Apple cider vinegar is a classic home remedy with traditional uses ranging from reducing age spots to easing arthritis. Only one use is scientifically proven—a specific effect on blood sugar that is beneficial for anyone with diabetes or prediabetes. Here’s what you need to know…

The scientific evidence of vinegar’s blood sugar benefits is strong and consistent. A recent statistical analysis of the 11 best studies concluded that consuming vinegar with a meal, compared with having the same meal without vinegar, reduced postmeal blood sugar spikes by an average of 40%. Why this matters: Much of the metabolic damage caused by diabetes—and prediabetes—is caused by these spikes.

Any vinegar works. Sorry, apple cider vinegar enthusiasts. It’s the acetic acid—in every vinegar—that blocks absorption of carbohydrates and helps clear blood sugar from the bloodstream.

Raw vinegar is best. Cooking can break down acetic acid.

You don’t need much. Studies suggest that two tablespoons of vinegar is a good “dose.” Less isn’t as effective—and more doesn’t add any benefit.

Timing matters. For the best effect on blood sugar, consume vinegar at or near the start of a meal.

Consider a premeal drink. For the most reliable effect, dilute two tablespoons of vinegar in a glass of water and drink it with the first bites of the meal. You can sweeten it with a non-nutritive sweetener such as stevia. Or try a commercial flavored apple-cider-vinegar drink made by Bragg.

Make your own vinaigrette if you’d rather incorporate vinegar into a salad or vegetable dish (after the vegetables are cooked). Why? Store-bought vinaigrettes often have more oil than vinegar. Mix your own using two parts vinegar to one part oil. Try red wine vinegar—it delivers acetic acid plus a healthy dose of cell-protecting polyphenols. Mustard counts, too—most mustards are rich in vinegar.

Start your next meal with a dish dressed with vinegar. And while you don’t want to be eating a lot of bread, if you do have a slice, instead of slathering it in butter, dip it in vinaigrette.