When we talk about sports nutrition, three elements almost always come up: carbohydrates for energy, protein for recovery, and hydration.
But there is another type of carbohydrate that is talked about much less: dietary fiber.
It does not provide readily available energy during a workout, and fiber alone will not make you run faster or lift heavier. Yet it plays an important role in digestive health, the gut microbiota, and probably several mechanisms that help keep athletes healthy.
The challenge?
Fiber is important every day… but it is not always our best friend just before exercising!
So it is mainly their quantity, variety, and distribution throughout the day which become relevant in sports nutrition.
Why is fiber important?
Fiber consists of carbohydrates that our digestive system does not completely digest. Some pass through much of the digestive system to reach the colon, where they can be used by the microorganisms in our gut microbiota.
And that is where things become particularly interesting.
Certain fermentable fibers serve as substrates for gut 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.
Among athletes, these mechanisms attract a great deal of attention because intense and prolonged training itself represents significant stress for the digestive system.
The athlete’s microbiota: more complex than we thought
Exercise can influence the gut microbiota, but diet also plays a major role.
Several studies have found differences between the microbiota of highly active people and that of sedentary people, particularly regarding certain short-chain fatty acid–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 microbiota.”
What we know much better is that a varied diet containing enough plant foods and fiber provides more substrates for the microbiota.
Conversely, certain sports diets very high in protein and refined carbohydrates, but low in fruits, 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 sports performance.
A recently published systematic review highlights that interventions targeting the microbiome produce highly variable results and that no consistent benefit for performance has yet been demonstrated.
A small study published in 2025 among university basketball players observed interesting changes after eight weeks of a high-fiber diet. However, only 19 players completed the study, and no significant difference between the two fiber doses tested was observed. 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 targeting approximately 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 also need to make sure you drink enough, particularly athletes who lose a lot of fluid through sweating.
But why is it sometimes recommended to consume less fiber 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 to the active muscles and, particularly in hot weather, to the skin to dissipate heat.
The digestive system therefore has to function in a different physiological context.
This is one reason digestive discomfort is common in endurance sports: bloating, reflux, cramps, an urgent need to have a bowel movement, nausea, or diarrhea can occur during exercise. The causes are numerous and include intensity, duration, heat, hydration, the mechanics of certain sports, and what is eaten before and during the activity.
However, a very large, high-fiber meal 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 easier-to-digest, lower-fiber foods around a workout 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
We often talk about carbohydrate periodization in sports nutrition. We can also apply a certain form of periodization to fiber.
The idea is very simple: Put more fiber into the periods when our digestive system has time to handle it, and less immediately before workouts, when digestion is more likely to cause problems.
Someone who trains early in the morning can, 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 around lunchtime can have a high-fiber breakfast, then choose a pre-workout snack that is easier to digest, such as Zenit snacks.
And for a late-day workout, lunch and dinner already provide several opportunities to include good sources of fiber before making the pre-exercise snack lighter.
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 10K 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 normal workout, it is often enough to avoid an exceptionally high-fiber meal immediately before the activity.
But before a major endurance event, particularly for athletes prone to gastrointestinal problems, temporarily reducing fiber or highly fermentable foods may sometimes be appropriate.
Strategies used in practice include, among other things, a lower-residue diet during the 24 to 48 hours before certain competitions or targeted FODMAP reduction in athletes who already have 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, rather than a reason to eliminate a multitude of plant foods all year round.
Where can you find fiber in everyday foods?
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.
What about Zenit?
When I created the Zenit products, one of my goals was precisely to incorporate simple and nutritious foods in convenient products for active people.
Many 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 flax seeds.
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 include, among other things, dates, cranberries, oats, pumpkin seeds, flax, hemp and chia.
These products can therefore contribute to a varied diet containing different plant sources.
However, even when a food is “healthy,” when you eat it matters.
Porridge 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.
Likewise, 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 foods during training before using them on race day.
This is exactly what it means to personalize your sports nutrition.
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 the readily available carbohydrates that 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.
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.
- 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 microbiome-targeted interventions.