We’ve talked about the law of thermodynamics and the concept of calories in vs calories out. To continue that discussion, in this article we’re going to learn about a few things:

  • BMR
  • TDEE
  • How to calculate Maintainance calories
  • How to calculate fat loss calories
  • How to calculate macronutrient needs from fat loss calories


Before we can do anything, we have to first of all calculate how much calories our body needs for basic functions. If we lay in bed all day and did nothing, we would need a certain amount of calories to ensure that the basic functions of the body like breathing happens. This is known as the Basal Metaboloic Rate (BMR). As a nurse, when I have a patient who’s in a coma, they typically will get tube feedings and the registered dietitian will calculate the BMR of the patient and that is the amount of calories that patient will get from tube feedings. So, this is the bare minimum number we can NEVER eat below. There a few scientific formulas to help us calculate our BMR but I don’t like math so here is a handy dandy calculator that I love to use. This particular calculator is based on the Mifflin-St. Jeor equations:

BMR Calculator


Now, we know our BMR, the next number we want to know is out Total Daily Energy Expenditure or TDEE. This is how many calories we need to maintain our weight taking into consideration our individual level of activity (getting out of bed, brushing your teeth, walking to the kitchen, and other basic daily activities). This number would be different for two people who are the same age, sex, weight, height but different level of daily activity. In other words, whether you’re someone who sits in an office chair or bartender has an impact on what your TDEE will be. Calculating your TDEE is another mathematical equation and since I’m not here for that, here’s another handy dandy calculator:

TDEE/ Maintenance Calories Calculator

Our TDEE can also be considered our maintaininace calories. So, let’s say your TDEE is 2000 calories, if you eat 2000 calories a day, you won’t gain any weight, if you eat less than 2000 calories a day, you’ll lose weight and if you eat more than 2000 calories a day, you’ll gain weight. Since this article is focused on weight loss, we need to figure out how much less than our TDEE we need to eat in order to lose weight in a manner that is sustainable.

Sustainability is important because our goal shouldn’t only be to lose weight, but to keep the weight off while enjoying our diet and not getting an hang ups over food. This is why it’s imperative that we only create a deficit large enough to achieve fat loss but small enough to allow our brains to make the habit changes we need to maintain said weightloss. In other words, we want to eat as much as we can while still losing weight. So, how much of a deficit is good enough?

My general recommendation is a caloric deficit of between 15-20%.

So, if you have a maintenance calories of 2000 calories, you’d want just a deficit of 300-400 calories a day. This means, you’ll keep your calories between 1600 and 1700 calories. This is a moderate deficit that won’t have you depriving yourself. This number however, is just an estimate and the true test will be eating at this deficit for a few weeks and adjusting as needed.

With diets that are solely focused on weightloss, this would be the stopping point. We know what our fat loss calories is, if we ate within those calories, we would lose weight. But we’re not trying to just lose weight. We’re trying to make sure that the weight we lose is mostly fat and not muscle. And to ensure that, we have to eat optimum amounts of protein. So, how much protein do we need to maintain muscle? Per research, the recommendation is to get in between 0.8-1 gram of protein per pound of body weight. So for someone who is 170lbs, they’ll need a minimum of 136 grams to 170 grams of protein to ensure they maintain as much muscle as possible. Each gram of protein is 4 calories which then means that they’ll be getting 544 calories – 680 calories of their daily intake from protein.

Each of the other macros also have an energy (calorie) value as below:

1gram of protein = 4 calories

1gram of carbohydrates = 4 calories

1gram of fat = 9 calories

After we get in our protein, the amounts of fat we should get in is generally recommend to be about 20-30 % of our total daily intake the rest can then be carbohydrates. We always want to keep moderation in mind which is why we don’t want to go too low fat or too low carbs because we need to eat enough fat to ensure optimum hormonal function as well as eat enough carbs to ensure enough energy to get through our day/workouts without being foggy or fatigued.

Let’s do a case study to put it all in perspective because I know this can be technical and somewhat confusing.

Let’s say we have a 33 year old woman who is 5’5″ and weighs 200 lbs who has a sedentary life. Her goal is fat loss. How many calories, protein, fat, and carbohydrates does she need to eat a day to lose weight?

Well first of all calculate her TDEE. This is the minimum amount of calories she has to eat everyday to MAINTAIN her weight of 200 lbs. Using our handy dandy calculator, we’ll arrive at:

TDEE = 1938 calories. This is their maintenance calories.


How many calories would they require for FAT LOSS? Remember, we only want a moderate deficit of 15-20%


Fat loss calories will be: 1550 to 1647 calories. We’ll split the difference and give her a  fat loss calories of 1598 calories.


This is the amount of calories she’ll have to eat a day in order to lose a small amount of weight per week.


How many of those calories should be protein?

Protein: 0.8 g to 1g of body weight (200lbs) will be 160g to 200g of protein. Again, we’ll split the difference and give them a protein intake of 180g


Total calories from protein will then be (180g x 4) = 720 calories


How many of those calories should be fat?

20 – 30 % of total calorie intake = 319 to 479 calories. The average being 399 calories from fat. And since 1g of fat is 9 calories, the total grams of fat will be 44.37g from fat


How many of those calories should be carbohydrates?


The rest of their calorie intake will be from carbohydrates. This means:


Calories from carbs = Fat loss calories – (calories from fat + calories from protein)


Calories from carbs  = 1598 calories – (399 calories + 720 calories)


Calories from carbs = 479 calories


Knowing that 1 gram of carbs = 4 calories, then amount of grams from carbs will be 119g


Our case study will then have the following calories and macros:


Fat loss calories: 1598 calories


Calories and grams from protein = 720 calories or 180 grams 


Calories and grams from fat = 399 calories or 44 grams


Calories and grams from carbs = 479 calories or 119 grams 


These numbers are an example only meant to underscore the point and show how the math will workout. It will different for each individual and would need to be personalized further based on several different criteria.

As you can see from this one example, tracking your calories and macros can be a very involved process and while tracking macros is effective and scientifically sound, there’s a learning curve. It’s simple in principle but depending on a person’s personality and tenacity, it may be steep and arduous or easy peasy.

On the flip side however, it means you can eat WHATEVER and WHENVER you like as long as you meet your macro targets. Yup, you heard right. You can be vegan, pescatarian, a meat lover…you name it and as long as you meet your macro target. Compared to other methods out there for fat loss, this is a much superior method and if you’re able to exercise the patience needed to overcome the learning curve, your fat loss goals can be met without developing weird hangups about food or denying yourself candy forever (if candy is your thing).

I️ know it’s kinda ironic to say tracking our macros is the most sustainable way to lose fat. You might think, who can maintain tracking their food for life? I know I can’t. I’ve tracked my macros for the last two years and while it’s gotten easier with time, I know that it’s not something I plan to do forever. But while I still have fat loss goals, it has proven to be the easiest way I’ve found to eat my cake and still achieve my fat loss goals and I’ve learned SO much about food and can make food work for me and not against me.

If you stuck through all 1500 words of that, kudos to you. This is not my favorite thing to write about. I just would rather calculate someone’s macros for them and call it a day but I think knowing the basics is incredibly important and hopefully, i gave you a head start on it.

Never stop learning and growing and as always, let me know if you have questions. Also, you can subscribe to my newsletter to get all the goodies that I don’t post on here delivered straight to your inbox.


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