For many people, it's hard to imagine a sandwich or burger without good, old-fashioned mayonnaise. However, there's no denying the appeal of mustard, especially since a tablespoon of mayo will set you back at least 110 calories and 11 grams of fat. Truth be told, this popular condiment is chock-full of fat and calories. Even the light version tacks on 50 calories and 5 grams of fat per tablespoon. Mayo is basically made of oil, egg yolks, lemon juice or vinegar. In fact, 65 percent of most mayo concoctions are derived from fat. From sandwiches to salads, many people use this high-fat condiment as a staple. It goes without saying that it would be smart to opt for healthier substitutions. The lower-fat or fat-free versions of sour cream, plain yogurt or pureed cottage cheese can all work to take the place of mayonnaise in tuna salads, potato salads and other recipes that call for the condiment. For sandwiches, whip up a batch of this mock mayo.