I remember reading about a certain group of people who were studied for their long lifespans. These people ate very low calorie diets but they combined them with excellent nutrition. The whole idea of Cron or calorie restriction is calorie restriction with optimal nutrition for the best results. I'd imagine if you restricted your calories but got your "nutrition" from pastries, transfats, etc. you'd cancel out any real benefits to be had by the calorie restricted diet.