As I sit in the kitchen enjoying my creamy Ben and Jerry’s Phish Food ice cream, my family members angrily watch me, chomping on Lactaid pills as they eat their boring, dairy-free Halo Top ice cream. A wild turn of genetics has spared me the indignity of such substitutions.

In my Western Studies course, I chose to explore lactose intolerance, an autosomal recessive condition caused by an inability to fully digest the sugar lactose. Lactose is present in dairy products like milk, yogurt, cheese, and ice cream, affecting around three million people in the  US. Decreased expression of the LCT and MCM6 genes caused by mutations are the main cause of lactose intolerance, as these are the genes that regulate the production of lactase in the small intestine. This condition is caused by having “too little of an enzyme produced [by cells in the lining of] your small intestine [called] lactase” (“Lactose Intolerance”).

Some symptoms include diarrhea, nausea, cramps, bloating, and gas, which usually occur between thirty minutes and two hours after dairy consumption. Lactose intolerance can be

diagnosed by a doctor through a hydrogen breath test or a lactose tolerance test. A hydrogen

breath test measures the amount of hydrogen in a person’s breath at different intervals after they drink a liquid containing high levels of lactose. If the person breathes “out too much hydrogen, [this] indicates that [they] are not fully digesting and absorbing lactose” (“Lactose Intolerance”). A lactose tolerance test measures the amount of glucose in a person’s bloodstream two hours after drinking a liquid containing high levels of lactose. If the person’s “glucose level doesn’t rise, it means [their] body isn’t properly digesting and absorbing the lactose-filled drink” (“Lactose Intolerance”).

The main treatment for lactose intolerant individuals is to consume a low amount of

lactose in their diets by limiting their intake of dairy products, consuming lactose free dairy

products, and taking a lactase supplement like Lactaid to help break down the lactose when they do consume dairy, as my parents and sister well know.

Ashkenazi Jews are one of many ethnic groups that suffer from an increased sensitivity to dairy products. According to “Genetics of Lactose Intolerance: An Updated Review and Online Interactive World Maps of Phenotype and Genotype Frequencies”, lactase non-persistence is found “in 83% of Ashkenazi Jews in Israel” (Anguita-Ruiz, et al.). Ashkenazi Jews lived in ghettos from the Middle Ages to the time shortly after the Holocaust. Geneticists theorize that being lactose intolerant might have been a “genetic advantage for Jews forced to live in tightly packed, often unsanitary ghettos” (Levin). Lactose intolerance could be a defense response to pathogens and other substances that come into contact with the digestive system, making it a selective advantage in unsanitary conditions. Being affected by lactose intolerance became a tradeoff for having increased protection against diseases like tuberculosis.

This selective advantage developed due to evolution and high rates of endogamy within

the Ashkenazi Jewish population. Historically, Ashkenazi Jews have practiced endogamy, also

known as marrying within the local community or tribe for many reasons. Some of these reasons include that they were isolated in ghettos as a result of antisemitism as well as to preserve Judaism and ensure the survival of future generations. This resulted in a small, isolated gene pool, causing the same genetic mutations to be passed down over and over again. As a result, mutations in the LCT gene and in the MCM6 gene became fairly common in the Ashkenazi Jewish population. The fittest individuals had these genetic mutations, so they survived and reproduced. Finally, the continuation of endogamy in the Ashkenazi Jewish population over many generations has resulted in the existence of lactose intolerant individuals today.

Lactose intolerance deeply resonates with me as an Ashkenazi Jew, particularly because nearly all of my relatives face this condition. Being the only family member without this trait intrigues me, prompting reflection on my genetic background and how specific traits can vary within our family. It drives me to explore the broader implications for health and identity, inspiring discussions that delve into the complexities of our biological experiences and their connection to our cultural narratives.