When we talk about sports nutrition, three elements come up almost every time: carbohydrates for energy, protein for recovery, and hydration.
But there is another type of carbohydrate that is discussed much less: dietary fiber.
It does not provide quickly available energy during a workout, and it will not, on its own, make you run faster or lift more weight. Nevertheless, it plays an important role in digestive health, the gut microbiome, and probably several mechanisms that help keep athletes healthy.
The challenge?
Fiber is important every day… but it is not always our best friend right before exercise!
It is therefore mainly the amount, variety, and distribution throughout the day of fiber that become relevant in sports nutrition.
In short
- Fiber supports digestive health and the microbiome, but it is not a supplement that directly improves performance.
- Aim for about 25 g per day (women) to 38 g (men); for athletes, a target of around 30 g is a good guideline.
- Increase your fiber intake gradually over several weeks while drinking enough fluids.
- Reduce fiber in the hours before intense training or competition to avoid digestive discomfort.
- Eat most of your fiber at meals that are farther away from your training session.
Why is fiber important?
Fiber consists of carbohydrates that our digestive system does not fully digest. Some travel through much of the digestive system to reach the colon, where they can be used by the microorganisms in our gut microbiome.
And this is where things get particularly interesting.
Certain fermentable fibers serve as a substrate for intestinal bacteria, which then produce various metabolites, including short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate.
These compounds are associated with several important functions, including maintaining the intestinal barrier, regulating certain inflammatory and immune responses, and energy metabolism. Research is also examining possible interactions between these metabolites, muscle, and exercise.
In athletes, these mechanisms attract a great deal of attention because intense, prolonged training itself represents significant stress for the digestive system.
The athlete’s microbiome: more complex than we thought
Exercise can influence the gut microbiome, but diet also plays a major role.
Several studies have found differences between the microbiomes of highly active people and those of sedentary people, particularly regarding certain SCFA-producing bacteria. However, the results vary widely, and it is difficult to separate the effect of exercise from that of diet, training level, and lifestyle.
In other words, it would be premature to say that there is a “perfect athlete microbiome.”
What we know much better is that a varied diet containing sufficient plant foods and fiber provides more substrates for the microbiome.
Conversely, some sports diets very high in protein and refined carbohydrates but low in fruit, vegetables, whole grains, and other sources of fiber could reduce the diversity of substrates available to gut bacteria.
This is also one of the important messages from the recent literature: a high protein intake should not come at the expense of fiber and plant foods.
Does more fiber improve performance?
Not necessarily.
It is important to make this distinction.
The mechanisms linking the microbiome, SCFAs, and muscle metabolism are fascinating, but we still do not have enough human data to claim that eating more fiber directly improves athletic performance.
A recently published systematic review highlights that interventions targeting the microbiome produce highly variable results and that no consistent performance benefit has yet been demonstrated.
A small trial published in 2025 among university basketball players observed interesting changes after eight weeks on a fiber-enriched diet. However, only 19 players completed the study, and no significant difference was observed between the two fiber doses tested. This is encouraging for research, but certainly not enough to conclude that “more fiber = better performance.”
The real message is therefore more like this:
Fiber supports an athlete’s digestive and metabolic health, but it is not an ergogenic supplement.
How much fiber should an active person eat?
The general recommendations often used are approximately 25 g per day for women and 38 g per day for men, although needs vary according to age, diet, and energy requirements.
In their 2025 article specifically devoted to fiber in sports nutrition, Mancin, Burke, and Rollo propose a particularly interesting approach.
When an athlete consumes less than 20 g of fiber per day, they suggest not doubling their intake overnight. Instead, they propose a gradual increase aiming for about 30 g per day.
An adaptation period of several weeks may be helpful, particularly for someone who previously ate little fiber.
Why gradually?
Because increasing legumes, bran, seeds, fruit, and whole grains very quickly can also cause bloating, gas, and digestive discomfort. The gut can adapt.
And let's not forget hydration: when increasing fiber intake, you must also make sure to drink enough, particularly for athletes who lose a lot of fluid through sweating.
But why is less fiber sometimes recommended before exercise?
Because what is excellent for long-term health is not necessarily ideal 30 minutes before running!
During intense or prolonged exercise, some of the blood flow is redirected toward the active muscles and, particularly when it is hot, toward the skin to dissipate heat.
The digestive system must therefore function in a different physiological context.
This is one reason digestive discomfort is common in endurance sports: bloating, reflux, cramps, the urgent need to have a bowel movement, nausea, or diarrhea may occur during exercise. The causes are multiple and include intensity, duration, heat, hydration, the mechanics of certain sports, and what is eaten before and during the activity.
However, a very large meal that is very high in fiber can slow gastric emptying and increase the amount of food present in the digestive tract.
That is why sports nutrition recommendations often suggest choosing foods that are easier to digest and lower in fiber around a training session or competition, especially for sensitive individuals.
This certainly does not mean that an athlete should follow a low-fiber diet all day.
The solution: periodize fiber
Carbohydrate periodization is widely discussed in sports nutrition. We can also apply a certain form of periodization to fiber.
The idea is very simple: put more fiber into the times when our digestive system has time to handle it and less in the period just before training, when digestion is more likely to cause problems.
Someone who trains early in the morning might, for example, have a small, relatively low-fiber snack before heading out, then use breakfast after training, lunch, and snacks to add oats, fruit, vegetables, whole grains, nuts, seeds, or legumes.
Someone who trains at lunchtime can have a high-fiber breakfast, then choose an easier-to-digest pre-workout snack, such as Zenit snacks.
And for a late-day workout, breakfast and lunch already provide several opportunities to build up good sources of fiber before lightening the pre-exercise snack.
However, there is no magic number of hours that works for everyone.
Digestive tolerance is highly individual and also depends on the type of activity. A leisurely two-hour hike and a high-intensity 10 km run do not place the same demands on the digestive system.
And before a competition?
This is where the strategy can be even more precise.
For a regular workout, it is often enough to avoid an exceptionally high-fiber meal immediately before the activity.
However, before an important endurance event, particularly for athletes prone to gastrointestinal problems, a temporary reduction in fiber or highly fermentable foods may sometimes be appropriate.
Strategies used in practice include a lower-residue diet during the 24 to 48 hours before certain competitions, or targeted FODMAP reduction for certain athletes who already experience symptoms.
Studies on low-FODMAP diets do indeed show potential for reducing certain gastrointestinal symptoms in sensitive runners. However, this is a targeted and generally short-term strategy, not a reason to eliminate a multitude of plant foods year-round.
Where can you find fiber in your daily diet?
There is no need to seek out extraordinary foods.
They can be found in fruits and berries, vegetables, lentils, chickpeas and beans, oats, barley and whole grains, whole-grain breads, nuts and seeds, chia and flax, as well as potatoes eaten with their skins.
And variety is probably just as important as looking only at the number of grams.
Different foods provide different types of fiber and therefore supply different substrates to the microorganisms in the microbiome.
And at Zenit?
When I created Zenit products, one of my goals was precisely to incorporate simple, nutritious foods into convenient products for active people.
Several products naturally contain ingredients that contribute to fiber intake.
The Zenit protein overnight oats, for example, are made with organic rolled oats and also contain chia seeds. Depending on the flavor, they also include apples, blueberries, almonds, or pumpkin seeds.
The almond and multigrain protein granola combines oats, almonds, pumpkin seeds, sunflower seeds, and flaxseeds.
The apricot and 5-grain energy square contains oats, dried apricots, pumpkin seeds, hemp, and chia, among other ingredients.
And the date, cranberry, and multigrain energy balls contain, among other ingredients, dates, cranberries, oats, pumpkin seeds, flax, hemp, and chia.
These products can therefore be part of a varied diet containing different plant sources.
However, even when a food is “healthy,” when you eat it matters.
Oatmeal with fruit, chia, and seeds can be wonderful for breakfast or after a workout. But someone with a sensitive gut might prefer something lower in fiber just before an intense competition.
Similarly, a Zenit ball or square may be well tolerated before or during a long hike or bike ride, but it is always best to test your foods during training before using them on competition day.
That is exactly what personalizing your sports nutrition means.
What I want you to remember
Fiber is not a nutrient to avoid when you are an athlete. On the contrary, a sufficiently fiber-rich and varied diet helps nourish the microbiome and support digestive function.
But unlike readily available carbohydrates, which we sometimes seek just before or during exercise, fiber is more of an investment in daily health than an immediate fuel for performance.
So, rather than asking: “Should I eat a lot or a little fiber?”
I prefer this question: “When during my day is it easiest for me to eat my fiber while still feeling good when I move?”
This is often where the best balance lies between digestive health, enjoyment of eating, and performance.
Frequently asked questions
How much fiber per day for an athlete?
Around 25 g per day for women and 38 g for men. A 2025 review suggests a target of around 30 g per day for athletes, increasing gradually.
Should fibre be avoided before exercise?
We reduce them in the hours before intense training or competition, because a meal very high in fibre can cause bloating and discomfort. The rest of the day, we eat enough of them.
Do fibre improve athletic performance?
Not directly according to current evidence. It supports digestive health and the gut microbiota, which helps athletes stay healthy.
Danielle Dubois, nutritionist
Founder of Zenit Nutrition
Scientific references
- Mancin L, Burke LM, Rollo I. Fibre: The Forgotten Carbohydrate in Sports Nutrition Recommendations. Sports Med. 2025;55(5):1067-1083. doi:10.1007/s40279-024-02167-1. PMC12106500
- Hughes RL, Holscher HD. Fueling Gut Microbes: A Review of the Interaction between Diet, Exercise, and the Gut Microbiota in Athletes. Adv Nutr. 2021;12(6):2190-2215.
- Pérez-Castillo IM et al. The athlete gut microbiota: state of the art and practical guidance. Benef Microbes. 2024.
- Scheiman J et al./review on SCFAs and the athlete: The Athlete and Gut Microbiome: Short-chain Fatty Acids as Potential Ergogenic Aids for Exercise and Training. Int J Sports Med. 2021.
- Pérez-Prieto I et al. Physical activity, sedentary behavior and microbiome: A systematic review and meta-analysis. J Sci Med Sport. 2024;27(11):793-804.
- Martinez IG et al. The Effect of Gut-Training and Feeding-Challenge on Markers of Gastrointestinal Status in Response to Endurance Exercise: A Systematic Literature Review. Sports Med. 2023.
- Mlinaric J, Mohorko N. Nutritional strategies for minimizing gastrointestinal symptoms during endurance exercise: systematic review of the literature. J Int Soc Sports Nutr. 2025.
- Lis DM et al. Low FODMAP: A Preliminary Strategy to Reduce Gastrointestinal Distress in Athletes. Med Sci Sports Exerc.
- Parker C et al. Effects of 24-week prebiotic intervention on gastrointestinal symptoms and markers of immunity in elite rugby union players. Eur J Sport Sci. 2023;23(11):2232-2239.
- Zha Y et al. High-dose Dietary Fibre Supplementation Enhances the Gut Microbiome, Health, and Athletic Performance of College Basketball Players. Int J Vitam Nutr Res. 2025.
- Gut Microbiota and Exercise: A Systematic Review of Interventions and Evidence Limitations. 2025. The review concludes that the evidence remains insufficient to attribute consistent performance improvements to microbiota-targeted interventions.