The weird way our genes affect how we absorb caffeine
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coffee DNA 23andme
Credit: gif by lauren kolm

When I signed up to get a genetic analysis from 23andMe, there were some things I knew about my genetic predisposition. My results confirmed what I already knew about myself: I have photosensitivity, my pee gets smelly from eating asparagus, and I’m 59 percent Ashkenazi Jewish. But one thing stuck out: I am, genetically, unable to absorb caffeine as regularly as most people. In fact, according to my results, I am “likely to drink less caffeine than average, if you drink caffeine at all.” Which, well, isn’t true. I love coffee—I’m up to three cups a day. What does “unable to absorb caffeine” mean? Am I bad at drinking coffee?

My first stop on the hunt for information was a phone call with Todd Graham, a DNA expert who serves as a consultant for the biotechnology industry. “OK, so this is all a little bit weird to explain,” said Graham, who clearly knew the pitfalls of trying to convey this information to someone with absolutely zero scientific background. “The marker they test for is Cytochrome P450," he said. "What that means in plain English is that these are enzymes that metabolize all sorts of toxic chemicals in your body. Think about all the drugs you take, various medicines, etc. The thing is, these enzymes also metabolize caffeine.”

Graham went on to say that everybody has these enzymes in their body, and some people’s enzymes metabolize caffeine better than others. “In your particular case, it means that your body metabolizes caffeine… not so hot.” Graham pauses for dramatic effect. “You know how some people need a cup of coffee to feel something and other people need, like, 12? It’s because they absorb it differently.”

As Graham explained to me, you can have two people of the same height, weight, and background who metabolize caffeine completely differently. So, while John Robertson needs one cup of coffee to get amped up, Robert Johnson doesn’t feel anything until his ninth cup.

Everything I knew about the way I consume coffee was flipped upside down. I thought I had the exact opposite problem in which I need more coffee to feel something, but somehow it was the opposite.

“This is more an issue with how your brain is wired,” biochemist turned naturopathic physician and author Dr. Jennifer Stagg said. “This behavioral trait is not considered abnormal. Genomic testing of this type determines specific variations within the genome which is ultimately what makes us all slightly different. These are not mutations or abnormalities.”

What’s more, that variable absorption might explain why there are so many coffee studies with conflicting information. As Stagg writes in Unzip Your Genes:

All of this information led me to reflect upon my habits. Perhaps it’s the underlying knowledge than an underperforming Cytochrome P45 is making me live a lie, but I never really finish my cup of coffee.

When it comes down to it, I only drink about a quarter of a cup of coffee—39 mg of caffeine—less than the average person per day. If anything, this has taught me that I need to stop wasting paper cups.