A new systematic review has revealed the best way for ultrarunners to fuel their training and racing while minimising unpleasant gastrointestinal symptoms.
The answer, the review says, is to eat a diet low in FODMAPs, which stands for Fermentable, Oligo-saccharides, Di-saccharides, Mono-saccharides And Polyols. These are carbohydrates that do not get fully digested or absorbed in the gut, and for those with a sensitive bowel can cause symptoms, such as gas, bloating, stomach pain, nausea and diarrhoea.
These symptoms are not only unpleasant but, according to the review, are potentially the most common cause of underperformance during endurance events – estimated to affect between 30 and 90% of ultrarunners.
A number of pathways may increase exercise-related gastrointestinal symptoms (GIS) –physiological, mechanical, psychological and nutritional – and these can be exacerbated by extreme environmental conditions, such as high heat, humidity and altitude.
Endurance athletes have long employed and experimented with a variety of nutritional strategies to manage gastrointestinal distress. However, the data on such practices within an ultra-endurance population hasn’t yet been compiled, making it a challenge for sport nutrition professionals to develop supportive recommendations.
In this systematic review, published in Nutrients, researchers explored seven existing studies, comprising 105 participants (50 male, 55 female), looking at nutritional strategies used before, during or after endurance sport in an attempt to alleviate exercise-induced GIS in ultra-endurance athletes.
It found that following a diet low in FODMAPs leading up to and during exercise – as well as throughout the recovery period – has the potential to support ultra-endurance athletes in reducing exercise-induced GIS. One of the reasons is because these foods create osmotic pressure, and as a result water is forced into the gastrointestinal tract. Additionally, they are easily fermentable in the colon and subsequently increase gas production. This can cause symptoms including bloating and discomfort.
Perhaps unsurprisingly, the review found that carbohydrates may be more favourable as an energy source during ultra-endurance training and racing – and that supporting carbohydrate tolerability via gut training ‘w0uld be extremely beneficial’ for long-distance runners. However, findings regarding the precise carbohydrate blend for optimum performance effects with minimum GIS incidence were inconclusive.
Moreover, researchers also looked at the impact of medium-chain triacylglycerols (MCTs) – these are shorter-chain fatty acids high in foods such as cow’s milk and coconut oil. It found that a high intake of MCT may be detrimental to performance due to its impact on GIS prevalence, but small amounts didn’t have any obvious effects.
The research also looked specifically at the impact of including dairy milk (a known FODMAP) within a pre-exercise meal but concluded that this didn’t appear to reduce GIS symptoms, explaining ‘the potential of dairy-rich pre-exercise meals to enhance or impair gut comfort during prolonged exercise remains unclear’.
High FODMAP foods include wheat-/rye-/barley-based breads and breakfast cereals, fruits such as apples, mangos and nectarine and certain vegetables like onions and garlic. Dairy milk and soy milk (made from whole soybeans) are also high FODMAP, as are legumes, cashews and pistachios.
While many of these foods are healthy – rich in protein, vitamins and fibres – there are low FODMAP alternatives. For example, pineapple, strawberries and mandarin are low FODMAP, as are vegetables like green beans, bok choy, carrots and cucumber. Low FODMAP proteins include eggs, firm tofu, meats/poultry/seafood, as are dairy products including camembert cheese, feta cheese and soy milk (made from soy protein).