It has not been definitively proven that vinegar causes weight loss in humans on its own. Despite this, vinegar can be a healthy way to add some flavor to bland meals without adding lots of calories.
The myth that vinegar causes weight loss came from a study where some mice were given the main ingredient in vinegar while others were given water. The mice were fed the same diet, and at the end of the experiment, the mice given the main ingredient of vinegar had 10 percent less body fat. While these results look promising, the body of a mouse is much different than that of a human, and more tests are needed to establish a link between vinegar and fat loss.