What the Heck Are Macros? The IIFYM Diet Made Simple

IIFYM If It Fits Your Macros Diet
Photo: Pond5

Can you get lean eating cheeseburgers? The IIFYM (If It Fits Your Macros) diet says order up. Well, sort of…

While many diets are meticulous about which foods you can and can’t eat, how much you can have, and even when you consume it, for some people, the excessive restrictions can be a recipe for failure.

Instead, the IIFYM diet aims to get away from that — focusing on the three most important energy sources needed for our bodies to function properly. We’re talking about protein, carbohydrates and fat (aka macronutrients, or macros). How it works: Calculate your daily caloric needs, then split those calories into 40 percent carbohydrates, 40 percent protein and 20 percent fat, the ratio that IIFYM proponents say is the most effective for muscle growth, fat burning and consistent energy levels.

Keep in mind, there has been some debate on whether or not this diet is in fact more or less effective than “eating clean,” and if a calorie is a calorie regardless of the macro composition of the diet you’re following. However, some studies support it and numerous individuals have reported success with this diet. If you think IIFYM could work for you, here’s what you need to know.

RELATED: When Is It OK to Cheat? The Pros and Cons of Cheat Days

If It Fits Your Macros: The Overall Equation

The first step in the IIFYM plan is to figure out how much energy (i.e. calories)  your body uses in a given day. The amount of calories you burn just by virtue of breathing and performing other vital functions is known as the basal metabolic rate, or BMR. Below, use the calculators to find out a rough estimate of your caloric needs, based on the Mifflin-St. Jeor equation. Later you’ll adjust this number based on your activity level.



Next, you have to take into account how active you are. Leslie Bonci, MPH, RD, CSSD, LDN, Director of Sports Nutrition at the University of Pittsburgh Medical Center, points out that adding calories based on activity level is a guesstimate and not a precise science. That said, there are general ranges she recommends using for men and women:

  • Lightly Active = BMR x 1.3-1.4
  • Moderately Active = BMR x 1.5-1.6
  • Very Active = BMR x 1.7-1.8

Add in calories for your activity levels, and then divide those calories into 40 percent carbohydrates, 40 percent protein and 20 percent fat. Remember that you want every meal to fit this 40/40/20 set-up. If it fits into your macro ratio, you can feel free to eat it.

Everything from roasted chicken to pizza can be “diet-friendly” if it hits your macros. Sound too good to be true? We asked Bonci to further explain IIFYM and why it can work.

RELATED: 5 Apps to Track Macros on the Go

Personalizing the IIFYM Diet

“As a starting point, it is always a good idea to log what you’re eating, then analyze it according to a program and see what would need to change for you to eat in a 40/40/20 way,” says Bonci. This way you can tell if drastic differences will need to take place, or if you’re already close to the ratio, which is a good jumping off point.

Find yourself far from the 40/40/20 ideal? Consider a 150-pound, 5’9” male who exercises five times a week as an example.

“He might need 2,550 calories to maintain weight [based on BMR and activity level calculations above] for the amount of exercise he does,” says Bonci. Here’s how he’d break that down in order to eat according to IIFYM.

RELATED: 12 Brilliant Meal Prep Ideas to Free Up Your Time

Sweet Potato Fries
Photo by Perry Santanachote

Carbohydrate Intake

To figure out his carbohydrate needs, he’d apply the following calculation:

  • 2,550 (total calories) x .40 (percentage of calories from carbohydrates) = 1,020

A gram of carbohydrates is about four calories, so divide the calories by four and you get 255 grams of carbs. That’s how many he’d need every day.

In theory, IIFYM doesn’t care if you get those carbohydrates from sweet potatoes or ice cream. As long as it’s within your ratio, you’re good to go. In practice, you’ll likely work out harder and better with a belly full of spinach, though, rather than you will if you’re loaded up with buffalo mac and cheese.

Also, keep in mind that endurance athletes will need to adjust their carbohydrate levels accordingly. “For someone exercising five days a week I would probably recommend a daily carb intake of three grams per pound or closer to 450 grams of carbohydrates a day,” she says.

“The more activity one does, the higher the carbohydrate requirements will be. But there is something to be said for being selective,” says Bonci. “Going for whole grains and higher fiber carbs will help you get the most nutritional value.”

RELATED: The Ultimate Guide to Pre and Post-Workout Carbohydrates

Chimichurri Steak
Photo by Perry Santanachote

Protein Intake

Protein will have the same calculation as carbs:

  • 2,550 (total calories) x .40 (percentage of calories from protein) = 1,020

Again, every gram of protein is approximately four calories, so divide the protein calories by four and you get 255 grams. This can be consumed as lean turkey or chicken breast, but if you’re going to put down some double cheeseburgers, be sure to factor in the amount of fat from the red meat and the carbohydrates from the bun as well.

Bonci has some personal reservations on IIFYM’s protein recommendations. “I should note that the maximum recommended amount of daily protein intake according to the Dietary Reference Intake data from the USDA is 0.9 to one gram per pound bodyweight,” says Bonci. “This comes out to be 135 to 150 grams of protein a day for this 150-pound man, so we have the potential for a protein overload if he’s aiming for the suggested 225 grams suggested above.”

RELATED: This Is What 25 Grams of Protein Looks Like 

Avocado Salad
Photo by Perry Santanachote

Fat Intake

The calculation goes through a slight adjustment for fat:

  • 2,550 (total calories) x .20 (percentage of calories from fat) = 510 calories

Since each gram of fat equals about nine calories, that amounts to about 46 grams of fat every day, which, according to Bonci, might be low for some athletes. “Fat guidelines actually range from 10 to 35 percent of daily calories and 20 percent fat may not be appropriate or adequate for all,” she says. “If one does primarily endurance exercise, the body uses fat as an energy source, so needs are higher.”

While you are allowed to on IIFYM, eating sticks of butter wrapped in bacon for your fat intake isn’t recommended. “Focus on good fats: nuts, nut butters, seeds, seed butters, olive oil, avocados.”

The beauty of IIFYM is the flexibility — you can adjust the ratios to fit your caloric needs and you can choose from any food to fill those needs. As an athlete, you’ll likely stick with complex carbs, lean protein and healthy fats, but IIFYM won’t put you on a guilt trip for the occasional pizza dinner or fried chicken lunch.

Originally posted December 2014. Updated July 2015. 

Related Posts

Scroll to Top