If It Fits Your Macros: Everything You Kneed to Know About the Wildly Popular 'IIFYM' Diet

IIFYM, alternatively referred to as "Flexible Dieting," offers a much greater degree of freedom than your typical diet. But is it right for you?

If It Fits Your Macros—a.k.a. "IIFYM"—is one of the most popular diets on the planet.

Here's what it entails and the pros and cons of this unique eating approach.


If It Fits Your Macros—a.k.a. "IIFYM"—is one of the most popular diets on the planet.

Here's what it entails and the pros and cons of this unique eating approach.

What Are Macros?

Macros is short for macronutrients. There are just three macronutrients—carbohydrates, fat and protein. Aside from alcohol, these three macronutrients are the source of all calories we consume. Fat contains 9 calories per gram, while carbohydrates and protein both contain 4 calories per gram.

How Do You Count Macros?

The essential activity of IIFYM is counting macros. This entails keeping track of the exact number (in grams) of fat, protein and carbohydrates you eat each day. Counting macros isn't all that difficult, as these three categories are displayed on any and every nutrition facts panel. For products without a nutrition facts panel (such as fresh produce), finding the macros is a simple Google search away. There are many apps designed specifically to help you track your macros. The reason you count macros is to ensure you hit your pre-determined daily macro goals. These personalized numbers are the "your macros" in If It Fits Your Macros.

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How Do You Calculate Your Macro Allowance?

IIFYM.com offers a macro calculator they claim is "the most accurate macro calculator there is." It requires entering things such as your gender, age, height, current weight, goal weight, daily activity level, exercise habits and dietary goals (do you want to lose weight or bulk up, for example). I gave the calculator a run using my parameters (a 6-foot-6, 215-pound 26-year-old who's lightly active throughout the day but does difficult exercise five times a week) and opted for the "suggested" goal of consuming 15% fewer calories than my total daily energy expenditure. IFFYM.com then sent me an email with these macros:

via IIFYM.com


It's interesting that IIFYM.com also recommends a daily fiber goal—an addition likely brought about by one big potential drawback of the diet we'll cover later. So the plan recommends a daily amount of 180 grams of protein (equal to 720 calories), 81 grams of fat (equal to 729 calories) and 262 grams of carbohydrate (equal to 1,048 calories). Your ratio may differ, as it depends on many factors. Body type, in particular, seems especially important. For examples, endomorphs—people who are naturally broad and thick with a slow metabolic rate—are generally recommended by the International Sports Sciences Association to use a ratio of 35% protein, 25% carbs and 40% fat. The allure of the IIFYM diet is that if you hit your macro goals every day, you'll soon see changes in your body.

What are the Potential Benefits of IIFYM?

We've long known that extreme calorie-restriction diets often fail for a multitude of reasons—one being that they can trick your body to go into "survival" mode where it's exceedingly difficult to burn fat. The biggest benefit of IIFYM is the fact that it's one of the least-restrictive diets available. It allows for plenty of calories and no food is off limits. The one and only rule is that you "fit" your daily macros. This is why IIFYM is alternatively referred to as "Flexible Dieting." While other diets might allow for "cheat days," a concept we know can often do more harm than goods, IIFYM allows for little indulgences throughout the day. IIFYM also ensures that neither carbs nor fat are demonized, which can help develop a more logical, positive relationship with certain foods.

"The main strength of IIFYM is that it doesn't promote a narrow set of magical foods that dodge your fat cells (which of course they incinerate) and go straight to the muscle. Of course, this magic list of foods would be great—if it were true. But of course, that's all an epic load of bull****," noted nutrition researcher Alan Aragon, MS, told IIFYM.com in an interview. "With a high degree of flexibility in terms of food choices and meal setups, IIFYM can be individualized in order to maximize adherence to the plan. And ultimately, adherence is the make-or-break factor in any diet."

Exactly how you fit your macros may vary drastically on a day-to-day basis, which is an appealing amount of freedom compared to the crippling restrictions that come along with most diets.

What are the Potential Drawbacks of IIFYM?

The biggest potential drawback of IIFYM is simply eating a diet that's not filled with a variety of healthy, nutrient-dense foods. Since the only requirement of IIFYM is that you match your macros, that can open the door to some less-than-ideal dietary habits. For example, one forum poster said they were once able to fit their macros by eating a meal of fried eggplant, chicken alfredo and cheesecake and then eating nothing else that day. You'll still lose weight as long as you stay in a calorie deficit—remember the Colorado high school science teacher who lost 60 pounds eating nothing but McDonald's for six months?—but such habits could negatively impact your long-term health. This is likely why IIFYM.com has also introduced a daily fiber goal into the equation.

Many healthy foods—such as fruits, vegetables, nuts, legumes and whole grains—are high in fiber. Fiber is crucial to a healthy diet, yet the average American falls woefully short of the recommended daily value. According to the National Institutes of Health, teens and adults should eat between 20 and 38 grams of fiber each day, and men need more fiber than women. But the average American eats only 10 to 15 grams of fiber daily. Fiber helps break down foods for easier digestion, maintains good bowel health, lowers cholesterol levels and helps you feel fuller longer. High-fiber diets have been linked with positive outcomes such as a reduced risk of diabetes and heart disease. Adding a daily fiber goal to IIFYM is a great way to ensure the diet remains flexible but also still values plant-based foods high in antioxidants.

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