The world of nutrition is awash in different diets and it’s safe to say that many of them hinge on rules surrounding what you can and can’t eat: nothing post-caveman for the Paleo diet, nothing from an animal for vegans, no fruit or grains on slow carb, and so on.
This is why the “If It Fits Your Macros” diet, also known as IIFYM, is seen by many as revolutionary. This method of eating allows you to eat literally anything from any food group — so long as it fits your macros. You’ll gain or lose weight if you’re consuming the right amount of calories, and you’re more likely to gain muscle and lose fat if you’re eating the right balance of protein, carbohydrates, and fat.
That’s IIFYM in a nutshell: keep your calories and macros in check, exercise appropriately, and your weight and body composition will improve. Want to make some buttery buffalo chicken? No sweat, just watch your quantities. Tempted by that coworker’s birthday cake? Have a slice, just deduct it from your daily calorie allotment.
For many, tracking calories feels very restrictive while for others, IIFYM is an unbelievable breath of fresh air after years of “clean food” diets consisting of chicken, broccoli, rice, and absolutely no pizza ever.
In this article, we’ve spoken to two registered dietitians to explore the following:
Editor’s note: The content on BarBend is meant to be informative in nature, but it should not be taken as medical advice. The opinions and articles on this site are not intended for use as diagnosis, prevention, and/or treatment of health problems.
What Is IIFYM?
- IIFYM emphasizes getting your intake of calories, proteins, carbs, and fats right as opposed to forbidding certain foods or emphasizing vitamins and minerals
Many diets simply block out certain foods. Good diets have a calorie goal that’s based on your goal and your activity level, and great diets tell you which macronutrients should fill those calories.
Here’s the most important information for people considering the diet.
There are three macronutrients: protein, carbohydrates, and fat.
- Protein has 4 calories per gram
- Carbohydrates have 4 calories per gram
- Fat has 9 calories per gram
All you have to do is find out what your numbers should be and fill them however you like.
It’s best to consult with a dietitian or a nutritionist, but many people have success following recommendations from their coach or just by getting a cookie cutter template online. Wherever you’ve found your diet, if it’s one that takes your body composition seriously then it’ll recommend a calorie goal and macronutrient goals, with the ratios likely changing based on what kind of exercise you’ve done that day.
Where do you start? If you only have a rough idea of your calories, most experts agree that it’s best to get between 0.75 and 1 gram of protein per pound of bodyweight. After that, experiment with ratios of carbs and fat until you find something that feels best for you. A 1:2 or 1:3 ratio or protein to carbs isn’t uncommon for active people and can be a useful place to start.
If you only have a rough idea of your calories, most experts agree that it’s best to get between 0.75 and 1 gram of protein per pound of bodyweight.
It’s essential to note that any calorie calculator will only give you a rough idea of your calorie goal and it takes a lot of trial and error to figure out what you actually need to consume. Patience is the name of the game when it comes to this approach.
[Work out your own diet plan with our macros calculator for fat loss and muscle gain!]
So IIFYM is both less strict than something like Paleo, because it allows you to eat any foods you want, but it’s also more strict because the foods you do eat need to be strictly tallied and their macros accounted for.
“At the end of the day, whether you gain or lose weight comes down to calorie balance, and the macronutrients you use to comprise your total daily calories can exert a significant effect on what kind of weight you gain or lose,” says New York-based registered dietitian Leyla Shamayeva, MS, RD. “Speaking broadly, athletes typically want to gain as much muscle as they can when they’re trying to bulk and they want to lose as little muscle as possible when they’re trying to cut.”
Here’s a pretty unremarkable template for an athletic male who is 6 feet tall and weighs 200 pounds.
Protein: 200 grams
Carbs: 400 grams
Fat: 67 grams
Some might recommend totally different macros, of course, but this is a pretty common approach for athletes: high protein, higher carbs, and not-that-high fat.
Whatever food you want to eat to fill those macros is up to you. There’s no “if it fits your micros” aspect — the IIFYM doctrine doesn’t technically say you need a certain amount of vegetables or Vitamin C.
Where Did IIFYM Come From?
The seed of the current wave of the IIFYM diet, it’s fair to say, was planted by Mark Haub, a professor of nutrition at Kansas State University.
Haub is the man who is best known for his famous “Twinkie diet.” For two months he ate a Twinkie every three hours along with corn chips, Oreos, and other processed snacks. He also consumed a protein shake and a multivitamin every day, practices that didn’t make quite as many headlines. The results? After two months of Twinkies every day, Jaub lost 27 pounds and improved his cholesterol and triglyceride levels to boot.
How can he have improved his body mass and his heart health on such a junk diet? Because as much as we want to believe a trim waistline will just come from eliminating candy or dairy or red meat or anything else, the fact is that for almost everyone, the only thing that matters for weight loss is calorie balance. (This is assuming you don’t have hormonal problems or other rare disorders that can interfere with a normal metabolism.)
After two months of Twinkies every day, Haub lost 27 pounds and improved his cholesterol and triglyceride levels to boot.
Haub ate about 1,800 calories a day and his daily calorie need to maintain his weight was 2,600. He therefore lost weight, and that’s good for your health and your heart. That’s all there is to it. The experiment received considerable media attention and renewed enthusiasm for flexible dieting.
Later, entrepreneur and fitness enthusiast Anthony Collova became well known for further popularizing the trend, launching a detailed macronutrient calculator at IIFYM.com to help curious dieters get started with their own experiment. People were successfully manipulating their body composition while making room for their favorite foods.
For many, the holy grail had been found.
How Should I Fill My Macros?
It’s up to you, but here are some foods you’ll probably find useful.
- Starchy vegetables
Note that a lot of these foods have combinations of macros — a ribeye is protein and fat, beans are protein and carbs, ice cream is carbs and fat.
[Many find it easier to track macros with shakes — check out our guide to the best meal replacement shakes!]
Pro: It Works Reasonably Well
- Provided a person is healthy and has no hormonal imbalances or other issues, counting calories is simply the most important component of gaining or losing weight
Calorie counting just works.(1) This is not to say that your calories and macros are the only things you need to be mindful of for your health but as far as body composition goes, it’s practically everything. It may indeed have the potential to impact your hormones or your sleep, as we’ll discuss below, but the fact is that calorie counting is the number one way to manage your weight. There’s no way around this, and embracing it — and the work it entails — is an extremely effective way to manage your weight.
[Interested? Then don’t miss these 6 tips to make counting your macros way easier!]
Con: There’s No Emphasis on Micronutrients
- Macronutrients matter for body composition, but micronutrients matter for sleep, recovery, and general health
“Your macros are important for reaching these goals, but it’s important to not forget about the ‘micros,’” says Shamayeva. “The more extreme factions of the IIFYM movement love to fill their days with hundreds, if not thousands of calories of junk food that happen to fit their macros. A calorie controlled diet can make room for treats, but if you go too far in one direction then you can easily find yourself missing out on nutrients that are also important for your goals.”
For example if you’re low on leafy greens, it’s not hard to run low on calcium and magnesium, which are really important for recovery.(2)(3) If you’re not getting enough Vitamin D or zinc, your testosterone levels may take a hit.(4)(5)
“Yes, your macros are critical for body comp, but don’t lose sight of the big picture. Moderation, as always, is still important.” – Leyla Shamayeva, MS, RD
“If you’re going to track macros because you like the freedom of choices, it’s important to realize that you should still choose healthy foods,” says New York-based registered dietitian Natalie Rizzo, MS, RD. “For example, you get a lot more pieces of fruit than candy within the carb allotment.”
Another important note is that while your body composition is almost entirely tied to your macronutrient and calorie intake, that may not mean it’s necessarily healthy. You might get leaner with junk food and steak, but most dietitians still warn against consuming too much saturated fat or sugar. It can be easy to forget that your diet may not be ideal for your long term health when it produces such great short term results.
[Make sure you keep track of these 7 micronutrients that are important for athletes.]
- Nothing is forbidden on IIFYM, which can reduce food stress for some followers
IIFM is often considered synonymous with “flexible eating,” which emphasizes the notion that you can eat “unhealthy food” in moderation and it won’t derail your progress.
It’s true that some IIFYM adherents have an enormous junk food intake, but what’s more often recommended by nutritionists is a limit of 10 to 20 percent of your calories from what you might call “empty calories.”
For many people, this flexibility makes it easier to adhere to their diet. IIFYM may receive criticism for seeming like a “free for all” but the truth is that judiciously making room for treats makes it a more sustainable practice.
Con: What Some Find Flexible, Others Find Restrictive
- Despite the food freedom, every calorie and macronutrient still needs to be monitored
It really depends on your personality type and the amount of time you want to put into managing your diet, but look: chronicling four sets of numbers (calories, protein, fat, carbs) for every single piece of food that enters your mouth can be too much work. It’s important to realize that while IIFYM has a lot of upsides, it completely depends on you knowing your calorie and macro intake every day.
“Macro counting can be too restrictive for some people,” says Rizzo. “Others, however, like it because it helps them eat in moderation but doesn’t limit food choices. There is no one standard macro ratio that works for everyone. The best way to figure out what macro ratio works for you is to consult a Registered Dietitian. From there, you have to be the type of person who likes to measure and track their food intake. Most people who count macros use a food scale and a nutrition app to make sure they are sticking to their numbers.”
IIFYM isn’t magic: it’s just one of the most popular reminders that calorie balance is fundamental to weight management. As is the case with most diets or, well, practically anything, this practice shouldn’t be taken to its extreme. Filling your calories with processed junk food will leave you hungry, unsatisfied, sleepy, and with diminished athletic performance.
The 80/20 rule remains ideal: know that whole foods are tremendously beneficial but know that if you’re eating in a way that will avoid nutritional deficiencies, it’s not the end of the world to drop some fast food into your macros.
Just make sure you track everything. If that’s doable, so is IIFYM.
1. Sacks FM, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med. 2009 Feb 26;360(9):859-73.
2. Zhang Y, et al. Can Magnesium Enhance Exercise Performance? Nutrients. 2017 Aug 28;9(9).
3. Flynn, A. The role of dietary calcium in bone health. Proc Nutr Soc. 2003 Nov;62(4):851-8.
4. Prasad AS, et al. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996 May;12(5):344-8.
5. Pilz S, et al. Effect of vitamin D supplementation on testosterone levels in men. Horm Metab Res. 2011 Mar;43(3):223-5.