The IIFYM Diet or “If It Fits Your Macros” focuses on macronutrients rather than calories. Macronutrients are the nutrients we need in larger quantities that provide us with energy [1].
When on a macro diet you track 3 types of macronutrients (There is a fourth which is alcohol, but this isn’t included in an IIFYM diet):
All you have to do to follow the IIFYM diet is to firstly calculate your macros based upon your height, weight, exercise amount etc. Once you’ve got that, just make sure you’re meeting those numbers every day! The diet is mostly used to lose weight but can be adjusted for those who would like to gain weight too.
So, your number one task, before heading into this diet, is to figure out your macros. Be ready for things to get…. Mathematical.
Head to the IIFYM website and you can calculate your macros with their free calculator here. This is a great place to start as you have something to work from, but you can just calculate them manually also. I feel this is better way to proceed as everybody is very different, so knowing how to calculate and adjust your macros correctly is going to be a big determining factor of how successful your diet will be.
Your BMR is the number of calories you burn whilst resting. So, if you’ve slept for a whole day, you’ll still burn these many calories.
The basic formula we use will require you to know your height in centimetres, weight in kg and your age. You then put those numbers into the below equation [3]. It’s modified slightly for men and women so make sure you’ve picked the right gender equation below.
Male:
(Height (cm) x 6.25) + (Weight (kg) x 9.99) – (Age x 4.92) + 5 = Male BMR
Female:
(Height (cm) x 6.25) + (Weight (kg) x 9.99) – (Age x 4.92) – 161 = Female BMR
I am a 23-year-old woman, who’s height is 160 cm and weight lands at 50.8 kg. My equation will be as follows –
(160×6.25) + (50.8 x 9.99) – (23 x 4.92) – 161 = 1233.3 Calories per day.
You don’t really ever want to drop below this even when trying to lose weight, as this would be considered too fast a rate to drop fat and very unhealthy.
We need to be able to figure out our REE and TDEE so we understand exactly what energy our bodies need every day to do what we want them to do. So we start with our REE and a common way to figure this out is to follow the below gender-based formula’s [4].
Of course, we don’t just lay around all day (that’s the dream) so we use our REE to figure out our TDEE. This calculation is dependent on your daily activity.
Your final equation to figure out your TDEE will be as follows:
For Males:
(10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5 ) x ACTIVY AMOUNT = TDEE
For females:
(10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161 = REE) x ACTIVITY AMOUNT = TDEE
I am a 23-year-old woman, who’s height is 160 cm and weight lands at 50.8 kg. I am very lightly active, so my equation will be as follows:
(10×50.8 + 6.25×160 – 5×23 +5 = REE) x 1.375 = TDEE
508 + 1000 – 155 + 5 = 1358 1358 x 1.375 = 1630
Now we have our target daily calorie intake we need to apply this to what we are eating in a day and break it down into your macronutrient ratios.
This is where you start adjusting for fat loss, weight gain or weight maintenance. In really simple terms, if you eat more than your TDEE you’re going to gain weight, if you eat less than your TDEE you’re going to lose weight and if you eat the same amount as your TDEE you’re going to maintain your weight. Obviously, it doesn’t work like this for everyone, but it’s going to help you understand where the numbers in your macros come from.
For weight loss you’re looking at dropping your calorie intake around 15-20%, dependent on how fast you’re looking to drop that weight. Someone who’s been bulking for a while might want to cut calories slower as to avoid losing too much muscle during their deficit. So, it’s really up to as to how much a drop you want to take. We wouldn’t recommend dropping any lower than 20% as this isn’t the healthiest approach to dieting and you’re 100% going to cave before you get to the end.
It’s pretty much the same for bulking. You’re looking at taking your calorie intake up 15-20%. But you have to make sure you’re sticking to your gym routine and using the extra energy you’re intaking otherwise, well… You’re just going to get fat.
Let’s start breaking it down into our three macronutrients – The numbers might not necessarily perfectly add up, so I’d add up your protein and fat intake and use what is left over for carbohydrates. But make sure it sits around the number you’ve calculated for carbs otherwise, there might be some numbers you’ve gotten wrong somewhere! ⬇️
Let’s start with protein because every athlete needs this to help with maintaining, repairing and building muscle tissues. Although it is often a debated, the recommended number of protein intake for a normal healthy adult is 0.8g/kg body weight. For an endurance athlete that number is slightly increased to 1.2-1.4g/kg body weight/day due to the recovery needed from intense training. Again, for a strength athlete the protein intake is higher at around 1.2-1.7g/kg body weight/day to support the wanted muscle growth. If you’re someone who has been resistance training for a while, you can probably stick to the lower end of that scale as your body would’ve adapted to use the protein you do intake more efficiently [5].
So, let’s go back to our example. At 50.8 kg, doing resistance training once or twice a week, I would probably go for the lower end of the ideal amount for the strength athlete. I’m not exerting too much energy, so don’t want to overdo it.
1.2 x 50.8 = 60.96 (lets round that up to make it easier) 61 g protein per day.
That amounts to 244 calories per day of my 1630 calories should be made up of protein.
A necessary component of everyone’s diet is fat. It provides energy and has associated nutrients such as vitamins A, D and E. The acceptable macros range for fat is around 25-35% of your TDEE [5]. You need to make sure these are healthy fats that you’ll find in products like whole milk, full fat yoghurt, olive oil and nuts and not in that Burger King we know you’re craving!
For our example, out of the 1630 calories I should be intaking, between 407 – 570 calories should come from fatty foods. The easiest way to get this number is to decide what % of fat you’re going to go for and multiply your TDEE by that percentage as a decimal point.
So I do 1630 x (25%) 0.25 = 407
407/9 (The amount of calories per gram of fat) = 45.2
So, we’re looking at 45.2g fat for my macros.
Finally, let’s work out our carbs target. Carbs are ultimately where your energy comes from, so you need to take care to make sure you’re getting enough especially if you’re a regular gym goer. So, with the number below just expect to be at the higher end of the spectrum if you’re a highly active individual. Whereas if you’re not expending so much energy, you’ll probably be nearer the lower number. This will also vary if you’re wanting to lose weight or gain muscle.
For an athlete you’re looking at 5-7 g/kg body weight/day [6].
Following our example that would be around 254-355g of carbohydrates per day, or 1016 – 1420 calories per day. We would probably go to the bottom end as I don’t exceed a crazy amount of energy during my week. So, let’s say 1016 out of 1630 calories a day goes to carbs, that’s 254g!
So, our example uses me who is a 23-year-old, 50.8 kg, 5 ft 3, lightly active individual, who wants to maintain my weight.
We figured out my Total Daily Energy Expenditure (TDEE) to be 1630 Calories.
We figured out my protein intake should be around 244 Calories per day/61g.
We figured out my fat intake should be around 448 Calories per day/49.7g.
We figured out my carbohydrate intake should be around 1016 Calories per day/245g.
This amounts to 1708 Calories per day – That’s very close to my 1630 Calorie TDEE. To make it more even we could add our protein and fat calories up to tell us our remaining amount for carbs. Use this a base and then you can adjust however you feel you need for your specific goals and personal aims.
Your goals and current training regimes are going to influence how your macros are calculated. If you’re someone who is wanting to gain more muscle you might want to up your protein intake to match your calorie surplus or balance it our between carbs and protein if you feel you don’t have enough energy. If you’re looking for weight loss, you might want to reduce your carbs to match your calories deficit or look into how you might be able to follow a keto diet whilst tracking your macros.
Diet and nutrition are very personal matters and the only person who is going to know what will work best is you. You’re the one who knows your body and there are going to be many personal factors like allergies and intolerances that might not make this calculation quite so simple. So, keep in mind this is just the base camp for figuring out your macros, and once you start your final climb into really testing those numbers, that is when you’re going to start understanding your macros.
Male:
(Height (cm) x 6.25) + (Weight (kg) x 9.99) – (Age x 4.92) + 5 = Male BMR
Female:
(Height (cm) x 6.25) + (Weight (kg) x 9.99) – (Age x 4.92) – 161 = Female BMR
Male:
(10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5 ) x ACTIVY AMOUNT = TDEE
Female:
(10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161 = REE) x ACTIVITY AMOUNT = TDEE
Go to the lower end the scale if you’re training 2-3 times per week. Go to the higher end of the scale if you’re training 4-5 times per week.
1.2-1.4g/kg body weight/day – Endurance Athlete
1.2-1.7g/kg body weight/day – Strength Athlete
Lower Fat Ratio – TDEE x 0.2
Higher Fat Ratio – TDEE x 0.35
5-7 g/kg body weight/day
[1] What are macronutrients?
[2] 6 Calories: Total Macronutrient Intake, Energy Expenditure, and Net Energy Stores.
[3] How to calculate BMR manually.
[4] A new predictive equation for resting energy expenditure in healthy individuals.
[5] Position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance.
[6] Guidelines for daily carbohydrate intake: do athletes achieve them?
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