If It Fits Your Macros (IIFYM) has taken the fitness and nutrition world by storm. But is this diet as effective as is often claimed? Or is it just another hype that’s here today but gone tomorrow?
In this article, you’ll discover the evidence-based truth. We’ll look at what IIFYM is and its effectiveness so you can decide whether this eating style is right for you. Let’s dive in!
What is “If it Fits Your Macros”?
IIFYM is more a lifestyle than a diet. It eliminates the labeling of foods as “clean” and “dirty” or “allowed” and “forbidden.”
Instead, IIFYM has you focus on hitting a daily target of calories and macros (protein, fat, and carbohydrates).
You base these targets on your personal situation and goals. For example, if you want to lose fat, you may have to consume 2,000 calories a day, made up of 150 grams of protein and the rest carbs and fat.
Where you get these macros from is up to you. So, you can get these 150 grams of protein from any source you want, such as chicken, beef, dairy, eggs, nuts, or even junk food like hamburgers or hotdogs.
You also decide when you want to eat your foods. This means you can fit your meals into your schedule and preferences and you’re not bothered by done-for-you meal plans.
Now, if you’ve been led to believe you must eat “clean” and snack on something every few hours, all this may sound too good to be true.
But it isn’t.
IIFYM is a proven way to help you build a “Hollywood hunk” body. What follows is a glance at the benefits this eating style has to offer.
The Benefits of IIFYM
Countless people have transformed their body and life with IIFYM. So, there must be something to it. Here are the four main benefits of this diet.
1. Excellent weight loss ROI
If you cruise Instagram for IIFYM advocates, it may baffle you to see how some of them sport a shredded figure while eating french fries and donuts. How can they lose fat and stay lean while eating junk food?
The reason is that when it comes to fat loss and muscle growth, eating “clean” isn’t as important as is often claimed. Instead, calorie intake is what matters the most.
- If you consume more calories than you burn, you’ll gain weight
- If you consume fewer calories than you burn, you’ll lose weight.
Because your main focus on the IIFYM diet is controlling your calorie intake, this eating style is excellent at helping you lean down.
Besides, on the IIFYM diet, you also make sure you get enough protein.
To show how effective managing calorie and macro intake can be for weight and fat loss, let’s look at an experiment by Mark Haub, a professor of human nutrition at Kansas State University.(5)
In 2010, he carried some excess pounds, and knowing the importance of macros, he decided to do an experiment.
For two months, he would only eat foods such as Twinkies, Oreos, Doritos, and protein shakes while hitting a protein target and maintaining an energy deficit of 800 calories a day.
In just two months, he lost 27 pounds and reduced his body fat from 33.4% to 24.9%.
2) May prevent weight regain
It’s often claimed that 95% of people who lose weight regain the pounds within a few months or years.
The primary reason for this is that most diets aren’t sustainable long-term. Following a bland and boring diet made up of broccoli with asparagus and chicken is just too restrictive for most people.
That’s where IIFYM comes in. Because this diet allows for flexibility in food choice, it’s more sustainable and thus tends to be better for long-term weight loss results.(6)
3) Can help you gain weight and build muscle
The most essential nutritional aspects for building muscle are calories and protein.
In other words, it helps you pack on muscle.
If you follow an IIFYM diet, your primary focus is on consuming enough calories and protein, which is why this eating style is excellent for you if you want to gain mass.
Later in this article, you’ll discover a six-step formula to figure out your ideal calorie and protein intake for optimal gains.
4) Relatively easy to adhere to
The more you forbid or suppress your desire for a particular food, the more likely you’ll crave it, as found by a 2010 study published in Eating Behaviors.(9) That’s why very restrictive diets tend to fail in the long run.
On an IIFYM diet, however, your food selection remains flexible, which makes it easier to maintain the diet. As a result, you’ll notice that you’ll crave junk food less because you don’t forbid it.
What’s more, contrary to restrictive diets, IIFYM fits well into your social life. You don’t have to decline a meatball-loaded spaghetti during a social gathering because you’re on a “clean eating” diet.
As long as you maintain your calories and macros, you’re fine to sample some junk food.
Not only does this freedom help you enjoy social events involving foods and drinks more, but it also makes it easier to stay on track with your diet long-term.
The Downsides of IIFYM
While IIFYM has many pros, it also has some cons. (All diets do.) Below are the four main potential problems of the IIFYM diet.
Please note that most of these downsides are a result of overeating junk food. If you were to eat primarily healthy, nutrient-dense foods, you would suffer these downsides less or not at all.
1) IIFYM may hurt calorie control
On the one hand, IIFYM can help you maintain your diet in the long run because it doesn’t forbid foods. But on the other hand, this eating style may make it harder to maintain a calorie deficit and thereby lose weight.
The reason is that many IIFYM dieters under-consume nutrient-dense, low-energy foods such as fruit and vegetables while over-consuming nutrient-poor, high-energy options like hamburgers and fries.
A study published in American Journal of Clinical Nutrition compared the difference in satiety between high- and low-energy density diets.(10)
For five days, twenty obese and non-obese subjects could eat as much as they wanted on a high-energy diet including foods such as bacon, roast beef, creamed potatoes, and chocolate cake.
Then, for another five days, the subjects could indulge to their heart’s content on a low-energy diet, including foods such as salad, baked chicken, broccoli, almonds, fresh fruit, and poached eggs.
The participants experienced fullness during the low-energy diet at an average of 1,570 calories. But to experience the same fullness on the high-energy density diet, they had to consume 3,000 calories.
That’s almost double the amount of energy!
This means that if you load your IIFYM diet with junk food just because you can, you’ll suffer more cravings, and thus it’ll be harder to control your calorie intake.
As a result, you’ll be more likely to overeat, which will stall your weight loss results or maybe even cause you to gain fat.
2) May hurt long-term progress by causing nutrient deficiencies
Following an IIFYM diet that lacks nutritious foods may cause you to become deficient in vitamins and minerals.
Not only do such deficiencies hamper your health, but they can also impede fat loss and muscle growth.
The reason is that many vitamins and minerals influence bodily functions such as hormone and energy production, protein synthesis, and fat oxidation.
An example is zinc. Getting enough of this mineral is vital for your figure for various reasons. One such reason is that zinc is needed for the production of testosterone – an essential hormone for muscle growth and fat loss.
Being zinc deficient can significantly lower testosterone levels and thereby may hurt fat loss and muscle growth.(11)
Besides, zinc is also crucial for your metabolism. Not getting enough zinc can downregulate metabolic rate. This makes it harder to lose weight because you’ll burn fewer calories each day.
One case study, for example, found that a zinc deficiency reduced the resting metabolic rate of a female by 527 calories a day.(12) Over a week, that equals more than one pound of pure fat in energy.(13)
Other examples of micronutrients that influence your figure are:
- Iron, which is crucial for energy production
- Calcium, which supports fat oxidation and metabolic rate
- Potassium, which reduces water retention
- Vitamin D, which is essential for hormonal health
Actually, all vitamins and minerals are in some way involved in your muscle growth and fat loss progress.
3) IIFYM may hurt health
If you look at the #IIFYM hashtag on Instagram, you’ll see many dieters pack their diet with a lot of junk food just because they can. That’s a terrible idea! For instance, research shows that:
- higher consumption of high-glycemic carbs increases the risk of chronic diseases such as heart disease, gallbladder disease, and breast cancer.(14)
- eating low-quality, processed meats may increase your risk of cancer.(15)
- the more trans fats we eat, the higher our risk of infertility, diabetes, and heart disease.(16)(17)(18)
That’s why IIFYM should never be an excuse to load up on junk food, no matter if it fits your macros. Ignoring this could cause severe damage to your health.
How to Use IIFYM for Optimal Fat Loss and Muscle Growth
If you feel IIFYM is right for you and your goals, use the following six-step formula designed to set up your IIFYM diet.
By going through the steps, you’ll figure out how many calories and macros you should eat each day for optimal results, based on your situation and goals.
Step 1: Calculate your BMR
Your basal metabolic rate (BMR) refers to how many calories you burn a day at rest. Calculating this number is the first step to figuring out your ideal calorie intake. Do so with the following formula (Harris-Benedict equation):
- Men BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
- Women BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
If you’re a male, weigh 78 kg, are 181 cm tall and 24 years old, here’s what your calculation would look like:
- (10 x 78) + (6.25 x 181) – (5 x 24) + 5 = 1,796
If you have troubles with the math, use this easy calculator to figure out your BMR.
Step 2: Adjust to activity level with an activity multiplier
You burn calories during physical activity. That’s why it’s essential to factor in your activity level when determining your calorie intake.
To do so, select the activity level below that best fits your current situation and use the activity multiplier on your BMR.(19)
- Sedentary (little or no exercise and desk job) = BMR x 1.2
- Lightly active (light activity with light exercise or sports 1–3 days a week) = BMR x 1.375
- Moderately active (moderately active with moderate exercise or sports 3–5 days a week) = BMR x 1.55
- Very active (very active or hard exercise or sports 6–7 days a week) = BMR x 1.725
- Extremely active (hard daily exercise or activity and physical work) = BMR x 1.9
If you have a BMR of 1,796 and you qualify as “moderately active,” your calculation would look as follows:
- 1,796 x 1.55 = 2,784
This number represents how many calories this guy or gal should eat a day to maintain current weight.
Step 3: Modify to your primary goal
For optimal fat loss, you must consume fewer calories than you burn. And for optimal muscle growth, you must consume more calories than you burn.
That’s why it’s important to adjust your daily calorie intake to your primary fitness goal. To calculate this number, modify the number of the previous step with the adjustment outlined below.
- If you want to lose fat, subtract 500 calories.
- If you want to gain muscle, add 300 calories.
- If you want to maintain your weight, don’t change your previously-calculated number.
Step 4: Determine your macros
By now, you know your daily calorie target. Your next step is determining from what macros you’ll get these calories. Here’s how to figure out your ideal macro intake.
The optimal daily protein intake depends on your body weight and primary goal.
To build muscle, get at least 1.6 grams of protein per kilogram of body weight daily (0.73 grams of protein per pound of body weight).
This amount optimizes muscle growth, as concluded by a 2018 meta-analysis published in British Journal of Sports Medicine.(20)
So, if you’re 80 kilograms, get at least 128 grams of protein. Since one gram of protein equals four calories, that equals at least 512 calories.
To lose fat, get between 1.8 and 2.7 grams of protein per kilogram of body weight a day (0.8 and 1.2 grams of protein per pound of body weight).(21)
This aids muscle maintenance and reduces hunger craving while maintaining room for calories from carbs and dietary fat.
Carbs and dietary fat
After you’ve set your protein intake, get the rest of your calories from carbs and dietary fat.
The ratio between the two isn’t essential to lose fat and build muscle – your focus should be on consuming the right amount of calories and protein.
That said, if you’re active (e.g., you’re a hard-training athlete or construction worker), it tends to be better to consume more carbs than fat.
And if you’re inactive, have an impaired insulin sensitivity, are overweight, or are a woman with polycystic ovarian syndrome (PCOS) or oligomenorrhea (a less frequent menstrual cycle), it tends to be better to consume more dietary fat than carbs.(22)
Step 5: Get at least 80% of your calories from healthy foods
Just because you can get ripped eating hamburgers, donuts, and french fries doesn’t mean you should.
To support your metabolism, hormonal health, and general health, get at least 80% of your calories from minimally-processed, nutritious foods.
Step 6: Track your calorie and macro intake
Congrats! You now know your recommended macro intake based on your situation, goals, and needs. It’s time to get started with your diet and hit these calorie and macro targets on a daily basis.
Just enter the foods you eat into the software, and it’ll calculate your calorie and macro intake for you.
Both apps are also available on Android and iOS so that you can always track your macros, no matter where you are.
The Bottom Line on IIFYM
IIFYM is a proven and tested tool to support your results, whether you want to lose fat, build muscle, or maintain your current figure.
And the reason IIFYM is effective is that you focus on the things that matter most: calories and macros.
That said, don’t abuse this newfound freedom by swapping all “clean” foods from your diet and replacing them with junk counterparts just because you can.
While calories and macros are most essential to build muscle and lose fat, they’re not the only thing that matters. Factors such as consuming the right amount of vitamins and minerals are also crucial to success.
What is your view on IIFYM? Or do you have any questions? Let us know by commenting below.
Certified Personal Trainer and Fitness Writer
Stefan de Kort is a certified personal trainer and fitness writer from the Netherlands. He focuses on creating science-based content, and always strives to present both sides of an argument. Alongside studying physical therapy at the Han University of Applied Sciences in Nijmegen, the Netherlands, Stefan has been ghostwriting for over seven years. Content he has produced for his clients has been published in publications like Men’s Fitness, Inside Fitness, Women’s Health, IRON MAN, and others. Besides, he has written four Amazon best-sellers for his clients. When Stefan is not writing and separating scientific facts from marketing mumbo-jumbo, he’s either giving personal training, working out, or exploring exotic countries.