Apple cider vinegar before meals

What is behind it

The active ingredient is acetic acid, not the apple. It delays gastric emptying, carbohydrates reach the small intestine more slowly and blood sugar rises more gently. This has been measured in humans by ultrasound: in ten people with type 1 diabetes and gastroparesis, the gastric emptying rate after 300 g of rice pudding was a median of 27 % without and 17 % with 30 ml of apple cider vinegar (p < 0.05).

Further pathways under discussion are activation of the FFAR2 receptor on the enteroendocrine L cells with increased GLP-1 release, stronger AMPK activation and a lowering of free fatty acids in the blood. What has been measured in humans is mainly the end point, not the chain.

What the effect depends on

The most important limitation is not a methodological but a practical one: vinegar only works if the meal would have produced a steep blood sugar peak without it. In the only study that compares both directly, vinegar lowered the glucose iAUC with mashed potatoes and low-fat milk from 311 ± 124 to 181 ± 78 mmol·min/l (p = 0.04). With wholegrain bread, salad and low-fat cheese, nothing happened (229 ± 38 versus 238 ± 25; p = 0.56).

The question of the dosage form is just as clear. In a four-arm crossover with twelve healthy young adults, liquid vinegar lowered the 60-minute glucose rise by 31 % compared with water and with whole tablets (p = 0.040 and p = 0.049 respectively) – even though the tablets, at 1.50 g, contained more acetic acid than the liquid vinegar at 1.25 g.

The price: tooth enamel

The damage has nothing to do with metabolism but with pH. In an investigation using an electron probe microanalyzer, 30 types of vinegar were tested, and five of them were incubated for up to eight hours on enamel samples from human wisdom teeth. Raspberry vinegar led to a mineral loss of around 20 % down to a depth of 30 µm after four hours, organic vinegar to a loss of around 20 % at 45 µm and 16 % at 60 µm depth after eight hours – both significantly more than all other vinegars tested (p < 0.0001).

In addition, there are data from practice: in a 15-year-old girl, erosive tooth wear was attributed, after a detailed analysis of risk factors, to the daily consumption of a glass of apple cider vinegar, and in an investigation of 2,385 fourteen-year-old schoolchildren the odds ratio for tooth wear with vinegar consumption was 1.36.

What the studies show

The meta-analysis on blood sugar after a meal

Systematic review of controlled studies in which vinegar was given with a meal and the area under the glucose curve was measured. Pooled, the result was SMD −0.60 for glucose (95 % CI −1.08 to −0.11; p = 0.01) and SMD −1.30 for insulin (95 % CI −1.98 to −0.62; p < 0.001). The confidence interval for glucose ranges from a very small to a very large effect – the individual studies are correspondingly heterogeneous.

High versus low glycemic load

16 people with type 2 diabetes, divided into two groups of eight each, matched for age, sex and HbA1c, each on two days with and without vinegar. With the high-glycemic meal, the glucose iAUC over 120 min fell from 311 ± 124 to 181 ± 78 mmol·min/l (p = 0.04). With the low-glycemic meal, no effect was measurable.

What longer intake brings – and where the numbers diverge

A meta-analysis of nine studies with ten study arms and a duration of at least two weeks found total cholesterol −6.06 mg/dl, fasting glucose −7.97 mg/dl and HbA1c −0.50, the latter with a heterogeneity of I² = 91 %. No significant effect on LDL, HDL, fasting insulin or HOMA-IR. Notably, in apparently healthy participants, vinegar intake was associated with an increase in fasting glucose.

Where the number comes from — and where it does not

The widely quoted percentage on insulin sensitivity cannot be verified: the original 2004 paper is only accessible in Europe PMC and via the publisher as a title and author record, the abstract is locked. The figures from it circulating online cannot be used for this page. The samples are also consistently small elsewhere: eight people per group in the glycemic load comparison, twelve in the tablet comparison, ten for gastric emptying. These are acute test-meal experiments, not everyday data.

The meta-analyses on longer intake are extremely heterogeneous and in part implausibly large. A GRADE-rated dose-response meta-analysis of seven controlled studies in type 2 diabetes reports fasting glucose −21.93 mg/dl and HbA1c −1.53 – an HbA1c effect on the order of a medication, from seven small studies. Such values are not suitable as an expected value for individuals. And the tooth enamel data come from laboratory experiments on extracted teeth with incubation times of four to eight hours.

How to do it

What the studies actually did: 25 g of liquid vinegar with 5 % acidity, corresponding to 1.25 g of acetic acid, diluted in 35 g of water and taken immediately with the carbohydrate-rich meal – that is the dose behind the 31 %. A tablespoon corresponds roughly to this order of magnitude. In the gastric emptying study it was 30 ml of apple cider vinegar in 200 ml of water before breakfast over two weeks, in the longest randomized study in type 2 diabetes and dyslipidemia 20 ml per day over eight weeks. The often-cited 15 minutes beforehand are a convention: in the studies, the vinegar was taken immediately with the meal. More important than the timing is that the meal has a high glycemic load and that the vinegar is liquid.

Safety

The teeth are the most concrete risk: dilute well, then rinse the mouth with water and do not brush right away, because weakened enamel is mechanically sensitive. The advice to drink through a straw is plausible but has not been tested with apple cider vinegar. According to the data, tablets are ineffective and have caused a documented esophageal injury; the subsequent analysis of eight products found considerable differences in pH, acid content and labeling. There is also a case report of hypokalemia, hyperreninemia and osteoporosis with very large amounts. Apple cider vinegar is unsuitable for reflux, esophageal complaints and above all diabetic gastroparesis – there, the delayed gastric emptying is a disadvantage.

Sources

• Shishehbor F et al., Diabetes Research and Clinical Practice 2017
• Liatis S et al., European Journal of Clinical Nutrition 2010
• Feise NK, Johnston CS, Journal of Nutrition and Metabolism 2020
• Hlebowicz J et al., BMC Gastroenterology 2007
• Hadi A et al., BMC Complementary Medicine and Therapies 2021
• Willershausen I et al., Clinical Laboratory 2014
• Gambon DL et al., Nederlands Tijdschrift voor Tandheelkunde 2012
• Hill LL et al., Journal of the American Dietetic Association 2005