Gary's gut is still off 5 months after a 5-day antibiotic

Gary took 5 days of antibiotics in March. His gut is still off in August.

Gary from Wichita wrote in: "I had a sinus infection in March and took a five-day course of antibiotics. My gut has been wrong ever since. Loose one day, sluggish the next. Foods I ate for years now turn on me. Can five days of pills still be pushing me around in August?"

Yes, Gary. The drug left your blood within days. That hole in your gut runs on a different clock.

And we know how long that clock runs, because a lab in Copenhagen sat and watched it tick.

Half a year on, nine of their old bugs had never come home.

Copenhagen dosed 12 healthy men for 4 days, then tracked their stool for 180

Oluf Pedersen's team at the Novo Nordisk Foundation Center took 12 healthy young men and gave each of them a four-day cocktail of three last-resort antibiotics: meropenem, gentamicin and vancomycin. Then they collected samples for six months.

The wipeout was near total. Over the next six weeks the count of species climbed back up, which sounds like a happy ending.

Then came day 180. Nine species that every man carried before the pills were still gone — and a handful of bugs nobody wanted had moved into the space. Why do the squatters get there first?

An emptied gut fills with squatters long before the old crowd returns

Antibiotics do not aim. A pill goes down your throat and your gut bugs meet the full dose on the way to your sinus. Billions die that had nothing to do with the infection.

That leaves open floor and free food. Tough, drug-hardy bugs grab it fast — E. coli, Klebsiella, Enterococcus faecalis, Fusobacterium nucleatum. They breed quick and they ask for almost nothing.

Your helpful bugs are fussy by comparison. They want fiber, no oxygen, and neighbors who pass them scraps. So they crawl back over weeks… while one crew took the worst beating of all.

Meet the butyrate makers: Faecalibacterium prausnitzii and Roseburia hominis

These two chew the fiber you can't. What they give off is butyrate — a short fat that the cells lining your colon burn as their main fuel.

In Copenhagen both crashed hard, along with Anaerostipes hadrus, Coprococcus and the Bifidobacterium you see printed on yogurt labels. Underfeed that lining and it goes thin and touchy. Water gets handled badly, so one day is loose and the next is stuck. Foods that never bothered you start to.

One snag. You cannot swallow F. prausnitzii in a capsule — it dies in open air in minutes, so it isn't in your probiotic bottle. The only way back is to feed the ones that survived.

Six groceries that feed the butyrate crew back into the game

Survivors multiply fast when the food shows up. Give them this:

The avocado line comes from Hannah Holscher's team at the University of Illinois: 163 adults, 12 weeks, more short-chain fats in the stool. Pick the cheapest item and start tonight.

Cook double the rice or potatoes tonight, eat the second half cold tomorrow

Heat, then chill. Cooling rearranges cooked starch into a form your own gut can't crack, so it rides all the way down and lands on the butyrate crew like a grocery delivery. Cold potato salad counts. A gentle reheat keeps some of it too.

Gary is five months out from those pills. Time was never his problem. Groceries were.