Lactose intolerance is not the same as an allergy to milk. Lactose intolerance differs from a milk allergy in that a milk allergy is an immune system reaction and true lactose intolerance is due to a deficiency of the enzyme lactase that digests the milk sugar lactose that does not cause an immune system reaction. Lack of this enzyme can cause some disturbing symptoms including but not limited to bloating, gas and diarrhea.

It is estimated that 68% of the world’s population have lactose intolerance, which is also referred to as lactose malabsorption. The 68% of the population with lactose intolerance also has a majority demographic in Africa and Asia, while in northern Europe, some people carry a gene where the C allele indicates lactase nonpersistence (they do not produce the enzyme lactase) and the T allele indicates lactase persistence (they do produce the enzyme lactase).

In the general US population high risk groups include: African Americans, Indigenous peoples of the Americas, Asian Americans, Hispanics/Latinos.

How is lactose intolerance diagnosed traditionally?

Doctors use a hydrogen breath test to make a diagnosis because typically there is a small amount of hydrogen (a gas) in our breath, but if you suffer from lactose intolerance and cannot digest the milk sugar lactose, hydrogen levels become very elevated and it is easy to capture with this test. The test itself is not fun for the lactose intolerant individual. You drink a liquid that contains a set quantity of lactose and every 30 minutes over a few hours you must breathe into a balloon type container that calculates the amount of hydrogen in your breath. Additionally, your symptoms will be monitored. The combination of increased hydrogen and symptoms results in a diagnosis.

There also is data indicating that a simple genetic test is as sensitive and specific as an H2 test, without the side effects for those who are positive on the breath test. The gene MCM6 rs4988235 is associated with the risk of lactose intolerance. A CC allele is strong evidence of lactose intolerance.

How is this connected to celiac disease?

There are three important points to mention with regard to celiac disease. First, celiac disease patients have a high prevalence of a positive H2-lactose breath test compared to healthy controls and a high prevalence of celiac disease was observed in patients with a positive H2-lactose breath test compared to healthy controls.

In layman’s terms, those with celiac disease are at a much higher risk of also having a lactose intolerance. In a study by Ojetti in the journal Digestion back in 2005, 24% of subjects with lactase deficiency tested positive for celiac disease and lactose intolerance was the ONLY symptom manifestation of celiac disease. The study authors went on to suggest serologic screening for celiac disease in all patients with a positive H2-lactose breath test before beginning a milk-exclusion diet.^[1]

If you have been diagnosed with lactose intolerance, you should also be tested for celiac disease. My previous article “What do you do if you think you may have celiac disease?” outlines the proper steps for diagnosis.

The second point is that many doctors believe celiac disease patients experience “secondary lactose intolerance”. Meaning even if they have normal H2 breath tests and are not CC genotype for MCM6, they simply lack the ability to digest lactose due to the fact that celiac disease shrinks or obliterates villi in the small intestine and the smaller hair like projections called microvilli (also known as the brush border) in the intestines is the location of where we would normally have lactase, the enzyme that breaks down lactose.

Damage to these structures decreases or eliminates the ability to have the enzyme present and therefore creates lactose intolerance. After six months of a strict GF diet to allow the villi to heal, this may normalize and you may no longer have a lactose intolerance.

Third, it is important to distinguish between primary lactose intolerance and secondary causes of maldigestion of lactose, including the aforementioned celiac disease, AND also infectious enteritis, or Crohn’s disease, which have distinct pathogenic paths and treatments.

If you were diagnosed with lactose intolerance and consume gluten, it would be wise to discuss with your doctor about being tested for celiac disease and vice versa.