We all love Dairy!I’m sitting in Milwaukee, Wisconsin, our home away from home and the epicenter of America’s Dairyland. What a great time to discuss a topic that is near and dear to my heart (and gut): Milk and all things dairy. As a genuine cheese head, I thought I might share some interesting things that I have learned about milk, and how I have come to appreciate the role the gut biome plays in how we digest milk and dairy products. 

There are important advantages to include milk and dairy in our diet.  In addition to the fact that it tastes great, dairy is a great source of calcium for our bones and heart function; it provides a means to meet your daily protein requirement and, depending on the brand, it can deliver important nutrients such as vitamin A, vitamin D and omega-3 fatty acids and other assorted minerals. It also contains indigestible complex sugars that feed microbes the biome, which in turn promote good gut and overall health (the subject of a future article coming soon).

Unfortunately, if you are one of the poor souls that drinks a glass of milk or eats cheese, yogurt or other dairy products and becomes nauseous or wrapped up with severe and painful stomach cramping (and other unmentionable symptoms), you probably won’t care about a scientific deep dive that initiates your dairy-derived-distress. 

For you, dairy is on your “foods to avoid” list and chances are that you have labeled yourself as lactose intolerant. However, while your intolerance to dairy is quite real, it is entirely possible that the root cause of your discomfort may not be due to lactose at all!

Some Background: What is Lactose?From chemistry class (or Wikipedia) we learned that lactose is a disaccharide (double sugar) formed by a chemical connection between two the simple sugars: glucose and galactose. Many of us are familiar with glucose; stringing a series of glucose “units” together forms complex sugars like starch or cellulose; connecting it with fructose gives you sucrose, the chemical makeup of white sugar.   

By itself, the glucose unit is one of the chemical fuels used to drive cell metabolism (ketone bodies from ketosis fame being the other). Galactose, perhaps a less-known related sugar, is also converted to the same metabolites as glucose and serves as useful component in prebiotic fiber beneficial for a vibrant and health-inducing biome (more on that in an upcoming article).

Lactose is a main ingredient in the very first menu-item we all request upon being born: mother’s milk. To successfully propagate our species, it would be counterintuitive and perhaps cruel of Mother Nature to serve up a meal that so many of us are not able to digest without the severe gastric discomfort of LI! But, as it turns out, nature actually equips the baby with a very special tool to facilitate lactose digestion. An enzyme called lactase is produced in the small intestine and tasked with one and only one job: to split lactose from mother’s milk into the simple sugar units as shown above. According to the original mammalian "plan", the metabolic machinery to digest lactose was only "turned on" when milk was the baby’s sole source of nutrition. Lactose is only found in milk; it is not found in any other natural food source, and as a matter of mammalian biology, it was never intended to be for adult consumption. Once a child successfully transitions to adult foods and the presence of lactose is weaned from the diet, the presence of lactase is no longer required and its production is switched off. Thus, according to the original human blueprint, innate lactose vanishes and all adults were designed to be lactose intolerant!

However, over evolutionary time, perhaps as a survival adaptation in response to periods of limited animal-based protein sources, some cultures such as those in Northern Europe, Northeast Africa and Central Asia began to include milk and dairy for adult nutritional supplementation. Genetic selection which favored individuals with lactase persistence, the state of producing lactase beyond weaning years, has led to distinct populations that today possess the means to produce the lactose degrading enzyme well into adulthood. Using genetic analyses like 23andMe, it is possible to determine whether you possess the genetic signature that codes for lactase persistence. If so, then you join the ranks of only about 30% of the world’s population that are capable as adults to innately digest lactose; the other 70% are old school-genetically lactose intolerant.

How Does this Help You??What if you have had your genome sequenced and you know for certain you do not have the genetic coding for lactase persistence?  Of course, you would know with certainty that you are genetically lactose intolerant, but does this mean you are not able to drink milk or consume dairy as an adult without the debilitating gastrointestinal problems? Does this mean that you will have dairy intolerance?  Not necessarily. 

Consider a recently published study of a group of healthy Japanese subjects who consumed varying quantities of milk and dairy. The Japanese, being a maritime culture have traditionally derived the mainstay of their dietary protein from the seas that surround their islands. Lacking deep pastoral norms (Kobe beef, notwithstanding!), dairy was an insignificant player in their dietary history and it should come as no surprise to learn that the Japanese are almost exclusively lactase non-persistent.

But, the Japanese are lovers of all things dairy; they are an important emerging market for dairy products and, if current trends continue, they will soon meet the qualifications to be cheese heads in their own right! Yet despite their genetic predisposition to be LI, the incidence of the debilitating gastrointestinal symptoms associated with LI are quite rare in Japan.  We can address this apparent contradiction by evaluating the biomes of the study subjects. The researchers discovered that the study groups' biomes are proportionately high in bifidobacterium, a microbe coincidentally known to break down lactose into its simple sugar components.  Furthermore, their data showed that higher milk and dairy consumption correlated to higher levels of bifidobacterium in their biome. In what may seem the height of irony, the study hints that the remedy to lactose intolerance might actually be - to consume more dairy! (Here is another study.) Better yet, it suggests that those who suffer from LI might be able to bio-hack their biomes by consuming (non dairy) foods that are known to ramp up their bifidobacterium numbers in a way that "preps" their biome to better assimilate milk and dairy.

A Caveat! Got to keep things moving! Here is potentially confounding factor that should be considered. Generally, it is thought that the symptoms of LI originate within the small intestine where the presence of lactose promotes excess water to be drawn into the GI tract.  Dietary strategies for those who are prone to LI include drawing out dairy intake over an extended period of time- presumably to prevent critical lactose concentrations that may trigger this water accumulation.  The Japanese study seems to imply that lactose degradation can be outsourced to bifidobacterium, but only if the lactose-containing food empties into the gut where the microbes reside.  Facile food transit from the stomach, through the upper GI and into the gut is critical! Factors that slow food passage will trap lactose within the upper GI and set up the conditions which lead to the symptoms lactose intolerance.

Does your milk put the brakes on digestion?Here is where the story of milk gets even more interesting.  It turns out that around 10,000 years ago (about the same time some human populations started exhibiting lactase persistence) a particular genetic change began to propagate through the cattle herds of Europe.  This change, or mutation, affected the makeup of the main protein in cow’s milk, β-casein.  To distinguish between the variants of this protein, researchers denote the mutated version to be the A1 variant, and the “original”, wild-type version to be the A2 variant. As A2 cow milk (found primarily in Alpine regions of Europe and New Zealand) is consumed, its β-casein is enzymatically broken down and normal digestion proceeds. However, when the “mutated” A1 variant undergoes digestive breakdown, it generates a family of opioid peptides called β-casomorphins!  Astoundingly, the milk most often sold here in the US -almost entirely produced from herds with the A1 β-casein variant- generates opioids that are comparable in potency to typical opioid pain medications such as codeine and oxycodone!! These peptides are known irritants of the human GI tract, and independent of lactose, can cause intestinal inflammation and induce allergic reactions in some individuals which can be mistaken as LI! Additionally, β-casomorphins exhibit similar side effect profiles as other opioids in that they tend to slow the movement of foods through the GI tract. This is exactly what we need to avoid!