In small studies in animals and humans, vinegar has been shown to reduce the rise in blood sugar and insulin that normally occurs after a meal (Diabetes Care, 2010;33:e27; Agric Biol Chem, 1988;52:1311-1312; Eur J Clin Nutr, 2010;64:727-732). Taking two tablespoons of vinegar with an ounce of cheese at bedtime lowered diabetics' morning blood sugar levels (Diabetes Care, 2007;11:2814-2815). In another small study, vinegar improved insulin sensitivity to a high-carbohydrate meal in subjects with type 2 diabetes (Diabetes Care. 2004;27:281-282).
However, I cannot find any large studies to show that vinegar is an effective treatment for diabetes. The dietary treatment and prevention of diabetes is to severely restrict foods that cause a high rise in blood sugar. Vinegar does not prevent the expected extreme rise in blood sugar after diabetics eat high-glycemic foods (J Diabetes Complications, 2012;26:460-461 and Eur J Clin Nutr, 2010;64:727-732).
How Vinegar May Reduce Blood Sugar
Vinegar is made by fermenting a wide variety of plant parts:
• fruits such as grapes or apples
• grains such as barley, rice or corn
• sugar cane and so forth
The resulting vinegar is about 95 percent water and five percent acetic acid. The high acid content of vinegar may delay the rise in blood sugar by keeping food in the stomach longer (Eur J Clin Nutr, 1998;64:886-893; American Journal of Clinical Nutrition, 1996;64:886-893).
Sugar is absorbed almost immediately after it leaves the stomach and enters the small intestines. Many of the sugars that you eat are paired as double sugars (such as sucrose or lactose), but you can absorb only single sugars into your bloodstream, so enzymes in your intestines work to break the double sugars down. Acetic acid in vinegar can reduce sugar absorption by inhibiting these carbohydrate-digesting enzymes such as amylase, sucrase, maltase, and lactase (J. Nutr, 2000;130:507–513).
Vinegar may also keep enzymes from breaking down the long chains of sugars called starches. Starches that are not broken down in your intestines are called resistant starches, which travel to your colon where they are digested by bacteria. Thus, while mashed potatoes are digested so quickly that they cause a high rise in blood sugar, a potato salad prepared with vinegar might take considerably longer to be digested and so would cause a much slower and lower rise in blood sugar.
Avoid Taking Large Amounts of Vinegar
None of the studies have shown that vinegar offers diabetics prolonged worthwhile benefits. To have any significant effect on lowering blood sugar, a person would need to take continuous, large doses of vinegar that could irritate the stomach, causing belching, burning and nausea (Nutr Rev, 2014;72:651-661). The acidity of large doses of vinegar could also cause osteoporosis (Nephron, 1998;80:242-243) and erosion of the teeth (Ned Tijdschr Tandheelkd, 2012;119:589-591).
Vinegar has been proposed as a home remedy for many conditions, but nobody has shown that it is an effective treatment for diabetes, high blood pressure, leg cramps, osteoarthritis, jelly fish stings, warts, cancer, obesity or anything else. Don't depend on vinegar to lower blood sugar. Treating and preventing diabetes and losing excess weight requires permanent diet changes including avoiding the foods that cause high rises in blood sugar: sugared drinks, sugar-added foods and other refined carbohydrates.
Lifestyle changes to prevent and treat diabetes
I believe that you should treat vinegar as a food, not as a medicine. Some resources for diabetics tell you to drink a couple of tablespoons of vinegar in a glass of water, but I would never do that. If you decide that you want to add vinegar to your diet, use it in your food. Try the many different flavors of vinegars and experiment with salads and other recipes that include vinegar to taste good. Here are some of Diana's favorite recipes that use vinegar:
Southwestern Bean Salad
New Potato Salad
Zippy Black Bean Dip