What is IIFYM? Everything You Need to Know

What is IIFYM? Everything You Need to Know

“IIFYM” is an abbreviation for “if it fits your macros”, that is often used in the bodybuilding world. Macros stand for macronutrients. There are 3 main macronutrients in our diet which are protein, carbohydates and fats.

Any food goes…

The IIFYM theory suggests that eating crisps will build as much muscle as eating rice, providing that the overall macronutrient ratio for the day is met. This proposes that the macronutrient ratio and calories are the sole factor affecting body composition, rather than the actual foods being eaten. Read below for more info on macronutrients.


Macros are thought to have a significant impact on the composition of your body. For example, if you plan to build muscle, an important aspect of achieving this goal is to eat in a calorie surplus. Now, this surplus of calories can be stored as fat or as muscle.

Macronutrients are believed to affect whether these excess calories result in additional muscle or fat storage. The correct ratio is deemed to be the best combination for achieving your desired outcome. In this example, using the correct ratio of protein, carbs and fats will encourage muscle over fat storage.


The common macronutrient ratio of a weight lifter trying to build muscle is 40/40/20. This means 40% of your calories will come from protein, 40% coming from carbohydrates and 20% from fats. The belief is that this ratio will aid muscle gain, as opposed to just hitting a certain calorie number.

A bodybuilder’s diet is well-known for being made up of healthy but often bland meals, enabling them to build muscle and stay lean. Rice, chicken, potatoes, egg whites and protein powder are just a few of these repetitive foods eaten several times each day.

All refined carb sources are forbidden and sugars are limited, whilst saturated fats are cut out and protein is kept high. However, with the IIFYM theory, a person will build the same amounts of muscle if they ate junk foods as opposed to these healthy but repetitive foods.

Studies and Evidence

Although no studies have been done on the principle of IIFYM, there have been experiments that conclude that the foods eaten, have no correlation on body composition (similar to the IIFYM philosophy).

Twinkie Diet

One experiment was done by professor Mark Haub, whom created the famous “twinkie diet”, consisting of doritos, twinkies, oreos, among other junk foods. He ended up losing 27lbs in just 60 days. This provided evidence that it is the calories that matter, not the foods, when trying to alter body composition (in this case losing weight).

With IIFYM suggesting you can eat whatever (as long as you hit an effective macronutrient ratio), this isn’t too dissimilar to Mark Haub’s experiment. All that was missing in the the twinkie diet is that it wasn’t aimed at hitting a specific ratio of proteins, carbohydrates and fats.


Word of Caution

Even if the IIFYM principle proves valid and gives you effective weight loss/muscle building results, it is important to note that although you can build a great body on the outside by incorporating junk foods, it can still harm your health (if overdone). Thus a sensible approach is recommended when following the IIFYM method.

My Experience

I personally tried a similar diet to the IIFYM protocol, and that’s eating any food I want – but staying within my calorie requirements. I actually went from 20% body fat to 6% from eating pizza, nachos, ice-cream etc.

Thus it’s obvious in my experience that the types of food do NOT matter for body composition. Aka what you look like on the OUTSIDE.

…As long as you fulfil your calorie needs.

However, the types of food you eat will determine your health, and thus your INSIDES.

So, if you want to add some junk food into your diet just make sure you stay within your calorie ratios for the day, if you want to keep improving your body composition.

Have you tried IIFYM? How did you get on with the diet and would you recommend it to others? Leave a comment in the box below!

Sharing is caring! 👇

Written by Juice Guru
Juice Guru is a bodybuilder with over 30 years of experience when it comes to steroids and performance enhancing drugs. Juice Guru uses Fitnessonsteroids.com as a platform to share his/her expert knowledge.

Leave a Comment

This article has been fact-checked and medically reviewed by a certified doctor and nutritionist. All medical information and statements made in this article can be verified by several credible academic references/sources, cited in this article.