Food intolerances are less clear-cut than food allergies. But one thing is certain: food intolerance are not the same as food allergies, and they are not dependent on interactions between food antigens and our immune system. In fact, a food intolerance is not dependent on any single interaction, and for this reason, it tends to be less predictable than food allergy and also less consistent.

Perhaps the best known example of food intolerance is lactose intolerance. Since one entire category of food intolerances work in the same way as lactose intolerance, it is worth taking a close look at lactose intolerance and how this process occurs.

Lactose is a sugar that is present primarily in milk of mammals, including cows. (For this reason, lactose is often referred to as "milk sugar.") Lactose is a compound sugar made up of glucose and galactose. (In technical terms, it is called a disaccharide.) Unless we can break lactose apart into glucose and galactose within our digestive tract, we cannot fully digest most milk or milk products. The way that lactose gets broken apart within our digestive tract is with the help of an enzyme called lactase. If enough lactase is present to break apart the amount of lactose present in the food, we do not become lactose intolerant. We are able to tolerate lactose because we have enough of the enzyme (lactase.) to break apart the amount of lactose that we consume. However, this "if" can be a big "if." Many people do not have enough lactase. enzyme in their digestive tract to break down the substantial amounts of lactose that they consume. (Over half of all adults experience this problem to varying degrees, and among Asian, African American, and Hispanic ethnic groups in the U.S., this percentage is substantially higher.) When there is insufficient lactase. enzyme to break apart the lactose in food, this lactose travels intact all the way down through our digestive tract until it reaches the large intestine, where it gets broken down by bacteria into water and carbon dioxide gas. As a result, we can get too much water in our bowel movements (diarrhea), as well as bloating and cramps from excessive gas.

Some people with lactose intolerance choose to avoid dairy foods altogether. This approach is effective, since dairy foods constitute our major source of exposure to lactose. (Other mammalian milks—like goat's milk—also contain lactose, even though the concentrations are typically lower than in cow's milk.) Many people find that fermented dairy products—especially hard cheeses and live culture yogurts—trigger fewer adverse reactions than fresh liquid milk. (This reduction in adverse reactions is due to the use of microorganisms in fermentation, which carry out either partial or thorough breakdown of lactose.)

Some people with lactose intolerance who enjoy cow's milk itself avoid problems through the purchase of lactose-free milk. Lactose-free milk has been pre-treated with the enzyme lactase to break the lactose apart into glucose and galactose. (We should note here that we are just beginning to see lactose-free versions of grass-fed cow's milk in stores. However, if this type of milk is not available in your area, you can still purchase regular grass-fed cow's milk and use the alternative method described below.)

An alternative method for enjoying milk yet reducing problems with lactose intolerance is to purchase lactase enzyme supplements in liquid form and add drops to the milk yourself. (About 10-15 drops per quart is often recommended.) You should let the milk sit overnight in the refrigerator if you use this method to allow time for the enzymes to take effect.

There is also an option with lactose intolerance involving the purchase of lactase enzyme supplements in chewable, caplet, or tablet form. Swallowing a supplement along with cow's milk (whenever it is consumed) is sometimes effective in lowering its lactose content. However, as you might guess, this approach tends to be less reliable than placing lactase enzymes directly in the milk because there are fewer complicating factors in the milk container than in your digestive tract. Inside of your digestive tract, it is more complicated for the lactase to pair up with lactose, and it is also more difficult for the chemical reaction to take place due to continuous changes in the digestive tract environment. Still, for some people, this approach to lactose intolerance is effective.

We want to remind you how different lactose intolerance is from cow's milk allergy (CMA). In CMA, the immune system is reacting to proteins contained in the cow's milk in a typically predictable and consistent way. (The most common cow's milk proteins involved in this process are called casein proteins, and they include alpha-s1-casein, alpha-s2-casein, and gamma-casein.) In the case of lactose intolerance, the process is not as predictable or consistent. The degree of problems that we experience is related to the amount of lactose we consume, the amount of lactase enzyme our body is making, and how favorable conditions are within our digestive tract for combining the lactose together with the lactase enzymes and breaking it apart into glucose and galactose. Before leaving the example of cow's milk, we would also like to note that it is possible for a person to experience both types of problems with milk, and to simultaneously experience milk allergy and lactose intolerance at the same time.

Lactose intolerance is just one example of an enzyme-related food intolerance. It is possible for a person to have an equal amount of difficulty breaking apart other sugars found in food. The general category of sugars involved in food intolerance is disaccharides. Each disaccharide is made up of two sugars. Below is a chemically simplified chart showing food disaccharides and the enzymes needed to break them apart.

Enzyme-related food intolerances also commonly occur in relationship to beans and legumes. The most common symptom experienced with this type of food intolerance is excessive formation of intestinal gas. In some cases, dietary supplements that provide alpha-galactosidase enzymes (often commercially obtained from the yeast aspergillus niger) can be used to help reduce gas formation. Instead of breaking apart disaccharide sugars, these alpha-galactosidase enzymes break apart sugar-related components of more complicated food molecules involving sugar-fat combinations (glycopilids) and sugar-protein combinations (glycoproteins).

Like food allergies, food intolerances are well worth investigating if suspected as a potential health problem. And like food allergies, they may require the help of a healthcare provider to identify with certainty.