What's the IIFYM Diet?

Proponents claim it doesn't matter what you eat as long as it fits your macros. Nutrition Diva weighs in on this latest fad.

Monica Reinagel, MS, LD/N, CNS
4-minute read
Episode #386

Bethany writes: “Have you heard of this new approach to flexible dieting called IIFYM, which stands for If It Fits Your Macros? A lot of people seem to be doing it and I'm interested in what this is all about.”

Yup, this is a thing! There’s an IIFYM website, mobile apps and community forums. You can get ebooks and meal plans and pay for IIFYM coaching sessions. It seems to be particularly popular with the body-building crowd. But there’s nothing particularly new or revolutionary about this approach.

How Does IIFYM Work?

It starts the way most weight management plans start: You decide how many calories you should be eating, based on your personal statistics (such as your age, height, current weight and activity level) and what you’re trying to accomplish (that is: lose, gain, or maintain).

Then you decide what percentage of those calories should come from carbs, fats, and proteins. Again, this is based on your goals.  If you’re trying to “bulk up” with a lot of muscle for example, your protein percentage is higher. If you’re trying to slim down, your carbohydrate percentage is lower.

Although it may seem as if these percentages are highly scientific and precise, they’re not. Virtually every dietary philosophy takes some sort of stand on what percentage of your calories each of the three macronutrients should contribute—and they certainly don’t all come up with the same answer. That’s because the various answers are all derived from a pretty shaggy mix of scientific data, speculation, philosophical commitments, and wishful thinking.

Eat Whatever You Want?

One you have your macro prescription, you’re ready to start your IIFYM diet. And the rules are simple: You can eat whatever you want as long as it fits your macros. My macro prescription, for example, allots me 60 grams of fat. According to the IIFYM principles, the source of the fat doesn’t matter, as long as I don’t go over 60 grams of fat. If I want to get it all from heavy cream, that’s perfectly fine.

Likewise, I can eat my entire 250 grams worth of carbohydrates in the form of Swedish fish if I want to. The source of the carbohydrates doesn’t matter as long as I don’t go over my allowance. You get the idea.


About the Author

Monica Reinagel, MS, LD/N, CNS

Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes' most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation's leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.