Food intolerances can share some of the same characteristics as some food allergies, such as nausea, gas and uncomfortable stomach pangs. However, intolerances and allergies are quite different. Intolerance symptoms often begin as the body is unable to completely digest a food. A popular food intolerance, such as lactose intolerance, which affects 70 percent of the world's population, stems from the inability to digest the milk sugar lactase. Thus, professionals often recommend that lactose intolerant individuals supplement with a lactase enzyme. Other sources of food intolerances include gluten, casein and soy.