When thinking about apple cider vinegar and its potential benefits, it's important to keep in mind that it is not a whole food, but rather a liquid derived from processing. While vinegar can be both delicious and nourishing, it is still not possible to consider it as a whole food, and we don't include vinegar on our website as one of our World's Healthiest Foods for this reason.
First and foremost, vinegar is usually highly acidic. The acidity of vinegar is typically related to its acetic acid content, and this content can vary fairly widely from vinegar to vinegar. For some individuals, especially those with stomach or digestive problems including acid reflux, vinegar might not be a desirable food component to include in their meal plan because it can serve as an irritant. I've seen some websites that recommend use of vinegar precisely because of its acidity. These websites suggest that vinegar can be used to help offset problems with acid deficiency in the stomach or other digestive problems. I'm not aware of any scientific research that supports this recommendation.
I'd group the claimed benefits of apple cider vinegar into two categories. First, there are some studies linking vinegar to improved control of blood sugar following a test meal. About half of the limited studies in this area have been conducted on genetically modified rats and do not provide any immediately helpful information about humans and the way we eat everyday. The human studies in this area tend to focus on delivery of a test food or test meal—typically highly processed and devoid of any whole, natural foods—that has been augmented with a dose of vinegar. While these studies do show a trend toward improvement in blood sugar response in the range of 2-20%, it seems reasonable to assume that a key problem here is the poor quality of the test foods and test meals.
Several authors have mentioned delayed stomach emptying as a likely mechanism for the impact of added vinegar on blood sugar response. If that hunch turns out to be correct, the idea of poor quality foods makes even more sense. Our stomach tends to empty too quickly if it is filled with highly processed, low-nutrient, fiber-free foods. I would expect whole, natural foods with excellent fiber content and nutrient variety to be more effective in improving blood sugar control than vinegar added to a meal that is composed of poor quality foods.
Second is the area of calcium absorption. This area has only been explored in animal studies so far, and both the doses and experimental conditions have been limited and difficult to match up with everyday consumption of vinegar on a salad or in a marinade. But the results of these studies showed the vinegar to increase the solubility of calcium within the intestinal tract of the test animals and to increase absorption in this way. Once again, I would question the value of these rat experiments for decision-making about whole, natural foods. From my perspective, the degree of calcium solubility in whole, natural foods that are properly handled and properly cooked is exactly what it should be.
Some websites tout the nutritional benefits of apple cider vinegar from a mineral standpoint. Based on nutrient database values, the amount of minerals in a tablespoon of this food is very, very limited and cannot be thought of as a significant contribution to any diet.
For more information on this subject, see:
Johnston CS, Buller AJ. Vinegar and peanut products as complementary foods to reduce postprandial glycemia. J Am Diet Assoc 2005 Dec;105(12):1939-42.
Johnston CS, Gaas CA. Vinegar: medicinal uses and antiglycemic effect. MedGenMed 2006;8(2):61.
Kishi M, Fukaya M, Tsukamoto Y, et al. Enhancing effect of dietary vinegar on the intestinal absorption of calcium in ovariectomized rats. Biosci Biotechnol Biochem 1999 May;63(5):905-10.
Liljeberg H, Bjorck I. Delayed gastric emptying rate may explain improved glycaemia in healthy subjects to a starchy meal with added vinegar. Eur J Clin Nutr 1998 May;52(5):368-71.
O'Keefe JH, Gheewala NM, O'Keefe JO. Dietary strategies for improving post-prandial glucose, lipids, inflammation, and cardiovascular health. J Am Coll Cardiol 2008 Jan 22;51(3):249-55.
Ostman E, Granfeldt Y, Persson L, et al. Vinegar supplementation lowers glucose and insulin responses and increases satiety after a bread meal in healthy subjects. Eur J Clin Nutr 2005 Sep;59(9):983-8.
White AM, Johnston CS. Vinegar ingestion at bedtime moderates waking glucose concentrations in adults with well-controlled type 2 diabetes. Diabetes Care 2007 Nov;30(11):2814-5.
Yamashita H, Fujisawa K, Ito E, et al. Improvement of obesity and glucose tolerance by acetate in Type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Biosci Biotechnol Biochem 2007 May;71(5):1236-43.