IIFYM, or "If It Fits Your Macros," is a type of flexible dieting that helps people lose weight without feeling overly restricted. Rather than focusing on calories, IIFYM tracks macronutrients instead - namely protein, fat and carbohydrates. This allows for much more flexibility since all foods can be enjoyed as long as they fit into your macros for the day. Here are the basic principles of IIFYM, details on how to follow it and the pros and cons of this approach.Macronutrient is a bucket term for the three types of nutrients that make up the bulk of what we eat: carbohydrates, fat and protein. Our bodies require ample amounts of each to function properly. On the other hand, alcohol also provides calories (7 calories per gram), but it's not considered a macronutrient because we don't need alcohol to survive, unlike fat, carbs and protein. Macronutrients are augmented by micronutrients, aka vitamins and minerals, to meet all of our nutrition needs.