Why intermittent fasting and running don’t mix | Canada Voices

When running became mainstream, circa 2020, it pulled popular fitness trends into its orbit. Some, like yoga or creatine supplements, appear to pair well with it and be relatively harmless. And then, there’s intermittent fasting: the longtime, dubious darling of the biohacking world.

For the uninitiated, intermittent fasting consists of restricting one’s caloric intake for hours on end in pursuit of weight loss, blood glucose regulation and cholesterol control. The actual effectiveness of the method is debated in literature, but health influencers like Brian Johnson – who often eats the majority of his day’s calories by 10 a.m. – famously implement it in their routines.

In recent years, the recreational running world has become interested in the potential benefits of running while hungry. Scientists are studying the intersection of running and fasting, running media is reporting on the trend, and Reddit threads on their interplay continue to lengthen. If you follow running influencers on social media, they may be telling you that restricting your caloric intake will make you a better runner.

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But is that really true? Some early theories do sound convincing. A popular one is that sometimes training in a fasted state can nudge your body to rely more on fat as fuel. For easy, low-intensity runs, that can feel fine and may help some runners become more comfortable relying on something other than carbs for energy.

Then, there is the question of intermittent fasting as binging control: where restricting late-night snacking could lead to better sleep and eating habits overall. There is also something to be said about developing an eating routine that frees one of digestive and gastrointestinal issues on the run.

All of it sounds promising; and yet, in my 15 years as a competitive distance runner, I have not been encouraged to intermittently fast by a single coach, teammate or competitor. Any seasoned runner will tell you: It’s just not something that we do.

There is a reason for that: Reaching for those potential, marginal benefits is like grasping at a $5 bill while standing on the edge of a cliff. There is far more to lose than to gain.

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Ignoring hunger signals and letting the clock decide when you should eat while training as a runner exposes you to short-, medium- and long-term pitfalls. Right away, you risk sabotaging your daily workout. Speed sessions, long runs, and even easy runs require glycogen. When in short supply, it makes it much harder to hit paces, finish runs feeling strong, and adapt to training. Hitting the wall becomes far more likely. Then, not eating afterwards delays protein and carb intake, reduces muscle repair, and even compromises immune function.

Even if you do not immediately feel the bonk, you will be setting yourself up poorly for your next week if you undereat. Distance running is already a tremendous physiological stressor. Add caloric restriction and you increase the risk of poor recovery, hormonal disruption, mood dips and injury. No diet in the world can compensate for the massive fitness losses brought on by months on the sidelines.

Beyond that, restricted eating can expose one to long-term problems. Relative Energy Deficiency in Sport (RED-S), where the body falls into a chronic pattern of low energy availability, is a real problem in endurance athletes. It can lead to performance decline, lower bone density, and hormonal imbalances that become difficult to shake.

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There are other ways to gain an edge without cutting meals. Add an extra run to your weekly plan, introduce more intensity to your training routine, lift weights regularly, or even train yourself to go to sleep at the same time each night. Distance running rewards boring fundamentals.

I wish I had cookie cutter advice for how to eat around runs. There are general suggestions (simple carbs like cereal or bananas in the hour before a run, protein and more carbs after the fact), but the specifics come down to the personal level. So, trial and error is your friend: Play with timing and types of foods, and note how different approaches make you feel on the run, and also the next day.

And as you do that, just remember that, in running, you will wrestle with scarier monsters when underfuelling than when overfuelling. So when you are hungry, eat.