How to Predict Your Diet Weight Loss Using Simple Calculations

If you have ever tried to lose weight during a diet, you might have asked yourself how much effort should I put in to drop a certain amount of weight in my diet? Also during a diet, you might simply ask yourself how much weight I have lost so far? For the second question, you might answer: I would weigh myself everyday to find out the amount of weight I have lost so far but the problem is not that simple. 

First of all the process of losing weight in a diet is not always gradual but instead it is sometimes a sudden process. In other words during your diet, you might experience 7-10 days with no significant weight loss and after that all of a sudden in a few days, you would experience a sudden weight loss in your diet. Second, if you scale yourself every morning to measure your weight loss, you might not always find the right answer. Your body might have extra body water or your stomach might not be completely empty and that makes a significant error in measuring your total weight loss during your diet.

Theory of our calculations

In this article, I am trying to introduce a method to calculate the amount of weight loss during someone’s diet using calorie counting. In order to maintain your weight in a day, someone’s intake calories should be equal to that person’s burning calories. In order to lose weight, your burning calories should be more than your intake calories and for gaining weight, your intake calories should be more than your burning calories. In our case, we definitely need to lose weight so our intake calories should be less than our burning calories but the main question here is how to find the calorie equivalent of everything in this process.

Calorie Calculations

For your intake calories, the answer is simple. You might measure how many calories you consumed during each day. Your burning calories during each day contains two parts (and we have to add them up together to evaluate your total burning calories in each day). Your Basal Metabolic Rate (BMR) and the amount of calories you burn during your activities in a day. 

Basal metabolic rate is the amount of calories your body needs to accomplish its most basic (basal) life-sustaining functions. One popular way to estimate BMR is through the Harris-Benedict formula, which takes into account weight, height, age, and gender (reference Here). Below is the BMR formula for women and men respectively: (you can alternatively use this website to calculate your BMR)

Women BMR = 655 + (9.6 × weight in kg) + (1.8 × height in cm) – (4.7 × age in years)

Men BMR = 66 + (13.7 × weight in kg) + (5 × height in cm) – (6.8 × age in years)

You also need to calculate your burning calories during your daily activities as well. That greatly depends on the source of your burning calories each day. Some fitness trackers estimate your burning calories so that’s an option. In my case my main source of burning calories during my diet was walking so I found a way to estimate my burning calories each day using my total steps. 

This website estimates the total burning calories of your walk using your age, gender, height, weight, speed and duration of your walk. I recommend calculating your burning calories for 100 minutes to minimize the approximation error. In my case, my burning calories per 100 minutes of walking with 10 min/km (16 min/mile) pace using my (age, height, weight)  was 622 calories i.e. 6.22 calories per minute. My walking cadence (number of steps in one minute) is usually 120 so my burning calories per each step on average is 6.22/120 calories. Therefore, my total burning calories for a certain number of steps is equal with (number of steps)*6.22/120 . 

Maximizing the accuracy of burning calories estimation

Remember during your diet as you lose weight, both your BMR and your burning calories by your activities would change so you’d better update your numbers in the websites I provided above once every month. For example my (BMR, burning calories of 100 minutes of walk) when I was 79.2 kg (174.4 lbs) were (1791,622) calories respectively but one month later when I dropped 3.2 kg (7 lbs) the corresponding numbers were (1748, 607) calories respectively. 

Required calories for losing weight and the assumptions

Now we have an idea about the calculation of intake and burning calories. For example, let’s assume at the beginning of my diet, I had 15000 steps in one day as the main source of my burning calories and my total intake calories in that day was 1500 calories. The question is how much weight loss should I expect after that day so let’s do the calculation. 

My BMR using the formula I provided above was 1791 calories. My burning calories for 15000 steps on that day using the formula above was 15000×6.22/120=777 calories. Therefore my total burning calories on that day is equal to 1791+777=2568. As a result, my burning calories minus my intake calories is equal to 2568-1500=1068 calories. But how much weight loss should I expect for burning 1068 extra calories?

The answer depends on whether you are burning fat, muscle or LBM/protein. There are 3500 calories worth of energy in one pound of fat (7709 calories per kg) and 700 calories worth of energy in one pound of muscle tissue (reference Here). If a person creates a 3500 caloric deficit, that deficit does not come solely from fat but for simplicity of our calculation, we assume that person is solely burning fat. Of course that would lead to an error in our calculations but remember we are just doing an approximation in our calculation. 

Back into our example and using the above assumption, a 1068 calorie deficit would lead to 1068/3500=0.305 lbs or 1068/7709=0.138 kg of weight loss.

Calculating weight loss for long term data using Google sheets   

Assume you have your intake calories data for one month and you have also stored your total daily steps as your main source of burning calories for one month. The question is how much weight loss you should expect during that month of your diet. I am answering that question using google sheets and I want to emphasize based on the above explanation, the accuracy of our method would decrease for data more than one month old and you have to rebuild your table every month. I am using my own data for one month to explain my method to you and I will compare the results with my daily weight measured every morning during that month. The final google sheets data is available in this file.

Let’s start with 7 days of data and we assume we would add each day’s data to the google sheets table at the end of each day. Our table starts with the following data:

ABCDE
1DateIntake CaloriesStepsWeight (kg)Weight (lbs)
208/05/20211490078.2172.2
308/04/202120608178.41172.7
408/03/202117302206078.4172.7
508/02/202121001532478.6173.1
608/01/20211160078.4172.7
707/31/20211380264178.3172.5
807/30/202114302569879.2174.4

Now our main goal is to see our weight loss each day and add them up together since day one to know our total weight loss. Therefore we would add two columns called weight loss and total weight loss in our google sheets file. The formula for my weight loss cell is as follows: 

=(1791+C2*6.22/120-B2)/7709*1000

If you want to generate the above formula for yourself, you might replace 1791 by your BMR, 6.22 by the amount of calories you burn in one minute of walking and 120 by your walking cadence (your total walking steps per one minute). 7709 would remain the same (there are 7709 calories worth of energy in one kg of fat). We drag this formula in the google sheets file to generate the entire column.

Remember in that column negative weight loss means gaining weight. Now in the last column, we want to approximate our weight by subtracting our initial weight minus the sum of each day’s weight loss from the beginning. In terms of google sheets formulas, in the last column, we want to have the following numbers respectively from the bottom to top: D8, D8-sum(F8:F8)/1000, D8-sum(F7:F8)/1000, D8-sum(F6:F8)/1000,…, D8-sum(F3:F8)/1000. For that purpose we need to use the $ sign in order to keep one variable constant. Therefore use the following formula in the column before the last one and drag it to the top to generate the formula for the entire column. The formula is:

=$D$8-sum($F8:F$8)/1000

By dragging the formula in google sheets, making the last two column and deleting the columns presented before we’ll have the following table:

DateEst. Weight Loss (gr)Estimated Weight (kg)Estimated Weight (lbs)
08/05/20213978.6173.2
08/04/2021-3478.6173.1
08/03/202115678.8173.5
08/02/20216378.8173.6
08/01/20218278.9173.8
07/31/20217179.0174.0
07/30/202122079.2174.4

I applied this method for three consecutive months and reported the results in the next three posts. The accuracy of the method was surprisingly good, especially for the beginning (first couple of months) of the diet.

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