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Lactose Intolerance

It is very common for people to drink milk, a common dairy product, during breakfast. In fact, not everyone can enjoy it. For some, consuming milk or other dairy products can lead to discomforting symptoms, such as diarrhea, gas, and bloating. It is mainly caused by lactose intolerance, also known as lactose malabsorption.

Lactose Tolerance

Back in ancient times, most people in the world did not have the trait of lactose tolerance. Lactose tolerance would only be beneficial for the people who were living in cattle cultures since it could provide extra sources of nutrition and even become a substitute for water during droughts. Over time, mutations that could switch the trait randomly occurred. Therefore, people who carry the trait of lactose tolerance might have direct advantages through natural selection.

Lactose and Lactase

Lactose is a kind of carbohydrate consisting in the form of a disaccharide. In order to absorb lactose, it is required to hydrolysis (break down) the lactose from disaccharide into monosaccharides. Normally, the small intestine in a human's body is supposed to produce an enzyme lactase that catalyzes the process of breaking down lactose in dairy products so the body can absorb it. The lactase activity increases from the eighth week of gravidity consistently until the thirty-fourth week reaching the peak. The lactase activity of infants is crucial during the breastfeeding period to absorb nutrition since lactose intolerance should be recognized in the first place. After a few months of early life, the lactase activity starts to decrease and remains constant.

Mechanism of Lactose Intolerance

People with lactose intolerance may not be able to digest and absorb lactose in the intestinal tract normally, which would result in some uncomfortable symptoms. In the small intestine, not enough lactase is produced then lactose is not completely broken down. The undigested disaccharide lactose that can not be absorbed into the bloodstream goes down to the colon directly, which increases the osmotic pressure, therefore leading to more water flowing in. It could potentially cause watery diarrhea, which is very indisposed. In the colon, the undigested lactose is metabolized by the bacteria inside called the process of fermentation, producing gases such as hydrogen gas, carbon dioxide gas, and foul-smelling methane gas. The excessive gases in the digestive system can lead to symptoms like bloating.

Clinical Diagnosis and Symptoms of Lactose Intolerance

Since most lactose intolerance is caused by lactase deficiency, lactose intolerance can be deduced when the sugar in the blood increases and the hydrogen breathed out increases. In addition, the symptoms reported by patients also help to infer lactose intolerance. Common symptoms include abdominal pain, bloating, borborygmi, and diarrhea. However, lactase deficiency only develops abdominal symptoms in partial people, which means the determination of patient reports is not fully dependable. Some tests like the measurement of lactase activity in mucosal biopsies from the duodenum can be used as the reference for the primary and secondary lactase deficiency. Often, people are asked to avoid all dairy products for 30 days to make sure there is no external influence. Besides the biopsy tests, genetic tests also play a role in assessment. Still, biopsy and genetic tests do not cover the evaluation of the symptoms. Thus, all the methods have their own limitations.


To avoid discomfort due to lactose intolerance, people should avoid foods that contain lactose: milk, cheese, yogurt, ice cream, butter, whey, and casein powder... It is also important to read the ingredients carefully. Taking lactase products that contain the enzyme lactase can also help people with lactose intolerance ease the symptoms. In most cases, the lactase products can be taken directly and also dropped into the dairy products before consuming them.

Figure 4: Lactase products should be taken before consuming the dairy products


Lactose Intolerance in Adults: Biological Mechanism and Dietary Management. (2015, September 18). NCBI. Retrieved February 26, 2024, from

Lactose Intolerance: Symptoms, Causes, and Treatment. (2018, November 13). Switch4Good. Retrieved February 26, 2024, from

Tishkoff, S. (n.d.). Got lactase? Understanding Evolution. Retrieved February 26, 2024, from

Treatment for Lactose Intolerance - NIDDK. (n.d.). National Institute of Diabetes and Digestive and Kidney Diseases. Retrieved February 26, 2024, from

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