What Causes Lactose Intolerance (And What You Can Do About It)

If drinking milk, snacking on yogurt, eating cheese, or treating yourself to ice cream leaves you with uncomfortable gastrointestinal (GI) symptoms, you probably can’t digest lactose. 

Lactose is a naturally occurring sugar found in milk and milk-based products. When you’re intolerant to lactose, your body doesn’t make enough lactase, the digestive enzyme that helps break down this dairy carbohydrate. 

Here, board-certified gastroenterologist Dr. Sam Weissman discusses the possible causes of lactose intolerance, explores how it might affect your digestive system, and explains what you can do about it. 

What is lactose intolerance?

Lactose intolerance means your body has trouble digesting the sugar (lactose) in milk and milk-based products like yogurt, cheese, butter, sour cream, custard, and ice cream. 

Processed foods made with milk-based ingredients — including many breads, baked goods, salad dressings, and flavored chip snacks — also contain lactose, usually in lesser amounts. 

If you’re lactose intolerant, your small intestine doesn’t produce as much lactase enzyme as your digestive system needs to break down the lactose in your diet efficiently and effectively.

A common problem

Lactose intolerance is a widespread digestive issue that affects people of all ages and backgrounds: Over one in three people in the United States and over two in three people worldwide have some degree of lactose intolerance. Tens of millions of Americans experience signs of lactose intolerance by the age of 20. 

Main symptoms

Symptoms of lactose intolerance typically emerge 30 minutes to 2 hours after consuming milk, dairy products, or processed foods made with milk-based ingredients. 

Depending on the amount of lactose you’ve consumed and your overall degree of intolerance, you may experience one or more of the following GI problems:

• Abdominal pain or cramping
• Bloating and flatulence (gas)
• Diarrhea, often with nausea 

Lactose intolerance is a highly individual problem — some people are sensitive to tiny amounts of lactose in processed foods made with milk-based ingredients, while others can eat more significant quantities of lactose-rich dairy products before they experience symptoms.

A simple diagnosis 

Diagnosing lactose intolerance is relatively straightforward. If Dr. Weismann suspects you have a lactase shortage based on your symptoms, he asks you to avoid all dairy products and foods made with milk-based ingredients for 1-2 weeks to see if your symptoms subside. 

When you return to the office following your lactose-elimination diet, he conducts a hydrogen breath test after you drink a lactose-rich beverage. This simple test measures your digestion of milk sugars to check for signs of a lactase deficiency. 

Why am I lactose intolerant?

Most babies have excellent lactase levels, so they can digest breast milk (lactose is present in all mammal milk). Lactase production declines after infancy, a trait other mammals share after they’ve been weaned from their mother’s milk.

Rarely, a baby may be born with a congenital lactase deficiency that requires them to be fed lactose-free infant formula. In most cases, people become lactose intolerant later in life when their small intestine makes even less lactase for some reason. Common causes are:

• Genetic predisposition to declining lactase levels (family history)
• Progressive GI disease damage (Crohn's, ulcerative colitis, celiac disease)
• Traumatic injury to the small intestine; intestinal infection damage
• Medical treatment that affects the small intestine (surgery, chemotherapy, radiation)

Most cases of lactose intolerance are primary cases, meaning they happen because the body makes less lactase as time goes on. Secondary cases, or those caused by disease, damage, or trauma, are less common. 

Should I avoid lactose? 

While there’s no way to lessen or cure lactose intolerance, there are helpful strategies to make living with a lactase deficiency much easier. For some people, that does mean strictly avoiding all dairy products and processed foods made with milk-based ingredients (look for the words “may contain milk” on the label). 

Your personal tolerance level

Unless you have a progressive GI disorder that complicates matters, lactose avoidance isn’t necessarily an all-or-nothing approach. After following a lactose-free diet for a couple of weeks, many people find a tolerable level of lactose in their diet through trial and error aided by a food diary.

Supplemental lactase tablets

Some people continue enjoying calcium-rich dairy products by taking a lactase tablet before consuming milk or milk-based foods. These supplements boost the lactase levels in your small intestine to prevent uncomfortable symptoms. 

Low-lactose and lactose-free options

You can also add a liquid or powder lactase enzyme to milk drinks to break down the lactose for you. Alternatively, you can look for low-lactose dairy products like milk and ice cream or switch to plant-based milk and food products such as soy ice cream or fortified almond milk. 

If you think you may have lactose intolerance, we can help. Call 609-793-9375 to reach our Brooklyn, New York, office today, or use the online booking feature to schedule a visit at Sam Weismann, MD, any time.