lactose intolerance

Lactose Intolerant? Here’s What You Should Know

We received a question from a website visitor asking, “Can you please give me advice on which foods will best help a person who is lactose intolerant?” To answer her question, we reached out to Dr. Dennis Savaiano from Purdue University and Best Food Facts registered dietitian Sarah Downs, MBA, RDN. What they told us may surprise you!

What is lactose? What is lactase?

Dr. Savaiano: “Lactose is the sugar found in dairy products. Lactase is the enzyme that digests lactose. Lactases are found in all mammals, particularly during infancy, and are also found in bacteria in the gastrointestinal (GI) tract.”

What is lactose intolerance? 

Dr. Savaiano: “Most of the world’s population has a large capacity to digest lactose when they’re infants. But once they’re weaned, and they mature, there’s a genetic reduction in the amount of lactase that the intestinal tract produces. If these individuals consume too much lactose, they could have symptoms of intolerance. Typical symptoms of lactose intolerance are flatulence, stomach rumbling, and in rare instances, short term diarrhea. Once the lactose has exited the GI tract, the symptoms end. Symptoms of lactose intolerance depend on several factors including dose of lactose, GI transit and regular milk consumption, which adapts the GI bacteria.”

Should those with lactose intolerance avoid dairy products?

Dr. Savaiano: “Not at all, in fact, that’s the wrong strategy. Although it seems intuitive, it’s actually inappropriate. Lactose intolerance depends on dose, so if one drinks a small amount of milk, or has a small amount of dairy food, the small dose will almost certainly be tolerated.

Regarding dose, drinking one cup of milk (8 ounces) or less usually does not cause symptoms. But those who have symptoms with this amount should try one-half cup. Soft cheeses and ice cream are better tolerated than milk. Hard cheeses have almost no lactose and should be well tolerated. Yogurt is also well tolerated due to the bacterial lactase in the product. Products with a lot of whey (and thus, lactose) such as “frozen yogurt” (which really isn’t yogurt) are often poorly tolerated.

Regarding transit, always drink milk and eat dairy foods with a meal. This slows transit, dramatically improving digestion and tolerance.

Regular milk drinkers (one to three small servings per day) have much better tolerance because they have adapted their intestinal bacteria to improve digestion of lactose.”

Sarah: “Those with lactose intolerance don’t need to abstain from dairy. There are many solutions that can keep dairy foods in the diet. This includes looking for lactose-free options (Guess what?! It’s still dairy, but just has the lactose removed!),  seek out products naturally low in lactose like low-fat cottage cheese, Swiss and mozzarella cheese and Greek yogurt, and start with small amounts of dairy and gradually increase over a few days or weeks. Keep in mind that lactose intolerance is different for every person and one person may be able to tolerate some foods others cannot.”

Is there a test for lactose intolerance?

Dr. Savaiano: “There is a very good test, called the breath hydrogen test, but it’s used primarily in research settings, not in clinical settings. Most physicians will simply use an exclusion diet – if you avoid lactose and don’t have symptoms, they will assume you’re lactose intolerant. However, if you want a more definitive test, your university hospital may be able to do a hydrogen test to determine if you are a lactose maldigester and subject to potentially having intolerance symptoms.”

Is lactose intolerance the same as milk allergy?

Dr. Savaiano: “No, they’re very different – they have different mechanisms. Milk allergy is quite rare. The typical symptoms for milk allergy (a true allergic response) often include skin rash. There could be some GI symptoms as well, whereas lactose intolerance is defined clearly by flatulence, stomach distention and diarrhea.”

Sarah: “Lactose intolerance is often misunderstood and is commonly confused with a milk allergy. A milk allergy is a food allergy, which is an overreaction of the immune system to a specific food protein. It can trigger an allergic reaction that may include a range of symptoms from moderate (rashes and itching) to severe (trouble breathing, wheezing, etc.).

Lactose intolerance has nothing to do with the immune system. Those with lactose intolerance are missing the enzyme lactase, which breaks down lactose, a sugar found in milk and dairy products. As a result, individuals who are lactose intolerant have difficulty digesting these foods and may experience an array of gastrointestinal symptoms such as cramps, bloating and diarrhea. While it can cause great discomfort, it is not life-threatening.”

Is lactose intolerance a common problem?

Dr. Savaiano: “About three-quarters of the world’s population has the potential for lactose intolerance, and about one-fourth of the U.S. population. Lactose intolerance is a genetic trait – it’s not an environmental trait. It’s a trait that is actually recessive, but most common among the world’s population.”

Sarah:  “It’s estimated that 10 percent of Americans are lactose intolerant, but because many are self-diagnosed, this percentage is probably much lower. Inaccurate self-diagnosis of lactose intolerance or misinformation about dairy may cause people to unnecessarily eliminate dairy from their diet and miss out on its key nutrients. This is why it is so important to visit your doctor or a registered dietitian if you think you may be lactose intolerant to ensure a proper and accurate diagnosis.”

If you are experiencing problems you think are associated with lactose intolerance, please visit your physician.

Listen to Dr. Savaiano discuss lactose intolerance.


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milk splash” by Benjamin Horn is licensed under CC BY 2.0.