The Most Accurate Way to Calculate Your Daily Calorie Needs and Macronutrient Breakdown

In the process of achieving physical fitness, nutrition is as important, if not more, as the workouts we do in the gym. Even if you do perfect workout best suited for your needs, if you do not feed your body with the right nutrients, you are not going to see results.

There are three aspects of nutrition that you need to consider while designing your diet

  1. Total amount of calories you are taking in
  2. Ratios of the macronutrients i.e. Proteins, Carbohydrates and Fats
  3. When to eat what

Lets discuss each of these one at a time

Calculating Calorie Requirements

There are a variety of ways been proposed on calculating your daily calorie needs, here we provide three methods in the order of increasing complexity.

Approach 1: This is a rather simple approach, just take your weight in pounds and multiply it by a factor of 20. As an example if your weight is 180 pounds, then your daily calorie requirement is 180 X 20 or 3600 calories a day. Although this calculation is really simple to perform, it is prone to great amounts of errors, since it does not consider your height, body composition, lifestyle age and gender into account. As an example a 5 feet 3 inch tall obese woman and a 6 feet tall male athlete with same 180 pounds of weight will get same calorie requirements through this approach, which obviously is incorrect. In our opinion this approach is only useful for physically fit men.

Approach 2: This second approach is more complicated then previous one and can provide relatively accurate calorie requirements. This is based on using the Harris-Benedict equation for daily calorie requirements. It involves two steps; first you have to calculate your basal metabolic rate (BMR). The table below shows the equations

BMR Men (Metric)66.5 + (13.75 X Weight in kg) + (5.003 X Height in cm) – (6.755 X Age in years)
BMR Men (Imperial)66 + (6.2 X Weight in pounds) + (12.7 X Height in inches) – (6.76 X Age in years)
BMR Women (Metric)655.1 + (9.563 X Weight in kg) + (1.85 X Height in cm) – (4.676 X Age in years)
BMR Women ((Imperial)655.1 + (4.35 X Weight in pounds) + (4.7 X Height in inches) – (4.7 X Age in years)

In the second step, based on your lifestyle you should multiply your BMR with an activity factor

Little to no exerciseDaily Calorie Needs = BMR X 1.2
Light Exercise (1-3 days per week)Daily Calorie Needs = BMR X 1.375
Moderate Exercise (3-5 days per week)Daily Calorie Needs = BMR X 1.55
Heavy Exercise (6-7 days per week)Daily Calorie Needs = BMR X 1.725
Very Heavy Exercise (twice per day)Daily Calorie Needs = BMR X 1.9

As you can see this approach is little bit more involved than just multiplying your weight with a factor of 20. These equations take into account you height, weight, age, gender and your activity level. For an average person who is not way off in their body composition, this approach is relatively accurate, but there will be errors if you have too much fat or too little fat. As you can see from the equation, the calorie requirement for two individuals of same height and same age increases as their weight increases. This means a person who has higher weight due to more muscle and a person who has higher weight due to more fat; both will get the same result. This is clearly not true; the calorie requirements for a person with more muscles will be higher than a person with more fat, as it is our muscles, which burn calories not the fat. This brings us to the third approach.

Approach 3: This is the most accurate approach one can use to calculate the daily calorie requirements, but is also the most complicated. This approach is based on the Cunningham Equation. Here you start off with measuring your body fat percentage, which is the percentage of your body weight, which is composed of fat. Measuring body fat percentage is beyond the scope of this article; just Google search for measuring body fat percentage and you will find guidelines on how to measure it.

Once you have figured out what your body fat percentage is, you can multiply that factor to your body weight to calculate the actual weight of fat in your body. As an example, consider our 6 feet tall athlete who has a weight of 180 pounds with a body fat percentage of 10%, then the weight of fat in his body is 18 pounds. Once you know this fat weight, you need to subtract it from your overall weight to calculate your fat free mass. Now you can calculate your resting metabolic rate (RMR), which is the energy you need to spend for just lying in bed and do nothing, through the formula

RMR = 500 + 22 X (fat free mass in KG) or

RMR = 500 + 10 X (fat free mass in pounds)

Now of-course most of us do not just stay in bed and do nothing, we perform our daily chores, move around, eat and digest food, talk and think (not really sure if this last one applies to everyone). All these processes require our energy. Below are the factors you need to multiply to your RMR based on your level of activity, keep in mind this is daily calorie needs outside of exercise, i.e. it does not include the energy needs in performing exercises, we will come to that later.

Bed Ridden Individual1.3
Person with Sedentary Occupation1.6
Person with Mostly Sedentary Occupation and Some Movement1.7
Person in Active Occupation with Prolonged Standing1.8
Person Performing Strenuous Labor Work2.2

As an example, suppose our 180-pound athlete with 10% body fat has an active occupation with prolonged standing, then that person’s daily calorie requirements outside of exercise will be calculated as follows

Fat Free Mass = 180 -180 X 0.10 = 162

RMR = 500 + 10 X 162 = 2120

Outside exercise calorie needs = 1.8 X 2120 = 3816

As another example we may consider a 120-pound woman with 25% body fat, who has a sedentary desk job then, her calorie requirements outside of exercise will be calculated as follows

Fat Free Mass = 120 -120 X 0.25 = 90

RMR = 500 + 10 X 90= 1400

Outside exercise calorie needs = 1.6 X 1400 = 2240

In summary on the days when they are not performing exercises, the 180-pond athlete needs to consume 3816 calories and the 120 pound woman has to take 2240 calories. On the day when they perform exercise, they need to add the calories they expended in performing the exercise.

To calculate that calorie expenditure for a particular exercise, you need to consider the intensity of an exercise into account. In general the intensity is defined through METs, it is a metabolic multiplier that is applied to any exercise based on how intense it is. Below is a list of METs for different types of exercises

High Impact Aerobics7
Low Impact Aerobics5
Vigorous Effect Bicycling (14-16mph)10
Light Effort Bicycling (10-12mph)6
Vigorous Walking5
Light Walking2.5
Running (6min/mile)16
Running (12min/mile)8
Intense Weightlifting6
Light Home Exercise, light to moderate effort3.5

You can calculate the amount of calories burnt in each exercise by multiplying the MET factor with your weight and the amount of time you spent in doing the exercise. The formula is

Calorie Burnt in an Exercise = Body weight (KG) X Duration (hrs) X METs

Calorie Burnt in an Exercise = (Body weight (lbs) X Duration (hrs) X METs) / 2.2

As an example for our 180 pounds athlete who performs intense free weight training for an hour and a half, his calorie burnt will be

Calorie burnt in Free Weight Training = (180X 1.5 X 6)/2.2 = 736

For a 120 pound woman, who performs low impact aerobics for an hour, her calorie burnt will be

Calorie burnt in Free Weight Training = (120 X 1 X 5)/2.2 = 273

Finally to calculate the daily calorie need, you need to add the outside exercise calorie needs and the calories burnt during exercise, so going back to our examples. Daily calorie need for a 180 pounds athlete on the day he performs weight training is 3816 + 736 or 4552 calories. And the daily calories need for the 120 pounds woman on the day she does light aerobics is 2240 + 273 or 2513 calories.

So these were the three approaches you can choose from to calculate your daily calorie needs. It all depends on your situation and how accurate you want to be in your estimate. Other important point to keep in mind is that, these calorie requirements are only to maintain the current body weight, if you want to gain muscle then you have to be in calorie surplus so add 500 calories to your daily needs. if you are interested in cutting fat then you have to be in calorie deficit , so subtract 500 calories from your daily needs. These 500 calories will cause you to gain/lose weight at roughly 1lb/week.

It should be noted that all the three calculations suggested above are just a starting point for you. Although they vary in accuracy, the only 100% accurate way to estimate you calorie needs is through trial and error. Continue to eat the calculated amounts of calories for a week and observe how much weight you gained or lost. Repeat this for a few weeks and notice on average how much weight you lost/gained per week. If it was significantly different from what you expected then adjust your calorie in take. Note the weight must be measured at the same time of the day and under similar conditions. Best time in our opinion is right after you get up in the morning

Ratios of the Macronutrients

Once you have determined your total required calorie intake, you need to break it down into the macronutrients, i.e. what percentage of your calories come from which macronutrient. The ratio of the macronutrients depends on whether you are trying to gain muscle, lose fat or maintain weight. The table below shows the typical breakdown of the macronutrients according to your goals

Gain Muscle40-60%25-35%15-25%
Maintain Weight30-50%25-35%25-35%
Lose Fat10-30%40-50%30-40%

Most of the food labels have the nutrients mentioned in grams, while we have calculated macronutrients into calories. To do the conversion keep in mind that each gram of carb and protein provides 4 calories, while each gram of fat provides 9 calories. Use the calorie numbers and divide them by the conversion numbers to get the macronutrient requirement in grams.

Going by the example of the 180-pound athlete whose calorie requirement was calculated to be 4500 calories a day. Lets say he wants to maintain his weight. He decides to use a breakdown 40-30-30. Then he needs 1800 calories from carbs and 1350 each from proteins and fat. Since 1 gram of carbs produce 4 calories, in all he needs 1800/4 or 450 grams of carbs. Same way he will need 1350/4 or 337.5 grams of protein and 1350/9 or 150 grams of fat.

Similarly for the 120-pound woman, whose calorie requirement is 2500 calorie and decides to lose fat, then she decides to take 2000 calories a day and a macronutrient ratio of 30-40-30. She needs 600 calories each from carbs and fat and 800 from proteins. Therefore she will take 600/4 or 150 grams of carbs, 800/4 or 200 grams of protein and 600/9 or 67 grams of fat. Please note these numbers are for the day when they exercise, on the day they do not exercise, these numbers will be different.

An important thing to keep in mind here is that although they are allowed to eat carbs and fat, this does not mean that they can eat any carb or any fat. They will choose to eat complex carbs and healthy fats. Refer to USDA recommendations for choosing the right food for each of your macronutrients.

When to Eat

Finally when should you be eating your food? The most popular recommendation is to breakdown your day into 6 smaller meals rather than the typical 3 big meals. This way you give your body a steady supply of nutrients, instead of eating everything at just one time. Breakfast is the most important meal of the day as the body has been starving for the longest time; provide your body with good carbs and fast digesting protein. Try to minimize your carbs during dinner and eat slow digesting protein so that your body has a steady protein supply through out the night. Fats should be taken through out the day. Eating atleast 5 servings of fruits and veggies is important to provide you essential micronutrients (Vitamins and Minerals).

Recently there has been new research recommending intermittent fasting as a great diet to follow for fat loss. Intermittent fasting diets recommends fasting during most of the day and eat all your calories in a short period of time during the day. You can give a try to both these types of diets and evaluate, which one gives you better results. You can refer to the previous blog on intermittent fasting  to learn more on it.

A small note on supplements: it sometimes becomes really difficult to ingest the recommended amounts of proteins naturally, so you may consider taking a scoop of whey protein in the morning. Moreover, right before and after a strength workout you should consider taking a pre- and post-workout shake to boost muscle gain and limit muscle soreness. Do consider supplementing your diet with fish oil to provide you the omega-3 fatty acids to boost your hormones for muscle growth.