Abstract: The aim of this review is to summarize the effects of vinegar on glucose and lipid metabolism. Several studies have demonstrated that vinegar can help reduce hyperglycemia, hyperinsulinemia, hyperlipidemia, and obesity. Other studies, however, have shown no beneficial effect on metabolism. Several mechanisms have been proposed to explain these metabolic effects, including delayed gastric emptying and enteral absorption, suppression of hepatic glucose production, increased glucose utilization, upregulation of flow-mediated vasodilation, facilitation of insulin secretion, reduction in lipogenesis, increase in lipolysis, stimulation of fecal bile acid excretion, increased satiety, and enhanced energy expenditure. 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.
Alex’s Notes: Words cannot describe how embarrassingly happy I was when I say this study summarizing the effects of vinegar on glucose and lipid metabolism. I mean, the stuff has been used since Hippocrates’s time as an antifungal & antibacterial. Now, there is strong evidence to support its use as a general health tonic.
The effects on glucose metabolism are the most well-known via the media sensationalism and internet gurus. Unlike many things, however, this one actually has strong scientific backing. Vinegar administration before a high-carbohydrate meal was found to improve not only postprandial glucose and insulin fluxes in insulin-resistant individuals but also whole-body insulin sensitivity by 34%! Interestingly, in that same study, type-2 diabetics only improved insulin sensitivity by 19% and had no statistically significant reduction in glucose and insulin levels, suggesting that vinegar is most beneficial when pancreatic function is preserved. Along these lines, numerous studies in healthy persons have found a single dose of vinegar prior to a starchy meal reduces postprandial glucose and insulin. These effects are not seen with consumption of monosaccharides or when vinegar is neutralized with sodium bicarbonate, suggesting that vinegar acts through both the digestive process of starch and through its acidity. Moreover, the effects are more pronounced when vinegar is ingested immediately before eating as opposed to five hours beforehand.
Why you good for blood sugar Mr. Vinegar?
There are several proposed reasons that vinegar helps control blood sugar. For one, the main component in vinegar is acetic acid and its presence may stimulate acidic sensors within the small intestine, which would slow gastric emptying. As the authors explain,
“Stimulation of these intestinal receptors by acids stops an effective gastric propulsive activity. However, acidity should cause the release of secretin and bicarbonates, which would neutralize the acid and promote gastric emptying. A further portion of acid gastric contents would be transferred to the duodenum, and the process would be repeated. The rate of gastric emptying is therefore determined by the amount of acid transferred from the stomach to the duodenum and by the rate of secretion of pancreatic and duodenal bicarbonates, which neutralize the acid.”
Another mechanism may be the suppression of carbohydrate absorption through the suppression of post-transcriptional disaccharidase processing. In other words, the enzymes that breakdown disaccharides such as sucrose, lactose, and maltose are inhibited, leading to a reduction of carbohydrate absorption and thus a reduced blood glucose and insulin response. This would definitely explain why vinegar’s beneficial effects aren’t seen with the consumption of dextrose, but strongly evident with starch.
Then there are studies that show vinegar ingestion before bed resulting in reduced fasting glucose concentrations, which suggests an effect of vinegar on glucose production by the liver. In a nutshell, acetate is converted to acetyl-CoA within the liver, resulting in a simultaneous production of AMP that leads to activation of the AMPk pathway, which then inhibits several key glucogenic enzymes that will result in a reduction in fasting blood glucose levels. On a related note, acetic acid is also able to suppress glycolysis in skeletal muscle, as well as possibly increase skeletal muscle expression of myoglobin and GLUT4. Thus, vinegar may elevate glucose uptake by skeletal muscle and lead to enhanced glycogen repletion and storage. Finally, vinegar may enhance blood vessel function and blood flow through stimulating nitric oxide (NO) release by the endothelium.
Fat what say you?
Vinegar doesn’t stop partying with sugars, although its effects on lipid metabolism are much more split. A bunch of animal studies show conflicting results, and the few human studies have important limitations. For instance, a double-blind, placebo-controlled trial conducted by a vinegar manufacturer studied the effect of either 15 mL or 30 mL of vinegar in 155 obese Japanese subjects during a 12-week period. Both vinegar doses resulted in a decrease in serum triglyceride levels, but the results also showed a decrease in body weight, body fat mass, waist circumference, and body mass index in both vinegar groups in a dose-dependent manner. So what decreased the triglycerides; the vinegar or weight loss? In another study of 19 hyperlipidemia subjects, which was not placebo controlled, the consumption of 30 mL of apple cider vinegar twice a day for 8 weeks was effective in reducing the serum levels of total cholesterol, triglycerides, and LDL-C. Finally, a prospective, randomized, double-blind, placebo-controlled clinical study in 114 nondiabetic subjects who consumed 30 mL of apple cider vinegar for 8 weeks found no evidence that vinegar affected triglycerides, total cholesterol, LDL-C, or HDL-C. But of course, one-third of the subjects were on statin or fish oil therapy. Confounding variable much?
Regardless of the inconsistent results, the effects of acetic acid on blood lipids could be through the inhibition of cholesterol synthesis and lipogenesis within the liver through the previously mentioned activation of AMPk. Moreover,
“The addition of vinegar to a high-cholesterol diet increases the expression of the acyl-coenzyme A oxidase (acox) gene, suggesting that acetate might increase fatty acid oxidation, thereby attenuating the cholesterol-mediated increase in the hepatic triglyceride concentration and, finally, suppressing the elevation of plasma triglycerides.[52, 57] Finally, acetate treatment has shown to promote the fecal excretion of bile acid, possibly through the stimulation of secretin release.”
So is it safe?
Very good question and the answer is YES! That Japanese study mentioned earlier reported no adverse events, although in another trial of 27 type-2 diabetics consuming either commercially made pills containing 15 mg of acetic acid, pickles containing 1400 mg of acetic acid, or vinegar containing 2800 mg of acetic acid, 50–56% of participants who consumed pickles or vinegar manifested at least one adverse event (acid reflux, burping, flatulence, or changes in bowel activity) at week 6 of the trial, as compared with 11% in the reference treatment group who consumed the pills, but this difference was not significant.
You have no reason not to consume about 2 tablespoons (30mL) of vinegar with each meal. I prefer to add it to club soda with some stevia to remove the tartness. It doesn’t matter if the meal is dominated by carbohydrates or fats, vinegar will assist in their metabolic disposal. Also, although it may slow transit time, I would still encourage 30 mL be taken post-workout with your protein shake as the benefits to blood flow, skeletal muscle insulin sensitivity and glycogen storage outweigh any minor increase in digestive time.