What Is IIFYM?

IIFYM (If It Fits Your Macros) is a nutritional concept that simply means eating foods that meet your macronutrient needs.

Appealing to many because of its flexibility in food choices and seemingly lax eating patterns, the IIFYM theory is adaptable to formal diet plans or can be followed on its own.

IIFYM is based on the proposition that calorie counts are the decisive factor in determining body weight changes, and macronutrient manipulation decides how many calories we ingest. If this sounds somewhat familiar to you, it should. The roots of IIFYM are planted firmly in the Calories In – Calories Out theory. The premise of this simplistic theory states that in order to maintain a specific bodyweight, an individual must ingest an amount of food calories equal to the amount of calories burned each day. Should that individual begin eating fewer calories per day than he or she burns, weight loss will occur due to a caloric deficit. Conversely, if the individual starts to eat more, the result will be a caloric surplus and eventual weight gain.

IIFYM expands on the theory by adding macronutrient ratios to the equation. Here’s how it works:

  • You begin by accepting that regardless of whether an individual is looking to lose fat or gain muscle, the amount of protein that they consume each day must be sufficient enough to preserve and/or build muscle.
  • Protein, along with fats and carbohydrates, comprise the three macronutrient groups.
  • For an individual to meet his or her total calorie intake for a particular day – while ensuring that their protein intake for that day is sufficient – that individual must manipulate the fat and carbohydrate amounts they ingest to compensate for the increased protein intake. Not doing so will result in the consumption of too many calories.
  • An individual may choose any food that he or she wants to consume in order to reach their calorie total for the day, but the combination of those foods must meet the required macronutrient ratio. In other words, if an individual follows a 40/40/20 nutrition plan, 80% of his or her diet will evenly consist of proteins and carbohydrates, and 20% will consist of fats. That means 1000 calories should come from protein, 1000 calories should come from carbs, and 500 calories should come from fats. IIFYM says that what foods the individual eats to achieve those macronutrient totals is irrelevant, as long as they are reached.

This macronutrient manipulation is important to the theory because each macronutrient has varying calorie amounts. Proteins and carbs have 4 calories per gram, while fats have 9 calories per gram. If an individual has 50 grams of fats in a given meal, as opposed to someone who has 50 grams of carbohydrates, the former will intake 200 more calories than the latter. This variance illustrates how food choices will guide IIFYM users towards food selections that will promote fat loss, weight maintenance, or muscle gain.