http://paleodietlifestyle.com/what-about-vinegar/

"… vinegar isn’t very far removed from a whole food. It’s really just another product of fermentation, like kimchi or sauerkraut. Unlike these other foods, vinegar can be made from anything rich in carbohydrates: grapes, apples, rice, oats, or barley, to name a few. So while it’s probably better to avoid oat and malt vinegar just to be on the safe side (although most of the gluten gets destroyed during fermentation), there are plenty of Paleo “base foods” to choose from.

To make the vinegar itself, the “base food” is fermented into alcohol, and then the alcohol is fermented again into vinegar. The traditional recipe calls for several weeks to several years of fermentation at a low temperature, producing a liquid rich in cloudy wisps of probiotic bacteria, with one main cluster at the bottom called the “mother.”

If you start with a food that’s Paleo-friendly and then reduce its sugar content while adding probiotic benefits through fermentation, you’ll end up with a food that’s more beneficial, not less. The research we have backs this up: although there haven’t been a lot of studies, the ones that exist are mostly positive and point to some exciting and interesting health benefits.

Health Benefits of Vinegar

Vinegar contains significant amounts of polyphenols, antioxidant plant chemicals responsible for many of the anti-cancer and anti-aging benefits of vegetables, but most of its virtues come from acetic acid, which is formed as a by-product of the fermentation process. The best-studied benefit of this acid is its effect on glucose metabolism, or the ability to digest starch. In one human study, approximately 4 teaspoons of white vinegar decreased glycemic response to 50 grams of carbohydrate by over 30%. Other studies with various different types of vinegar found similar effects, especially in diabetic subjects.

Contrary to these findings, one 2012 study found that 4.5 teaspoons of vinegar did not alter insulin secretion or blood glucose in response to a milkshake containing 75 grams of pure glucose. Comparing their negative results to the benefits shown in previous studies, the researchers speculated that taking vinegar with a mixed meal, or with complex carbohydrates instead of pure glucose, might make the difference. Since most people eat their carbs as foods, rather than glucose shakes, this shouldn’t present a serious concern.

A helping hand with carbohydrate metabolism is already good news for diabetics, but it gets even better. One study found that taking vinegar with meals improved HbA1c (a long-term measurement of average blood glucose) in diabetic patients. And a study in diabetic rats showed that balsamic vinegar improved the expression of beta-cell ABCa1, an important cholesterol transporter that also affects the insulin response.

Relatedly, vinegar seems to have benefits for weight loss. One study assigned obese Japanese subjects to drink 0, 15, or 30 mL of vinegar a day, and found that in the vinegar groups, all the markers of obesity (body weight, BMI, fat area, waist circumference, and triglyceride levels) were lower than in the placebo group. Since obesity is so closely related to impaired glucose metabolism, it’s possible that this is just another effect of vinegar’s ability to increase glucose tolerance, but it may also be a separate benefit.

The other potential upsides of vinegar consumption are less well documented. In hypertensive rats, either vinegar supplements or straight acetic acid supplements reduced systolic blood pressure, although these results have never been duplicated in humans. Other rat studies found improvements in blood cholesterol (higher HDL and lower triglycerides and LDL) from daily vinegar consumption.

Vinegar also seems to have some anticancer properties, although laboratory tests have only been performed in rodents. The epidemiologic data for humans is conflicting: one study associated vinegar with a decrease in cancer risk, while another associated it with an increase.

Another study noticed that women who ate more oil and vinegar salad dressing had better heart health, even after controlling for the obvious fact that more salad dressing implies a higher vegetable intake.

Vinegar is also an old folk remedy for heartburn and acid reflux, although this has never actually been examined in a lab. However, the amount of anecdotal evidence is intriguing, and you’d definitely be hard-pressed to come up with a cheaper therapy to try."