Between 30 and 50 million Americans have mild to severe lactose intolerance, a condition that causes digestive symptoms within 30 minutes to two hours of eating dairy products, according to the Cleveland Clinic. While some infants exhibit symptoms of lactose intolerance, you can develop the condition with age or after an injury or surgery on the intestines. Regardless of the etiology, the symptoms occur only after ingesting a food containing lactose.

Lactose, the primary sugar in milk, occurs naturally in dairy products such as cream, milk, sweet cream, sour cream and cheese. The fat content in the product does not effect the amount of lactose. Because dairy products are used in so many processed foods, people with lactose intolerance must read food labels carefully to determine if the product contains dairy products. Look for ingredients such as buttermilk, evaporated milk, sweetened condensed milk, whey, casein, dry milk products, whipped topping, milk chocolate and caramel. Baked goods, including bread, waffles, biscuits, cookies, cakes, pancakes and muffins, contain lactose, as do many desserts, candies, baking mixes, spaghetti sauce with cheese, macaroni and cheese mixes and processed meats.

Your body needs an enzyme called lactase to digest lactose. A person who does not produce enough lactase enzyme cannot digest lactose properly, so the bacteria in the large intestine breaks the food down, producing gas, diarrhea, bloating and abdominal cramping. You can experience mild symptoms with lactose intolerance while others have more severe problems. With mild lactose intolerance you can manage your symptoms by eating smaller amounts of dairy products. A greater level of sensitivity may require eliminating dairy products altogether.

Soy milk does not contain any type of dairy product and, therefore, has no lactose. Soy milk is made from a lactose-free plant source -- soybeans. After harvesting, the manufacturer presses the soybeans in filtered water, removes insoluble fiber and, in some cases, adds vitamins, minerals and vanilla or chocolate flavoring. Some manufacturers also add sugar or another sweetener.

Because soy milk contains no lactose, it cannot cause lactose intolerance symptoms such as gas, bloating, diarrhea or abdominal cramping. However, consumers should be aware that infants and, increasingly, adults can develop an allergy to soy. Symptoms of soy allergy may include tingling in the mouth; hives, itching or eczema; swelling of the face, tongue, throat and lips; wheezing, runny nose or trouble breathing; or dizziness and fainting. Rarely, someone may have a severe anaphylactic reaction that constricts the airway, compromises breathing and puts the patient into shock.