Knowing how many calories your body burns a day will help you to accurately estimate how much you need to reduce the calories you are consuming in order to lose weight. A quick Google search will provide you with formulas to calculate your daily requirements for calories and macros based on your resting metabolic rate (RMR). In my opinion these are often not very accurate as they are primarily based on your body weight instead on your body composition. Two people with the same body weight might not have the same RMR because one of them might have more muscle mass and less body fat and the other one more body fat and less muscle mass which affects metabolism significantly. They ask you to multiply your "RMR" by an activity level multiplier and BOOM! You have the number of how many calories your body burns a day. Although you don't really.
Very often together with these formulas there are recommendations for how much we should reduce the calories we eat in order to lose weight. Popular claim is that in order to lose weight you need to reduce between 300 and 500 calories a day from the calories you need to maintain your body weight. Reducing 500 calories form your daily diet is one thing when your maintenance calories are 2500 and another when they are 1500. In the first case you would be reducing your calorie intake by 20% and in the second by 33%. In this article I want to share with you a more accurate way to calculate how many calories your body is actually burning in a day and how many you need to eat in order to safely lose weight. LET'S GO! Let's begin from your resting metabolic rate. These are the calories which your body burns in a day in resting state, say if you were to lay in bed all day. Like I mentioned earlier, this number will depend on the amount of body fat you have and the amount of lean body mass (LBM, everything else which is not body fat) in your body. To have an idea about how much LBM and fat mass there is in your body you need to calculate your body fat percentage. You can estimate your body fat percentage using the illustration below. Remember that these are only estimates. If you want to know your accurate body fat percentage you would have to take a bioimpedance analysis.
After you have your body weight and your fat percentage you have to multiply them to see how many kilograms of your weight is body fat. For example let's take Annie who weighs 60 kilograms and has estimated her body fat percentage to be 20. Her equation would look like this: 60 x 0.2 = 12 (where 0.2 is 20% body fat and 12 is the number of kilograms body fat mass) The remaining 48 kilograms is lean body mass (LBM). 1 kilogram of lean body mass burns 26.4 kcal a day, whereas 1 kilogram of body fat burns only 4.4 kcal. This is very important for accurately determining your resting metabolic rate. Naturally, the next step would be to multiply these numbers (26.4 and 4.4) with the kilograms of LBM and fat mass respectively and add them together. For our Annie it would look like this: (48 x 26.4) + (12 x 4.4) = 1320 So in our example the RMR is 1320 kcal a day.
"1 kilogram of lean body mass burns 26.4 kcal a day, whereas 1 kilogram of body fat just 4.4 kcal."
Now that you have calculated your RMR the next step it to multiply it by an activity multiplier. With this I advise you to be realistic with yourself regarding how active you are on a daily basis as wrong perception would mean wrong calculation. Keep in mind that if you do exercise on a daily basis it is not included here. There is a different multiplier for that. Your activity level simply describes how you spend most of your day. If you work on a desk and you have little to no additional activity, your activity level is probably sedentary. If you do deliveries all day it's probably moderate to high. You can choose the multiplier from the chart below. RMR x Activity Level Multiplier = How many calories you burn a day
If Annie is sedentary the calories she burns a day would be equal to 1320 x 1.3 = 1716 kcal. This means that to maintain her body weight she needs to eat 1716 calories a day. These are her maintenance calories. But if she considers herself moderately active this number would be 1320 x 1.6 = 2112. You see that this is nearly 400 calories difference so be honest with yourself about your activity level. MOVING ON! In order to lose weight (presumably body fat) you would want to be eating less calories than the calories you are burning. There are a few ways to do that: - Increasing the calories you burn a day by adding exercise; - Reducing the calories you eat; - A mix of both;
I recommend a mix of both for a few reasons. One is that it is very difficult to lose weight with exercise alone if your diet is not in accordance. It is also difficult to lose weight with healthy diet only because without exercise you would need to eat even less calories. The last is that the benefits of exercise go well beyond the mere losing of weight. Improving your strength, mobility, balance and your mood are just a few of them. For a safe weight loss to occur there should be no more that 20% difference between the calories burned and the calories eaten on a regular basis. Difference of more than 20% might give you undesired outcome (slow metabolism, messed up hormones, fatigue, etc.). So if our Annie wants to lose weight and she is burning 2112 kcal a day she needs to create a negative imbalance of 422 kcal (this is 20% of her maintenance calories). She can choose between burning 422 calories daily with exercise, reducing her food intake by 422 calories, or burning 211 calories with exercise and reducing her calorie intake by another 211.
To calculate how many calories your daily deficit should be just multiply your maintenance calories by 0.2. ADDING EXERCISE Let's assume that you want to add some exercise to your routine to help you with creating that deficit. To calculate the calories which specifically your body will burn doing different exercises you would be using an exercise activity multiplier. In the chart below you can see the multiplier for 1 whole hour of each activity.
Let's use our example person Annie. She has a resting metabolic rate of 1320 calories. She is moderately active and therefore chose the activity level multiplier of 1.7. She plans to do weight training to help her create a daily calorie deficit and she wants to know how many calories she will burn for the whole day. For 1 hour of weight training a day Annie will add the corresponding 0.2 multiplier. Now her multiplier is 1.9 and in a day she will burn 2508 calories (1320 x 1.9 = 2508). If she is planning to do half an hour of weight training for example she can take the multiplier to be not 0.2 but 0.1. With the formulas we covered so far you will be able to calculate how many calories your body burns a day and in exercise. But that's only calories. We need to pay specific attention to macronutrients as well. Did you know that 1 gram of fat provides 9 calories, whereas 1 gram of protein or carbohydrate provides only 4? WHAT ABOUT MACROS? Figuring the right amounts of different macros daily intake is important part of your fitness journey. I know that it can be quite confusing because it also varies depending on how active you are. Here we will discuss the daily requirements for protein, fat and carbohydrates.
1 gram of fat provides 9 calories, whereas 1 gram of protein or carbohydrate provides only 4.
Protein Protein makes up everything in our bodies. It is essential to eat enough protein especially for people who exercise on a regular basis. We need it to repair and rebuild our muscles. In the chart below you can see the requirements for daily protein intake for adults based on the type of exercise being added to their routine.
If you already calculated your LBM (lean body mass) from the formula above you can multiply it with the corresponding number from the chart. For example Annie has 48kg of LBM which is equal to 105.6 lbs. We know that she is doing weight training and is dieting for weight loss. Therefore her daily protein intake requirement is 105.6 x 1.2 = 126g. Foods rich in protein are meat, fish, dairy products, eggs, chickpeas, beans, lentils, nuts and seeds. Fat In my opinion when calculating daily macro intake requirements it's better to calculate first protein, then fat and after this - carbs. Fat has a vital role in our endocrine system as hormones such as estrogen and testosterone are derived from cholesterol. The dietary guidelines from the World Health Organization recommend fat intake between 20 and 35% of total calories. And to ensure that minimum of 20% of the calories consumed come from fat. This is a rather general approach and while the gentlemen might find it reasonable it might not apply all the time correctly for ladies. Women's bodies requirements for dietary fat change throughout the month. During the follicular phase of your cycle insulin sensitivity is higher and your body is better at burning carbohydrates for fuel. This changes in the luteal phase when your body is better at utilizing fat as an energy source. Lyle McDonald (The women's book) recommends an intake of 25% during the follicular phase and 35% during the luteal phase going up to 40% as optimal for treating insulin resistance and PCOS if present. It's recommended to not go below the minimum requirement of 20%.
For example for a 2000 calorie diet, at least 400 calories should be coming from fat in order to support healthy hormones and healthy body. This is approximately 45 grams of fat. Focus on healthy fats such as the ones in olive oil, avocados, nuts and seeds and try to avoid trans fats such as the ones in store-bought sweets and baked goods. Carbohydrates Naturally, after you have calculated how much protein and fat your body needs a day and you know how many calories that is, the rest of the calories in your diet should be coming from carbohydrates. Remember that they are essential fuel for your workouts and for your brain and don't skip them as this can cause you to feel fatigued and weak not only during your workouts but in your day in general. For optimal health and performance focus your carbohydrate intake on wholegrain foods, fruits, vegetables and legumes. BOTTOM LINE Figuring out the right amount of calories and macros for you is very important step towards a healthy weight loss and sustainable diet in the long term. Focus on foods which your body needs to fuel and rebuild itself rather than the ones you should avoid.
References The Effects of Strength Training on Women - Vanya Sakazova, 2018 https://www.theseus.fi/handle/10024/144332
A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion - Ann G. Liu, Nikki A. Ford, Frank B. Hu and Co. 2017 -https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5577766/#:~:text=Dietary%20guidelines%20from%20the%20World,calories%20%5B12%2C%2013%5D. The Women's Book: A Guide to Nutrition, Fat Loss, and Muscle Gain - Lyle McDonald, 2017