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2 Reasons To Decrease Fiber

Dr. Nick Belden • March 27, 2023

Today, we’re going to talk about a topic near and dear to not only my heart and your heart, but probably your and my gut. Fiber. We’re going to talk about fiber, probably not in a way that you are accustomed to hearing about. We all know there are plenty of benefits of fiber, from cardiovascular health, to gut health directly, to appetite suppression, to favoring the growth of beneficial bacteria. But today, I’m going to talk about situations where it may be best for you to actually decrease your fiber intake. I’m going to talk about two situations in particular where that may be worth experimenting with.

1. Before Exercise

This is going to depend on the intensity of the exercise. If you’re going to engage in any sort of high intensity exercise, where your heart rate is going to be really elevated and your respiratory rate, breathing rate, is going to be super high, that tells me that it’s going to be a pretty intense exercise session. If you’re going to have a pre workout meal, I would not want it to have a lot of fiber. Why? Fiber actually slows down digestion. It’s called slower gastric emptying, which is just the rate at which food goes from your stomach into the first part of your intestine, the small intestine. GI problems were more likely to occur in those consuming fiber before a half-ironman (1). At high exercise intensities, gastric emptying slows down (2). You can hopefully see a double whammy scenario, where gastric emptying is slowed down by both intense exercise and fiber intake.

Now, if you eat a lot of fiber before you go and do a lot of intense exercise, your stomach and belly are going to feel really, really full. It’s going to be really, really uncomfortable if you’re trying to do a max out effort on the rower, or the assault bike, or if you’re trying to do a max effort deadlift or a back squat and trying to generate a lot of intra-abdominal pressure. That’s just that’s a feeling no one really wants to have to deal with. This is where sometimes you even run into situations where people have to vomit, because food is still partly in the stomach; then once you start breathing a lot, your body’s just like, hey, let’s get rid of everything in the GI tract, and it can go one of two ways. If it’s still in the stomach, it’s probably coming out of your mouth.

If you’re just going to go for a walk, or light aerobic work and your heart rate and breathing rate really aren’t going to get that elevated, then it’s still OK to eat fiber beforehand. Why this time? You’re not really going to be exercising at a rate that will start diverting blood flow from your GI tract; not at a rate that’s really going to cause you to feel really bloated and really full. But again, if you’re going to do any intense running, rowing, CrossFit, weightlifting, even something like swimming, I would try to limit the fiber intake and stick to some more simple carbohydrates like fruit or rice. If you’re low carb, maybe just experiment with fasting or maybe just a few eggs.

2. The Healthier You Eat, the Worse You Feel

I sometimes hear this statement from patients: “I eat a really, really clean diet and it seems the better I eat, the worse my gut feels.” That tells you that there is some sort of gut dysbiosis going on. If they’re eating lots of vegetables, lots of whole, minimally processed foods, and they’re always feeling bloated, fatigued, having abdominal pain, potentially even having constipation or diarrhea, to me, that says that they are eating the wrong types of fibers in or the wrong types of plants for their gut bacteria. What I would recommend in that situation is something like a low FODMAP diet.

For those of you unfamiliar with FODMAPS, they’re just types of carbohydrates, including fiber, that are poorly absorbed in the small intestine (where most nutrient absorption takes place). These carbs then become fermented in the intestines by our gut bugs. Unfortunately, some of us have certain gut bugs that create problems for us when they ferment these carbs (bloating, constipation, diarrhea). The low FODMAP diet actually reduces a lot of fermentable foods that can really aggravate people’s gut. These can be things like onions, garlic, avocados, and apples. Foods that have fiber in them and that can be beneficial for overall health. But in people that have maybe, IBS or any underlying gut dysbiosis, they can’t handle that degree of fiber.

The low FODMAP diet is very complex, and it’s also very individualized. I would recommend that you do it under the guidance of an experienced dietician, or a practitioner that has experience working with the low FODMAP diet. For some people, their problem is one class of FODMAPs (lactose from milk), for some people it’s a different class (maybe fructans from wheat), so you need to work with a clinician or a physician that knows how to tailor it to you. There’s a very specific way you take out foods, and then there’s a very specific way you reintroduce them.

Why reintroduce them? Like we touched on, a lot of these foods are beneficial for overall health. They just need to be temporarily removed so you can kill off some of the bad guys that are feeding off too much of the FODMAPs.

Again, just to reiterate, fiber, very, very important. I always recommend people try and get fiber into their diet, particularly different kinds of fiber. One of the best ways to have a healthy gut is to eat as diverse-array of foods as your body can handle. But there are very specific situations like we just talked about, where it may be advantageous or beneficial for you to TEMPORARILY reduce your fiber intake.

As always, Trust in Your Gut.

Disclaimer: The contents of this article are for educational purposes only, and are not intended to diagnose or treat any condition. Do not apply any of the information in this article without first speaking with your doctor.