What sort of a grade would you get on the F. Scott Fitzgerald intelligence test?

The writer best known for The Great Gatsby (though Tender Is the Night really is a better novel) believes the litmus test for “first-rate” intelligence is “the ability to hold two opposed ideas in mind at the same time and still retain the ability to function.”

While the accuracy of Fitzgerald’s assessment can be debated, this cannot. To make what science has learned about the goings-on inside your gut enhance your health, acing Fitzgerald’s test really helps.

And what a first-rate mind infers from a study published in the June 2019 issue of Cell Host & Microbe using humans and their pooh is that the broccoli that’s oh-so good for my gut health may not be quite as good for yours. Even though it’s an inference that refutes a long-held belief that broccoli is always a superfood.

Yet this contradiction “kind of makes sense” to Dan Knights, the researcher who spoke to Live Science about the University of Minnesota study back then. It does so not only because the associate professor in the Department of Computer Science & Engineering at that institute possesses first-rate mind, but also because there’s what he calls “dark matter” in foods - elements besides the vitamins, minerals, and micronutrients that nutritional labels typically don’t list and scientists don’t usually consider, but should.

The impact of dark matter on diet via the gut microbiome clearly comes to light in the aforementioned study.

Knights and his colleagues had 34 healthy volunteers write down every bit of food and drink they consumed for 17 consecutive days. All the while, the volunteers provided stool samples.

The researchers then used what’s called shotgun metagenomics on the stool, which “allows researchers to comprehensively sample all genes in all organisms present,” according to Illumina.com. This enabled them to evaluate the abundance and the diversity of the microbes in the volunteers’ guts - and recognize the role of dark matter.

As they compared the volunteers’ food-and-drink journals to the stool samples, the researchers searched for clear-cut relationships between consuming certain foods and the existence or abundance of bacteria in the gut microbiome.

And they found them. What they didn’t find was much of a pattern.

While they detected 109 such relationships in the group as a whole, only eight of those relationships were shared by more than two volunteers. And in five of those instances, the food consumed had the opposite effect.

In other words, a single vegetable like broccoli could cause a certain good bacteria to multiply in one person yet not in another.

The logical explanation for this is that the effect of a food’s dark matter on the gut biome is a highly personalized one. That’s to be expected, Knights’ explains, since each person whose body digests dark matter possesses a unique mixture of gut microbes.

So why review an old study about gut bacteria that provides far more questions than answers when, as mentioned in last week’s column, new studies about gut bacteria are being published faster than I can read them? Because one new study of particular note focuses on a different “dark matter”: how sugar and fat can adversely affect the gut biome and thereby your overall health.

While prior studies established about 70% of your immune system resides in your gut and that good gut bacteria certainly support it, one published in the Sept. 15, 2022 issue of Cell using mice shows how bad bacteria weaken it. And that bad bacteria gain strength from poor eating.

And in this specific case, the poor eating was created by feeding mice what Americans typically eat. It’s sometimes called the Western-style diet and is always too full of fat and sugar.

Before feeding the mice a variant of the Western-style diet, however, the researchers worked their magic so that the mice’s guts were replete with a bacterium that goes by the abbreviation SFB, the preferred food of an immune cell in mice that’s abbreviated as TH17. After four weeks on this diet the mice had gained weight and developed glucose intolerance and insulin resistance - the holy (as in cow) trinity for type 2 diabetes - and that was no surprise.

What was closer to one was what happened to the SFB bacteria that had been thriving inside the mice’s guts before they began eating the Western-style diet. Now they were few and far between.

In their place: a “bad” bacteria that thrives on sugar.

As a result - and this is a serious result - the mice lost TH17 immune cells.

In short, in the same way fiber, amino acids, fatty acids, vitamins, and minerals can cause “good” gut bacteria to thrive and multiply, too much sugar does the same for the “bad.”

While this study was performed on mice, a possessor of first-rate intelligence infers the same occurs in most humans. Not all. But most.

Which is why possessors of first-rate intelligence never stop experimenting with their diets.