# A Scientific Method to Calculate Your Weight Loss in a Diet Using Calorie Counting

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 weight loss and after that all of a sudden in a few days, you would experience a significant amount of 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 is by walking so I found a way to estimate my burning calories each day using my total steps.

This website estimates your total burning calories using your age, gender, height, weight, speed and duration. I recommend calculating your burning calories for 100 minutes to minimize the approximation error. In my case my burning calories per 100 minutes was 621 calories i.e. 6.21 calories per minute. My walking cadence (number of steps in one minute) is usually 120 so my burning calories per each step is usually 6.21/120 calories. Therefore, my total burning calories for a certain number of steps is equal with steps*6.21/120 .

Maximizing the accuracy of burning calories estimation

Remember by means of time during your diet as you lose weight, both your BMR and your burning calories by your activities during the day would change so you’d better update your numbers in the websites I provided above once every month. For example my (BMR,100 minutes walking burning calories) when I was 79.5 kg were (1795,621) calories respectively but one month later when I dropped 3.5 kg 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 has been 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 1795 calories. My burning calories for 15000 steps on that day using the formula above was 15000×6.21/120=776 calories. Therefore my total burning calories on that day is equal to 1795+776=2571. As a result my burning calories minus my intake calories is equal to 2576-1500=1076 calories. But how much weight loss should I expect for burning 1076 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 for our calculation.

Back into our example and using the above assumption, a 1076 calorie deficit would lead to 1076/3500=0.307 lb or 1076/7709=0.139 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 and you have to rebuild your table every month. I am using my own data for one month to show you my method and I will compare the results with my daily weight I 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:

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:

If you want to generate the above formula for yourself, you might replace 1795 by your BMR, 6.21 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 and we would get a table like this:

Remember in that table negative weight loss means gaining weight. Now in the last column, we want to have the sum of elements of column D. In terms of google sheets formulas, in the last column, we want to have the following numbers respectively from the bottom: sum(D8:D8), sum(D7:D8), sum(D6:D8),…,sum(D2:D8). For that purpose we need to use the \$ sign in order to keep one variable constant. Therefore use the following formula in the last column and drag it to the top to generate the formula for the entire column. The formula is:

After generating the formula for the entire column we have:

Finally we would make the last column which is our approximation for each day’s weight using calorie counting and compare it to the actual weight of that day measured at the beginning of the day by scale. The formula for the last column is:

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

Now I will show the google sheet result for the entire 30 days:

As you can see, the result is surprisingly accurate. After 30 days when I experienced my last sudden weight loss, my actual weight was 76.0 kg and my calorie counting weight was 76.1 kg and the error was literally negligible.