One of the most common issues during endurance running is runners stomach or gastric upset – cramps, vomiting, diarrhea. There is no one cause of this, and it is often very individual, however there are a number of things you can do to minimize the chances of this happening.

1. Hydration.

If you become dehydrated your stomach will no longer be able to absorb carbohydrates effectively. It only takes a 2% variation in your hydration for issues to start occurring. The best way to work out how much water you need is to do a sweat test. This is easily done on one of your training runs. Some people lose 500mls water per hour others lose twice this. A guideline is around 600mls per hour for females, 850mls for males – though it is also very dependent on your body weight.

2. Practice absorbing carbohydrates (sugar).

Use your training runs to practice absorbing carbs when your body is under stress. There may be times when you don’t actually “need” the carbs ( run is less than 90mins) , but if you are someone who suffers from gastric upset, then it is important to practice absorption during training. Carbohydrates absorb best into the small intestine when in a less than 10% solution. So if you are taking on board 20gms of carbohydrate (ie a gel or bloks) you will need a minimum of 200mls water ( 20/200 =10%) . 6-8%solution is preferable for the sugar to be more readily absorbed – so that would be closer to 250-300mls of water.

3. Different types of sugars. Not all carbohydrate gels or drinks are created equal.

There are endless mixed messages in the market place over which sugar is best for fueling. Glucose, fructose or maltodextrin ? The answer – whichever works best for you. If you have a sensitive tummy, try using different brands – choose one without fructose, and perhaps one that is 100% maltodextrin, or if gels are not working, try some blocks/chews or a liquid fuel.

4. Avoiding fibre.

If you would like to have “real food” as part of your nutrition make sure that you chose low fibre and low fat to reduce your risk of gastric upset. Examples are white bread, potato, bananas, pikelets, white rice. Running a marathon is not the time to be super healthy with a multigrain sandwich, nuts and seeds or homemade muesli slice made with oats – these will potentially have you taking a detour to the loo. If you are someone who suffers gastric upset, then stick to low fibre foods for a few days prior to your event.

5. Have a plan, but be flexible.

Try to stick to your nutrition plan that you have practiced in training. However, if you start to feel sick during the race, back off the fuel and sip water for then next 20-30 mins and try again. Here is how I planned an ran the New York Marathon