BMJ Group retracts apple cider vinegar weight-loss study amid data flaws

BMJ Group has retracted a study that claimed a daily shot of apple cider vinegar could help people lose weight, more than a year after it was published in BMJ Nutrition, Prevention & Health. The retraction, announced by the BMJ Group on Thursday, cites concerns over multiple analytical errors and irregularities in the data set used by the authors, who were affiliated with the Holy Spirit University of Kaslik in Lebanon. The decision follows an internal review prompted by critics who argued the trial was deeply flawed and that its conclusions were not supported by the data.

According to the paper, 120 overweight or obese volunteers with BMIs between 27 and 34 were randomized into four groups of 30. Participants were assigned to drink a daily shot of apple cider vinegar before breakfast at 5, 10, or 15 milliliters, or to receive a placebo. The 12-week trial asked participants to track their diet and exercise. The study reported that those who consumed the vinegar lost about 11 pounds (5 kilograms) and saw their BMI fall by 2.7 to roughly 3 points, depending on dose, while the placebo group experienced an average loss of about 0.7 pounds (0.3 kilograms). The protocol also noted that some volunteers were as young as 12, raising questions about sample demographics.

Experts quickly raised questions about the study's design and reporting. Professor Helen Truby, a professorial research fellow in nutrition and dietetics at the University of Queensland, said that although the design could test cause and effect, there were substantial problems that could undermine the conclusions. The subjects were not weight-stable at the start and self-reported diet and activity data left room for bias. She also noted that the study did not report whether participants used any weight-loss medications during the trial.

Professor Miguel Ángel Martínez González, of the University of Navarra, added that the researchers relied heavily on t-tests and did not describe the total diet or caloric intake changes, which are essential for interpreting weight changes. He urged caution about drawing firm conclusions from the results and highlighted the need for more robust designs in nutritional research.

The BMJ Group's retraction notice said that the statisticians consulted for the paper were unable to replicate the results and that multiple analytical errors were identified. The notice also cited 'inadequate reporting of methods' and 'implausible statistical values' that violated the group's editorial policy. The authors said the identified errors were honest mistakes and supported retracting the paper.

Dr Helen Macdonald, BMJ Group's publication ethics and content integrity editor, stressed the importance of correcting the scientific record. 'Tempting though it is to alert readers to an ostensibly simple and apparently helpful weight loss aid, at present the results of the study are unreliable,' she said. 'This retraction reflects our strategic and proactive approach to investigating concerns raised about the content we publish. We act where necessary in the interests of openness and the importance of correcting the scientific record.'

Martin Kohlmeier, editor in chief of BMJ Nutrition Prevention & Health, noted that the research team came from a scientific environment that is underrepresented in nutritional research, and that the journal aims to prioritize high-quality evidence, typically from clinical trials. He added that such trials are relatively uncommon in nutrition science because of the large numbers of participants and time required.

The retraction comes amid broader public interest in apple cider vinegar, a commodity that can cost as little as £2.50 in health-food stores. The notion that a simple household beverage could deliver meaningful weight loss – and perhaps other health benefits – has attracted celebrity attention in recent years. Elizabeth Hurley, Victoria Beckham and Jennifer Aniston have publicly endorsed the tipple, helping to keep sales brisk even as researchers cautioned about drawing broad conclusions from small, flawed studies.

Despite the publicity, experts say the evidence for apple cider vinegar’s health effects remains mixed and controversial. The retraction underscores the journal's commitment to rigorous methods and transparent reporting, and it serves as a reminder that in nutrition science, seemingly simple interventions require robust, well-controlled trials to establish any reliable claims.