Vinegar consumption can attenuate postprandial glucose and insulin responses; a systematic review and meta-analysis of clinical trials
Farideh Shishehbor, Anahita Mansoori and Fatemeh Shirani (2017) Diabetes Research and Clinical Practice https://doi.org/10.1016/j.diabres.2017.01.021

Background

What is vinegar?
The word vinegar comes from the French words vin egre, meaning 'sour wine'. It is produced from the fermentation of alcohol to acetic acid and includes cider, wine and malt vinegars.

Before 2016, only vinegars obtained from the fermentation of agricultural products were allowed to be named ‘vinegars’ in some EU Member States. However, from March 2016 both products obtained from the dilution with water of acetic acid, as well as vinegars obtained from the fermentation of agricultural products, can be marketed in the EU under the name ‘vinegar’.

Vinegar has been touted to be the cure-all for a range of health issues, including helping with weight loss, reducing the risk of type 2 diabetes, reducing inflammation in conditions such as arthritis and improving skin and hair. However, there is very limited research behind these claims. The lack of substantiation has led to all the submitted health claims on vinegar to date (e.g. weight loss and vascular health) being rejected by the European Food Safety Authority (EFSA).

The effect of vinegar on postprandial (after-meal) blood glucose appears to be the most researched, supported by laboratory studies which suggest acetic acid (the acid found in vinegar) may interfere with one of the enzymes that helps to breakdown starch to glucose (Ogawa et al. 2000). However, human intervention studies investigating the effect of vinegar on postprandial glucose have shown conflicting results.

Study Objective

  • To systematically review controlled human intervention studies on the effect of vinegar intake on postprandial glucose response.
  • Postprandial insulin response was considered as a secondary outcome.

Study Design

  • A systematic review and meta-analysis were carried out using a protocol constructed according to the Cochrane systematic review recommendations and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement.
  • Three major databases were searched – PubMed, Scopus and Web of Science – for controlled studies published between 2000 and 2016.
  • Studies were included that looked at the effect of vinegar on postprandial glucose and insulin. Included studies evaluated the total change in blood glucose, the glucose area under the curve (AUC), after a test meal with or without vinegar (control). Insulin AUC was also considered.
  • Study quality was assessed using the Jadad score.
  • Data from the included studies were used to carry out a meta-analysis using random effects models.
  • Heterogeneity analysis was performed using the Cochrane’s Q test and I2 index.

Characteristics of included studies

  • After screening, eleven cross-over human intervention studies, involving a total of 204 participants, met the inclusion criteria and were included in the meta-analysis.
  • Two studies used apple cider vinegar, one used wine vinegar, one used grape vinegar and the rest used white vinegar.
  • The doses of vinegar used ranged from 2 ml to 50 ml (median 20 ml).
  • Glucose and insulin AUC were assessed in response periods that ranged from 60 min to 300 min (1 – 5 hours).
  • Studies predominantly included those in healthy individuals and those with type 2 diabetes but also included individuals with type 1 diabetes (1 study) and those with insulin resistance (2 studies).

Main findings

Pooled analysis of the 11 studies showed a significant reduction in postprandial blood glucose AUC when participants consumed vinegar compared to no vinegar [estimated standardised mean difference (SMD) = -0.60, 95% confidence interval (CI) -1.08 to -0.11, p = 0.01]. 

However, heterogeneity was high (p<0.001, I2 = 80.2%), partly explained by the type of vinegar used and the degree of insulin sensitivity of the study participants (e.g. healthy or individuals with type 2 diabetes). 

Leaving out the one poor quality non-randomised study reduced heterogeneity and increased the effect size.

Eight studies reported insulin AUC data and pooled analysis showed a significant reduction in this outcome when participants consumed vinegar compared to no vinegar (SMD = -1.30, 95% CI -1.98 to -0.62, p<0.001). Again, heterogeneity was high (p<0.001, I2 = 86.1%).

Author conclusions

Results suggest that consuming vinegar (about 1 - 2 tablespoons) with a meal can reduce postprandial glucose and insulin responses in both healthy participants and those with insulin resistance or diabetes.

Limitations of the study

Small numbers
There were only a small number of studies included in the meta-analysis and the studies had small sample sizes (8 – 16 participants). Therefore, the positive findings of this meta-analysis would need to be confirmed in further studies using larger sample sizes. Moreover, for some studies, data was extracted from charts presented in the study papers, rather than raw data, which may have generated a source of error in the meta-analysis.

Significant heterogeneity
Both glucose and insulin AUCs had significant heterogeneity, meaning that there was a lot of variation in the studies being grouped together. Subgroup analyses suggested that some of this variability could be explained by the type of vinegar used and the health status of the participants. In a subgroup meta-analysis of studies using individuals with diabetes, impaired glucose tolerance or insulin resistance, the authors observed both greater overall effect size and significant heterogeneity in glucose AUC.

The glycaemic load of the test meal can influence the effect of vinegar on glucose metabolism. Therefore, some differences in the composition of the test meal used in the studies might have contributed to the heterogeneity.

Clinical relevance
The clinical relevance of the findings are unclear as the included studies did not seek to assess long-term aspects of glucose metabolism, such as HbA1c and insulin sensitivity.

It is also unclear whether consuming vinegar with meals would, in the long-term, have any health benefit, such as reduced risk of type 2 diabetes.

Mechanisms
More research is needed to understand the effects of vinegar (or most likely acetic acid) on glucose metabolism. However, evidence to date suggests the effects may be due to some combination of delayed or reduced carbohydrate absorption and increased insulin sensitivity and glucose uptake.


Relevance

Healthy individuals
In healthy individuals (no glycaemic disorders), blood glucose levels are tightly controlled within a normal range. This means that after a carbohydrate-containing meal, a rise in blood glucose levels will be coupled by a rise in blood insulin levels to bring blood glucose back to fasting levels within 2 hours.

There are some mechanistic studies linking postprandial glycaemia or glycaemic variability to the development of type 2 diabetes. However, there are many other risk factors to consider which have an impact on risk of type 2 diabetes. To reduce the risk of type 2 diabetes, there is a considerable body of evidence to suggest that losing excess body weight, increasing physical activity and eating a healthy, balanced diet which is high in fibre, may be effective (Diabetes UK, SACN 2015).

Type 2 diabetes
Several studies have shown that consuming small amounts of vinegar before a meal containing starchy carbohydrates may blunt the subsequent rise in blood glucose and as such, reduce the glycaemic response. However, the effect is small, when compared to medicines prescribed for type 2 diabetes and, therefore, vinegar should not be used as a replacement for current pharmacologic treatment options.

In diabetes management attenuating increases in post-prandial blood glucose can be achieved by selecting higher fibre, lower glycaemic index starchy carbohydrates (such as granary bread and porridge oats) rather than refined or simple carbohydrates. Interestingly, with low-glycaemic meals, vinegar does not appear to influence blood glucose (Liatist et al. 2010, Johnston et al. 2005), suggesting the potential benefit of consuming vinegar may only be relevant in certain contexts.

A healthy weight, good dietary patterns and regular physical activity are at the cornerstones of diabetes management. Currently there is insufficient evidence to recommend use of vinegar to manage diabetes.

Effect of action of vinegar on body weight
It has been suggested that vinegar can perhaps be useful in diabetes management or in the prevention of type 2 diabetes by helping with weight loss. Despite the wealth of internet claims supporting vinegar for weight loss there have been very few trials looking at this.

  • A randomised, double-blind, placebo-controlled trial (Kondo et al. 2009) assigned155 overweight adults (BMI 25 – 30) to receive a daily 500 ml beverage containing either 15 ml of vinegar (750 mg acetic acid), 30 ml of vinegar (1,500 mg acetic acid), or 0 ml of vinegar (placebo) for 12 weeks. Body weight and BMI, were significantly lower in both vinegar intake groups than in the placebo group, although the amount of weight loss was small – body weight and BMI were reduced by 1–2 kg and about 0.4–0.7 points over a week 12 period, respectively.
  • A randomised, double-blind, placebo-controlled trial (Park et al. 2014) assigned 78 overweight women (BMI ≥ 25) to receive either 200 ml pomegranate vinegar (1.5 g acetic acid and 700 μg ellagic acid) or a lactic acid placebo per day for 8 weeks. Both groups experienced small reductions in bodyweight and total fat mass but there were no significant differences between groups. However, the pomegranate vinegar group did show a significantly greater reduction in visceral fat mass than the placebo group (-10% vs. -2%).

The evidence for the effect of vinegar on weight loss is very limited, and has only shown a very modest effect.

Vinegar may modestly lower post-meal blood glucose and insulin levels although the mechanisms are currently not well understood and the clinical value of adding vinegar to meals needs to be further investigated in larger, longer-term, placebo-controlled trials.

 

References

Diabetes UK How can I reduce my risk of type 2 diabetes? [online] Available at: https://www.diabetes.org.uk/Preventing-Type-2-diabetes/Can-diabetes-be-prevented/ [Accessed 24.07.2017]

European Commission EU Register of Nutrition and Health Claims [online] Available at: http://ec.europa.eu/food/safety/labelling_nutrition/claims/register/public/?event=register.home [Accessed 24.07.2017]

Johnston CS, Buller AJ. Vinegar and peanut products as complementary foods to reduce postprandial glycemia. J Am Diet Assoc 2005;105:1939-42

Kondo T, Kishi M, Fushimi T, et al. Vinegar intake reduces body weight, body fat mass, and serum triglyceride levels in obese Japanese subjects. Biosci Biotechnol Biochem 2009;73:1837-43

Liatist S, Grammatikou S, Poulia K et al. Vinegar reduces postprandial hyperglycaemia in patients with type II diabetes when added to a high, but not to a low, glycaemic index meal. Eur J Clin Nutr 2010;64:727-32

Ogawa N, Satsu H, Watanabe H, et al. Acetic acid suppresses the increase in disaccharidase activity that occurs during culture of Caco-2 cells. J Nutr 2000;130(3):507–513.

Park JF, 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;8:274-281

SACN (2015) Carbohydrates and Health report [online] Available at: https://www.gov.uk/government/publications/sacn-carbohydrates-and-health-report [Accessed 24.07.2017]