IIFYM: What You Need to Know

Today we’ll be discussing the popular form of dieting known as “if it fits your macros” or “IIFYM” for short. Some people love it, some people hate it, but what does science say?

First, let’s break down exactly what IIFYM is. IIFYM (also known as flexible dieting) relies on the tracking of the three macronutrients: protein, carbohydrates, and fat. These are called macronutrients because you need to consume them in large quantities. Micronutrients (vitamins, minerals, trace elements, amino acids, etc.) conversely, are only needed in trace amounts. Optimally, IIFYM also includes tracking your micros, though this is often mistakenly overlooked by IIFYMers.

IIFYM generally starts with the calculation of your BMR (basal metabolic rate) to determine your total calories burned at rest during a day. There are many online calculators that will do this calculation for you such as this one (https://www.bodybuilding.com/fun/bmr_calculator.htm). This gives a starting place for determining your optimal macronutrient intake. Tracking your macronutrient intake also allows for indirect tracking of calories as each macronutrient has its own caloric value. 1g of protein = 4 kcal, 1g of carbohydrate =4 kcal, and 1g of fat =9 kcal. It should also be noted that 1 g of alcohol = 7 kcal. Therefore, tracking your intake of protein, fats, carbs, and alcohol allows for you to indirectly track your total calories for the day as well.


Once you’ve figured out your BMR, you can add or subtract calories based on goals, activity level, and current diet. If looking to gain weight you will need to eat more calories than you burn through your BMR+exercise. Fat loss occurs when you eat less kcal than you burn through your BMR+exercise. It is important not to make too drastic of cuts however in order to see continuous, long-term progress. This calculator (https://www.bodybuilding.com/fun/macronutcal.htm) will help to determine your optimal daily caloric intake.

The last step in preparing to start IIFYM is determining the percentage of daily caloric intake that each macronutrient should make up. Some popular percentages are shown below:



Note that while the above percentages may stay the same as you get closer to your goals, your totally caloric intake will need to change accordingly. If you’re looking for more help choosing your initial macros check out this calculator: https://www.bodybuilding.com/fun/macronutrients_calculator.htm.


Now all you have to do is enter your food into any popular macro tracker such as https://www.myfitnesspal.com/ and make sure you hit your macros.



The benefits of IIFYM are vast and attractive. For many people, they love the ability to eat anything they want, as long as it fits into their macros. Whereas many traditional diets would eliminate junk food completely, flexible dieting allows you to eat pop-tarts, donuts, candy, etc. as long as it fits your macros. It allows you to live a more normalized life and eat out with friends, while still following your diet. This makes it significantly easier to stick to for some people, because they do not have to entirely cut out foods that they love. For many gym-goers who are used to bringing tupperware full of food with them everywhere they go, this alone is enough to sell them on the diet. Scientifically, this is sound. When it comes to weight loss and caloric value, a gram of carbohydrate is a gram of carbohydrate, a gram of fat is a gram of fat, etc.


While calorically speaking any gram of carbohydrate is the same as any other gram of carbohydrate, a poptart will not keep you as full as an entire salad. Satiety (fullness) is generally an issue for IIFYMers, who often blow all of their carbs on a treat early in the day and then have “poverty macros” left for the rest of the day. This also makes it nearly impossible for them to hit their micronutrient goals as discussed earlier in this article. They will also likely miss out on their fiber goals due to a decreased intake of vegetables. An optimal IIFYM diet and “clean-eating” diet look very similar. Don’t let the instagram posts of IIFYMers eating ice cream and donuts fool you. They are able to eat these things, but in limited amounts and the rest of their days probably consist of little to no sweets. Sugar has been demonized by the media, however various studies have shown sugar to have no statistically significant effect on weight loss when calories are controlled. (1)  While sugar does not have a direct effect on weight loss, it does elevate insulin levels. Chronically elevated insulin will lead to insulin resistance, and can eventually cause type II diabetes. (2) Therefore, while sugar may not be solely responsible for weight-gain, sugar consumption should still be kept in check.


While many dieters find IIFYM easy to stick to, many others struggle with the idea of indulging in junk food but limiting yourself to what fits your macros. It may be easier for them to cut out junk food entirely. There is nothing about IIFYM that makes eating junk food a necessity, it is simply an option that some dieters may choose. Some may also find it annoying or stressful to track all of their food. However, it is essential if you’re serious about getting results from flexible dieting. That said, stressing over the accuracy of your estimations is largely pointless. Rather than stressing unnecessarily, just do your best to estimate and move on!


The Verdict:

Even given the above criticisms, what if someone were to hit all of their macros using vegetables, lean meat, and other “clean” foods? They’d likely hit all of their micronutrient goals, take in plenty of fiber, and feel plenty full throughout the day. While criticisms of IIFYM are vast, most are based on the fake, junk-food based posts that flood social media daily rather than the ideal IIFYM diet. When performed correctly, IIFYM allows you to eat more flexibly while still hitting your caloric, macronutrient, micronutrient, and fiber goals. It allows you to go to a friend’s house and eat what they made for dinner, rather than bringing your own dinner in a Tupperware container (we’ve all been “that guy” before). The flexibility of the diet is great and makes it easy to stick to for many people. The diet also allows for variability and longevity through the adjustment of macros and total calories. That’s not to say that IIFYM is the only diet out there that works, there are several others! However, IIFYM may be an easier, more sustainable diet for you. You may even be able to combine the principles of IIFYM with another diet in order to better monitor your progress!


Tips to Remember When Doing IIFYM:

  • Don’t stress about measuring exact quantities all the time. Don’t get me wrong, measure as closely as you can! However, if you’re going out to eat there’s no reason to bring a food scale to the restaurant. Do your best to estimate and move on. Remember, the point of this diet is to be more normal!
  • Do what you can sustain! Eating desserts is a great option that is made possible when doing flexible dieting. However, if you aren’t able to control your dessert intake after one bite, it may be best to stick to “clean,” healthy foods.
  • If you fall off the diet and blow your macros all in one meal, don’t give up for the day. Try to limit your consumption of excess calories for the rest of the day, and move on! One meal won’t halt your progress as much as one entire day can.


Have you tried IIFYM? Did it work well for you? Let us know in the comments below!


Alex Gaynor




  1. https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance



Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s