Claim: Eat fiber snacks and flatten your belly in 24 hours. Fiber acts like a sponge in the stomach, soaking up liquids and whisking them out of the body to smooth your tummy.
Truth: Eating enough fiber helps prevent constipation and reduces your risk of heart disease and other illnesses. "It can also help you lose weight in the long run, but it won't reduce your waistline in a day," says Susan B. Roberts, PhD, professor of nutrition at Tufts University. "You may even look bigger because fiber can bloat you."