Detailed ATTAIN-MAINTAIN results published in Nature Medicine

A randomized trial published in Nature Medicine on May 12, 2026 reported that a daily capsule of pasteurized Akkermansia muciniphila MucT, a heat-treated gut bacterium, helped adults with overweight or obesity keep off more weight after an eight-week low-calorie diet than a placebo did ^[4]. The study was led by Maastricht University and collaborators and registered as NCT05417360 ^[3].

The design was small and tightly run. Ninety adults with overweight or obesity first followed an eight-week low-energy diet. Those who lost at least 8% of their body weight then moved into a 24-week maintenance phase, taking either the pasteurized bacterium or a matching placebo alongside a healthy, unrestricted diet ^[3]. The trial was double-blind and placebo-controlled ^[4].

How big was the effect — and why the number changed

This is where the sources disagree. A press release from Danone, which supported the work, described the supplement group as regaining "on average about three kilograms less" than placebo ^[3]. Reviewing the published paper, internal medicine specialist José Pablo Miramontes González put the gap at "approximately 2 kg during the maintenance phase" ^[4]. The published figures are the ones to go by; the roughly 3 kg description came from the manufacturer's summary, not the article.

Beyond the scale, the trial reported better-preserved insulin sensitivity in the supplement group over the 24 weeks ^[3][4], plus higher energy content in stool ^[4]. Analyses of fat tissue showed less inflammatory gene signaling and more activity in pathways tied to energy metabolism ^[3]. Benefits looked largest in people who started with low levels of Akkermansia in their gut, who also showed favorable changes in blood pressure ^[3].

Notably, hunger and appetite hormones did not shift much. Prof Kieran Tuohy of the University of Leeds said "little difference in immune parameters or hormones that regulate hunger and energy intake like GLP-1 were observed in this human study," adding that detecting such changes may require differently designed trials ^[4].

Independent reviewers called the method sound but the evidence early. Miramontes González described the design as "randomised, double-blind and placebo-controlled" with a positive primary outcome, while cautioning it was "a small, short-term study conducted in a highly selected population and without comparison to current anti-obesity drug treatments," and that the effect size "does not allow us to conclude that this intervention is an alternative to incretin agonists, but rather a possible complementary strategy" ^[4]. Francisco Jesús Gómez Delgado noted the small sample, short follow-up, limited weight effect and lack of active comparators ^[4]. The study did not directly measure gut permeability ^[3].

Why it matters for patients

Weight regain after any weight loss — diet, surgery or medication — is the central problem in obesity care, and Tuohy pointed specifically to people who "put weight back on quickly once they stop taking these hormonal drugs" as a group this line of research could eventually help ^[4]. But none of the 90 participants here were coming off a GLP-1 medication; they had dieted ^[3]. There is no trial yet testing this supplement in people stopping semaglutide (Ozempic, Wegovy, Rybelsus) or tirzepatide (Mounjaro, Zepbound).

The size gap is worth keeping in mind. On the same day, Nature Medicine also published ATTAIN-MAINTAIN, which tested switching from injectable incretins to once-daily oral orforglipron (Foundayo). People previously on tirzepatide kept 74.7% of their weight loss on orforglipron versus 49.2% on placebo, and those previously on semaglutide kept 79.3% versus 37.6% ^[2]. In kilograms, Lilly reported that participants switching from Wegovy to Foundayo maintained all but 0.9 kg of prior loss at 52 weeks, and those switching from Zepbound maintained all but 5.0 kg ^[1]. A roughly 2 kg difference from a bacterial supplement sits in a different league than prescription maintenance therapy.

What happens next

The researchers say future work will look at longer-term outcomes, how the supplement interacts with different diets, and whether microbiome testing could identify who benefits most ^[3]. Both Tuohy and Miramontes González called for longer mechanistic studies in humans, including comparisons that could pin the effect to specific components of the bacterium ^[4]. For now, the authors' own framing — a proof of concept, not a reason to change practice — is the fair reading ^[4].