The Beginner’s Guide To Flexible Dieting (IIFYM) For Weight Loss.

flexible dieting iifym diet 700

Hello everyone Maria here. Today I have the pleasure to welcome Nathan on the blog. Nathan is a personal trainer and big fan of flexible dieting, otherwise known as “If it fits your macros” diet.

This diet is one of the most popular ones among more serious exercisers as it allows you to eat whatever you want as long as you meet your macro (= protein, fat, carbs) percentages of the day.

Now how you set those percentages greatly depends on your goals – today Nathan will focus on weight loss (fat loss) in particular.

Enjoy this comprehensive guide for IIFYM beginners who want to lose weight:

It is no secret that many people fail when dieting because they find it hard to resist cravings, and go crazy eating the same thing day after day.

What if I told you that:

  • A diet exists where you can eat any type of food you want and still lose weight?
  • A diet where you no longer must rely on constantly eating chicken and broccoli repeatedly for every meal?
  • A diet where you are able to eat that delicious slice of pizza without hindering your progress or feeling pangs of guilt about cheating on your meal plans?

Introducing the IIFYM diet:

The IIFYM diet stands for “If It Fits Your Macros,” and is also referred to as flexible dieting.The  concept of the IIFYM diet is that you are given a specific number of protein, carbs and fat to eat every day. These are your macronutrient numbers. You can essentially eat whatever foods you want, as long as you end each day by hitting these numbers.

flexible dieting pizza

Now, the aforementioned statements of eating any type of food you like needs to be understood correctly, and taken with a grain of salt.

Obviously, you can’t have 5 cheeseburgers and 5 slices of pizza and expect to hit the correct numbers, as the macronutrient breakdown of these food sources will be heavily skewed towards fat and carbs.

However, if you manage your cravings in a reasonable fashion, you can certainly fit in a slice of pizza or a cupcake into your daily macronutrient numbers!

What in the world is a macro?

Alright so let’s take a deeper look into the term macronutrients so that we can better understand the key concepts of the IIFYM diet. Food consists of 3 major nutrients. Even if you haven’t thought much about them in depth as we will look at below, I’m sure you’ve at least acknowledged these macros when you look at nutritional facts on the labels of the foods you eat.

iifym diet
Awesome infographic by jcdfitness

These 3 nutrients are protein, carbs, and fats (there’s also alcohol but that is not exactly the nutritious macro you should be aiming for.) I’d wager that at some point you’ve probably, at the very least, looked at the nutritional facts to check at least one of these categories before eating the food in question. If you’ve dieted before you may have avoided some foods altogether because of high fat or carbs. The IIFYM diet revolves around manipulating these macronutrient numbers to achieve your physique goals.

To show this in an applicable example, let us say that, based on your weight loss goals, your macronutrient numbers for the day were:

  • 150 grams of protein
  • 100 grams of carbs
  • 50 grams of fat

How do macronutrient numbers fit into flexible dieting?

iifym diet cheeseburgerIf you eat those 5 cheeseburgers we talked about before, you will certainly go over your allotted 50 grams of fat. Again, it is called flexible dieting because you can still eat foods that aren’t considered “healthy” foods in order to meet your cravings and have a diet that is less repetitive and boring. However, you still need to be smart about it, because at the end of the day you have to hit those macros.

Of course, it is healthier to eat more “clean foods,” and most likely the majority of your foods will be clean in order to get your macros in order. IIFYM just happens to leave some wiggle room for you to indulge, which in turn helps you stay more committed to your dieting plans as you will feel less constricted in your dieting.

Now, let’s break down each of these macros a bit so that we can further understand how to go about choosing your numbers to set your macros up for flexible dieting.

Flexible dieting: Protein.

eggs iifym dietProtein is 4 calories per gram. So, when you see 10g of protein on your food label, you’re looking at 40 calories of protein. Proteins are made up of amino acids, which are smaller chemicals in the body that we as humans require to perform a variety of functions. We can produce half of these internally, but need to acquire the rest through food consumption.

Protein provides the necessities for tissue repair, as well as essential enzymes and hormones that are required for your metabolic functions. Furthermore, they attribute to antibodies that assist in the body defending against infections. Muscle growth is reliant on protein, as I’m sure you’ve been told before.

To sum all that up, protein is very important, and because of this is weighted heavily in your macronutrient breakdown for this flexible diet, which we will go into more later.

Flexible dieting: Carbs.

carbs iifym dietLike protein, carbs are also 4 calories per gram. When we’re talking about carbs, we’re talking about energy for your body. Our bodies use carbs to make glucose, which is a type of sugar that is used for either immediate energy or stored for later usage.

Carbs also have important functions besides energy. They support immune functions and regulate digestion. They also protect our muscles by being the first source of energy used in our bodies. Without carbs, muscle proteins can be used as energy causing loss of muscle.

Flexible dieting: Fat.

fats flexible dieting

Unlike protein and carbohydrates, fat is 9 calories per gram. Because of this, when it comes time to calculating your numbers, your grams of fat will be considerably less than those of protein and carbs.

Fat helps store energy, assist in nerve and brain function, and help us maintain healthy skin and other tissues. They also transport fat-soluble vitamins throughout the bloodstream to where they are required.

Get started with the IIFYM diet by calculating your daily macronutrient numbers.

Alright so at this point you are probably asking yourself, “How do I know what the correct numbers are for my protein, carbs, and fat?” These numbers depend on your goals, activity level, gender and weight. Fortunately, the IIFYM diet has been around long enough that there are some general formulas established to help you use the aforementioned factors in determining your macros.

You figure out what your Basal Metabolic Rate is, and then generate your macronutrient numbers based on that result. Basal Metabolic Rate, or BMR, is essentially the amount of calories it takes to maintain body weight.

First, here’s how to calculate your BMR:

The Harris-Benedict Equation for calculating BMR is as follows:

  • Women:
    665 + (4.35 x weight in lbs) + (4.7 x height in inches) – (4.7 x age in years)Therefore a 35 year-old woman who measures 5’4” and 165 pounds would be
    665 + (4.35 x 165) + (4.7 x 64) – (4.7 x 35) = 665 + 717.75 + 300.8 – 164.5, equaling 1519 calories.
  • Men:
    65 + (6.2 x weight in lbs) + (12.7 x height in inches) – (6.8 x age in years)Therefore a 35 year-old man who measures 5’9” and 195 pounds would be
    65 + (6.2 x 195) + (12.7 x 69) – (6.8 x 35) = 65 + 1209 + 876.3 – 238, equaling 1912 calories.

exercise equipment isometricNow we must add in the factor of activity level. This is in no way a direct science but is more or less an estimate. Leslie Bonci, the Director of Sports Nutrition at the University of Pittsburgh Medical Center, came up with the following estimations when determining the effect of activity level on BMR:

  • Lightly Active (some exercise and sedentary job): BMR x 1.3-1.4
  • Moderately Active (intense exercise and sedentary job): BMR x 1.5-1.6
  • Very Active (active job and additional exercise): BMR x 1.7-1.8

Let’s continue with our two examples.

  • Let’s say our 35 year-old woman from before is moderately active. We multiply her 1519 BMR x 1.5 to get 2278 calories needed to maintain body weight.
  • Our 35 year-old man is only lightly active, so we multiply his 1912 BMR x 1.3 and get 2485 calories needed to maintain body weight.

Next, now that you know your BMR let’s find out your daily macro percentages.

Now that we have our maintenance weight, we need to determine our breakdown of protein, carbs and fat. There are different percentage breakdowns that are recommended for figuring out your macros. Most often you will see recommendations in percentage ranges. A good example as well as further explanation can be found in an article by the US National Library of Medicine (1).

Naturally, this gives us a lot of combinations to try for an effective caloric breakdown. Through personal trial and error, additional research, and anecdotal evidence, I’ve come to the following general guideline as a starting point for developing one’s macros:

  • Protein 30 percent
  • Carbs 45 percent
  • Fat 25 percent

These numbers fall into those recommended by US government standards in their 2010 Dietary Guidelines guide (2).

I’ve found that better results occur when protein is on the higher end of the scale, and fat and carbs on the lower end of their scales. Most individuals crave a leaner physique, and that is easier to achieve such a physique with this breakdown.

As I mentioned you are open to eat any foods you desire but here are some suggestions for the IIFYM diet:


  • Chicken
  • Beef
  • Pork
  • Eggs
  • Protein Shakes
  • Eggs
  • Fish
  • Milk


  • Rice
  • Sweet Potatoes
  • Bananas
  • Apples
  • Oatmeal
  • Vegetables


  • Cashews
  • Almonds
  • Any sort of nut butter
  • Avocados
  • Eggs

I highly suggest utilizing a lot of vegetables in your diet. They are extremely low in calories and you can use them to help fill you up. Personally, when I’m a bit hungry but don’t want to put an extra meal in because I know I have a meal coming up and don’t have a lot of calories to play with, my go to are pickles. Extremely low calorie and oddly filling.

Next, now that you know your daily macro percentages, let’s translate that into grams.

Steak salad calories

Let’s check back in with our examples once more.

  • For weight maintenance our example woman will require 683 calories of protein, 1025 calories of carbs, and 569 calories of fat. Now, since we know that protein and carbs are 4 calories per gram, and fat is 9 calories per gram, her macros come to 171 g of protein, 256 g of carbs, and 63 g of fat.
  • Our man will require 746 calories of protein, 1118 calories of carbs, and 621 calories of fat. This comes out to 187 g of protein, 279 g of carbs, and 69 g of fat.

Now, if you recall, I referred to the percentage breakdown of 30/45/25 as a good starting point. As I’ve alluded to above, there is some debate on how much protein per bodyweight should be consumed. In a report published by NRC Research Press (3), it was noted that .36 g per body weight (in lbs) is the Recommended Dietary Allowance (RDA).

However, an RDA is simply the minimum amount or protein required for normal body function and to keep from getting sick. Daniel, Pendick, former Executive Editor for Harvard Men’s Health Watch, recommends that this number can be at least doubled.

Both ideologies fit into government standards (2), that recommend protein anywhere from 10% to 35% of daily caloric intake. This recommendation is for both men and women.

Flexible dieting: try adding more protein for better results.

I believe in protein on the higher end of that scale when it comes to clients because they will couple diet with some manner of physical activity. Physical activity promotes muscle growth, for which protein plays a major role.

flexible dieting protein

Due to this, I recommend approximately 1g of protein per pound of body weight. However, for those that are simply changing their diet without adding exercise into the equation, 1g of protein per body weight may not be necessary, as it is sometimes difficult to eat the required foods to reach that number.

If the 30/45/25 breakdown has protein at significantly lower or higher than body weight, it doesn’t hurt to shift the percentages around a bit to adjust to the proper protein g/body weight.

Does this sound complicated? Use the myfitnesspal app to do the macro calculations for you.

There are a variety of online sites or apps that can do these conversions for you. One good example is the app myfitnesspal. It essentially takes manual calculations out of the equation (no pun intended).

You input your height, weight, and goal weight, then can adjust the percentages to get the macros that you shoot for each day. Additionally, the app puts in general suggestions for sodium, fiber, sugar, cholesterol, vitamins, and other useful numbers that you may be interested in keeping track of.

Gone are the days of writing in your numbers every day in a diary. Seriously I cannot give myfitnesspal enough praise as it personally has transformed the way I track my macros. Before we talked about how it can get you your macro numbers by inputting your statistics, activity levels, and percentages. That’s just the start of what myfitnesspal can do.

How to use myfitnesspal when grocery shopping.

iifym diet tracking

Once you’re setup you can input everything you eat into the app and it will keep track of where you’re at throughout the day. There are two ways that you can do this.

  • First, an awesome feature they have is that you can scan barcodes of products and it will automatically enter the data for you. It’s really that simple.
  • If for some reason the barcode doesn’t work, which I find is maybe 3% of the time at most because they have a very vast library of products, you can manually input the macros in by putting a title on what you’re eating and just entering the protein, fat and carbs. If you want to be more detailed you can input all of the other nutritional categories you would find on the food product.

How to track your foods with myfitnesspal when eating out.

Now let’s say you’re at a restaurant and order food. You can’t really scan a barcode and you’ll most likely get a stare of incredulity if you go back into the kitchen to ask for one. No need to worry, myfitnesspal has you covered again!

As I said before, there is a vast library of products, and most popular restaurant foods are already in the system. Simply search for the item in the search bar and you can most likely find it. If you are more old school you can certainly just use a notebook and a pen to add it up, or an excel spreadsheet.

How to use flexible dieting to lose weight.

Now, since we’ve calculated the macros you want based on BMR, it’s time to adjust them to meet fitness goals. As time progresses and you become more comfortable and successful in meeting your macros and keeping up with this flexible diet, you should begin to see results. These results will obviously vary, because all the applied percentages and ratios may not be 100% on point for each individual.

iifym diet fitness

For example, let’s say you consider yourself a “very active” individual, but when you start partaking in your IIFYM diet you notice that you’re not getting the type of cardio that you anticipated, and aren’t seeing results because the BMR you’ve calculated has you needing more calories than you actually require. That being the case, you’ll want to drop your calories a bit. Once this is done you should begin losing weight.

Then, as you keep using the same macros, you will weigh yourself and at some point once again find you haven’t lost as much weight if any at all during that weigh-in period. Once again you will lessen your caloric intake. This is due to the fact that as you lose weight you will then require less calories, so your macros need to be dropped down accordingly.

What if you follow the IIFYM diet but don’t lose weight?

So, let’s say you started at 250 grams of carbs per day. After two weeks you weigh yourself and realize that you didn’t lose any weight. That being the case we can assume, if you’ve kept a strict diet counting your macros and meeting them, that you’re about at your BMR in terms of caloric consumption. You would then drop carbs from maybe 250 to 225. You’d then re-weigh yourself after a week or two and gauge your progress.

progress iifym dietAt this point the process continues. You will lose weight, and then because you’ve lost weight your BMR changes and perhaps a few weeks later you notice you haven’t lost weight, so you drop the carbs again. Soon enough you will have the process down and it will be a smooth routine.

As mentioned, you can drop the fat number as well. Protein can be adjusted slowly. Since I’ve said before that protein should be 1 g per pound of bodyweight, you can adjust that as your weight drops. The first couple weeks takes some trial and error to get your exact numbers since everyone is different. The great thing is once you get those numbers it is very easy to make changes to further progress.

What else can I do to improve my results with flexible dieting?

flexible dieting cardio

Cardio is a great tool to couple with your IIFYM diet plan. Dropping your caloric intake is tough, but as we saw before, you can maintain a higher caloric intake the more active you are. In addition to simply being able to eat more calories, you get a stronger heart and lungs, increased bone density, reduced risk of heart disease, and various other benefits.

Strength training is also immensely beneficial to coincide with the IIFYM diet. Lifting weights leads to muscle growth and increased metabolism. Having a consistent weight lifting program is another way to transform your body. When used in tandem with proper flexible dieting you can achieve significant results.

How many meals a day should I eat with flexible dieting?

My answer is in the name of the diet itself. If it fits your macros, then it really does not matter. Use whatever you feel comfortable with and what fits your schedule (and keep in mind frequent meals will not help you lose weight by boosting your metabolism.)

The best diet for you is the one that you can stick to.

iifym diet works

In my opinion, almost every diet works. It is just a matter of sticking to it. I love flexible dieting for myself and my clients because it is extremely easy to stick to and more sustainable for the long term. You will also quickly learn what exactly is in the foods you eat concerning macro breakdown and calories, which is immensely useful knowledge to attain for the future.

With the IIFYM diet, I’ve found that you will naturally gravitate towards highly nutritious foods in order to hit your numbers. Doing so will help you to fit that craving food in, perhaps even once a day. Having this freedom certainly aids you in keeping your sanity throughout your diet and not getting frustrated with eating the same boring clean foods every day.

Have you tried the IIFYM diet? What makes you excited about it? Share your your own experiences with flexible dieting in the comments. 

About the author:
flexible dieting authorpic

Nathan Robinson holds a Bachelor’s Degree in Exercise Science and a personal training certification from the American College of Sports Medicine. A lifelong athlete and fitness enthusiast, he owns a fitness company called Elev8 Online Personal Training where he and his partner create customized monthly workout plans.

Click here to view the sources referenced in this article.

Related Articles


Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.