Peak alcohol readings roughly tripled after one‑anastomosis gastric bypass in a 10‑person study

People who had one-anastomosis gastric bypass reached peak breath alcohol readings nearly three times higher after surgery than they did before it, drinking exactly the same amount of wine. That is the finding of a small prospective study published September 9, 2026 in Obesity Facts.

One-anastomosis gastric bypass, often shortened to OAGB, is a newer bypass procedure. Changes in how alcohol behaves after surgery had already been described for Roux-en-Y gastric bypass and for sleeve gastrectomy. For OAGB the researchers say this had not been reported before.

The design was simple. Ten adults were tested before their operation, then again at one month and four months after it. At each visit they drank 200 mL of red wine at 13.5 percent alcohol, about 21.3 grams of ethanol, which is roughly a large glass. Breath alcohol was then measured at set points over two hours with a calibrated breathalyser. Participants also filled in a standard questionnaire about how intoxicated they felt.

Peak breath alcohol rose from 0.43 to 1.24 g/L on the same glass of wine

Before surgery the average peak reading was 0.43 g/L. At one month after surgery it was 1.19 g/L. At four months it was 1.24 g/L.

Total exposure rose further. The researchers measured the area under the concentration curve, which captures how much alcohol was in the system and for how long rather than just the highest single reading. That figure went from 21.0 before surgery to 71.2 at one month and 91.2 at four months, in units of grams times minutes per litre.

So the peak roughly tripled, and total exposure roughly quadrupled by four months. The difference held up after the researchers adjusted for BMI, which matters because people weigh less after surgery and a smaller body would raise alcohol concentration on its own. The change was larger than body size alone explains.

Alcohol also took longer to clear, and people felt it more

The elimination half-life, meaning the time taken for the concentration to fall by half, was longer after surgery. Alcohol was arriving faster, reaching higher, and leaving more slowly.

Reported intoxication symptoms went up after surgery too, and those scores tracked the measured numbers. The strongest relationship was with peak concentration. In other words people did not simply register a number on a device without noticing anything; they felt the difference, and they felt it most when the peak was highest.

The authors' practical point is that even a modest amount of alcohol can produce a high reading after this operation, and that surgical teams should raise the subject with patients rather than leave it unspoken.

Ten people, four months, and nothing on what happens after that

This is an exploratory study in ten participants, with an average age of 42 and 60 percent women. Ten is a very small number. Findings from a group that size can move a long way if one or two people respond unusually, and the study cannot tell you how much any individual reader would be affected.

The authors also report participant attrition, meaning not everyone completed every visit, and they say plainly that the results should be read with caution for that reason.

Follow-up stopped at four months. Whether the effect stays at that level, grows, or settles back over later years is not answered here. The study also tested one drink type at one dose in a controlled setting, which is not the same as ordinary drinking over an evening.

This is information about how a body processes alcohol after a specific operation. It is not guidance on whether or how much to drink. That conversation belongs with the surgical team, who know the individual case, the timing since surgery, and any medicines involved.