Are you lactose intolerant?

The types of milk available at grocery stores and in coffee shops has been increasing in the last 10 years. What used to be just low fat cows milk and 2%, has now become almond, oat, soy, cashew and coconut milk. The options are only increasing. This may be due to a combination of reasons including the rise in veganism or awareness of animal treatment in factory farms or in the rise of self-reported lactose intolerance.

Lactose is digested by the lactase enzyme in the small intestine. This enzyme is typically only present in infancy to allow proper absorption of breast milk. The enzyme typically degenerates and stops being expressed as the individual gets older and no longer requires breast milk (Jansson-Knodell et al., 2020. However, with the domestication of cows humans continued to have a intake of lactose into adulthood and we have observed a persistence of lactase expression into adulthood. It is still unclear exactly how and why this has occurred. 

To begin there are two ways people might interpret lactose ingestion. First, lactose intolerance requires clinical diagnosis of reduced or lack of the lactase enzyme at the intestinal boarder (Jansson-Knodell et al., 2020). Lactose maldigestion is subjective to the individual by reporting gastrointestinal discomfort post-lactose ingestion (Jansson-Knodell et al., 2020). Typically, lactose intolerance is diagnosed via a positive lactose hydrogen breath test (LHBT) and maldigestion is self-reported symptoms to the ingestion of lactose. In a study done in 2021, a double-blind procedure was conducted on 42 individuals who were a mix of lactose intolerant and maldigesters (Carroccio et al., 2021). The researchers found that many lactose tolerant (present lactase enzyme/negative LHBT) individuals presented with GI discomfort post-lactose ingestion suggesting that there is something other than lactose in cow’s milk that individuals are responding to (Carroccio et al., 2021).

In another study looking at the contents of milk that may be increasing GI discomfort after ingestion of cow’s milk, leading to self-reported lactose intolerance, response to the ingestion of two proteins common to cow’s milk A1 and A2 beta-casein were recorded (Jianqin et al., 2015). They concluded that consumption of A1 beta-casein had a higher chance of GI inflammation, post-dairy digestive discomfort (PD3), and reduce speed and accuracy of cognitive processing compared to consumption of only A2 beta-casein (Jianqin et al., 2015). None of these symptoms were reported in consumption of only A2 beta-casein type cow’s milk (Jianqin et al., 2015).

So, if you are someone who has self-reported lactose intolerance, maybe it is not the lactose but a different protein present in milk that your GI tract is having an increased immune response to or having difficulty responding to.

Carroccio A, Soresi M, Mantia B, Fayer F, La Blasca F, Seidita A, D’Alcamo A, Florena AM, Tinè C, Garlisi C, Mansueto P. Whole Cow’s Milk but Not Lactose Can Induce Symptoms in Patients with Self-Reported Milk Intolerance: Evidence of Cow’s Milk Sensitivity in Adults. Nutrients. 2021; 13(11):3833. https://doi.org/10.3390/nu13113833

Jansson-Knodell C. L., Krajicek E. J., Savaiano D. A., Shin A. S., Lactose Intolerance: A Concise Review to Skim the Surface, Mayo Clinic Proceedings 95, 7 (2020), Pages 1499-1505, ISSN 0025-6196, ttps://doi.org/10.1016/j.mayocp.2020.04.036.

Jianqin, S., Leiming, X., Lu, X. et al. Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows’ milk. Nutr J 15, 35 (2015). https://doi.org/10.1186/s12937-016-0147-z