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Obesity

856 Koreans had bariatric surgery in the first two insured years. Two years on, 71 percent of the diabetes had gone

Weight down 22.1 kg, waist down 17.4 cm, and which operation they had made no difference to the outcome. Just over half reached the 20 percent weight-loss threshold.

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In short

In a nationwide Korean cohort of 856 people who underwent bariatric surgery between 2019 and 2020 — the first years it was covered by national health insurance — and who had health checkups both two years before and two years after, mean body weight fell by 22.1 kg, body mass index by 7.9 kg/m² and waist circumference by 17.4 cm, the number meeting the study definition of diabetes fell by 71 percent (245 of 345) and of hypertension by 52 percent (267 of 513), fatty liver disease improved in 70 percent of cases, 56.3 percent achieved 20 percent or more total weight loss and 76.6 percent achieved 50 percent or more excess weight loss — while the type of operation performed was not significantly associated with the result.

Key takeaways

  • 856 Koreans who had bariatric surgery in 2019 and 2020 were followed using national health checkup data from two years before to two years after.
  • Mean body weight fell by 22.1 kg, body mass index by 7.9 kg/m² and waist circumference by 17.4 cm.
  • The number of patients meeting the study definition of diabetes fell by 71 percent, from 345 to 100.
  • The number meeting the definition of hypertension fell by 52 percent, from 513 to 246.
  • Metabolic dysfunction-associated fatty liver disease improved in 70 percent of cases.
  • 56.3 percent achieved total weight loss of 20 percent or more, and 76.6 percent achieved excess weight loss of 50 percent or more.
  • Younger age, female sex, higher baseline body mass index and higher systolic blood pressure predicted sufficient weight loss; the choice of operation did not.

Korea began covering bariatric surgery through national health insurance in 2019, which created something unusual: a complete national record of who had the operation and what happened to them, rather than a series of reports from individual centres with an interest in the answer.

What two years produced

71% and 52%

fall in the number of patients meeting the study definition of diabetes and of hypertension, two years after bariatric surgeryKim J et al., Journal of Obesity & Metabolic Syndrome, 2026

Diabetes went from 345 patients to 100, hypertension from 513 to 246, and fatty liver disease improved in 70 percent of those who had it. Weight fell by a mean of 22.1 kg. Those are large effects by the standards of anything else offered for metabolic disease.

The framing matters, though. This is the number of people who no longer met a study definition based on checkup measurements — not a durable cure, and not necessarily the same as being taken off medication. Two years is also early for a condition being managed across decades.

The operation did not matter. The patient did

Roux-en-Y gastric bypass, sleeve gastrectomy and biliopancreatic diversion with duodenal switch were not significantly different in whether a patient achieved sufficient weight loss. What predicted it was younger age, female sex, a higher starting body mass index and a higher systolic blood pressure.

The number that is not 71 percent

56.3 percent reached 20 percent or more total weight loss, the threshold the study set for a sufficient result. That is the figure a patient deciding whether to have the operation should be given alongside the mean, because it says close to half did not reach it.

Two design limits shape everything here. The cohort is restricted to people who happened to have national health checkups both two years before and two years after, which selects for engagement with the health system. And there is no comparison group — no matched people with similar obesity who did not have surgery — so the improvements cannot be separated from what would have followed the same two years of clinical attention without an operation.

Sources

  1. 1

    Kim J, Choi HS, Kim M, Kim H, Kim KA, Lee SE

    Clinical Outcomes of Contemporary Bariatric Surgical Procedures: A Nationwide Cohort Study

    Journal of Obesity & Metabolic Syndrome 2026

    doi:10.7570/jomes25096 · PMID:42289997

    https://doi.org/10.7570/jomes25096