Breaking Down Lactose Intolerance

Have you ever felt bloated, gassy, or uncomfortable after enjoying a scoop of ice cream or an extra cheesy pizza? These are all common symptoms of lactose intolerance, a condition that makes it difficult for people to digest milk and dairy products. Though lactose intolerance is not necessarily dangerous, living with it can be very inconvenient. Luckily, science has created ways to relieve discomfort that comes along with intolerance.

Causes

Lactase is an enzyme that breaks down lactose, which is a sugar found in dairy products. Lactase splits lactose into two sugars: glucose and galactose. These sugars are then easily absorbed by the bowel (LACTASE: Uses, Side Effects, and More, 2020).

Figure 1. Structural diagram of lactase splitting lactose into glucose and galactose (Kohlmeier, 2013).

To digest breast milk, infants produce large amounts of lactase. As the child is weaned off breast milk and baby formula, the child’s digestive system adapts to digest other foods. For some people, this means they no longer produce enough lactase to adequately process foods containing lactose, known as primary lactase deficiency (Institute for Quality and Efficiency in Health Care [IQWiG], 2024). This kind of lactose intolerance is more common in people of African and Asian descent, a phenomenon attributed to the different lifestyles of their ancestors. A Cornell University study found that people whose ancestors could raise dairy herds safely and economically tend to be able to digest milk. People whose ancestors lived in extreme climates or regions with deadly cattle diseases often lose the ability to digest milk after infancy. For this reason, up to 75% of African Americans and American Indians and 90% of Asian Americans are lactose intolerant (Lang, 2005).

Other people develop secondary lactase deficiency, which is a bowel disease resulting in reduced lactase production. This disease is often caused by celiac disease or inflammation in the small intestine, like in Crohn’s disease (IQWiG, 2024).

Diagnosis and Symptoms

The most common method to test for lactose intolerance is the hydrogen breath test. For this test, the patient consumes a liquid containing large amounts of lactose. The patient’s breath is then checked repeatedly for high levels of hydrogen, which indicate lactose intolerance. Another method, called the lactose intolerance test, checks how a patient’s digestive system absorbs lactose. After drinking a liquid containing lactose, the patient will have their blood sugar taken over a two-hour period. If the patient’s blood sugar levels remain the same, then they are most likely lactose intolerant (Johns Hopkins Medicine, n.d.). Having enough lactase would allow the lactose to be broken down into glucose, raising the patient’s blood sugar level. For infants and small children, their stools are tested for fatty acids, which indicate lactose intolerance.

Figure 2. A patient undergoing a hydrogen breath test (Rocky Mountain Gastroenterology, n.d.).

Symptoms of lactose intolerance begin thirty minutes to two hours after consuming foods with lactose. They may include stomach cramps, nausea, bloating, gas, and diarrhea, but they vary across individuals. Their severity depends on the amount of lactose consumed and the amount of lactase produced by the body (Johns Hopkins Medicine, n.d.).

Living with Lactose Intolerance

To manage lactose intolerance, people should avoid not only dairy products but also certain canned, frozen, and prepared foods. Lactose is added to processed foods such as bread, cereal, and salad dressings (Johns Hopkins Medicine, n.d.). Lactose-intolerant people can also take lactase tablets before consuming foods with lactose or add lactase drops to drinks (National Institute of Diabetes and Digestive and Kidney Diseases, 2018). Dairy-free milk alternatives, such as oat milk, almond milk, and soy milk, allow people to enjoy typical milk-based products without the discomfort caused by lactose.

Figure 3. Lactaid pills to manage lactose intolerance (LACTAID^®, n.d.).

Key Takeaways

Lactose intolerance is a common condition resulting from inadequate production of lactase by the body. Its prevalence in certain ethnicities can be explained by the diets of early human populations. Fortunately, lactase tablets and dairy alternatives have made it easier for people to enjoy their favorite foods without pain. Of course, there are many lactose-intolerant people who decide that any discomfort is worth it for the chance to enjoy ice cream, cheese, or a latte—at least every once in a while.

References

1. Hydrogen Breath Test Services in the Denver Metro. (n.d.). Rocky Mountain Gastroenterology. Retrieved August 16, 2025, from https://www.rockymountaingastro.com/services/hydrogen-breath-test/

2. Kohlmeier, M. (2013). Lactase—An overview | ScienceDirect Topics. ScienceDirect. https://www.sciencedirect.com/topics/medicine-and-dentistry/lactase

3. LACTAID® Original Strength Caplets for Lactose Intolerance. (n.d.). Lactaid. Retrieved August 16, 2025, from https://www.lactaid.com/products/lactaid-original-strength-caplets

4. LACTASE: Overview, Uses, Side Effects, Precautions, Interactions, Dosing and Reviews. (n.d.). Retrieved August 16, 2025, from https://www.webmd.com/vitamins/ai/ingredientmono-540/lactase

5. Lactose Intolerance. (n.d.). Johns Hopkins Medicine. Retrieved August 16, 2025, from https://www.hopkinsmedicine.org/health/conditions-and-diseases/lactose-intolerance

6. Lactose intolerance: Learn More – Causes and diagnosis of lactose intolerance. (2024). In InformedHealth.org. Institute for Quality and Efficiency in Health Care (IQWiG). https://www.ncbi.nlm.nih.gov/books/NBK310263/

7. Lang, S. S. (2005, June 1). Lactose intolerance seems linked to ancestral struggles with harsh climate and cattle diseases, Cornell study finds | Cornell Chronicle. Cornell Chronicle. https://news.cornell.edu/stories/2005/06/lactose-intolerance-linked-ancestral-struggles-climate-diseases

8. Treatment for Lactose Intolerance—NIDDK. (n.d.). National Institute of Diabetes and Digestive and Kidney Diseases. Retrieved August 16, 2025, from https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/treatment