A tablespoon of red wine vinegar taken before bedtime may be an effective way to reduce belly fat. Several studies have pointed to the effectiveness of red wine vinegar as an appetite suppressant that can lead to weight loss, including a reduction in belly fat. These benefits may not be exclusive to red wine vinegar, however, and also seem to apply to vinegar produced from apple cider.
When red wine is fermented for long enough, it becomes vinegar. The active ingredient in red wine vinegar is acetic acid, which serves to keep food in the stomach for a longer period of time. According to a study published in a 2007 edition of the medical journal "BMC Gastroenterology," this causes a delay in the release of a hormone called ghrelin, which stimulates the sensation of being hungry.
Acetic acid can also contribute to weight loss by helping to keep blood sugar stable. A European study titled published in the September 2005 issue of the "European Journal of Clinical Nutrition" found that the acetic acid found in red wine vinegar can lower the glycemic index of some types of foods. According to this study, levels of both blood sugar and insulin were normalized for a minimum period of 45 minutes after subjects at a meal of bread and approximately 2 tbsp. of vinegar.
The acetic acid in red wine vinegar can cause a feeling of satiation for anywhere from 60 to 90 minutes after eating. According to findings of a report published in the May 2009 issue of the journal "Bioscience, Biotechnology, and Biochemistry," researchers from the Central Research Institute of the Mizkan Group Corp. found that animals that were fed a high-fat diet supplemented with acetic acid experienced a 10 percent reduction in fat production.
A report published in the November 2007 issue of the journal "Diabetes Care" indicated that taking vinegar at bedtime helps regulate blood sugar levels the next morning. The study also noted that "the anti-glycemic effect of acetic acid, the active ingredient in vinegar, has been attributed to reduced starch digestion and/or delayed gastric emptying." Because taking red wine vinegar on its own may not be palatable for many people, one suggestion is to mix a tablespoon of vinegar in a glass of still or sparkling water. Based on this assorted research, it does appear that a tablespoon of red wine vinegar before going to sleep can contribute to weight loss.