General

What is lactose intolerance?

People with lactose intolerance cannot fully digest the sugar (lactose) in milk. As a result, they experience diarrhea, gas, and bloating after consuming dairy products. This condition, also known as lactose malabsorption, is generally harmless, but the symptoms can be uncomfortable.

A very low level of the enzyme (lactase) produced in your small intestine is usually responsible for lactose intolerance. You might have low lactase levels and still be able to digest dairy products. However, if your levels are very low, you will have lactose intolerance and experience symptoms after consuming dairy.

Most people with lactose intolerance can manage their condition without completely eliminating all dairy products.

Symptoms of Lactose Intolerance

Abdominal Pain and Bloating

Abdominal pain and bloating are common symptoms of lactose intolerance in both children and adults. When the body cannot break down lactose, it passes through the intestines until it reaches the colon.

Carbohydrates like lactose cannot be absorbed by the cells lining the colon, but they can be fermented and broken down by naturally occurring bacteria known as microbiota. This fermentation produces short-chain fatty acids and gases such as hydrogen, methane, and carbon dioxide. The increase in acids and gases can cause abdominal pain and cramps, typically located around the navel and in the lower abdomen.

The feeling of bloating is caused by an increase in water and gas in the colon, which leads to the stretching of the intestinal wall, also known as bloating. Interestingly, the amount of bloating and pain experienced is more related to an individual’s sensitivity to the feeling of bloating rather than the amount of lactose consumed. Therefore, the frequency and severity of symptoms can vary significantly among individuals.

Finally, bloating, distention, and pain can sometimes lead to nausea and even vomiting. This is rare but has been observed in certain cases, including children.

Diarrhea

Diarrhea is defined as an increase in stool frequency or liquid consistency. It is officially classified as producing more than 200 grams of stool in a 24-hour period.

Lactose intolerance causes diarrhea by increasing the water volume in the colon, which increases stool bulk and fluid content. It is more common in infants and young children than in adults.

In the colon, microbiota ferment lactose into short-chain fatty acids and gases. While not all of these acids are reabsorbed, an increase in acids and lactose raises the amount of water the body releases into the colon. There are many other causes of diarrhea beyond lactose intolerance, including diet, other malabsorption disorders, medications, infections, and inflammatory bowel diseases.

Increased Gas

The fermentation of lactose in the colon increases the production of gases such as hydrogen, methane, and carbon dioxide.

In fact, the colon microbiota in people with lactose intolerance becomes very efficient at fermenting lactose into acids and gases. This leads to further fermentation of lactose in the colon, increasing bloating.

Interestingly, the gases produced from lactose fermentation are odorless. In fact, the odor of gas comes from the breakdown of proteins in the intestines, not from carbohydrates.

Constipation

Constipation is characterized by hard, infrequent stools, a feeling of incomplete bowel movements, abdominal discomfort, bloating, and excessive straining. While bacteria in the colon ferment undigested lactose and produce methane gas, methane is thought to slow the transit time of food through the intestines, potentially leading to constipation in some individuals. So far, the effects of methane on constipation have only been studied in individuals with irritable bowel syndrome and small intestinal bacterial overgrowth. Therefore, although reported as a symptom, constipation is generally not associated with lactose intolerance.

Other causes of constipation include dehydration, a lack of fiber in the diet, certain medications, irritable bowel syndrome, diabetes, hypothyroidism, Parkinson’s disease, and hemorrhoids.

Other Symptoms

While the primary known symptoms of lactose intolerance are gastrointestinal in nature, some case studies have reported additional symptoms, including:

  • Headaches
  • Fatigue
  • Difficulty concentrating
  • Muscle and joint pain
  • Mouth ulcers
  • Urinary issues
  • Eczema

However, these symptoms have not been definitively identified as true symptoms of lactose intolerance and may have other causes.

Additionally, some individuals with a milk allergy may mistakenly attribute their symptoms to lactose intolerance.

In fact, about 5% of people have a cow’s milk allergy, which is more commonly observed in children.