A headline-grabbing study that helped fuel the apple cider vinegar (ACV) boom has now been pulled from the scientific record, striking a blow to the authors, the wellness community and journal publisher BMJ Group. The research, which claimed that a daily teaspoon or two of ACV could drive striking weight loss and metabolic improvements, was found to have “multiple errors” and results that couldn’t be proven.
After concerns about the oft-cited study escalated – from letters to the journal to a formal investigation by BMJ’s content-integrity team and independent statisticians – experts were unable to reproduce the sensational findings and flagged “implausible statistical values,” unreliable raw data, inadequate methods of reporting and a lack of prospective trial registration. The authors agreed to the retraction, calling the errors honest mistakes.
“The paper is being retracted because the authors’ analyses could not be replicated and multiple errors were identified,”a journal spokesperson said. “The authors supplied dataset also demonstrated patterns inconsistent with random allocation of participants to treatment groups, improbably small p-values given the limited number of participants included in the study.”
While the published study has been scrubbed from the journal BMJ Nutrition, Prevention & Health, details of the study are covered in this March 2024 news release. In a three-month trial investigating the weight-loss benefits of ACV, 120 participants were prescribed different daily doses, which, according to the authors, resulted in an average loss of 6–8 kg (13-17.6 lb) and a BMI drop of 2.7–3 points. While the researchers included the study’s limitations, the findings were remarkable and widely reported on.
It’s worth noting that at the time the study was published, BMJ Nutrition, Prevention & Health co-owner Shane McAuliffe commented: “Whilst in this study design the intervention has demonstrated feasibility and effectiveness serving to encourage further trials designed to assess scalability and wider applications, at this stage caution should be exercised regarding the generalisability of the conclusions drawn on the independent effects of apple cider vinegar on the outcomes observed … Further research in this area would need to include detailed reporting of dietary recall or nutritional intake to explain any potential confounders and future explanatory trials would further elucidate mechanisms of impact on biochemical markers (lipids and blood glucose) in addition to weight loss.”
BMJ Nutrition, Prevention & Health editor-in-chief Professor Martin Kohlmeier acknowledged the journal’s error in publishing a trial that had not been prospectively registered – an explicit breach of policy.
“In hindsight, this was the wrong decision to make,” he said. “But the authors come from a scientific environment that is underrepresented in nutritional research and the journal aims to prioritise 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 numbers of participants and time needed to obtain meaningful results.”
As such, nutritional research is often observational, with health records pulled from large datasets like the UK Biobank, where only correlation, not causation, can be demonstrated.
“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, and journalists and others should no longer reference or use the results of this study in any future reporting,” said Dr. Helen Macdonald, Publication Ethics and Content Integrity Editor at BMJ Group.
One of the key issues with the study was that attempts to replicate it failed. Replication is a critical and often overlooked side of research, helping to prove the validity of the initial findings. While not foolproof – replication failures can occur due to human error, inaccurate details of study design and many other variables that may be difficult to control for – results that remain unproven are a huge red flag.
In this study, scientists not involved in the research cited issues with data collection and transparency, as well as the ages of the participants.
“The problems I see with this paper are that these were young people with an average age of 17 ± 5 years,” said Dr Rosemary Stanton OAM, Nutritionist and Senior Visiting Fellow at the School of Medical Sciences, University of New South Wales. “That means some were as young as 12. Some may have still been growing and this would affect their weight. We are also told that ‘subjects consumed their normal diets throughout the study. The contents of daily meals and snacks were recorded in a diet diary,’ but no details are given so we have no idea whether some may have been consuming less – or changed the amount they were eating during the study.”
Professor Helen Truby from The University of Queensland agreed: “The subjects were not weight stable at the beginning of the study, so may have been on a weight-loss journey before they began taking the vinegar. Diet and activity were self-reported so we cannot be sure that these large weight losses were not due to lifestyle changes, plus the use of weight loss medications has not been reported.”
Other experts found fault in how the scientists handled their findings, suggesting that their analysis failed to fully represent the data.
“They only apparently use t-tests (a statistical tool for making comparisons) and they should have used other models that allow for the valuation of fixed and random components,” said Miguel Ángel Martínez González, Professor of Preventive Medicine and Public Health at the University of Navarra. “There are several repeated measures over time, but they don’t use the proper statistical methodology for repeated measures in a longitudinal design of this type. They also don’t describe the total diet of the participants and how their caloric intake changes, the consumption of fruits, vegetables, ultra-processed foods, and so on.”
Dr Evangeline Mantzioris, Program Director of Nutrition and Food Sciences at the University of South Australia, noted that while the research showed promise: “This study was undertaken in people between the ages of 12-25 years, so the results can not be generalized to everyone. Additionally, from the statistical analyses that were done we can’t be confident that everyone who tried this would lose this average amount of weight. While they kept records of the participants’ diet and exercise this was not published in the paper, which makes it more difficult to determine if the diet or exercise might have had an impact. For example, did they change the amount they ate or the types of food they ate? Another concern is that even though participants were blinded to the treatment they received, the researchers did not check afterwards whether the participants guessed correctly which group they were in. Furthermore, the authors did not report if anyone dropped out of the study.”
While this study has been discredited largely due to poor execution and detail, there are numerous papers that have investigated the potential health benefits of ACV. In 2009, a Japanese study sparked widespread interest in ACV, when researchers found that it could result in modest weight loss. In the decade following, many researchers attempted to replicate the findings, including the team behind this study, which is often cited in media. However, so far evidence is mixed – and no research supports the 6–8-kg (13-17.6-lb) weight loss that the retracted study claimed.
What’s more, as this 2014 review details, scientists remain divided on just how ACV interacts with glucose and lipid metabolic processes.
“Although some evidence supports the use of vinegar as a complementary treatment in patients with glucose and lipid abnormalities, further large-scale long-term trials with impeccable methodology are warranted before definitive health claims can be made,” the researchers noted.
Nonetheless, the global ACV market is now valued at more than US$1 billion (2023-2024) and continues to grow – something that one retracted study is unlikely to impact.
“While findings showed apple cider vinegar may offer some benefits for weight loss and for lowering blood sugar, cholesterol, and triglycerides, it is unlikely to be a silver bullet for health,” said Dr Daisy Coyle, an Accredited Practising Dietitian at The George Institute for Global Health.
“While a number of effects of acetic acid on the expression of genes involved in fatty acid oxidation have been reported in animal studies, the mechanism of any effect observed here is unclear,” added Margaret Morris, Professor of Pharmacology and Head of the Environmental Determinants of Obesity Group at the University of New South Wales. “This study provides some good evidence for future larger and longer studies to be conducted across a range of ages to provide more robust evidence to see if apple cider vinegar could be a useful aid for weight loss.”
Source: BMJ Journals
