Although many people confuse it with milk allergies, lactose intolerance is a less serious condition characterized by the complete or partial inability of your body to break down the milk sugar known as lactose. Understanding exactly what goes on in the body of a person suffering from lactose intolerance highlights the fact that lactose intolerance is a manageable and sometimes temporary health problem.
Digestive Process
When a lactose-intolerant person swallows a dairy product, it travels to their stomach, just as it does in healthy people. In healthy individuals, digestion of the dairy product's milk sugar -- called lactose -- occurs in the small intestine where a special enzyme -- called lactase -- breaks the milk sugar into smaller molecules for absorption into the intestinal walls. If you're lactose intolerant, some or all of the milk sugar travels intact and undigested through your small intestine, eventually arriving in the large intestine. Once in the large intestine, the lactose comes in contact with colonic bacteria, which proceed to break it down.
Physical Symptoms
As soon as lactose enters the large intestine, bacteria interact with the milk sugar, producing short-chain organic acids and gases, such as methane, hydrogen and carbon dioxide. Potential symptoms resulting from this lactose-bacteria interaction include diarrhea, cramps, nausea, bloating and gas. These symptoms usually develop 30 to 120 minutes after you consume the offending dairy products, and they generally aren't severe. If you experience symptoms of lactose intolerance, your physician may conduct special tests that assess your body's ability to digest the milk sugar: the hydrogen breath test and the stool acidity test. If you have lactose intolerance, the hydrogen breath test will indicate higher levels of hydrogen in your breath after you consume lactose-rich foods, while the stool acidity test will show increased fatty acids, such as lactic acid, in your stool.
Time Frame
Many individuals suffering from lactose intolerance don't start experiencing symptoms until their teenage or adult years. This form of lactose intolerance -- called primary lactose intolerance -- occurs because the body gradually stops producing as much lactase as people get older. Most of these people still produce small amounts of lactase in their small intestines; they just don't produce enough to process large amounts of the milk sugar, which explains why you might not experience troublesome symptoms when you consume a small serving of dairy-based food. Contrary to popular belief, individuals suffering from this form of lactose intolerance often can consume up to 2 cups of milk daily without experiencing adverse effects, especially if they divide it into several smaller servings throughout the day, says Linda K. DeBruyne, registered dietitian and co-author of "Nutrition and Diet Therapy."
Considerations
In certain cases, your lactose intolerance may arise as a result of another condition or problem. Called secondary lactose intolerance, this form of the condition typically develops when your body lowers its production of lactase as a result of an illness, medication, surgery or a small-intestine injury. The underlying cause, often an intestinal disease such as celiac disease or inflammatory bowel disease, temporarily damages the intestinal mucosa secreting the enzyme that breaks down milk sugar, which limits your body's ability to digest the lactose. Secondary lactose intolerance typically resolves over time once your doctor provides treatment for the underlying condition.
References
- "Nutrition"; R. Elaine Turner, R.D., et al; 2009
- National Digestive Diseases Information Clearinghouse; Lactose Intolerance; June 2009
- "Nutrition and Diet Therapy"; Linda K. DeBruyne, R.D., et al; 2008
