Milk. Some people love it, some hate it, and some simply have trouble digesting it. Today, we’ll explore why some people are lactose intolerant and some aren’t.

Why Are Some People Lactose Intolerant?

When we were younger, milk was a big staple in most of our lives. What would our breakfast cereal be without it? Letting your Cocoa Pebbles soak and turn your milk brown, then drinking the resulting ‘chocolate milk’ was (and for some still is) a morning delight. At some point, usually in the mid-teens to early 20s, a percentage of the population started to feel increasing discomfort or bloated after consuming a few glasses of milk. They became lactose intolerant.

The Missing Lactase

The reason for this is a lack of the enzyme ‘lactase’ which is responsible for breaking down the lactose (a sugar in milk) in your digestive track. Scientists have discovered that most people develop at least some degree of intolerance as they age.

Why we lose this ability still remains a bit of a mystery. Most scientists believe that we all originally lost the ability to digest lactose as we got older, and thanks to a fairly recent genetic mutation, the lactase producing gene was left “switched on” throughout adulthood.

Those with the intolerance will still continue to produce some lactase, but at a substantially lower rate. The decreased production will then reach a critical point where your digestive tract can no longer break down lactose and it will pass undigested through your intestine until it reaches the colon. Once there, the lactose undergoes a kind of fermentation by the bacteria that hang out there. As the bacterium interacts with the lactase, gas is produced. This gas is what causes the discomfort, pain as well as cramping and diarrhea.

Should We Cut Out All Dairy?

For all but the most severe cases, being lactose intolerant doesn’t mean you should permanently cut out all dairy. Several studies have shown that those who are intolerant can drink one to two glasses of milk a day without a problem. According to the studies, the negative symptoms can actually improve when milk is consumed regularly, but in lower levels. Researchers have speculated this is because the bacteria in the colon build up over time, which causes a stronger reaction than if the bacteria had been continually exposed to lactose — and the bacteria also becomes more efficient.

Just don’t forget the most important reason to drink milk: calcium. If children don’t get the amount of calcium they need, their growth and skeletal health will be put at risk. A New Zealand study showed that kids who cut dairy completely out of their diet only get one-third of their needed daily calcium which was directly responsible for a substantially higher bone fracture rate than children who consumed dairy products. Milk does in fact, do a body good.

While it’s certainly possible to get calcium from other food sources, you would have to consume unreasonable amounts of it to equal the same amount found in many common dairy products. If you miss the days when you could enjoy dairy products without a care or worry, consider giving lactose digestive-aids a try. Many with light to mild symptoms have reported great results and a sizable portion can now consume dairy products again without ill effects.

Bonus Science Fact: Milk is white because of the casein protein. Thanks to its spherical shape and being suspended uniformly throughout the liquid, the light is deflected throughout most of the visual spectrum. This causes milk to be fairly opaque and appears white to our eyes.

References:

Itan Y, Jones BL, Ingram CJ (2010). “A worldwide correlation of lactase persistence phenotype and genotypes”. Evolutionary Biology 10:36.

Nature Genetics “Identification of a variant associated with adult-type hypolactasia”. Nat. Genet. 30: 233–7. doi:10.1038/ng826. PMID 11788828.

Flatz G, Rotthauwe HW (1971). “Evidence against nutritional adaption of tolerance to lactose”. Humangenetik 13 (2): 118–25.

Coles Harriet (2007-01-20). “The lactase gene in Africa: Do you take milk?“. The Human Genome, Wellcome Trust.

Ingram CJ, Itan Y, Mulcare CA (January 2009). “Lactose digestion and the evolutionary genetics of lactase persistence”. Hum Genet 124 (6): 579–91.

Swallow DM (2003). “Genetics of lactase persistence and lactose intolerance“. Annual Review of Genetics 37: 197–219.