Ok firstly, the M here stands for Macros (as in macronutrients). A macronutrient is a type of food e.g. a protein, carb or fat.
Every decent diet you can buy that is training related should be macro based and it should tell you how many grams of protein, carbs and fats you should eat each day to make up your calories.
Now when you are dieting, the belief for most people, is that you should eat good single ingredient whole foods (e.g. 150 gram chicken breast = Protein:30 grams Carb:0 Fat:1 gram) and avoid processed foods that may not have the same nutrient density.
If someone is an advocate of IIFYM they may replace a certain amount of whole foods with strategically placed treats (for want of a better word) and implement a more flexible approach into their diet – I’ll give a couple of examples later.
How do people use it?
There are a few different approaches to IIFYM some may consider each right and wrong and each method will suit some better than others, each to their own.
When you receive your nutrition plan, your coach will tell you how many grams of protein, carbs and fats you should eat.
Option 1, you chose from a list of ‘clean foods’ and make your diet 100% squeaky clean with no processed foods.
Option 2, you give yourself a 10-20% calorie allowance, so for the most part your diet is squeaky clean, however you have something in there each day to keep you sane and avoid binging.
Option 3, your diet for the most part is quick and easy food, mostly processed, that you can pick up on the go, but you still managed to hit your protein, carb and fat targets each day.
What are the benefits?
The benefits are that it can lead to some people being more compliant on their diet. If they know they have cravings they can have a small treat each day without it escalating to an all out binge. On the other hand there are some people like the Pringle man and once they pop they cant stop.
What are the negatives?
Some of the foods may be less nutrient dense and you may miss out on some vitamins and minerals.
Some of the food may contain less fibre which will mean nutrient uptake will be lesser as well as decreased detoxification.
Some processed foods may also lead to inflammation in the gut.
Do I use it?
The answer is yes, but don’t be so surprised, i probably fall somewhere between option 1 and option 2.
Here are a couple of examples of how i use it in my diet.
Example 1.
Skittles (yes! I must be mental eh)
After I train, I would usually have an 100 gram serving of Smart Tec Complete Fx, This gives me, [Protein 27 grams, Carbs 49 grams, fat 3 grams].
If I am struggling that day (I’ll usually do this on leg day) then I will replace the ‘Smart Tec Complete Fx’ for ‘Smart Tec Whey Fx’, this gives me; [Protein 27g, Carbs 2 grams, Fat 3 grams].
This means I have 47 grams of carbs spare that I can get from 50 grams of skittles. It doesn’t blow my macros target and it doesn’t put me above my calories and it adds a level of sanity whilst dieting. I even do this coming up to a show and get my body fat as low as 4% ish. However in context, it is less than 10% of my calorie allowance one day of the week.
Example 2.
Say for instance you wanted to go out for food. Let's use Nandos as an easy example. You would look at the menu and figure out what you want, the nutrition value is online so have a look before you go.
Let's say you like the look of a double chicken breast fillet wrap, this gives you [Protein 65 grams, Carb 60 grams, Fat 23 grams]
This means that you would take a look though your meal plan and remove these amounts via other food sources in the plan, so if you had two chicken breasts, 300g of sweet potato and 30g of brazil nuts in your meal plan that day, you could remove it to make your wrap fit your macros.
Summary?
With diet, there is no right or wrong answer, you need to find what works for you, I have had clients eat 100% clean because they can, and on the other hand I have have had clients eat 100% foods that are easy on the go as they have busy jobs, work long hours and are always on the go from meeting to meeting.
In terms of results, consistency over time will always get you the best results so you need to find what works best for you and find the method that you will be able to comply with the most over the longest period of time.