12 Feb Should Runners be Fibremaxxxing?
Should Runners Be “Fibremaxxxing”? A Sport Dietitian’s Thoughts
If you’ve spent any time on TikTok lately, you may have come across the term fibremaxxxing.
At first glance, it sounds… aggressive. Like we’re about to turn eating fibre into some sort of extreme sport. Which, in nutrition is typically never a good thing.
But when we strip away the trendy name, fibermaxxxing is simply this:
Trying to meet — or exceed — the daily recommended intake for fiber.
And honestly? As a Sport Dietitian, I’m not mad about that, like at all.
Because here’s the reality:
Less than 10% of adults are meeting their daily fiber needs.
This isn’t just something that nutrition research supports either, I see this daily with the clients I work with. When reviewing their food logs and intake data, the same pattern emerges again and again. Most people are getting in barely half of the fibre they need on a daily basis.
So if fiber is finally getting some attention, I’m here for it and ready to cheer everyone on.
But as runners, there are a few extra considerations we need to keep in mind before we go all in on eating the max amount of fibre possible.
Let’s break it down.
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What Is Fibremaxxxing?
Fibremaxxxing is the idea of intentionally increasing your fiber intake to hit (or surpass) recommended daily targets:
- 25g per day for women
- 38g per day for men
These daily suggested targets are based on research showing that higher fiber diets are associated with:
- Better digestive health
- Reduced risk of colorectal cancer
- Improved heart health
- Better blood sugar control
- Improved appetite regulation
- Reduced risk of type 2 diabetes
And in my experience reviewing client food logs, most runners are sitting around 10–15g per day.
So yes, even in people who generally eat well and care about good nutrition, there is usually room for some improvement.
Why Fibre Matters (Beyond Just “Being Regular”)
Fibre isn’t just about bowel movements (although yes, it helps a lot there too).
It plays a major role in:
Gut Health & The Microbiome
Fibre feeds your gut bacteria. Those bacteria then produce compounds that influence everything from inflammation to immune function to mood via the gut-brain axis.
One suggestion I love and recommend to my clients all the time comes from the book Love Your Gut by Dr. Megan Rossi. She recommends aiming for 30 different plant foods per week to support microbiome diversity.
And what I want people to understand about that recommendation is that even within the goal of hitting our total daily fibre target, variety is also key. Eating different high fibre foods throughout the week provides us with more benefits.
Nutrient Density
High-fibre foods also provide us with:
- Vitamins
- Minerals
- Polyphenols (plant compounds linked to reduced inflammation)
- Healthy fats
- Plant protein
Fibre is never eaten in isolation, it comes packaged with many other beneficial nutrients, both macro and micro nutrients that support good health and reduce health risks.
Appetite & Body Composition
Another major benefit of fibre is that it slows digestion and improves satiety.
That means:
- More stable blood sugar after meals
- Fewer blood sugar highs and lows during the day
- More regular appetite, better control of hunger and fullness cues
- Easier fat loss (without feeling starved)
When I work with runners on body composition goals, the two questions I always want them to ask at meals are:
Where’s the protein?
Where’s the fiber?
That combination of foods does a huge amount of heavy lifting when it comes to checking off all our nutrient boxes for the day.
How to Increase Fibre (Without Overhauling Your Diet or Overdoing It)
Fibremaxxxing doesn’t usually mean a 180° diet transformation.
It’s usually about small swaps and additions:
- Swap fruit or veggie juice → make a smoothie with whole fruit, flax, chia, or oats
- Instead of white rice → choose brown rice or make a 50/50 combination of rice and beans or lentils
- Swap white bread → for whole what bread
- Instead of regular pasta → choose whole wheat or lentil/chickpea pasta
- Add nuts or seeds to snacks
- Include beans or lentils a few times per week in your meals
I often get asked which foods are “best’ for getting in fibre, and the reality is that fibre builds up in 2–4 gram increments throughout the day. So it isn’t about eating 1 or 2 magic foods that will meet your fibre goal, it’s about everything you eat over the course of the day adding up to your total daily target.
Two Important Types of Fibre
There are two main types:
- Soluble fibre – this helps regulate blood sugar and cholesterol and can improve digestion by acting as a gel in the digestive tract, softening bowel movements and making it easier to ‘go’.
- Insoluble fiber – this helps with stool bulk and moving things through the digestive tract so you can go more regularly.
Most plant foods contain a mix of both, so you don’t need to micromanage any sort of ratio of different fibre types, just aim for variety with the plant foods you choose.
The Downsides of Fibremaxxxing (Yes, They Exist)
Any nutrition trend that includes the word “max” deserves a pause.
More isn’t always better. Especially as a runner, fibre can be both a tremendous benefit for our overall health, but also be an issue if we don’t time it properly around our workouts or races. Here are a few tips to help you avoid the pitfalls of going too crazy on fibre.
1. Don’t Increase Your Fibre Intake Too Fast
If you go from 10g per day to 35g overnight, your gut will probably have something to say about it, and it won’t be nice.
Fiber intake should increase gradually, for example:
- Week 1: 15g
- Week 2: 20g
- Week 3: 25g
- And so on
Your digestive system will adapt and appreciate the extra fibre boost, but it needs time to adjust to the change.
2. Increase Fluids Alongside Fibre
Adding in extra fibre to your diet without enough water can be a recipe for constipation. Which is the last thing you want if you reason for increasing your fibre intake was to mange your constipation in the first place.
When increasing fibre, just remember that fluids need to increase too, especially if you’re a runner who needs more fluids to adjust for sweat losses too.
3. Supplements Aren’t Always an Easy Shortcut
Yes, products like Metamucil exist and can be helpful for some people to boost their fibre intake above and beyond the recommendation. Those greens powders on the other hand that claim to give you 10 servings of fruits and veggies in a single scoop? Skip em, cause that’s BS.
But before running out to get a supplement, remember that fibre supplements:
- Don’t provide the polyphenols we get from actual, whole fruits and vegetables
- Don’t provide the same micronutrients we get from eating a variety of whole high-fibre foods
- Don’t provide the protein we get from high fibre plant protein sources
I know I’m a Dietitian, but to be honest I can build a 40g fiber meal plan shockingly easily using food alone. Most people can get there without a supplement if they’re intentional.
Supplements can help, but they shouldn’t replace the foundational food habits that give us the overall nutrient and diet quality we’re striving for.
Special Considerations Around Fibremaxxxing for Runners
This is where things get important if you’re a runner who wants to boost your fibre intake.
Timing Around Workouts
Eating high fiber right before a run can cause GI distress. But, that doesn’t mean runners should eat low fiber overall.
It means:
- We want to be mindful of timing of our fibre intake, and just minimize it immediately before training.
- Limiting high fibre foods during carb loading when the extra carbs can already make you feel overfull.
- Consider saving heavier fibre meals for post-run or non-run days.
But, I’m also a huge fan of “if it ain’t broke don’t fix it”. So, if your current high-fibre breakfast works just fine for you before runs?
Keep it.
If it doesn’t?
Then we can adjust.
Fibremaxxxing and Carbohydrate Availability
Here’s another aspect of high fibre eating that can be a pitfall for some runners.
In some cases, especially in very health-conscious or plant-based runners an extremely high fiber intake (I’m talking 50–80+g/day) can:
- Crowd out usable carbohydrate (because while fibre is great, we don’t actually use it as an energy source)
- Contribute to low energy availability
So, if all your carbs are very high-fiber sources, your body may not be getting the accessible fuel it needs for performance. It may look like you’re meeting your carbohydrate needs on paper, but once we subtract the fibre, it tells a very different story about the available energy an athlete might have to work with.
This is not common, but it’s something I’ve come across with a few athletes I’ve worked with over the years.
If you’re experiencing signs of low energy availability or RED-S, this is worth assessing with a sport dietitian.
Want to learn more about the signs you might be underfueling as a runner? Click here
So… Should Runners Fibremaxxx?
In general?
Yes, most runners would benefit from increasing fibre intake.
But, we want to do it right, and in a way that actually supports our digestive health and is sustainable over the long term.
- Build up your fibre intake gradually
- Increase fluids alongside a boost in fibre
- Time fibre strategically around workouts
- Avoid overdoing it to the point of crowding out usable carbs
- Focus on whole foods first
Fibre definitely deserves a nutrition spotlight, it’s been overshadowed by protein hype and low-carb diet trends for years.
And while “fibermaxxxing” might sound dramatic, the real goal is simple:
Meet the RDA. Improve diet quality. Support long-term health.
Want to Know If Your Fueling Is Supporting Your Training?
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