First of all, I don’t track my calories on a daily basis because I think it is just too much work compared to the goals I have. And, unless you want to get to 6% body fat, you don’t have to either. However, I think it is important to track your calories for a limited amount of time to get a feeling of what you eat and how your body responds. This post will show you how to estimate your daily energy expenditure and therefore determine your daily calorie intake.
So how much calories do you need a day? This is an important question to ask yourself, no matter if you want to lose weight, build some muscles or want to provide optimal energy supply for your body.
You need food to sustain your metabolism and drive your muscles. The food you eat basically consists of carbohydrates, fats, proteins, alcohol, water, vitamins, and minerals. Carbs, fats, and proteins get burnt to generate energy while water, vitamins, and minerals are not broken down and are used by the body in the form in which they are absorbed.
Since energy is hard to measure we need some reference that tells us which amounts of energy the food we eat is providing, so basically which foods to eat and which ones to avoid. To determine the energy value of food, the food is burnt and the heat energy it releases is measured. This is similar to our body’s process which processes food to break down the proteins, lipids, and polysaccharides to smaller molecules so our cells can use them. The most important factor for the primary energy currency in the cell is adenosine triphosphate (or ATP). This molecule is used to build complex molecules, contract your muscles, generate electricity in nerves, and light fireflies. During physical activity, ATP is built without oxygen (anaerobic) for the first one or two minutes using creatine phosphate and glucose, creatinine and lactic acid are waste products of this process. Exercise that goes above 2 minutes will require oxygen to produce ATP (aerobic) the waste product of this process is carbon dioxide.
So how much calories does our food contain? The following table shows calories per gram of proteins, carbs, fats, fiber, alcohol, and minerals:
For your body carbs are an effective way to produce energy. A study shows that approximately 80% of ATP demands are covered by glycogen (polysaccharide) which is mainly stored in your liver, muscles and fat cells.
The graphic below shows you the basic process of ATP production:
Now that we know the basic process of energy production and how many calories our food contains we have to be able to estimate how much food/calories we should eat during the day.
Our daily calorie intake can be divided into three blocs:
1. Basal metabolic rate (BMR)
Even if you do nothing at all and lay in your bed all day your metabolism needs energy to function. The basal metabolic rate provides energy for all the basic functions of your body like breathing, blood circulation, body temperature and brain functioning. This rate is primarily dependent on your muscle mass and training intensity and is usually responsible for about 60-70% of your total daily energy expenditure.
2. Thermic effect of activity
This is the amount of energy spent on every extra movement you do during the day. So your walk to work or school, putting your clothes on in the morning or working out. (Side note: if you want to save some calories just drive to work without putting your clothes on and try to use the elevator as often as you can :D). On average this will take up 30% of your daily energy expenditure. However, this is the most volatile component of the equation. As you can see above you can distinguish between basic daily activities which are the same for most people and physical activity. The amount of physical activity highly depends on the individual person. So if you are very active the thermic effect of activity will be much higher than 30%.
The last component of your daily energy expenditure is thermogenesis which is the thermic effect caused by consuming food. This effect can vary depending on the type of food you eat. Research shows that eating high protein food and especially prior to exercise results in greater caloric expenditure. Vice versa exercise prior to a meal can increase the thermic effect of food by 73%.
How can you estimate your daily calorie intake?
Basically, men need around 2,500 kcal to maintain their health, while women only need 2,000 kcal. However, as we have seen above this number can vary for each individual based on their physical activity, metabolism, and age. In the following, I will show you two ways how you can estimate your daily energy expenditure.
1. Approach (quick solution)
The first one is fairly simple. If you don’t want to calculate anything and only want a more or less rough estimate you can follow the suggestions for daily calorie intake below:
|Age and gender||Estimated BMR||Category 1: limited physical activity||Category 2: high amount of physical activity||Category 3: very high amount of physical activity|
|Men||kcal per day||kcal per day||kcal per day||kcal per day|
|15 – 19 years||1,820||2,500||3,300||4,000|
|20 – 51 years||1,740||2,400||3,100||3,800|
|51 years and older||1,410||2,000||2,500||3,100|
|Women||kcal per day||kcal per day||kcal per day||kcal per day|
|15 – 19 years||1,460||2,000||2,600||3,200|
|20 – 51 years||1,340||1,900||2,400||2,900|
|51 years and older||1,170||1,600||2,100||2,600|
Based on where you fall for age, gender and activity level you will get to a certain recommended value.
2. Approach (more precise calculation)
If you want to be a little more precise you can calculate your daily calorie intake based on your lean body mass (LBM).
Lean body mass = Body weight – Body fat
This way you will be more precise taking into account your individual body composition. To get to this lean body mass you can either use a specific weighing scale which will display body weight, body fat percentage, lean muscle mass etc. or get a professional body fat measurement. Either way, once you have this value you can use the following calculation (Please note: the calculation is based on your LBM in kilograms):
22 x LBM + 500 = BMR
Daily calorie intake = BMR x Activity factor
|Sedentary jobs, no or little physical activity. No sports||1.4 – 1.5|
|Mainly sedentary job with limited amount of walking or standing. Little physical activity, light exercising||1.6 – 1.7|
|Work is mainly done in standing position or walking. Competitive sports.||1.8 – 1.9|
|Physically demanding job (Construction worker, lumberjack). Highly competitive athletes.||2.0 – 2.4|
I weigh around 80 kilograms, my body fat percentage is approximately 12% which equals an LBM of 70.4. At the moment my work is mainly sedentary but I work out 6 times a week which means a high level of physical activity. So my activity factor would be 1.8.
BMR= 22 x 70.4 + 500 = 2049
Daily calorie intake = 2049 x 1.8 = 3688 kcal/day
My daily calorie intake would, therefore, be around 3688 kcal/day. This doesn’t mean that I have to eat exactly 3688 kcal a day because this still is an estimate but nevertheless it is a food reference you can work with.
No matter which way you chose to estimate your daily calorie intake you should keep track of your performance and adjust accordingly. To make your life easier just assume that if
Calories in > calories burnt = weight gain
Calories in < calories burnt = weight loss
So if you are looking in the mirror and don’t see any physical changes and your weighing scale still displays the same weight you might want to increase the number of calories you take in to build muscle. On the contrary, if your waist is growing a lot faster than your chest, arms etc. you should decrease your daily calories since you are consuming much more calories than you actually burn and these extra calories are stored in your body.
Like with most things you will need to get some experience first. But once you wrapped your head around this you won’t have to measure calorie by calorie every day.
If you are not a professional bodybuilder just use the Pareto principle and remember that 20% of the effort will bring you 80% of the results. So if you don’t plan to get to 6% body fat which would require the remaining 80% of effort take it easy and try to get a good feeling for everything you eat. What I do is track the nutritional value of the food I frequently eat, for example, the oatmeal that I have almost every day for breakfast. So if there are things you consume regularly just track them once and you will be able to include them in your mental calculation. By doing this you will get the experience and a better feeling for your daily intake.
To check your progress just look into the mirror and see if there are any positive or negative changes. If you want to be more exact you can measure the body parts you are training, e.g. your arms, legs, chest etc. and see if they increased in size.
So I hope this post cleared some things up and will help you stay healthy, energized and in a good shape!
Take care and talk to you soon!
Photo credit: Steve Buissinne, check out his cool pictures!
 Lambert, C. P., Frank, L. L., & Evans, W. J. (2004). Macronutrient considerations for the sport of bodybuilding. Sports Medicine, 34(5), 317-327.
 Kreitzman, S. N., Coxon, A. Y., & Szaz, K. F. (1992). Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. The American journal of clinical nutrition, 56(1), 292S-293S.
 Calculate Your Basal Metabolic Rate (BMR)!: https://www.bodybuilding.com/fun/bmr_calculator.htm.
 Stiegler, P., & Cunliffe, A. (2006). The role of diet and exercise for the maintenance of fat-free mass and resting metabolic rate during weight loss. Sports medicine, 36(3), 239-262.
 Calculating Your Daily Caloric Expenditures: http://krupp.wcc.hawaii.edu/BIOL100L/nutrition/energy.pdf
 More on Dietary Thermogenesis: http://www.robertbarrington.net/more-on-dietary-thermogenesis/, by Robert Barrington.
 Binns, A., Gray, M., & Di Brezzo, R. (2015). Thermic effect of food, exercise, and total energy expenditure in active females. Journal of Science and Medicine in Sport, 18(2), 204-208.
 Denzer, C. M., & Young, J. C. (2003). The effect of resistance exercise on the thermic effect of food. International journal of sport nutrition and exercise metabolism, 13(3), 396-402.
 What should my daily intake of calories be?: http://www.nhs.uk/chq/pages/1126.aspx?categoryid=51.