What is Lactose Intolerance?
Lactose intolerance is when the body is unable to digest lactose due to a lack of the lactase enzyme. Lactose is a complex sugar that must be broken down in the small intestine into simpler sugars—glucose and galactose—by lactase, in order to be absorbed and utilized by the body.
Lactose intolerance is not considered a disease. In fact, among mammals, the ability to digest lactose usually diminishes after weaning. In many human populations, this enzyme production naturally decreases after infancy. However, in certain dairy-consuming cultures, genetic adaptations over thousands of years have allowed continued lactase production into adulthood.
Symptoms of Lactose Intolerance
Lactose intolerance can cause a range of uncomfortable digestive symptoms that typically appear 2–4 hours after consuming food or drink containing lactose. When undigested lactose reaches the colon, it attracts water (due to its osmotic activity), leading to loose stools or diarrhea. The lactose is then fermented by gut bacteria, producing gases and acidic byproducts, which can result in:
- Bloating
- Abdominal cramps or spasms
- Rumbling stomach
- Nausea
- Headaches
Symptom severity can vary depending on the individual's gut flora.
Diagnosing Lactose Intolerance
When lactose isn’t properly digested, gut bacteria break it down, releasing hydrogen and methane gases. Hydrogen can be measured in the breath after lactose consumption during a hydrogen breath test, which typically lasts 2–3 hours. However, this test can sometimes give false negatives, especially if the bacteria produce only methane and not hydrogen.
Genetic testing using a saliva or blood sample can also confirm lactose intolerance. These tests look for specific gene variants, such as C/T-13910 or G/A-22018. People with the T/T or A/A variants can continue producing lactase into adulthood, while those with C/C or G/G variants typically experience a decline in lactase activity over time.
Types of Lactose Intolerance
- Primary Lactose Intolerance:
A genetically determined condition in which lactase production decreases after infancy. This is the most common type worldwide, especially prevalent in populations that have historically not consumed dairy (e.g., in parts of Africa and Asia). - Secondary Lactose Intolerance:
A temporary condition caused by damage or inflammation to the intestinal lining—such as from infections, imbalances in gut flora, inflammatory bowel diseases, celiac disease, or parasites. Once the underlying issue is resolved, lactase production may resume. - Congenital Lactase Deficiency:
A rare inherited disorder where lactase is absent from birth. It’s typically diagnosed in early infancy due to severe diarrhea following breastfeeding.
Treatment and Management
The primary approach to managing lactose intolerance is to follow a lactose-free diet. During the fermentation of milk, lactose is naturally broken down, often making fermented products like sour milk or cultured dairy lactose-free. Also, many lactose-containing foods can be rendered lactose-free by adding lactase enzymes.
