Everyone has one friend who can nosh on bagels all day long and not gain an ounce, but if you’re not so lucky, your saliva may tell you just how many carbs you can (and should) be eating for optimal health. Dr. Oz explains that how a simple test with an unsalted cracker can help determine your “carb type.”

First, coat your mouth with as much saliva as you can. Eat one cracker, setting a timer for 30 seconds as soon as you begin to chew. As you chew, make note of how long it takes for the cracker to start to taste differently—it should be begin to taste sweet. Swallow it at this point, making note of the time.

If you notice a taste change in 14 seconds or under, you can tolerate carbs well, whereas 30 seconds (or longer!) means you should restrict carbs in your diet. Watch the video above to see how Rach did!

Want more tips from Dr. Oz and his daughter, Daphne? The daddy-daughter duo shares the perfect cold-fighting juice, a smoothie that helps morning sickness, and a genius tip to keep your salad from getting soggy!