If you swap your mayo for mustard you’ll save about 90 calories per tablespoon. And, here’s another reason to make that change… You’ll burn more calories, too. Scientists at England’s Oxford Polytechnic Institute found that one teaspoon of mustard can boost metabolism by up to 25% for several hours afterward. It’s thanks to the spices and phytochemicals in mustard. And the hotter the mustard, the bigger the metabolism boost.