I often say that “dairy is fine and even healthy if you tolerate it.” But what exactly does that mean? How do you know if it’s “not okay”? You could be reacting poorly to the lactose, the casein, the whey, or all of it. You could just ditch all dairy forever more and be perfectly fine – but you shouldn’t eliminate a food group, especially one as delicious, nutrient-dense, and potentially rewarding as dairy, unless you absolutely must. Plus, it’s just good to know what you can and cannot tolerate. You don’t want to tiptoe through life, scared of food because you’ve never taken the time to determine your ability to tolerate it. You want to be empowered with knowledge and venture forth boldly – or carefully, if caution is warranted – through the cheese aisle.
The most common dairy components that people have trouble with are lactose and casein, with intolerance to each presenting differently. Let’s look at both.
Lactose intolerance occurs when people stop making lactase, the digestive enzyme located along the small intestinal wall that breaks lactose into glucose and galactose for easy digestion. This usually occurs around the age of four or five (lactose intolerance is incredibly rare in infants, for obvious reasons). Without lactase, lactose is instead metabolized by bacteria, which can cause stomach upset, flatulence, diarrhea, bloating, nausea, and a host of familiar but unwelcome gastrointestinal symptoms also seen in FODMAPs intolerance. In fact, the disaccharide lactose is a FODMAP. Lactose intolerance generally isn’t life threatening (unless you’re a baby who depends on a lactose-containing food) but it is annoying and can make life difficult and unpleasant.
Causes: Most lactose intolerance develops because people stop producing lactase after weaning. No more breast milk, no more need to expend the energy necessary to produce lactase. This is usually genetically determined, and people with milk-drinking ancestry are far more likely to possess the gene(s) for lactase persistence (it takes just one copy to keep making lactase into adulthood).
Some lactose intolerance is transient and stems from damage to the epithelial cells lining the intestine, which are responsible for producing lactase in the gut. If something like viral gastroenteritis or food poisoning damages enough gut lining, lactase production and thus lactose digestion may be hampered for the duration of the sickness.
Other lactose intolerance stems from gut dysbiosis. Many gut bacteria, particularly Lactobacillus, produce lactase that help the host (that’s us) break down and absorb lactose. If your gut flora composition is missing the right species or overcrowded with the wrong ones, lactase production may suffer.
Prevalence: About 75% of the world’s population shows decreased lactase production into adulthood, but distribution varies wildly by ethnicity and nation. Looking at this global map is probably a better way to understand the prevalence of lactose intolerance than throwing out a single number. Among Northern Europeans, who have a long history of dairy consumption, prevalence is around 5%. In most of Sub Saharan Africa, where dairy is rarely consumed, lactose intolerance nears or surpasses 90% prevalence.
How to determine: The medical profession uses two main tests for determining lactose intolerance. Both involve the test subject consuming a lactose-rich drink. The hydrogen breath test measures the amount of hydrogen in your breath. If you’re unable to digest lactose, any lactose you consume will make it to the colon to be digested by hydrogen-producing bacteria; this hydrogen will show up in your breath. Another option is the blood glucose test. If your glucose doesn’t go up after eating lactose, you’re not cleaving it into digestible monosaccharides and you are probably lactose intolerant.