How Many Calories Do We Need?

Nearly all of us seek to lose extra weight, build a more muscular body, or simply maximize health and vitality. But what is the right amount of calories to eat in order to accomplish our fitness goals?

Are the formulas reliable, or is the number on the scale everything that matters?

As we will see in a moment, nutritional advice can be grouped into three categories. How to maintain weight, how to lose it and how to gain it. We already know that nutrition can’t always be reduced to a mere calorie calculation. However, having an idea of our energy intake can give us interesting information.

Energy Requirements

There is one way to measure with fairly high precision the amount of calories one person needs. It consists in putting a person into an insulated chamber and then measuring the amount of heat that person releases to perform a series of activities. This method is called direct calorimetry. Unfortunately, it is extremely unpractical and also quite expensive.

Another, more convenient, way to determine energy expenditure is by indirect calorimetry. Unlike direct calorimetry, indirect calorimetry works backward. First, you measure the amount of oxygen consumed by a person to perform an activity. Then, you attempt to estimate the relative caloric consumption.

Indirect calorimetry works with acceptable precision. It is not as accurate as direct calorimetry, but it’s also less expensive and simpler to carry out. This makes it optimal for large-scale population studies.

By integrating indirect calorimetry measurements from several subjects performing different activities, it is possible to build tables that give us an indication of how much energy is spent, on average, to perform an activity. Other than that, large-scale indirect calorimetry studies also give us the possibility to build predictive equations. Those equations are normally used to estimate energy requirements.

Let’s see how they work.

How Many Calories to Maintain Weight?

It doesn’t matter if our goal is to lose weight (fat), gain weight (muscle) or both. The first thing we need to know is the number of calories we need to maintain our current body weight.

Why? Because that is our energy balance. The energy balance is our starting point. From there, we adjust our calories according to what we want to accomplish.

So, how many calories do we need to maintain our current body weight?

It depends. If our weight has not significantly changed over the last weeks, then it’s easy. The calories we need to maintain our weight are the exact same amount we are eating now. This is logical because, if our weight is relatively stationary, we already are in an energy balance. At that point, all we have to do is keep track of the calories we eat on a daily basis. The daily average amount is our Total Daily Energy Expenditure (TDEE).

If instead our weight has been changing over the last weeks, or we have no clue when it comes to counting calories, it’s better to start off with some formulas. Among the many options out there, one of the most popular is the Harris-Benedict formula.

The Harris-Benedict Formula

This Harris-Benedict formula estimates the Basal Metabolic Rate (BMR) in healthy individuals.

Healthy individuals here means neither obese nor too lean. If we fall in one of these categories, the formula will respectively overestimate, or underestimate our BMR.

Other formulas might be more accurate at estimating BMR, but they also require more accurate data. Additionally, all formulas produce a guess at best. The popularity of the Harris-Benedict formula lies in its simplicity. To use it, we only need to know three simple data. Age, height and body weight.

The Harris-Benedict formula utilizes different equations for men and women:

Metric BMR = (13.4 x weight in kg) + (4.8 x height in cm) – (5.7 x age in years) + 88
Imperial BMR = (6.1 x weight in lbs) + (12.2 x height in inches) – (5.7 x age in years) + 88
Metric BMR = (9.2 x weight in kg) + (3.1 x height in cm) – (4.3 x age in years) + 448
Imperial BMR = (4.2 x weight in lbs) + (7.9 x height in inches) – (4.3 x age in years) + 488

As an example, let’s say we have a man and a woman. The man is 30 years old, 180 cm tall and weighs 80 kg. The woman is 30 years old, 170 cm tall and weighs 55 kg.

According to the formula, their theoretical BMR would be:

Harris-Benedict Formula Weight Height Age BMR
Man 80 kg 180 cm 30 years 1853 kcal
Woman 55 kg 170 cm 30 years 1352 kcal

Total Daily Energy Expenditure

Once we know our BMR, we want to estimate the Total Daily Energy Expenditure (TDEE).

The BMR is only part of the TDEE because it’s the amount of energy we need to maintain our basic vital functions. However, during the day, we also need energy to move around and perform all our daily tasks and activities.

For this reason, we have to multiply the BMR by an activity factor. This factor depends on our lifestyle and level of physical activity.

Lifestyle And Training Frequency Activity Factor
Sedentary (little or no exercise) 1.2
Lightly Active (training 2-3 days per week) 1.375
Moderately Active (training 4-5 days per week) 1.55
Very Active (training 6-7 days per week) 1.725
Extremely Active (training and physical job) 1.9

For example, let’s say our man is moderately active and our woman is sedentary. Their estimated TDEE would be respectively:

Harris-Benedict Formula BMR Activity Factor TDEE
Man 1853 kcal 1.55 2872 kcal
Woman 1352 kcal 1.2 1622 kcal

These are the calories per day they should theoretically consume to maintain their current body weight. Why theoretically? Because these are only estimates.

Calculations and the Reality of Dieting

It’s essential to realize that any calculation will be a guess at best.

First of all, the formulas were developed based on averages. The data come from a statistical analysis of the population. The closer we are to the average value, the more accurate the data will be. The more we deviate, the less reliable the data.

Secondly, there is no way to know with any true accuracy the exact amount of calories we are eating. Food labels are only accurate within 5-10% most of the time.

Thirdly, we all vary in subconscious reactions to diet changes. Some of us get more fidgety when in a caloric surplus. Some others get more lethargic when in a caloric deficit. This is known as Non-Exercise Activity Thermogenesis (NEAT) and varies greatly between people. No calculation can take into account these differences.

Lastly, there are many formulas that endeavor to help us determine “exactly” how many calories we need. However, the reality is that we all have a different metabolism.

For example, let’s say we calculated our TDEE but eating those calories actually makes us lose weight. This means the formula underestimated it. The TDEE is the amount of calories we need for maintenance. Not weight loss. As a result, we need to increase our caloric intake.

Similarly, if the theoretical TDEE causes an unexpected gain in weight, the formula overestimated it. This time, we need to cut calories.

The bottom line is that calculations are just our best guess. We can use the formulas but they are just starting points. They need to be adjusted until the weight on the scale moves in the direction we intend it to. We have to adjust the numbers based on real-world data.

How Many Calories to Lose Weight?

Once we have calculated and adjusted our TDEE over time, it’s easy to know how many calories we need to lose weight. Less than we need to maintain it!

A caloric deficit, anything below our TDEE, will cause a negative energy balance. Over time, this brings about weight loss.

However, recklessly cutting calories is not the way to go. Especially if our metabolism is already slow or damaged. This is a very common mistake. Unfortunately, that’s also what most people do. There is a difference between losing weight and losing fat. Changes in body weight within a day or a week are mostly due to water, glycogen, and muscle mass variations. Over weeks and months, mostly to fat mass.

So, while a significant caloric deficit will cause a faster weight loss, not all the weight lost will be fat. Depending on how severe the restriction is, a considerable amount of muscle mass will also be lost in the process. That is not desirable.

Additionally, a too aggressive caloric deficit can wreak havoc on metabolism. Because of evolutionary reasons, in the effort to keep us alive, the body will slow metabolism down to make us consume less. The exact opposite of what we want.

On the other hand, a smaller caloric deficit will slowly but safely allow us to improve our body composition. The goal is to lose body fat while preserving muscle mass and keeping the metabolism running. Reducing our caloric intake of as little as 10-20% of our TDEE can be enough to accomplish that.

Depending on how much body fat we carry, aiming to lose anywhere from 0.5-1% of body weight per week is ideal to lose weight in a more sustainable fashion. Even if it takes more time and patience.

How Many Calories to Gain Weight?

If you guessed more than we need to maintain it, you are correct. A caloric surplusanything above our TDEE, will cause a positive energy balance. Over time, this brings about weight gain.

Studies show that a caloric surplus of 30-40% in excess of our TDEE increases anabolic hormones production and promotes muscle growth, even in sedentary subjects. However, doing so will also significantly cause our fat mass to increase.

Our body can only synthesize so much new muscle every day. If we eat too much, the rest is likely going to be stored as adipose tissue. For this reason, it’s safer to increase our caloric intake of no more than 10-20% of our TDEE. Depending on our level of training advancement, we should aim to lose anywhere from 0.5-1% of body weight per month.

In a caloric surplus, it’s normal to put on a bit of fat along with new muscle mass. Even if we train correctly. The important thing is to keep the situation under control. To that end, I strongly recommend integrating weight measurements on the scale with anthropometric measurements.

This way, we will always have a clear picture of our body composition. No matter how approximated. Whether in a caloric surplus or deficit, we will know which tissue is responsible for changes in body weight.

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