I personally love iifym because it gave me a great base that made life easier to "eat right" as opposed to a diet that I couldn't hold on to after it was over. You must first understand macronutrients before you apply iifym. Macros are the nutrients needed to fuel your body everyday. Whether you want to lose weight, maintain your weight, gain muscle, if you workout or don't workout. Science has proven that our body needs a certain amount of protein, fat, carbs and fiber every day. The amount you need may be much more than you've previously been eating, so sometimes you have to ease in to the new macro numbers. Let me give you am example
Before I started counting macros, I was counting calories. I shot for 1200 calories and would get the lowest amount of carbs possible. Usually between 50-75 carbs MAX! I was beyond exhausted, had no energy, no patience and was just skinny. Yes, I lost weight, but if I increased calories or carbs, I gained weight, so I always went back to this 1200 cal calculation to lose weight.
When I first calculated my macros (www.iifym.com) it wanted me to eat 1900-2200 calories and 150g of carbs!!!! I had to ease in to those calculations, but by about two weeks in, I was eating 2000 calories and 150g carbs and was getting leaner! I essentially ended up gaining weight, but because of muscle. I was losing more inches and getting leaner by eating more food!
What iifym means is the body actually does not differentiate between white carbs and brown carbs. For example, you have heard brown rice is better than white rice? Well, science says all carbs break down in to glucose the same way. (Keep in mind, brown rice will absorb slower keeping you fuller longer). The point is, you can lose weight eating white rice or white flour the same as brown rice or complex carbs. Some people have taken this literally and somehow poptarts have become the mascot food of iifymers, because they can "fit" the carb grams in to their days macros. Of course a poptart will not keep you as full as a bowl of brown rice.
This is the debate about clean eating vs "flexible dieting" Of course clean eating will fuel your body the best, hitting your macros with flexible dieting will still give you the same results and allow you to not feel guilty when you indulge in a Froyo, or glass of wine, or a poptart!!!
Although I usually fuel my body with nutrient sense foods, it is still great to be able to enjoy a treat and make it fit my macros, with the added guilt I once felt from eating these foods. As a result I have less time off the wagon and more time focused on eating healthy. Essentially eating the foods to fuel my body.
For more information and most accurate science based take in macronutrients, please refer to www.iifym.com as well as www.biolayne.com. Dr. Layne Norton has a bachelors in BioChemistry and his PhD in Nutritional Science. He has the most accurate account of the science behind fueling our bodies.