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Correspondence on ‘D.S. Valdes, D. So, P.A. Gill, N.J. Kellow, Effect of Dietary Acetic Acid
Supplementation on Plasma Glucose, Lipid Profiles, and Body Mass Index in Human Adults: A
Systematic Review and Meta-analysis., J. Acad. Nutr. Diet. (2021).
https://doi.org/10.1016/j.jand.2020.12.002.’
Title: Acetic acid does not reduce triglyceride levels in overweight or obese adults, and it reduces
them only marginally in those with diabetes.
Note: The editor-in-chief forwarded my letter to the authors who will implement my suggestions in a
corrigendum to the original article. To avoid redundancy, my letter will not be published, and instead
credits to me will be included in the author’s corrigendum. The editor full email is reported at the end
of this document.
Dear Editor,
In the Journal of the Academy of Nutrition and Dietetics, Daniela Valdes and colleagues1 report on their
meta-analysis around the effects of dietary acetic acid on various metabolic parameters. They
calculated several meta-analyses by variously combining the 16 included studies involving 910
participants. On carefully examining the results, numerical inaccuracies are revealed in several of the
meta-analyses. In one case, the authors estimated statistically significant large positive effect of acetic
acid in reducing triglyceride levels, where in fact the effect was not statistically significant and of a
lesser magnitude. In other cases the corrected meta-analyses do not significantly change the original
authors’ conclusions, albeit the precision of the effect estimates is reduced.
In the meta-analysis for triglyceride levels in overweight or obese adults, where acetic acid is compared
to placebo or low-dose acetic acid, three studies are included2–4. However, perusing the data from the
third study4 (study ID ‘Park 2014’ in Figure 1), the follow-up values in the meta-analysis have been
swapped between intervention group and control group. Indeed, the study reports that the change from
baseline was -23.17 mg/dL in the placebo group, and 2.75 mg/dL in the acetic acid group, favouring
placebo. Figure 1 reports the corrected meta-analysis. As a result, the effect estimate is not statistically
significant and smaller than the one calculated in the original meta-analysis, i.e., -10.14 mg/dL, 95% CI
[-36.33, 16.06] versus -20.51 mg/dL, 95% CI [-32.98, -8.04], with an obviously much higher statistical
heterogeneity (I2=78% versus I2=4%).
In several other meta-analyses that included the results drawn from a report of a study evaluating the
effect of dates vinegar on several metabolic parameters in adults with diabetes,5 the effect estimates are
imprecise due to the wrong standard deviation values extracted for this included study. Indeed, the
standard deviation values used are of unusually small magnitudes compared to other studies in the
analyses. These values were obviously extracted from a table in the study report. However, the same
report states much larger standard deviations in its abstract. In a personal communication, the article’s
corresponding author has kindly confirmed that the correct standard deviation values are those in the
abstract. After having received from the author all other relevant standard deviation values, the
corrected meta-analyses were calculated, which included data extracted form several others of the
included studies.6–9 The revised results do not differ substantially from the original results, apart from a
reduction of the precision of the estimates, without changing statistical significance. However, one
change worth noticing is that, in adults with diabetes, triglyceride level reduction becomes only
marginally statistically significant, i.e., -7.86 mg/dL, 95% CI [-15.40, -0.31] versus -7.37 mg/dL, 95%
CI [-10.15, -4.59] (Figure 2).
Overall, most of the analyses by Daniela Valdes and colleagues are not significantly affected. However,
the revised estimate of triglyceride level reduction in overweight or obese adults, compared to a large
and statistically significant effect originally reported, showed a lesser effect which was not statistically
significant. In addition, triglyceride level reduction in adults with diabetes becomes only marginally
statistically significant.
Figures
Figure 1. Forest plot for follow-up triglyceride levels in overweight or obese adults.
Figure 2. Forest plot for follow-up triglyceride levels in adults with diabetes.
References
1 Valdes DS, So D, Gill PA, Kellow NJ. Effect of Dietary Acetic Acid Supplementation on Plasma
Glucose, Lipid Profiles, and Body Mass Index in Human Adults: A Systematic Review and
Meta-analysis. J Acad Nutr Diet 2021. DOI:10.1016/j.jand.2020.12.002.
2 Kim EK, An SY, Lee MS, et al. Fermented kimchi reduces body weight and improves metabolic
parameters in overweight and obese patients. Nutr Res 2011; 31: 436–43.
3 Kondo T, Kishi M, Fushimi T, Ugajin S, Kaga T. Vinegar intake reduces body weight, body fat
mass, and serum triglyceride levels in obese Japanese subjects. Biosci Biotechnol Biochem 2009;
73: 1837–43.
4 Park JE, Kim JY, Kim J, et al. Pomegranate vinegar beverage reduces visceral fat accumulation
in association with AMPK activation in overweight women: A double-blind, randomized, and
placebo-controlled trial. J Funct Foods 2014; 8: 274–81.
5 Ali Z, Ma H, Wali A, Ayim I, Rashid MT, Younas S. A double-blinded, randomized, placebo-
controlled study evaluating the impact of dates vinegar consumption on blood biochemical and
hematological parameters in patients with type 2 diabetes. Trop J Pharm Res 2018; 17: 2463–9.
6 Mahmoodi M, Hosseini-zijoud S-M, Hassanshahi G, et al. The effect of white vinegar on some
blood biochemical factors. J Diabetes Endocrinol 2013; 4: 1–5.
7 Nazni P, Singh R, Devi RS, et al. ASSESSMENT OF HYPOGLYCEMIC EFFECTS OF APPLE
CIDER VINEGAR IN TYPE 2 DIABETES. Int J FOOD Nutr Sci 2015; 4: 206–9.
8 Kausar S, Abbas MA, Ahmad H, et al. Effect of Apple Cider Vinegar in Type 2 Diabetic Patients
with Poor Glycemic Control: A Randomized Placebo Controlled Design ®. Int J Med Res Heal
Sci 2019; 8: 149–59.
9 Gheflati A, Bashiri R, Ghadiri-Anari A, Reza JZ, Kord MT, Nadjarzadeh A. The effect of apple
vinegar consumption on glycemic indices, blood pressure, oxidative stress, and homocysteine in
patients with type 2 diabetes and dyslipidemia: A randomized controlled clinical trial. Clin Nutr
ESPEN 2019; 33: 132–8.
Letter from editor-in-chief
Dear Mr. Suadoni,
We appreciate you submitting your Letter to the Editor “Acetic acid does not reduce triglyceride levels
in overweight or obese adults, and it reduces them only marginally in those with diabetes." Your letter
(without your name) was sent to the authors of the article. The authors were very appreciative of your
careful review of the data and for identifying an error which they indicated occurred during the data
extraction and verification process. The authors contacted Ali and colleagues to request the correct
standard deviations so that they could amend their original forest plots. In addition, the authors of the
other included studies were contacted to confirm their results were published correctly. A formal
correction has been submitted by Kellow et al to be published in the Journal with an updated summary
results table. The corrigendum is attached for you to review.
To avoid redundancy, the Journal plans to publish only the corrigendum rather than the two letters and
the corrigendum. You would be given credit in the corrigendum for bringing this error to the attention
of the authors.
Please let me know if you have any concerns regarding this process.
Again, we so appreciate your bringing this to our attention.
Sincerely,
Linda Snetselaar, PhD, RDN, LD
Editor-in-Chief
Journal of the Academy of Nutrition and Dietetics
