Doughnuts have no purpose in your diet, providing loads of calories and little, if any, fiber, vitamins and minerals. Biting into one of those crumbly chocolate donuts that are perfectly coated with just the right amount of glaze surely pleases your palate, but it does nothing for your waistline.
A single glazed chocolate cake doughnut that is around 3 3/4 inches in diameter can have close to 250 calories. Depending on the recipe, some varieties -- like chocolate-frosted chocolate cake doughnuts -- can have as many as 370 calories. If you do come upon some that are smaller -- closer to 3 inches -- you'll get about 175 calories from a single doughnut.
Just because the base of the doughnut is plain doesn't make it a lighter option. A plain doughnut topped with chocolate frosting that is roughly 3 1/2 inches in diameter often contains at least 270 calories. But some varieties can have more than 300 calories each. Having a slightly smaller chocolate-frosted doughnut at 3 inches in diameter provides you with fewer than 200 calories.