Hundreds of other substances can cause reactions. Mild fructose intolerance is not uncommon, and its symptoms of stomach and intestinal cramps become very noticeable during exercise. Severe symptoms include vomiting, weakness, dizziness, hunger, headaches, jaundice, and abnormal sweating. Drinking sweetened soda, fruit juices, and other high-fructose beverages is most likely to bring on symptoms. Fructose is found in thousands of sweetened food products.
Many sports drinks contain it.
As long as fructose is not the sole or the first sweetening ingredient listed, there is usually not enough to cause a problem. If you're sensitive to fructose, you should avoid large amounts, especially before exercise. Foods that contain amines also can cause reactions. The most notorious amine is monosodium glutamate, or MSG, a flavor enhancer. Glutamate is also found in tomatoes, bananas, avocados, oranges, mushrooms, chocolate, wine, and Parmesan cheese.