IIFYM (If It Fits Your Macros): Quick Guide To This Diet Trend

IIFYM is an acronym for If It Fits Your Macros and has become one of the fastest growing dieting trends. IIFYM is sometimes called Flexible Dieting.

Why is IIFYM so popular?

Because it revolves around the concept that dieters can eat ANYTHING as long as it fits their prescribed set of macros. This is refreshing for many who are coming from most other dieting trends that are very restrictive.1

With If It Fits Your Macros (Flexible Dieting):

  • There are no forbidden or “bad” foods.
  • People feel they can eat “normally” again.
  • It’s much easier to stick with during social events.
  • People can generally eat more and eat the foods they love while still reaching their weight loss or muscle building goals.

Your IIFYM TDEE and Your Set of Macros

The crux of IIFYM revolves around two main concepts; establishing your personal TDEE (Total Daily Energy Expenditure)2 and establishing your personal set of daily macro (macronutrient) targets.

Establishing your TDEE

The first thing a dieter must do when beginning IIFYM is to establish their TDEE or in other words, how many calories their body burns during a 24 hour period considering their REE (Resting Energy Expenditure), their general movement/activities, and their intentional exercise.

The formula that most people use to find their TDEE is the well respected Mifflin, M. D., St Jeor formula3 for finding a person’s REE (Resting Energy Expenditure).

The formula for men:

10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5 = REE

The formula for women:

10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161 = REE

This is then factored in with the amount of exercise or movement a person does to establish the TDEE.

These can be broken done into 4 categories:

  • Sedentary
  • Lightly active
  • Moderately active
  • Extremely active

Establishing Your Set of IIFYM Macros

Most calories are made up of 3 macronutrients; Carbohydrates, Protein, and Fat and each is essential for a healthy functioning body.

iifym macro ratio

The only calories that don’t fall under these three are calories from alcohol.

Generally, 25% of your calories should come from fats. This can vary and IIFYM allows dieters to adjust this macro to a level that works with his or her body and goals.

Your protein amount is determined by your body weight. Again, this varies based on what your goals are.

IIFYM isn’t a low carb diet so this macro generally ranges between 35-40%. Carbs are what fuels your body and your workouts.

Read the guide to calculating your macros, or use our super easy-to-use macro calculator.

Losing Weight with If It Fits Your Macros

To lose weight with IIFYM, you simply eat less than your established TDEE for maintaining your current weight.

IIFYM doesn’t cut calories as drastically as most low-calorie diets but advocates a moderate reduction of 20%. This allows for slow and steady weight loss.

This way, the metabolism doesn’t slow and the body doesn’t switch over to “starvation mode”4 because of too few calories being consumed to support both the metabolism and a person’s activity level.

This too is flexible, some may do better with a little more calorie reduction and some may do better with a little less. Our IIFYM calculator has a starting point of 20%.

Gaining Weight

Although IIFYM can be used to gain weight in general by simply eating more calories than your maintenance TDEE, most use it to gain muscle mass without adding fat.

This can be a delicate balance for most people and also requires dedication to a good muscle building workout routine at the gym.

In general, increasing calories to 20% more than your maintenance TDEE in combination with strategic weight bearing exercise will result in an increase in muscle.

However, some may find at this level, fat doesn’t burn or some fat is gained. To get a shredded physique with flexible dieting, it’s a tiny bit more complicated. Here’s a more in-depth article on the subject.

Why are macros tracked?

IIFYM tracks macros because they fine tune your results. The TDEE determines whether you lose, stay the same, or gain, but keeping track of your macros helps you lose or gain in a way that allows you to reach your body composition goals.

If muscle building is your goal, then you want to make sure you are eating adequate protein so that your muscles will have the raw materials needed for growth.5

If weight loss is your goal, you want to be eating enough protein that your body doesn’t start cannibalizing muscle tissue for extra energy instead of your fat reserves.

Others may need to make sure they are eating enough carbs to properly fuel their intense workouts. Tracking macros really helps the flexible dieter be in control of their eating and what effect it will have on their body.

This is why essentially dieters can eat any food they want as long as it fits their prescribed set of macros. It doesn’t matter so much where the macros are coming from, but rather, not eating too much or too little of a macro.

IIFYM Embraces Technology

Another reason why IIFYM is so popular is because it uses our devices as powerful tools that we can use to keep track of what we eat, our calories, our macros, and our calorie burn through exercise.

Of course, a person could use paper and pencil to do this diet, but that would be very tedious. Technology makes the whole process much quicker and even fun.

A flexible dieter that I know described the process like a game, which helped him think of the process of tracking food and macros fun instead of a chore.

If you have a computer, smartphone, or tablet then you are all set to give IIFYM a go and be successful at it.


Popular Apps for IIFYM

MyFitnessPal (iOS) or Android: MFP is perhaps the most popular app used to keep track of food eaten, calories, macros, and calories burned. See our tutorial on how to get everything set up.

MapMyFitness IOS or Android: MMF is a more robust fitness tracker than what MFP offers on its own. It links up with MFP and send your calorie burn data to your daily diary.

MyMacros+: This app is also pretty popular and although it is designed for people who are more into body building, it can be used for general food and macro tracking as well.

Here’s a list of 11 other helpful If IT Fits Your Macros tools to help you be successful.

Tracking the Food You Eat

One of the most important aspects of IIFYM is tracking the food you eat as this allows you to know if you’ve satisfied your prescribed set of daily macros.

The above-mentioned apps greatly help with this process and make it pretty simple with extensive food databases and bar code scanners. However, flexible dieters probably will need to get a digital food scale and a good set of measuring cups, so the macros in the portions of homemade food can be accurately tracked. Here’s a detailed guide on how to find the macro amounts in food.

Whatever your goal, IIFYM is a great way to reach it and eat the foods you love all the while consuming more calories than you would on typical weight loss diets.

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    Scientific References:

  1. Chapman, G. E. (1999). From “Dieting” to “Healthy Eating” An Exploration of Shifting Constructions of Eating. Interpreting weight: The social management of fatness and thinness, 73.
  2. Rising, R., Harper, I. T., Fontvielle, A. M., Ferraro, R. T., Spraul, M., & Ravussin, E. (1994). Determinants of total daily energy expenditure: variability in physical activity. The American journal of clinical nutrition, 59(4), 800-804. Study abstract
  3. Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., & Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. The American Journal of Clinical Nutrition, 51 (2), 241-247.
    URL http://www.ajcn.org/content/51/2/241.abstract
  4. Schwartz, M. W., & Seeley, R. J. (1997). Neuroendocrine responses to starvation and weight loss. New England Journal of Medicine, 336(25), 1802-1811.  Study link
  5. Kumar, V., Atherton, P., Smith, K., & Rennie, M. J. (2009). Human muscle protein synthesis and breakdown during and after exercise. Journal of Applied Physiology, 106(6), 2026-2039. Study Link

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