There came a point just a few months ago when I felt I was on the brink of gastrointestinal ruin.

As an interim restaurant critic for The New York Times, I had eaten dinner at a restaurant every night for three straight weeks. I felt fine. Yet I’d wake in the middle of the night thinking about all the sugar I’d just ingested, or the steak I’d polished off, distressed over what all this eating was doing to my body — and specifically, what it was doing to my gut.

I am obsessed with gut health. I grew up in a family that talked openly about digestion. My father couldn’t live without his daily cocktail of milk and psyllium husks. We believed that gut health was key to our overall well-being.

The American public has come to a similar conclusion. Supermarket shelves are lined with prebiotic sodas, probiotic supplements and fiber-rich cookies and bars. Influencers discuss their irritable bowel syndrome openly on TikTok.

And today there are services that can analyze a stool sample and tell you what kind of bacteria populate your gut. So I embarked on a two-month experiment on that microbiome to chart the effects of all of those restaurant meals on my gastrointestinal health.

The results surprised me. I also learned that when it comes to the gut, few things are black-and-white.

I enlisted the help of two Stanford University scientists who run one of the leading microbiome laboratories in the United States: Justin Sonnenburg, a professor of microbiology and immunology, and his wife, Erica Sonnenburg, a senior research scientist in microbiology and immunology.