The term IIFYM, or If it Fits Your Macros, is a dieting approach used by weightlifters and bodybuilders to help them practice moderation. In a nutshell, IIFYM says that once your macronutrient needs are met, you can choose to fill the rest of your caloric intake with foods of your personal preference.
Unfortunately, a large number of weightlifters and bodybuilders misunderstand the concept. For instance, MachineMuscle.com says that "With IIFYM, the basic idea is that you can consume whatever food you like, not caring if the food is considered healthy or not, as long as you hit your macros for the day."
Official sources that explain the concept of IIFYM show that this isn't true--in fact, this is the opposite of what IIFYM advocates.
What is IIFYM?
To simplify it, IIFYM basically advocates eating the foods you love--such as ice cream, pizza or candy--in moderation. The original IIFYM document, which can be found on Bodybuilding.com, explains that IIFYM advocates meeting your macronutrient goals first, and then, if any discretionary calories are left, can be filled with the foods of your choice. Macronutrients are energy-yielding nutrients you need in mass quantities, such as protein, fat and carbohydrates.
In addition, IIFYM recommends meeting most of your macronutrient needs by eating whole foods, which are rich in micronutrients and are needed to maintain a person's health.
For example, let's take a weightlifter with a 3000 calorie intake. He needs 150 grams of protein, 250 grams of carbohydrates and 70 grams of fat per day. This means at the maximum, he needs 600 calories from protein, 1000 calories from carbohydrates and 630 calories from fat. To meet all of his macronutrient needs, he needs to consume 2230 calories total.
But, as you can see from the previous paragraph, his total caloric intake is more than that. Here's where the IIFYM protocol fits in. To help him reach his caloric goal, he can consume any type of food he wants, even foods that are typically considered "bad" or "dirty" by bodybuilders or weightlifters. As long as it helps him reach his calorie goals, and does not exceed it, it won't be detrimental or affect his strength or weight goals--whether that's to lose body fat or gain mass.
However, it is important to emphasize that you should meet most of your macronutrient needs by eating whole foods to ensure you're getting enough micronutrients. Micronutrients are nutrients you need in small quantities, which are responsible for a range of physiological functions necessary for your health. Many people often make the mistake of thinking IIFYM means you can eat whatever foods you want to meet your macronutrient goals, when that's simply not true.
Common IIFYM Fallacies
Since the IIFYM acronym was coined, many bodybuilders and weightlifters have misunderstood it, instead claiming it's an excuse to eat whatever you want. This is not factually supported.
For instance, let's go back to the MachineMuscle.com article about IIFYM. One of the claims the author makes is that with IIFYM, you can consume whatever foods your desire--that it doesn't matter if the food is healthy or not, as long as your macronutrient needs are met. It also goes on to say that the concept of IIFYM does not put any importance on micronutrients.
In the original IIFYM document, this was simply not stated. It specifically stated that you should meet most of your macronutrient needs with wholesome foods, which are rich in micronutrients. Nowhere in the document does it advocate eating whatever you want to meet your macronutrient goals. It's only after you meet your macronutrient goals when you can fill the remainder of your calories with foods of your personal preference.
In essence, IIFYM is a way to practice moderation in your diet--a way to eat more flexibly. This certainly isn't a recommendation to eat chips or doughnuts all day, which is contrary to what some bodybuilders or weightlifters believe IIFYM means.