Up to 70% of endurance athletes experience GI problems during an event. The symptoms can cause mild discomfort or be so debilitating the athlete has to withdraw. The reason GI distress is so common in endurance events is that, during intense exercise, 80% of the blood that normally goes to the GI tract is shunted to the muscles thereby affecting the movement of food from the small intestine. Here are some ways to minimize GI upset:
Graze, don’t feast.
Your body can absorb about 70g of carbohydrate per hour.
If you consume those 70g in the 59th minute, you will probably get sick.
You can greatly reduce the possibility of GI distress by consuming smaller amounts more frequently.