lactose is some sort of enzyme or something to that effect that is in dairy products. Some people do not have the bacteria in their digestive system to break it down .. and as a result get bloated, gassy, and have the "milk shits" (hence the lactose "intolerant"). Certain foods like yogurt have natural bacteria that breaks the lactose down so your body doesn't have to. I find that i can eat yogurt, cheese, etc but a big glass of milk will produce some pretty nasty results.