Cookbooks may be partly to blame for Americans' expanded waistlines. Cornell University researchers analyzed changes in 18 recipes that appeared in all seven editions of the classic Joy of Cooking, which was published roughly every 10 years from 1936 to 2006. Recipes ranged from macaroni and cheese and beef stroganoff to brownies and apple pie. The results, published in the February 17 issue of the Annals of Internal Medicine, found that in the past 70 years, the average calories in a recipe increased by 44%, and the average calories per serving rose by 63%, because of a jump in calorie-rich ingredients and larger suggested portion sizes.