Hillary Duff drinks straight apple cider vinegar in the morning before dropping her son off at school. Fergie loves taking shots of organic, unfiltered apple cider vinegar because, as she explained in an interview with Glamour back in 2008, "For some reason I've noticed a difference on my stomach." Katy Perry once bragged to SELF that she's been drinking apple cider vinegar since she was a young girl, as per her mother's orders. So what's so good about apple cider vinegar that all these celebrities are raving about it? What are the benefits of apple cider vinegar, anyway?

It's not like apple cider vinegar is anything new. According to the editors at Cook's Illustrated, apple cider vinegar has been popular in the United States since the colonial era, and vinegars have been common to Western diets since the Middle Ages. And it's not like apple cider vinegar is made of any magical ingredients. As the name suggests, is made from yeast-fermented apple juice. As Harold McGee writes in On Food and Cooking: The Science and Lore of the Kitchen, apple cider vinegar "includes some of the characteristic aroma components of apples" because of its apple juice-base.

In fact, people have been drinking apple cider vinegar for the health benefits for nearly as long as it's been around. Even Hippocrates, the father of modern medicine who lived in Ancient Greece, used vinegar, though not necessarily that of the apple cider variety, to fight infections. These days, many people swear by apple cider vinegar as a weight loss supplement, and there is evidence that drinking apple cider vinegar before you eat makes you feel fuller—or, as researchers from Arizona State University put it in a review of literature, "increases short-term satiety." However, a 2004 review of weight loss supplements conducted by researchers at Harvard Medical School found that the efficacy of apple cider vinegar as a weight loss supplement was ultimately "uncertain."

Perhaps the most compelling benefit of apple cider vinegar is to keep blood sugar under control. A 2007 study published by the American Diabetes Association found that individuals with diabetes who drank vinegar before going to bed were better able to maintain stable blood sugar levels overnight. The reason this works is because acetic acid, the active ingredient in vinegar, inhibits the digestion of starches, and as Carol S. Johnston, associate director of the nutrition program at Arizona State University and author of the 2007 study, explained to the Washington Post, that prevents blood sugar levels from spiking. That undigested starch then feeds the good bacteria in your gut, which can help regulate some digestive issues. However, it should be noted that a lot of these effects can be seen if you eat any type of vinegar with acetic acid, not just ACV.

So can apple cider vinegar cure everything that ails you? Almost definitely not. But is it a good ingredient to keep in your pantry? Absolutely—especially since apple cider vinegar takes years to go bad, and it seems that some of the health benefits are real. And if nothing else, at least it tastes good!