The Weird Science of Lactose Intolerance


Imagine if your eyes changed color one day; that’s almost the same thing as the development of lactose intolerance on a genetic level.

Not only is lactose intolerance common, it’s so prevalent across the world, doctors are hesitant to even acknowledge it as a diagnosable condition.

In fact, 65% of people across the world are lactose intolerant after childhood.

“Then why have I only ever met two people who are lactose intolerant?” you ask.

For whatever reason, Americans and Europeans can more easily digest milk.

Genetics, injury, disease, environmental influences, and medication can also promote lactose intolerance.

Interestingly, scientists are suggesting that lactose intolerance may even be (kind of) reversible.

Let’s talk cheese.

How Does Lactose Intolerance (Not) Work?

Lactose is the name for the kind of sugar in milk, which is broken down by an enzyme called lactase in those who are tolerant.

The lactase gene, also known as the LCT gene, provides the blueprints for the lactase-producing cells that line the small intestine and secrete this enzyme.

Thanks to these cells, lactose from passing food is broken down into glucose and galactose, two forms of sugar that the body can always absorb.

But genes are either on or off, aren’t they?

If the issue of lactose tolerance is dictated by genetic makeup, then how is it that initially lactose-tolerant people can just shift into intolerance when growing into adulthood?

Isn’t that like your eyes suddenly turning from brown to blue?

This is where the science goes off the rails a bit.

The Lactase Gene Off Switch

In English, these researchers from the University of Toronto found that in lactose-intolerant individuals, the lactase gene is subjected to a chemical change that impairs its function as they age into adulthood.

It’s not the sequencing of the gene itself that is altered, but the addition of certain molecules (methyl groups) to the DNA molecule that prevents cells from responding to the lactase gene.

In other words, people who are hereditarily predestined to become lactose intolerant after childhood chemically modify their DNA (without rewriting it) to “gunk up the lactase button,” so it no longer works. 

Since lactose intolerance is the norm, it’s more appropriate to say that lactose-tolerant people are the ones with the “deformity.”

Exploring the origin of lactose tolerance requires revisiting the investigation of “great-great-great…x100” grandma and her beloved cows.

Ethnicity and Lactose Tolerance

An interesting review from the French National Museum of Natural History goes into great depth about when and where in the world “lactase persistence” began to emerge.

As suspected, when looking at a particular ethnic group, the emergence of lactose tolerance usually coincided with the rise of animal domestication.

There are some peculiar exceptions, however, like that of modern-day Asians (highly lactose intolerant) descended from herders, which speaks to the presence of other factors that can modify tolerance.

In reference to the countries with the highest lactose tolerance rates, the study lists the following:

Highly common: Northern and central Europe, populations with European ancestry (USA, Canada, etc.)

Fairly common: West Africa, East Africa, and the Middle East.

Many scholars also support the notion that the electrolyte content, fat, and other life-affirming nutrients in milk were precious enough to trigger natural selection, which would explain the spread of lactose tolerance and decline of intolerance in the above groups.

Environmental Influences

Toxic runoff may transform average Joes into superheroes in the comics and movies, but in our much less romantic reality, exposure to certain toxins can create the superpower nobody asked for: lactose intolerance.

A University of North Carolina study cites a number of objectively verified “environmental triggers for DNA methylation alterations,” which is the same type of chemical alteration (mentioned above) that causes lactose intolerance.

Per the study, these environmental triggers include:

  • Air pollution
  • Arsenic
  • Lead
  • Mercury
  • Tobacco smoke
  • Certain foods
  • Chromium

These triggers may be secondary to a person’s pre-wired genetics when it comes to the ability to influence lactose tolerance, but they still raise the overall risk, and most of them come with more serious health consequences (cancer, lung disease, etc.) to boot.

Disease, Trauma, and Antibiotics

Finally, lactose intolerance can be achieved through injury to the small intestine.

Whether it’s a traumatic injury, a disease, reaction to antibiotics, or a combination, normally lactose-tolerant people can lose their ability to digest this form of sugar.

This loss can be temporary or permanent, regardless of whether or not the underlying issue has been adequately addressed.

In this narrow context, lactose intolerance is technically “reversible.”

Experts have been exploring other avenues by which lactose intolerance may be “switched off,” but they’ve only found band-aid solutions to this point.

Is Lactose Intolerance Really Reversible?

The gut microbiome—a miniaturized ecosystem in our intestines consisting of 100 trillion benevolent (and some malevolent) bacteria—can be especially helpful in this regard.

To leverage the power of the gut microbiome for lactose intolerance symptom relief, you have to increase the population of lactic acid bacteria.

Think of these bacteria as stand-ins for your non-existent lactase-producing cells; the bacteria “eat” the lactose and excrete lactic acid instead of gas. 

Among many critical immune, digestive, and other functions, this is why foods containing these bacteria, i.e., probiotics, are widely praised. 

This finding from Tel Aviv University confirmed the gas-relieving potency of probiotics; participants demonstrated decreased bloating and flatulence upon consuming dairy throughout a six-month probiotic regimen. 

Some experts argue that feeding your existing bacteria (prebiotics) instead of replacing or supplementing them (probiotics) is more effective since lactic acid bacteria don’t tend to stick around in our systems too well.

Neither track constitutes a “cure,” but you can at least cut down on gas and bloating with these methods.

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