6. "Trans-fat-free" labels can be misleading After scientists proved how harmful trans fats are to the heart, most major food manufacturers scrambled to rejigger their recipes in order to label them "trans-fat-free." But though the new and improved products are free of these fats, many are still loaded with unhealthy saturated fat from palm oil, butter, or other sources.

It's also important to know that you can't always believe everything you read: Even those products that claim to be trans-fat-free can legally still contain up to half a gram per serving. While that may seem like a minimal amount, Harvard scientists found that women who consumed as few as 4 grams a day were three times as likely to develop heart disease. To spot hidden sources of trans fat, scan ingredient lists for partially hydrogenated oil or shortening.