Researchers recommend eating a mix of high-fibre foods, such as nuts, berries and whole-grain carbs.iStock
Modern sports nutrition guidelines are nothing if not detailed, with meticulous advice about exactly when, how much, and in what form you need macronutrients such as protein, carbohydrate and fat or micronutrients such as iron and calcium.
But there’s a notable omission in the guidelines: dietary fibre. It’s not as sexy as the latest super vitamins, but getting either too little or too much fibre at the wrong time can be the difference between victory and defeat, and can also affect your gastrointestinal comfort and long-term health.
A recent paper in the journal Sports Medicine, from a team of sports nutritionists led by Laura Mancin of Liverpool John Moores University in Britain, aims to fill this gap. Mancin and her colleagues draw on a mix of lab research and practical experience with competitive athletes to suggest a set of guidelines for how athletes and exercisers should get their fibre.
The trouble with fibre
When athletes think about fibre, it’s usually because they’re trying to avoid it.
Dietary fibre is defined as the parts of plant foods that pass through the stomach and into the colon without being digested. Some types of fibre are then fermented by the bacteria in the colon, leading to gas, bloating, and other GI symptoms – not what you want to experience during a workout or competition.
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As a result, athletes who struggle with stomach issues have long been advised to stick to low-fibre foods in the day or two prior to competition. For example, pro cyclist Mike Woods once described his vegetable-free pre-race meal plan as a “five-year-old’s diet.”
Mancin and her colleagues suggest avoiding high-fibre foods for one to two hours before workouts and three to four hours before competitions. But they caution against making a consistent habit of avoiding fibre.
Though experts recommend avoiding high-fibre foods before workouts and competitions, consistently excluding them from your diet can be detrimental.Ted Johns/Getty Images/iStockphoto
The case for more fibre
In the general population, fibre is recommended for a variety of health benefits such as lowering cholesterol and reducing the risk of heart disease. For athletes, fibre is of particular interest because of its effects on the gut microbiome, the community of microbes that live in your intestines.
When fibre is fermented by microbes in the gut, it helps keep the various strains of bacteria in the microbiome healthy and diverse, which in turn reduces inflammation throughout the body. The fermentation also produces short-chain fatty acids as a byproduct, which bolster the immune system and can serve as an additional source of energy during exercise.
Figuring out exactly which foods will deliver these benefits isn’t straightforward. Some types of fibre are more easily fermentable by the microbiome than others – and the specific foods that your colon can ferment depend on which strains of bacteria are present in your microbiome.
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In practice, though, it’s good to have a mix of both fermentable and non-fermentable fibre in your diet, since the unfermented fibre helps speed the passage of waste through your digestive tract. As a result, you don’t need to stress about which foods your microbiome can ferment as long as you’re getting a variety of different high-fibre foods.
For example, foods like vegetables, pasta and rice are generally highly fermentable. Berries and quinoa are moderately fermentable. Almonds, peanuts and celery are less fermentable.
Overall, Mancin suggests, athletes should aim for about 30 grams of fibre per day, similar to the levels suggested for non-athletes. A typical breakdown might be seven grams of fibre at meals plus two or more snacks with three grams each. A sample dinner could include 200 grams of cooked quinoa, 150 grams of chicken breast and two cups of mixed vegetables.
If you’re currently getting less fibre in your diet, ramp it up slowly and increase your fluid intake to help the extra fibre through the digestive tract. Allow about four weeks to gradually increase from 20 to 30 grams per day, or longer if you’re experiencing GI symptoms.
Alex Hutchinson is the author of The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map.
