Cutting fiber on event day?

A few podcasts ago you mentioned cutting fiber the evening before an event. I was hoping you could elaborate on that. Is this because of water retention?
Do you tweak your pre event meals regarding fiber? If so could you provide an example of what you might eat and what you are looking to limit? I wonder how this might affect the current winning in the kitchen ingredients I am eating.
Hope you’re both well at Haute Route!

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hey @kmscott2438! thanks for a great question.

This is a super individual issue, as some people can handle a ton of fiber and others not so much around exercise, as the gut adapts to breaking it down depending on what you eat, which then changes the makeup of your gut microbiome, etc. But the basic rule of thumb is to reduce the fiber down in the days leading up to a major event or training session for a few reasons.

  1. fiber is essential for gut health and keeping our bowel movements regular and of good quality. This isn’t as important during a race, as excessive pooping isn’t ideal while you’re on the bike for obvious reasons! Cut it down to avoid producing too much bulk in your stool.
  2. Fiber is indigestible by us, and tends to fill up the gut without providing any energy. So this is a two fold problem around competition. Having a lot of fiber means we’re not filling up the tank with energy-dense foods, but also feeling full as fiber increases satiety. It can also take a bit longer for our gut flora to digest depending on the person, and so may cause GI distress and indigestion when exercising (try this for yourself by eating a big salad before a ride - no fun)
  3. fiber also retains water and pulls it into the digestive system to digest and excrete waste, thus requiring more fluid intake, which is why those of us on higher fiber diets tend to require more general water consumption. Obviously this has implications for athletes as we go through fluids at a faster rate, so dropping the fiber can help spare some of that for when we need it!

Hope that helps! Focus on white rice and other simpler foods right before the race, and experiment. The gut can adapt but definitely don’t overdo it. You gotta win in the kitchen at the macro level and then when it’s gametime, drop the fiber down a bit.

ps - in case you haven’t seen it, check out my TEDx talk on all things fiber :wink:


Hey Jackson,

I recently conducted a gut microbiome test ( I was surprise to find out my superfoods, which foods to avoid and which food to minimize. The typical superfoods like Kale and Spinach are on my minimize list, while other greens like Chard are on my superfood list. Almonds are on my Avoid list and sunflower seeds are on my superfoods list. My point… shouldn’t our nutrient plan be personalized based on our microbiome? The test feels like a $100 well spent. Thoughts?

Richard Williams

Hey Richard,

These kind of tests can definitely be interesting but they are still very new and likely not completely scientifically validated, so I just urge you to tread with caution about reading too deeply into the results. I am highly skeptical of any service or test that would say you shouldn’t eat kale or spinach or almonds (unless you have an actual allergy to them). There’s still sooo much we don’t know about the microbiome but what we do know is that the makeup of our gut flora is highly dependent on what we eat, so just eating based on how our microbiome currently looks is only half the battle - we have to cultivate a healthy and thriving gut colony which comes from eating a variety of healthy whole plant foods (including kale!). Unless you specifically have GI issues with eating those “minimize” foods, I wouldn’t necessarily avoid them just because of this test. Did they explain why you shouldn’t eat them?

Our nutrient plan should be based on the decades of mechanistic and epidemiological data pointing towards an eating pattern centered around a variety of whole, unprocessed plant foods. The microbiome is critical for health of course, but it takes time to get it healthy too, and it’s based on what we eat so we have to develop that symbiotic relationship! For more info on this area, check out this video:

and I also just picked up the new book called The Athlete’s Gut which I’m reading, and interviewing the author on my podcast In The Flow Nutrition next week so I’ll ask him about this as well. Hope that helps!

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^^^^^^ what @Jackson says :nerd_face:plus be wary of a service that sells this sort of information. that flies in the face of the science

Hi Jackson,

Yes. They provided insight into why I should avoid each item. For almonds, it mentions that they contain phytic acid which has been shown to impair the absorption or utilization of essential nutrients if not degraded by specific microbes. This makes practical sense to me, because I noticed on several occasions I did not fully digest almonds. Almond restriction doesn’t apply to almond milk or almond butter; and if I were to soak the almonds to a point where I could fully digest them, then I’m sure it would be fine. Other nuts are easy to digest.

For the Minimize foods, there isn’t an explanation. However, I suspect it probably had to do with me easy tons prior to my test. This highlights your and my general approach… eat a variety of healthy foods. Still super interesting. I’m going to retest in a month or so to see how it changed… a little geeky. I know.


Also… So, might be some validity.