The Science of Fat Loss: How to Determine your Calories and Macros for a Calorie Deficit Phase

Now this may sound like a lot, especially if you are not a fan of math, and especially if you are brand new to the idea of tracking calories or macros. But I can promise you over and over again that it is SO worth it. Flexible Dieting and tracking macros has grown like wildfire over the past couple of years; and there’s a reason for that — it is backed by science and it WORKS.

I have included the steps and calculations below for how to calculate your OWN macros. Because in order for macros to work, you need them to be tailored to YOU. Your macros won’t be the best fit for susie and vice versa. So let’s get into it!

Some definitions to understand before we begin:

Basal Metabolic Rate (BMR) = the number of calories your body burns just by existing. This includes sleeping, breathing, stay warm, and other cellular processes.
Non-Exercise Activity Thermogenesis (NEAT) = The number of calories you burn doing any additional movement that is not defined as actual exercise. This includes fidgeting, tapping, walking, etc.
Total Daily Expenditure (TDEE) = the TOTAL number of calories you burn each day. This measurement encompasses your BMR, exercise, and any extra daily movement (NEAT).

Now, we must first determine our maintenance calories, or the calories that we are currently maintaining our weight at, before we can make adjustments and targetable goals.

Here is an overview of what we will cover to keep us organized:
1. Determine your current maintenance calories
– Calculate BMR and TDEE
2. Determine your caloric deficit
3. Determine your protein intake
4. Subtract this number from your overall calorie deficit
5. Determine fat and carb intake from remaining calories

STEP 1: Determine your current maintenance calories

This can be done in one of two ways:

1. Track what you have been eating for at least a week, eating EXACTLY how you normally would.

This is what I would recommend as it is the most accurate way of seeing where you are at! Which is essential moving forward 😉

You should be tracking every single thing you put into your mouth, without making any adjustments in your habits just yet. This will tell us about your current habits and the amount of calories needed to maintain your current weight. You want to be as close as possible so we have the most reliable data moving forward.

2. Calculate it utilizing one of the science-backed calculations provided below.

If you’ve ALREADY been counting your macros or calories and KNOW what amount you are eating to maintain your current weight, you can also skip to this step.

***DO TAKE NOTE that if you are already consuming too low of calories or have been “dieting” for a while, it may be useful to compute your maintenance calories below instead to see what you should ideally be maintaining at (no woman should be maintaining on 1500 or 1600 calories). If you notice that the calories you are currently eating is below this by a good amount, it would be more beneficial for you to base your new macros off of the information the equation gives instead, because you do not want to go too low!

*PART A of determining maintenance calories: Determine BMR.

Typically, the Harris-Benedict equation has been defined as the best to measure a person’s BMR. This formula has since been revised to include sexual distinction, height, and age, making it quite a bit more accurate.

Revised Harris – Benedict:
For men: 88.362 + (13.397 × body weight) + (4.799 × height in cm) – (5.677 × age) = BMR
For women: 447.593 + (9.247 × body weight) + (3.098 × height in cm) – (4.330 × age) = BMR
**Weight is in kg (to find just divide weight in pounds by 2.2)
**Height is in cm (to find just multiply height in inches by 2.54)

Let’s just look at my stats: 117 lbs = 53.2 kg; 63 inches = 160 cm; 25 years old

If we plug in me in for example, the formula would look like this:
447.593 + (9.247 × 53.2) + (3.098 × 160) – (4.330 × 25) = BMR

So, my BMR, or amount of calories my body burns just by existing is 1326.8 calories (according to this equation).

An even more accurate formula is the Muller Equation. This one is considered the “Golden Standard” because it encompasses not just weight, but lean body mass into the equation. This is ideal since lean muscle contributes more than fat to metabolic rate. This is also the equation obese people should use since it does base the BMR off of lean body mass.

Mueller equation:
(13.587 × LBM) + (9.613 × FM) + (198 × Sex) – (3.351 × Age) + 674 = BMR
**For men, enter 1 for sex; for women enter 0
**LBM = lean body mass in kg
**FM = fat mass in kg

**To determine LBM and FM, the easiest (and cheapest) way is to invest in a scale that that measures this along with weight. No method will be 100% accurate. KNOW THAT, But it’s pretty close, and as long as you consistently use the same method, you’re good.

I use YUNMAI Premium Body Fit Scale that I ordered off Amazon. It calculates fat mass as well as a leu of other things. The other awesome part is that it comes with a downloadable app on your phone so you can easily track your progress!! Remember, the fat % the scale gives is an ESTIMATE. But again, it’s pretty close and every calculation is an estimate. Macros can be adjusted later on depending on how you are responding. We just need to find a starting point.

My scale, for example, tells me I am at 24% body fat. That just means I would multiply 0.24 times my weight in kg to find my fat weight in kg (0.24 x 53 = 12.7 kg). Meaning that out of my weight, 12.7 kg of that is fat.
To determine LBM weight, just do the same thing.
Subtract the difference out of 100% to find the LBM %. (100% – 24% = 76% = 0.76)
Then multiply by your weight in kg:
(0.76 x 53 = 40.3 kg of LBM.)

If we plug that into the equation, we get this:
(13.587 × 40.3) + (9.613 × 12.7) + (198 × 0) – (3.351 × 25) + 674 = 1260 calories = BMR

You can see that the two equations are close! It’s okay if you don’t know your lean mass or fat mass. Any equation will always be an estimate, but since the Muller encompasses lean body mass and I have a good idea of mine, this is the one I chose to use to calculate my macros.

*PART B of determining maintenance calories: Determine TDEE

To determine your total daily energy expenditure (remember this encompasses everything, all the extra movement you do on a daily basis depending on your lifestyle, etc.) we just use the formula:

TDEE = BMR x AF
where AF refers to activity factor. How active are you?

1.2 – Sedentary (you work a desk job and don’t exercise)
1.375 – Light Activity (you work a desk job but exercise. Or you have a job that you’re on your feet a good amount (i.e. teacher, nurse) and you don’t exercise)
1.55 – Moderate Activity (you exercise 5-6 times a week and have a desk job but go on walks, or you have a fairly active job. Or you work out INTENSELY 4-5 times a week and have a desk job. OR you don’t workout and have a physically demanding job (i.e landscape, construction worker, etc.)
1.725 – Very Active (exercise hard most days and also have active job where you’re moving around a lot)
1.9 – Extra Active (exercise hardcore and have a job that is physically intense by nature)

I would consider myself moderately active, and if we inputed my information into the equation, we would get:
TDEE = 1260 x 1.55 = 1953 calories

SO, we have now calculated that my total daily energy expenditure is 1953 calories.

***I want to note that this IS actually the amount of calories I was maintaining at before I started my calorie deficit/diet phase. Since I dieted for 12 weeks, my maintenance calories adapted to lower amount of calories I was eating to lose weight. So while I am not currently at these calories, this is where I started my calorie deficit at. Since this post is about beginning a calorie deficit, I will take you back to how I calculated my initial macros for my diet with my maintenance calories.

STEP 2: Determine your calorie deficit

Sure it’s important to have an idea of how much you want to lose, but what’s even more important is the rate at which you decide to lose this weight.

It’s also important to note that we want the rate to be fast enough to where we are actually seeing changes, but not too aggressive to the point where lean body mass is being lost as well.

From all the research I’ve done on this topic, science points to 0.4-0.8% of body weight in kg PER WEEK as the ideal rate to achieve fat loss. It is not recommended to go over 1%.

Decide your rate of fat loss per week:
0.4% – conservative
0.6% – moderate
0.8% – aggressive

In order to maintain my muscle mass but still see consistent results, I went with the moderate approach.
So if my weight is 117 lbs (53 kg) and I multiplied that by 0.6%
(53 kg x 0.006 = 0.32 kg)

Meaning that my target would be to lose 0.32 kg (or 0.7 lb) each week, on average.

Since 1 lb = 3500 calories, we can multiply 0.7 lb a week by 3500 to determine how many calories find how much of a deficit in calories I need for the week to lose 0.7 lb.
0.7 x 3500 calories = 2450 calorie deficit each week
If we divide this by 7 (each day of the week) that would come to a deficit of 350 calories each day.

The final step is just subtracting this deficit from your maintenance calories to determine your starting daily calorie intake for fat loss:

Maintenance calories – daily calorie deficit = Starting daily calories for fat loss

Again, using my stats for an example:
1960 calories – 350 calories = 1610 calories
SO, I would start my calorie deficit phase at 1610 calories!

STEP 3: Determine your protein intake

Now that we have the hard part out of the way, the rest is pretty simple.
The FIRST macronutrient that is the most important to consider is protein. We need to ensure adequate protein intake to minimize muscle mass loss and protein being burned for energy as opposed to fat.

According to the research, 1g of protein per pound of body weight in pounds has been found to be optimal for most people.

I would recommend not going below 0.72g of protein per pound of body weight, since this would begin to increase the risk of muscle mass being lost with the calorie deficit.

Greater than 1g is typically not necessary since the other macronutrients still need to be considered and consumed in adequate amounts as well.

If you are obese, it would far more appropriate to base protein intake off of lean body mass instead (2.0 – 2.2% per kg of LBM).

Determined protein intake = 117g (based off my weight of 117 lbs)

STEP 4: Subtract protein calories from overall calorie deficit

Because 1g of protein = 4 calories, we can multiply our determined protein intake in grams by 4 to determine the number of calories of protein that is to be consumed.
117g protein x 4 calories/g = 468 calories of protein daily

We can then subtract this number from our overall calorie deficit:
1610 calories – 468 calories = 1142 remaining calories.

These are the calories that will be divided between fats and carbs.

STEP 5: Determine fat and carb intake

Finally the last step! This is the part where a lot of people get tripped up. But given everything else we already covered, the ratio between carbs and fat in the overall scheme of things is less important. Overall calorie deficit and protein intake is what matters MOST!

As far as carbohydrate to fat ratios go, it honestly comes down to personal preference.
Which ratio would you be more likely to adhere to?
Which ratio would you enjoy and perform well on?

It is important to remember that fats have more calories per gram (9 cals/g) than carbohydrates do (4 cals/g). But calorie to calorie there has not shown to be a significant amount of research to highlight one over the other when it comes to fat loss.

Like I said, it is MOST important that you choose a ratio that works best for you and one that you can stay consistent with!

With that being said, I chose a 60/40 ratio of carbs/fats. This is what I feel that I perform the best at and what I know I can stick to.

Inputing the remaining information:
Remember I had 1142 calories remaining after subtracting protein already.
First carbs:
If we multiply 1142 calories by 60% to be consumed by carbs:
1142 calories x 0.6 = 685 calories of carbs
685 calories of carbs divided by 4 cals per gram of carb = 171g carbs
Then fats:
1142 calories x 0.40 = 457 calories of fats
457 calories divided by 9 cals per gram of fat = 51g fats

Step 6: Putting it all together

To summarize, you need to have a general idea of what where you’re starting to have the most accurate to use and modify going forward. This is honestly the most important part!

  • Establish maintenance calories
  • Establish your calorie deficit
  • Establish protein intake
  • Determine best carbohydrate/fat ratio that is sustainable for you

More information in the blog posts to come about diet/fat strategies, how to combat plateaus, etc. Let me know what else you are interested in learning more about either through my email, laurenfitfoodie@gmail.com or my instagram, @Laurenfitfoodie.

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