What are the causes?  The reasons why gastrointestinal disturbance (GI) occurs are not yet precisely explained. It is suggested that it is blood moving from visceral to active tissues (muscles) which takes place during high intensity training. It causes increased permeability of mucous membrane and provokes nausea, vomiting, stomachache and diarrhoea. Additionally, badly selected meals before and during training/match can cause problems. The results of the survey conducted at the beginning of the 1990 on Half Ironman runners have demonstrated a link between nutrition and the appearance of GI during the start. Particular attention was drawn to nutrition components such as: fibre, fat, protein, drinks containing carbohydrates of high osmolality (>500 mOsm /l).

What are the symptoms? Main symptoms of GI are: loss of appetite, heartburn, nausea, vomiting, reflux, abdominal cramps, splashing in the belly, belching, acute pain and flatulence.

How to avoid the GI occurrence during the training? – This few pieces of advice can prevent occurrence or ease the symptoms of GI.

• If you are prone to gastrointestinal disturbance, give up products rich in fibre at least one or even few days before the performance. Choose clean products: wheat bread, white pasta, give up wholemeal products. Check fibre content on the etiquette. Most of fruit and vegetables are rich in fibre, choose those with a smaller amount of fibre such as tomatoes (without skin), zucchini, olives, grapes, grapefruit.
• Avoid dairy products containing lactose, even with small intolerance. Choose vegetable based milk: soya, rice or almond milk which do not contain lactose.
• Dehydration can intensify the symptoms. Take care of good hydration before the start and on the road. Practice the pattern of hydration during the training. Get to know what type of liquids will be served on the road and test them during the training.
• Avoid aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. Acetyl salicylate and NSAIDs can cause the growth of intestine permeability and can increase the frequency of discomfort from alimentary canal.
• Eliminate products  with high fructose content, especially drinks which contain only fructose (combining fructose with glucose can be easier to tolerate).
• Take care of proper pre-training/match meal time (> 2h).

Train new food strategies on the training. Do not experience with new products before an important match. “The training of the intestine” can improve tolerance and size as well as type of eaten meals.