By Nicole Malamed
Many individuals can ingest milk and dairy products without any problem. However, 4 billion people in the world, myself included, cannot digest lactose, the sugar contained in milk, properly. Lactase is the enzyme responsible for breaking down the lactose into glucose and galactose. Lactose intolerance appears when lactase quantities in the body diminishes, thus not having enough to break the lactose in the body correctly. In most mammals, levels of lactase are high during infancy, but fall rapidly following weaning. For those who are lucky enough to have never suffered from it, it is important to detail that lactose intolerance causes a variety of symptoms, including cramps, bloating, and diarrhea. Even a small amount of lactose consumed by lactase-deficient individuals will give rise to these and other non gut-related symptoms.
How is it that production of a single enzyme can make us feel so bad for drinking a little milk or eating some ice cream? When the lactose is not digested correctly, it can be fermented by gut microbiota. The undigested lactose passes into the colon, then bacteria in the colon break down the lactose, producing gasses and fluid which are responsible for the symptoms. Because of this, there is considerable variability in the severity of the clinical manifestations between individuals, and between different ingestions by the same individual. We all have heard a lactose intolerant who decides “I will eat cheese today and risk the consequences,” or have heard them say “this is/is not worth it,” but how is it that some foods are “worth it” while others are not? While some people have enough lactase to digest a pizza with cheese but not a milkshake, others cannot even have solid cheese or yogurt without regretting it afterwards. And because of this variability it can also confuse the diagnosis, sometimes confusing a milk allergy with lactose intolerance. We need to be clear that while lactose intolerance is caused by problems digesting lactose, milk allergies are caused by the immune system’s response to one or more proteins in milk and milk products. Lactose intolerance can cause uncomfortable symptoms, while a serious allergic reaction to milk can be life threatening.
This variability in people can lead us to think about genetic variability, as genes are the ones in charge of the production of enzymes like lactase. Studies show that the global distribution and the age at which lactase expression declines vary with ethnicity. This is mainly because of differences in the eating habits of some cultures, with some of them consuming more lactose than others. In South America, Africa, and Asia, more than 50% are lactase non-persistent (meaning that they were born with enough lactase, but its quantity diminished making the person lactose intolerant). The condition is also common in Mediterranean or Southern European populations. In some Asian countries, up to 100% are lactase non-persistent, as their culture does not include much lactose ingestion. So depending on where your family originally came from, the probabilities of developing a lactose intolerance at some point in your life can be determined.
Which finally leads us to our main question: “Is the future of human beings set to be lactose free?” It is hypothesized that before animal domestication and dairy production, the normal condition for all humans was adult lactase deficiency (lactose intolerance). However, with the introduction of lactose into the adult diet in some cultures as discussed, this new scenario favored the genotype for adult lactase production (yes, lactose intolerance indeed has a genetic component, thank you grandpa!) This does not mean that it is rare to be lactose intolerant, in fact, approximately 70% of the global adult population are lactase non-persistent. With this in mind, one could argue that because of all the dietary changes occurring in the last few years, where lactose-free production and consumption is on the rise, it is a big possibility that dairy products will slowly get replaced by its non-dairy competitors, and slowly more people will once again be born with lactase deficiency. And with the rise of lactase deficiency, new methods and techniques of producing non-dairy milk will make the costs lower, proving pointless to invest in the high costs of dairy milk production.