Why Grown Humans Aren’t Meant to Drink Milk

Greetings, Primals!

If you look across the animal kingdom, humans are the only species that continues drinking milk after we’ve been weaned. And not just that, we drink the milk of another animal! You don’t see a lion circling back to its mother for milk. And you certainly don’t see a gorilla pouring a glass of cow’s milk! So why do we?

In today’s issue:

WEEKLY DEEP DIVE

I’ll be 44 this year, and I grew up during the height of the “Milk Does a Body Good” campaign. I still remember flipping through magazines in the 90’s and seeing Jennifer Aniston and Cindy Crawford rocking milk mustaches like it was a badge of health. And let’s not forget Tyra Banks! As a then teenage boy these images are etched in my memory!

And to be fair milk does do a body good… when that body is an infant!

Human milk is perfectly designed for early growth. It’s loaded with sugar (lactose), fat, and protein. These are the exact macronutrients a rapidly developing brain and body need. During infancy and early childhood, we produce an enzyme called lactase in our gut lining. This enzyme breaks down lactose which is a disaccharide into its more simpler form galactose and glucose so they can be absorbed through our gut lining and into our bloodstream. Once they arrive in our bloodstream they are delivered to our cells to fuel growth.

But here’s the part most people never hear. As we’re weaned from our mother’s milk, lactase production naturally declines. That’s biology doing exactly what it’s supposed to do.

When lactose isn’t broken down, it passes through the small intestine undigested and reaches the colon, where gut bacteria ferment it. That fermentation process produces gas, bloating, cramping, and discomfort. The body also pulls water into the gut to move the undigested sugar along often resulting in diarrhea. That’s not a “weak gut.”
That’s a species-appropriate response!

Now, some people can tolerate milk into adulthood. They’ve inherited a genetic adaptation called lactase persistence. Im one of those people. But just because I can tolerate it I don’t consume it because maintaining optimal body weight is my goal. Milk is essentially growth signaling in liquid form.

It strongly stimulates insulin, which tells your body to store energy. That’s perfect for babies who need to grow fast. For adults already carrying excess weight, that signal often works against them. That’s why, even if you can digest milk, removing it often makes fat loss easier.

The Primal Takeaway

If you enjoy dairy, a better ancestral option is fermented dairy. This includes things like kefir, yogurt, and aged cheeses. During fermentation, bacteria consume much of the lactose, lowering the sugar content and making these foods far easier to digest.

While I don’t drink milk I do buy whole milk regularly to make my own kefir. Kefir delivers beneficial bacteria, along with the compounds those bacteria produce during fermentation. From mouth to anus, we carry roughly 2–3 pounds of bacteria, and nourishing them sends powerful “all is well” signals to the brain through the vagus nerve.

So the next time you reach for milk, ask yourself: Is this food aligned with my stage of life? Do I have the appropriate enzymes to process this macronutrient? Eat in a way that matches your biology and keep your choices species appropriate. By doing so you can remove digestive issues and bring your body weight back in balance.