Lactose Intolerance: Symptoms, Causes & Treatment

Lactose intolerance is a syndrome caused by a decrease or lack of lactase in the body. Lactase is the enzyme responsible for digesting and absorbing lactose, a sugar found in milk and dairy products such as yogurt, butter, ice cream, and cheese.

Difficulty digesting and absorbing lactose can cause symptoms like abdominal bloating, excess gas, diarrhea, abdominal pain, and headaches. These symptoms usually appear after eating or drinking foods that contain lactose.

Lactose intolerance can appear in the first days of life or later in adulthood. It can also happen as a result of conditions such as chemotherapy, Crohn’s disease, or gastroenteritis.

Main symptoms

The main signs and symptoms of lactose intolerance are:

• Excess gas

• Abdominal pain

• Diarrhea

• Nausea

• Headache

• Bloating

• Fatigue

• Decreased concentration and memory

In more severe cases, lactose intolerance may lead to dehydration, weight loss, or delayed growth in children, especially if symptoms are not properly managed.

Confirming a diagnosis

Lactose intolerance should be diagnosed by a gastroenterologist or primary care provider, who will review the person’s symptoms, health history, and eating habits.

The provider may also recommend removing lactose-containing foods, such as milk, yogurt, and cheese, from the diet for 2 weeks to see whether symptoms improve.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, diagnosis may also include tests such as a hydrogen breath test. Other tests that may be ordered include an oral lactose tolerance test, stool test, and blood test.

Different types

Lactose intolerance can be classified based on a person’s age and underlying health conditions as follows:

1. Congenital lactose intolerance

This type of intolerance is very rare and appears in the first days of life after lactose is consumed through breast milk or other types of milk, causing severe diarrhea, vomiting, dehydration, difficulty gaining weight, and mucus in the baby’s stool.

Congenital lactase deficiency happens when a baby is born unable to produce enough lactase because of inherited genetic mutations. It is a serious condition that can lead to severe diarrhea, dehydration, and dangerous weight loss, and it may become life-threatening if it is not recognized and treated early.

2. Primary lactose intolerance

This type of lactose intolerance is the most common and happens because of a decrease or absence of the enzyme lactase in the intestine, caused by a natural process that occurs in the body over time.

However, some adults may have genetic changes that maintain normal lactase production, allowing them to digest lactose and preventing intolerance from developing.

3. Secondary lactose intolerance

Secondary lactose intolerance is a condition that may be temporary and is caused by damage to the intestinal cells responsible for producing the enzyme lactase.

This type of intolerance may be caused by conditions such as rotavirus, gastroenteritis, medications such as antibiotics and chemotherapy, radiation therapy, chronic diarrhea, celiac disease, and bacterial intestinal infections.

Possible causes

Lactose intolerance may be caused by a genetic change that prevents production of the enzyme lactase. It may also be caused by the natural drop in lactase production that happens with aging.

Some conditions that damage the cells lining the intestine, such as chemotherapy, radiation therapy, oral antibiotic use, chronic diarrhea, Crohn’s disease, and bacterial, viral, or protozoal infections such as giardiasis and amebiasis, may also cause lactose intolerance.

CMPA vs lactose intolerance

Cow’s milk protein allergy, or CMPA, is an immune system reaction to one or more proteins found in cow’s milk, such as casein, lactoglobulin, lactoalbumin, serum albumin, and immunoglobulins.

CMPA occurs when a person consumes or has skin contact with products containing cow’s milk, such as dairy foods including ice cream, cheese, butter, and baked goods, leading to symptoms like hives, vomiting, diarrhea, and delayed growth in children.

Lactose intolerance, on the other hand, is a difficulty the body has digesting and absorbing lactose because of a decrease or absence of the enzyme lactase in the intestine. It mainly causes symptoms such as excess gas, abdominal pain, and diarrhea.

Treatment options

According to the National Institute of Diabetes and Digestive and Kidney Diseases, treatment for lactose intolerance may include limiting lactose-containing foods and using lactase products, since many people can tolerate small amounts of lactose without symptoms or with only mild symptoms.

In primary lactose intolerance, the recommendation is to reduce lactose intake and keep it to a maximum of 15 g of lactose per day. This is equal to about 10 oz (300 mL) of milk or 1¼ cups (300 g of yogurt), and should be divided into 2 or more meals throughout the day.

However, reducing milk and dairy products in the diet may not improve symptoms in some people. In these cases, taking the lactase enzyme with meals that contain lactose may be recommended.

In cases of secondary lactose intolerance, it may be recommended to completely remove milk and dairy products from the diet for 1 month or longer, until the intestine recovers. This should always be done with guidance and follow-up from a doctor or dietitian to help prevent deficiencies in nutrients such as calcium, vitamin D, vitamin A, and phosphorus.