The IIFYM Diet: A Flexible And Sustainable Lifestyle


‘If It Fits Your Macros,’ or the IIFYM diet as it’s colloquially known, may be your best bet for sustainable and healthy living.

Often, there’s a balancing act between a healthy lifestyle and one filled with enriching experiences.

Even though the two don’t have to be mutually exclusive, for a lot of people, it’s one or the other. But if you stick to the IIFYM diet, you’ll strike that ever elusive balance.

IIFYM promises a fulfilled and balanced lifestyle while maintaining a healthy and fit body. But as with any health regimen, to get the full value, you should familiarize yourself with some basics.

For example, do you have to rigorously stick to the numbers to achieve your goals? Does IIFYM’s effectiveness depend on what those goals are? Is there any research backing up the promised benefits?

The Idea

Unlike diets that work solely on calorie restrictions, you follow IIFYM by consuming a pre-set number of carbohydrates, proteins, and fats.

Hence, based on your pre-determined figures, you might consume a 30% protein, 45% carbohydrate, and 25% fat macro split.

How you arrive at these numbers is up to you, but luckily there are plenty of resources that help with getting the right mix. We’ll go over some of them later on.

The biggest advantage of the IIFYM approach is that you have total freedom over what you’re eating, unlike other diets that restrict your calories and your dietary choices.

So are there any recommended proportions? Does muscle gain require different macros than weight loss?

Luckily, there’s enough research guiding us in the right direction.

The Science Behind the Macros

In 2004, a University of Arkansas study1 examined bodybuilders’ nutrition intakes to determine if a particular macro combination leads to muscle growth.

First, the researchers confirmed what by now are truisms; “adequate protein must be available to provide amino acids for protein synthesis,” “a 15% positive energy balance should be available for muscle anabolism,” and “when ‘cutting,’ a 15% negative energy balance should be maintained for optimal muscle retention and fat loss.”

But that’s not what we’re here for. We want to know if different fitness goals require different macro proportions. Luckily, the researchers did too.

www.pixabay.comAfter examining subjects during the off-season and contest preparation phases, the study authors concluded that the “composition of diets for bodybuilders should be; 55-60% carbohydrate sourced to fuel the workout, 25-30% protein based for muscle synthesis and greater thermic effect, and 15-20% reliant on fat for optimal testosterone circulation, for both the off-season and pre-contest phases.”

The value of these findings lies in one reason above all others. While they demonstrate that it’s beneficial to hit your macros, they do so for both the off-season and the pre-contest phase.

Hence, a 55-60% carbohydrate, 25-30% protein, and 15-20% fat macro split works well whether your goal is maintenance, concurrent fat loss and muscle retention, or vice versa.

HIIT and the IIFYM Diet

Beyond bodybuilding, another study2 examined whether there’s an optimal macro breakdown for high intensity interval training.

Initially, the researchers observed that a “diet deficient in carbohydrate consumption causes a dramatic (approximately 10-30%) reduction in exercise capacity.”

This initial observation already validates a carb consumption threshold. But if carbohydrates are necessary, how many?

In conclusion, the study authors recommended a relatively high – 70% of total energy intake – carbohydrate intake. But, when considering that it’s specifically for high intensity interval training, the high figure makes sense.

Carbs and Bodybuilding

A 2018 study3 looked further at carbohydrate macros. Unlike it’s HIIT focused counterparts, this research focused solely on bodybuilding.

The researchers examined the practices of “high level natural bodybuilders – ‘natural through rigorous testing and polygraph tests by the British Natural Bodybuilding Federation.’”

This increased level of scrutiny ensured that findings were based on natural practices and that athletes and casual gym goers alike could use them as a template.

The study authors separated subjects into two groups; those who ‘placed’ in the top 5, and those who fell outside the ranks.

Researchers then compared both groups’ dietary habits from the competition’s preceding weeks.

While there was no specific set of numbers, they found a “greater carbohydrate intake in the placed competitors, which could theoretically have contributed towards the greater maintenance of muscle mass during competition preparation compared to the non-placed competitors.”

The difference between both placed and non-placed contest participants was 1.3 grams of carbohydrates per kilogram of body weight.

Hence, if professional bodybuilders vary their nutrient intakes to such extremes, a casual gym goer shouldn’t stress inexact macro levels.

Dietary Fat

Clearly, there’s consensus that protein and carbs are necessary, even if we don’t have specific numbers.

But what about dietary fats? A 2014 paper4 reviewed the available scientific literature to get a better idea.

Based on their findings, the researchers recommended the following for optimal cutting; “15-30% of your diet should come from dietary fats, 2.3-3.1 g/kg of lean body mass per day of protein, and the remainder of calories from carbohydrates.”

Making Sense of all the Numbers

Pouring over all the numbers and studies doesn’t make the IIFYM diet any more user-friendly. As always, that data has one purpose; a foundational understanding. We can exert all the discipline in the world, but if there’s no basis, we’re wasting our time.

Fortunately, the studies suggest that IIFYM is worth pursuing, just maybe not the way you initially imagined.

IIFYM isn’t an exact science, it’s a lifestyle.

As the studies suggest, hitting your macros is beneficial. But there are no exact numbers, instead, there are recommended ranges. 

The lack of specificity is good news. After all, if you’re interested in the IIFYM diet you’re probably looking for a more flexible health regimen. Fortunately, that’s exactly what a range allows.

A macro range has numerous benefits over adherence to precise digits. For one, if your meals are more or less balanced, you may hit your macros without even trying.

The average ‘meal’ will have a protein, accompanied by a carb and a dietary fat. By the end of the day, you’ll have several meals which – due to the wide recommended ranges – will fill up your pre-set macro goals.

That’s what the IIFYM diet really is, a balanced diet. So as long as you’re not binging exclusively on carbs all day, you’ll hit your macros anyway.


Another thing to keep in mind is that most of the available data examined bodybuilders and their macro intakes. How relevant are those numbers to the average gym goer though?

Yeah, you may be trying to cut, bulk, or maintain just like the pros, but is it your career? Are you competing?

Unlike someone whose livelihood depends on their body, numerous studies suggest that casual gym goers can flexibly hit their macros and still achieve their goals.

Hence, if you’re not competing and fitness is a part of your life, not your whole being, you don’t need exact numbers.

More, More, More

The IIFYM diet has another benefit, while you’re hitting your macro range, you’re fulfilling your macro minimum.

The ‘required’ numbers are forever elusive, but there’s little dispute that your diet must have some protein, carbs, and dietary fats.

Fortunately, if you’re following the macro ranges, you’re incidentally hitting these minimums.

After all, the macro ranges mentioned in the above studies are based on rigorous review of real-world athletes and competitors. Hence, whatever the recommended range, you can be sure that it fulfills the threshold without worrying.

Since the three nutrients are essential to a wholesome diet, IIFYM is useful as a ‘sum of its parts’ lifestyle. Even if you don’t believe in ranges and thresholds, you at least know that IIFYM makes your diet more wholesome and nutrient dense.


If hitting three macros is too much work, there’s a different approach. You can think of it as ‘IIFYM lite.’

This alternative concentrates on sticking to set protein and calorie figures.

Here’s the idea; since all carbohydrates and dietary fats have the same caloric value – four and nine calories per gram respectively – hitting a specific number of calories and protein will ensure that only a limited amount of calories come from carbs and fats.

For example, let’s say you’re on a 2,000 calorie a day diet and you want 150 grams of protein. Since each gram of protein is four calories, that’s 600 calories. This leaves you with 1,400 calories for your fats and carbs.

Here’s the best part, even if you’re not intending to hit those macros, there’s a great chance that fat and carbs will inadvertently fill those remaining calories. Why?

Unless you’re eating chicken breast all day, your meals will have a combination of the three nutrients. Further, if your protein is capped at a certain amount, the rest of your meals will have more the other nutrients.

The Power of IIFYM

The IIFYM diet succeeds where others fail because it’s flexible and sustainable.

It doesn’t have ‘bad’ or ‘good’ foods, and if you stay within bounds, you can have your ‘cheat meals.’

Instead, it has wide-ranging parameters that you may choose to fill in any way you like while staying on course to your health and fitness goals.



  1. Lambert CP, Frank LL, Evans WJ. Macronutrient considerations for the sport of bodybuilding. Sports Med. 2004;34(5):317-27.
  2. Maughan RJ, Greenhaff PL, Leiper JB, Ball D, Lambert CP, Gleeson M. Diet composition and the performance of high-intensity exercise. J Sports Sci. 1997 Jun;15(3):265-75.
  3. Chappell AJ, Simper T, Barker ME. Nutritional strategies of high level natural bodybuilders during competition preparation. J Int Soc Sports Nutr. 2018 Jan 15;15:4.
  4. Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr. 2014 May 12;11:20.



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