"Nutrition A-Z" from the Dietitians of Canada website provides links to resources covering a range of topics related to healthy eating, among them a quick substitution guide called "Cooking 101."
Specific Dietary Concerns "Low-Calorie, Lower Fat Alternative Foods." from the U.S. National, Heart, Lung and Blood Institute "A World of Flour Beyond Wheat." from the Academy of Nutrition and Dietetics.