be sure to carry an extra layer with me. Hot coffee and tea help. If I'll be traveling, I'll make a smoothie ahead of time and have it chilled in a thermos so it will be ready when I need nutrition. You can find one of my favorite recipes here.

I'd love to hear of your experience with fasting and/or intermittent fasting. I'm also happy to answer any questions. Just post them below.

As with any significant change to your diet, check with your physician if there's any doubt whether it's right for you. This is especially true if you have any medical conditions or are using medication.






  • Brian Maslach

    Jay Morrison — I appreciate the feedback!

  • Brian Maslach

    RunnerHK — I have read various reasons why Intermittent Fasting should not be done, but wanted to try it myself for the reasons I wrote and have since become a fan. Obviously, I’m not female and can’t speak to how well it will work for women other than to say I know of female endurance athletes who have told me of similar experiences.

    My body comp changes were observed through skin caliper measurements and bodyweight changes, as well as unscientifically by how my clothes fit.

    Thanks for the questions!

  • RunnerHK

    Interesting topic. I’m not an expert so I’m not here to debate the merits — and I’m always one to say that if it works for you, do it! — but I’ll point out that Dr. Stacy Sims has written about why IF is a bad idea for female endurance athletes. Curious to know if the author has had before/after DEKA scan (or comparable) to support his view that IF has altered his body comp. Thanks for the write-up.

  • Jay Morrison

    I practice IF every week no matter what. Race weeks it’s usually two days a week and my eating windows are 4 hours long, so a 20 hour fast. Training weeks usually upto 6 days a week… but usually 4 to 5 days from 16 to 20 hours a day of IF.

    I also periodize my carbohydrate intake. Training weeks I’ll try to eat low carb, higher fat to an extent. The carbs that I do eat are always natural… vegetables, fruits, etc nothing super refined. One of the main reasons I like the Enduro Bites and Beta Red products, they fit this in my book!

    Coming out of a fast I try to eat super healthy. Right mix of vegetables, meats, etc and I try to keep it natural/earthy.

    IF and this training has helped me take off and keep off 20lbs of weight while actually increasing my bike FTP. Less inflammation, quicker to recover from workouts. It’s been a great success for me.

    For my long races the periodization to carbohydrates has been tremendous as the week leading up to a race I will slowly increase my intake of natural carbs, usually sweet potatoes and Enduro Bites to keep the glycemic stores topped off…. then come race day a mixture of Beta Red to start, electrolyte drink mix and Enduro Bites on the bike makes me feel like I am on rocket fuel.

    Thanks, Jay

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