Really good article explaining IIFYM - it's short but addresses the main concepts.

http://www.muscleandfitness.com/nutrition/lose-fat/everything-you-need-know-about-iifym?


"It’s late in the afternoon and time for your fourth meal of the day: Six ounces of grilled chicken, one cup of rice, and a mix of green veggies. Sound familiar? And monotonous? Even the most dedicated bodybuilder or physique competitor dreads the same old routine. Hence, flexible dieting, or "If It Fits Your Macros" (IIFYM), has taken root in fitness culture and gone mainstream. IIFYM is a based on the principle of “calories in, calories out” which means you won’t gain weight, regardless of food choice, so long as you don’t exceed your total caloric needs for the day. For the fitness enthusiast, IIFYM takes this concept a step further by taking macronutrient requirements for building muscle and fat burning into account.

Suddenly, pizza, burgers, and ice cream are all back on the menu. But there’s a lot you need to know before you dive in. Below, we’ve culled five crucial points from our panel of experts. If you decide that IIFYM is right for you, you can calculate your daily needs using the Muscle & Fitness food pyramid. Then, be prepared to write down everything you eat and calculate the macros throughout the day; IIFYM won’t work for you if you’re not careful about measuring your portion sizes.

1) Body Composition and Health are not the same thing: Just because someone looks healthy, doesn’t necessarily mean that they are healthy. Health is more than a six-pack and a nice pair of biceps. But while the premise of IIFYM might seem unhealthy, that’s not necessarily the case, says Alberto Nunez, a bodybuilding coach at 3DMJ (3D Muscle Journey), and perhaps the web’s best example of IIFYM taken to its most successful extreme. Nunez says IIFYM, when done properly, fulfills all the requirements of a balanced, healthy diet first. The junk food comes in later. “If you can track those grams of fat, carbs and protein accurately, I don’t think [some junk food] is necessarily going to effect body composition for better or for worse,” says Nunez. “I know that for my athletes, we make sure that they fulfill a certain amount of fruits, vegetables and fiber intake. Once you fulfill those needs, it’s nice to have other food that isn’t typically in a bodybuilder’s diet.”

2) You need self-control: Pictures of pizza, pop tarts and other delicious treats plague the IIFYM hashtag on Instagram, giving the viewer the wrong idea. Most people think that those who follow IIFYM use it to justify eating habits that are sub par. In reality, those foods only make up a small portion of a flexible dieters daily intake. “There is a lot of misconception around food choices in general,” says Anthony Covella, owner of IIFYM.com and myoatmeal.com. “Obviously if we eat too much dessert we run the risk of going over in our carbs and our fats. If we eat too much pizza or wings we are going to hit our fat first. We have to incorporate micronutrient dense foods that are nutritious ... clean foods.”

3) Take it slow: Change can be scary. There is a certain safety in sticking with what you know, but sometimes change can be good. Nunez suggests slowly easing your way into the lifestyle change. “The thing with flexible dieting is there is going to be a learning curve, but once you have it down you are going to have a diet that is just as effective as any nutritional menu out there, if not better than. It is going to be customizable to your situation,” says Nunez. “So I would say have poise and don’t leave the pocket. Once you learn the system, then you will be really glad you did.”

4) Eat mostly whole foods: Mother Nature isn’t stupid. All of the foods that are considered “bad” for us are of our own creation; sugar and fat-laden processed foods — while all of the foods that are full of nutrients and minerals are found in nature. While IIFYM promotes diversity in one’s diet, you need to make sure that your food choices are coming mostly from the right sources. Nate Miyaki, a ISSA certified specialist in sports/fitness nutrition, is a proponent of what he refers to as an island style diet; eating animal proteins, fruits, veggies and starches such as rice and potatoes. “Emphasizing your diet on whole foods automatically improves most peoples’ numbers,” says Miyaki. “If you’re eating the typical highly refined American diet, you’re eating 3,000 calories and you don’t even know it ... and it’s just unfunctional nutrients. If you switch to whole foods, you can get the same amount of functional nutrients and feel more satiated with half the calories. It is food choices that are important for those reasons.”

5) IIFYM isn’t an easy way out: On paper, the idea of IIFYM seems like every dieters dream — the ability to eat what you want when you want. But like anything else, you get out what you put in. So while you are allowed dietary freedom, IIFYM still requires dedication. “I think the biggest [misconception] is the fact that it’s for competitors or physique enthusiasts who are trying to look for an easy way out of a lot of hard work,” says Nunez. “I think in reality, flexible dieting if anything lends for you to be a bit more precise. You don’t just exchange foods, but you break down your calories into macronutrients.”