About four teaspoons of apple cider vinegar with a 93 g carb breakfast: blood sugar was lower at the one-hour mark, but over the full two hours the difference could have been chance

The idea is older than the wellness trend that made it famous. In 2005 a Swedish group at Lund University served 12 healthy volunteers white bread with and without vinegar, on separate mornings, and found that blood sugar rose less at 30 and 45 minutes when vinegar was added, and that people felt fuller. A Greek study in 2010 found that vinegar blunted the rise after a high glycaemic index meal of mashed potatoes in people with type 2 diabetes, but did nothing after a low glycaemic index meal of wholegrain bread. Since then 'a spoonful of vinegar before carbs' has become standard advice in blood sugar videos. A 2020 systematic review of 13 human studies of apple vinegar was less excited: some benefit was possible, but the evidence was 'insufficient' because most studies were small and at risk of bias.

The new trial, published in World Nutrition on 30 September 2026, comes from a dietitian at a city hospital in Tekirdağ and a family medicine department at Trakya University in Edirne, Türkiye. Thirty-eight healthy adults aged 18 to 50 were randomised into two groups of 19. After an overnight fast, everyone ate the same breakfast inside ten minutes: 135 g of toast, 36 g of processed cheese and 150 mL of peach nectar, about 508 kcal and 93 g of carbohydrate. That is close to twice the 50 g load used in most earlier vinegar studies, and the authors chose it on purpose, because real breakfasts are rarely that tidy. One group had 20 mL of apple cider vinegar at 5 to 6% acidity, diluted in water and stirred into the nectar. The other had water stirred into the nectar. Blood sugar was measured by finger prick before the meal and at 30, 45, 60 and 120 minutes. One person in the vinegar group withdrew before the test, and one in the other group was dropped because their fasting sugar was over 100 mg/dL, leaving 18 in each group, 19 women and 17 men, mostly in their late twenties and of normal weight.

The vinegar line sat below the other one at every point after the meal. At 30 minutes the average was 127 mg/dL with vinegar against 136 without; at 45 minutes 121 against 132; at 60 minutes 110 against 124; at two hours 100 against 104. Only the 60 minute gap, 13.9 mg/dL, passed the usual test of significance, and only just: its 95% confidence interval ran from 27.5 mg/dL lower to 0.3 lower, and the adjusted p value was 0.045. The total rise over two hours, measured as the area under the curve, was 25% smaller with vinegar, but that difference was not significant (p = 0.108), and the confidence interval stretched from a large saving to a small increase.

The figure that matters most for a reader is one the paper reports but does not put in its highlights. The statistical model asked whether the two groups' curves had different shapes over time, and the answer was no (group by time interaction p = 0.288). The paper's 60 minute comparison was then made anyway, at four time points with a correction for multiple tests. That is a legitimate way to explore where a difference might lie, but when the overall test finds nothing, a single time point just under 0.05 is a lead, not a finding. The authors' own conclusion is careful on this, saying vinegar 'may' lower glucose in the early phase 'but not net iAUC or the overall two-hour response'. The highlights box is bolder: 'significantly reduced blood glucose concentration at 60 min'.

Several design choices made a clear answer hard to get. Each person had only one breakfast, either with vinegar or without, so the comparison is between two groups of 18 different people, and blood sugar responses to the same meal vary a lot from person to person. The Swedish and Greek studies gave every volunteer both versions, which is far more sensitive; the authors say a crossover design should be next. Glucose came from a finger-prick meter rather than a laboratory analyser, and no insulin was measured. The trial was single-blind: the investigator who mixed the drinks knew which was which, and although the paper says the drinks were matched for taste and smell after pilot testing, 20 mL of vinegar is not easy to hide, and the participants were not asked which drink they thought they had. Women's menstrual cycle phase was not recorded. And there is a gap the paper does not explain: the ethics approval is dated February 2021, while the manuscript was received in June 2026, and the paper does not say when the volunteers were tested.

None of this makes the trial useless. It is randomised, it had a placebo, it reports confidence intervals and effect sizes, its limits are listed by the authors, and its numbers point the same way as the older studies. What it can't do is settle anything on its own. In healthy young adults whose blood sugar never went much above 136 mg/dL and was back near normal within two hours, the most it shows is that 20 mL of vinegar with a large carbohydrate breakfast might take the edge off the first hour.

Our reading: if you like vinegar on food, a dressing on the salad you eat with a starchy meal is a reasonable habit with some evidence behind it and little risk. As a treatment, the case is still thin, and it is weakest exactly where people hope for most: there is no good evidence here or in the 2020 review that it changes long-term blood sugar control. Drinking vinegar neat or taking it as tablets is where the reported harms are, from worn tooth enamel to a throat injury from a tablet. If you have diabetes or take medicine that lowers blood sugar, talk to your doctor before adding it as a daily routine. The study had no outside funding and the authors declare no conflicts of interest.