Should I Do a Long Run or Race the Day After Fasting?

two men on an early morning run
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Marathoners-in-training know they're supposed to hydrate and carbo-load during the days leading up to their long training runs, but what happens when you throw a 24-hour fast (no fluids or food) into the mix? That's the reality for those who observe religious holidays that require them to fast from sundown to sundown.  Many Jewish runners I know who observe Yom Kippur run into this situation because the holiday often falls during peak training for Fall marathons.

If you're fasting for Yom Kippur or another religious holiday, the ideal solution would be to do your long run before you start your fast or a couple of days after your finish. Of course, this can get complicated, especially when the holiday falls during a weekend. For many runners with busy work or school schedules during the week, running long on a weekday is not always an option.

So, if your schedule puts your long run the day after a fast, don't shoot for a super long run. Use it as an opportunity to take a rest week and go down in mileage. The fasting may make you feel a little more fatigued than usual during your run, so take it easy. Make sure that you hydrate really well and carbo-load until the start of your fast. As soon as you break your fast the next day, continue with the hydrating and carbo-loading. On the day of your long run, make sure you eat a decent breakfast (mostly carbs) and drink about 16 ounces of fluid an hour before you start running.

But Can I Run a Race the Day After a Fast?

So, what if you really want to run a race that falls the day after Yom Kippur or other religious holiday that requires fasting?  If it’s longer than a half marathon, I wouldn’t recommend it, since you just wouldn’t have enough time to eat and hydrate the way you should before an endurance event.

  I also wouldn’t recommend it if you’re hoping to PR or shooting for a very strong performance. But if you’re planning to do the race for fun and you’d take it easy, then you should be fine to do the race (assuming you follow the nutrition/hydration advice listed above).

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