Lactose intolerance is simply the body’s inability to digest lactose. Lactose is a disaccharide, or a molecule made up of two types of sugars, in this case, glucose and galactose. Most people have an enzyme (a protein molecule that breaks down other molecules) lactase in their digestive systems. This enzyme breaks down lactose into glucose and galactose. The body can then absorb and use these sugars for energy. When someone has a lactase deficiency, lactose cannot be digested and remains in the digestive system causing a wide range of unwanted symptoms, including abdominal pain, gas, diarrhea, nausea, and a bloated stomach.

When you eat any food, your body has to process it. You can think of your digestive tract, that path between your mouth and your anus, as a system that is essentially outside of your body, just contained within it. It’s the job of your digestive system to break down the foods we take in, allowing the nutrients to “cross-over” into the different body systems and organs for use as fuel. Each different part breaks these foods down differently. For example, the mouth chews it up into smaller parts. The stomach uses enzymes and acids to further break it down. The food then goes to the small intestine where most of the nutrients that come from our food (proteins, fats, and carbohydrates) get absorbed into the bloodstream by a process called diffusion. What is left over is then passed to the large intestine whose main job is the absorption of water that remains in the indigestible residue of food.

Lactose, for the most part, gets broken down by lactase in the small intestine. If this is done quickly enough, and completely, then no lactose reaches the large intestine. If lactose does reach the large intestine, it will begin to ferment creating lactic and other fatty acids (ahhh the cause of the burning, stabbing pain your watery stool invokes is revealed). Several types of bacteria (called intestinal flora) will also begin to digest and use the sugars. Their resulting metabolism can create the unwanted flatulence submarine dwellers everywhere fear! The longer the lactose stays in your colon, the greater the problem becomes. So pray your colon works quickly!

The question then becomes, how does one develop the lactase deficiency that causes lactose intolerance? There are two types of lactase deficiencies, primary and secondary.

Primary lactase deficiency (sometimes known as Congenital Lactase Deficiency), for the most part, begins after age 2 and develops slowly over time. Before the age of two, children have a much higher level of lactase in their digestive tract. This is thought to help them better digest breast milk from their nursing mothers. After the age of two the body begins to produce less lactase, presumably due to the decrease in milk consumption. As a person develops, the symptoms begin to reveal themselves in late adolescence and early adulthood.

If you suffer from primary lactase deficiency, blame your parents! Researchers have now identified the gene (specifically chromosome 2q21), most likely, responsible for lactase deficiency and as such is thought to be passed on from your parents. Although extremely rare (in one study, since 1966, only 42 patients in Finland have been diagnosed), primary lactase deficiency can happen before the age of two.

Secondary lactase deficiency is the result of injury or illness affecting the small intestine, or the body’s ability to make lactase. Some common causes include chemotherapy, celiac disease, or Crohn’s disease. So not only do you have cancer and have to be treated with a poison, but you might not even be able to enjoy a nice cup of warm milk to settle your nauseated stomach! The fates can be cruel!

Bonus Facts:

There is good news on the lactose intolerance front. The mutated gene responsible is recessive, meaning both your parents would need to pass on the mutated gene for you to have the problem. Over time, as long as people don’t take examples from British royalty and procreate with family members, we should hopefully see the affliction steadily be reduced in the general population.

In the United States, about 33% of the population is lactose intolerant, or around 40 million people. 75% of Adults have a decrease in their body’s lactase activity. If you are Asian-American, you have a 90% chance of being lactose intolerant. Here I thought that Yo-Yo Ma’s pained look and constant fidgeting while playing the cello was from the intensity with which he rocks. It appears I could be wrong!

Premature infants, especially those born before the third trimester, are much more likely to have a lactase deficiency. Lactase levels do not begin to increase until the third trimester.

There is a common misconception that people with lactose intolerance cannot drink milk. The U.S. Agency for Healthcare Research and Quality has found that people with lactose intolerance can generally tolerate up to 1 cup of milk (about 12 grams of lactose) without any symptoms. They can handle about 2 cups if they spread that intake throughout the day. This means that most can consume their daily recommended level of dairy products. So long as they don’t imbibe it all at once! Although, I used to know a girl who would get seriously ill if she had even a single small slice of lightly cheesed pizza, due to an extreme case of lactose intolerance, but in the general case, most people who are lactose intolerant can handle a bit of dairy every day.

Should you have symptoms that include abdominal pain, diarrhea, excessive flatulence, or bloating, you might not necessarily have lactose intolerance. You might have Irritable bowel syndrome (IBS).
Unlike lactose intolerance which is caused by a deficiency in a specific enzyme for a specific food, IBS is the result of an abnormally functioning small and large intestine. The intestines move food through by contracting and relaxing layers of smooth muscle known as muscularis mucosa, and muscularis externa. This will happen at normal intervals depending on a few factors like what we eat; how much we eat; and how fast we eat. All this happens because the brain sends signals to the muscle to help mediate how fast and hard to contract the muscles. When these signals are stressed (like from an infection) they become more active and cause the muscles to contract more, or abnormally. The result is the uncomfortable symptoms that cause unwanted, infrequent, or just plain crappy trips to the bathroom.

If you should go to your doctor with these common symptoms, he might want to perform tests to diagnose which ailment you might have. To do this, they will try and “rule out” lactose intolerance by testing your stool for acidity. As we’ve talked about previously, lactose can create excessive acids in your colon. Should your stool contain this, and possibly excessive glucose from the undigested lactose, you might have lactose intolerance. Congratulations! Another test that can determine if you have lactose intolerance is a hydrogen breath test. Undigested lactose will create an abnormally high amount of hydrogen that can be detected on your breath or in your blood. The most common test is known as the elimination test. This involves not eating for a given number of hours and then consuming a drink containing at least 50 grams of lactose. The patient is then monitored for symptoms.

Should you be lactose intolerant, the average time it takes for symptoms to appear after eating enough lactose is 30 minutes.

Not being able to consume milk, or milk products, can lead to other deficiencies within the body such as calcium and vitamin D deficiencies. Because of this, people who do not consume milk products are often times put on calcium and vitamin D supplements by their doctor.