Your Sweetener Barely Matters. Your Fiber Does.

-Morgan McSweeney, PhD (@dr.noc)

For decades, the implication was that artificial sweeteners are inert: they provide the taste of sugar but then slip through you untouched and largely invisible to your body.

And, to be fair, that does hold up with respect to the health outcomes you probably are most concerned about: cancer, heart disease, preterm birth, early death, etc.

Consuming diet sodas or other products with sweeteners has not been shown (in high quality studies) to increase risk for any of those outcomes.

But if you take a moment to speak with your friendly gut microbiome, you will find that sweeteners are not totally inert. As you know, you are not the only one sitting down at the table to crack open a diet beverage or zero-sugar yogurt. You coexist with a friendly swarm of trillions of living cells, and you get to choose what they eat. (Oh the power!)

That landscape is where the artificial sweetener conversation becomes just a little bit murky.

Not in a “oh, this is concerning for my health” type of way, but in a “oh, I guess there is more uncertainty here than I realized.. I guess there’s a lot left to learn” type of way.

• What happens if you conduct a study where you feed mice some sweeteners, collect their poop, and then transplant their poop into other mice?

• What happens if you enroll some people in a study, feed them sweeteners, collect their poop, and then transplant their microbes into mice?

Well.. something happens. Today we will examine what’s going on in your gut when you consume sweeteners.

I have no ads, no sponsor, and no affiliate products - this letter is fully reader-supported. Here’s everything in the rest of today’s letter:

• The results of the poop-bacteria-transfer experiments. (Yuck.. but cool?)

• A breakfast recipe that will have your microbiome giving you thunderous applause. (My foray into the world of writing recipes. Don’t get your hopes up too high! Simple to make, though..)

• An overview of the microbiome: what those trillions of bacteria actually do for you, and why “gut health” content online oversells its confidence.

• A few key studies that found nothing: key null results, and why the exact same sweetener has sometimes led to opposite headlines.

• Sweeteners as tiny drugs for bacteria: this is one of the more strange concepts, wherein sweeteners may help bacteria swap genes amongst eachother (… in vitro).

• The lab signals that researchers continue to debate: a sucralose impurity that damaged DNA in cultured cells, and a reminder about what that 100,000-person observational cancer study saw when it looked for an association with sucralose.

• The key lifestyle factor that overshadows the impact of sweeteners by a wide margin.

• (Commentary): On mechanisms vs. outcomes for the gut microbiota.

A paid subscription also opens the archive. A few recent reader favorites:

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Here’s why I run my letter with a paywall rather than with advertisements: I take no money from any company and I don’t sell a gut cure, a probiotic, or earn a commission on anything. This is fully reader supported, which means I answer to you and you alone.

On a topic where most of the loudest voices are also selling you a probiotic or a fourteen-day “gut reset,” I’d rather provide my unfiltered read, free of commercial bias.

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