The BMJ Group retracts study claiming apple cider vinegar supports weight loss

A study indicating that apple cider vinegar may help overweight or obese people lose weight has been debunked. The BMJ Group has retracted last year’s research on this and advises people not to reference its findings. 

The paper was published in BMJ Nutrition, Prevention & Health in March 2024, and received widespread international attention and continues to feature in media publications. 

However, the BMJ Group cites quality of work as the main issue, noting its approach to statistical analysis of data and implausible statistical values. Other issues concern the reliability of raw data, inadequate reporting methods, and lack of prospective trial registration.

These factors breach BMJ’s editorial policy. Dr. Helen Macdonald, Publication Ethics and Content Integrity Editor, comments: “At present, the results of the study are unreliable, and journalists and others should no longer reference or use the results of this study in any future reporting.”

“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.”

The BMJ Group explains that critiques and complaints about the apple cider vinegar study prompted its content integrity team to review and forward it to statistical experts to check for reliability.

Statisticians’ attempts to replicate the results failed, and they noticed several analytical errors, along with irregularities in the data set and the report. They add that data from each participant needs further independent scrutiny.

Honest mistakes

According to the study authors, the identified errors were “honest mistakes,” and they have agreed to the study’s retraction. Macdonald comments: “While we deal with allegations as swiftly as possible, it’s very important that due process is followed. Investigations are often complex.” 

“This one involved detailed scrutiny of data and correspondence with researchers, institutions, and other experts, for example. Reaching a sound, fair, and final decision can therefore take several months.”

Commenting on the decision to publish the study despite the lack of trial registration, professor Martin Kohlmeier, editor-in-chief of BMJ Nutrition Prevention & Health, explains: “In hindsight, this was the wrong decision to make. But the authors come from a scientific environment that is underrepresented in nutritional research, and the journal aims to prioritize high-quality evidence, which usually comes from clinical trials.”

“These are relatively unusual in nutritional research, as they can be challenging to undertake because of the number of participants and time needed to obtain meaningful results.”

The small clinical trial claimed that apple cider vinegar was also linked to drops in blood glucose, triglycerides, and cholesterol levels, tested over three months. The product was tested in 120 young people with a body mass index of 27 to 34. They were randomly assigned to drink 5, 10, or 15 ml of apple cider vinegar, while the fourth group received a placebo.

The researchers cautioned against generalizing the findings and acknowledged that 12 weeks was not enough to test long-term effects.