How to know the daily calories you need?

Some of the most common questions amongst those people or athletes who want to look after their nutrition are; how many calories do I need per day? What does it depend on? What if I want to gain muscle mass? What if I want to lose fat? Is it risky to assume an excessive calorie deficit? 

In order to answer these questions, the first thing is to carry out a series of calculations based on the person’s characteristics, the kind of training performed or the amount of daily physical activity done, and lastly the goal set, either maintaining body weight, increasing muscle mass or losing fat. 

What are calories?

The first thing is to define the units to measure energy, either the ingested through food or the expended through physical activity or different metabolic processes. 

Kilocalories (Kcal) are used and can be defined as: 

“The amount of heat necessary to increase 1º the temperature of one kilogram of water from 15º to 16º at sea level” 

Another unit that can be used to measure energy are Kilojoules (Kj). One kilojoule is 0.24 kcal or, 1 Kcal equals 4.184 Kj.   

How to calculate energy expenditure?

A person’s energy expenditure is the total amount of energy consumed along the day. Since each day is different and the activities or workouts are different, the energy expenditure for each day is going to be different. 

This will depend on some involuntary factors such as resting energy expenditure or the thermodynamic effect of food, and other voluntary factors such as energy expenditure due to physical activity. 

The elements of total energy expenditure are:

1. RESTING ENERGY EXPENDITURE: energy used to maintain the body’s vital functions.
2. THERMODYNAMIC EFFECT OF FOOD: energy required to digest food. 
3. PHYSICAL ACTIVITY ENERGY EXPENDITURE: energy consumed according to the kind of physical activity and/or workout performed. It depends on the workout’s duration and intensity.

The TOTAL energy expenditure is the sum of all these elements, which can be estimated as follows: 

Resting Energy Expenditure (REE)

There are two ways to calculate resting energy expenditure. 

First is using predictive equations based on gender, height and age. The most common one is Harris & Benedict:

• Women: 655 + (9.6 x Weight [kg]) + (1.85 x Height [cm]) – (4.7 x Age)
• Men: 65.47 + (13.7 x Weight [kg]) + (5 x Height [cm]) – (6.8 x Age)

The second option, and quite more precise, would be to carry out a metabolic resting rate study with a gas analyser. This would be done fasted, with the person having waken-up recently and lying down. During at least ten minutes (ideally twenty), oxygen consumption and carbon dioxide production are evaluated using the equipment’s software.

Thermodynamic effect of food (TEF)

This value is an estimation and considers around 8 to 10% of the resting energy expenditure previously calculated. 

Physical activity energy expenditure (AEE)

There are also two options.

First is to multiply the resting energy expenditure by a coefficient, according to the person’s grade of activity. 

The coefficients are:

• Women: 1.46 (Sedentary) / 1.64 (Active) / 1.82 (Athlete)
• Men: 1.55 (Sedentary) / 1.78 (Active) / 2.1 (Athlete)

Since this is a subjective value, there’s an alternative such as recording and calculating calorie expenditure using electronic devices such as smart watches, activity wristbands or smart rings.

With the devices’ applications it’s possible to track both daily calorie expenditure and calorie expenditure of a specific workout, which depends on its intensity and duration.

Total energy expenditure (TEE)

There are three ways to calculate total energy expenditure:

1. Using only equations:

Kcal / day:  (REE x AEE) + TEF 

2.  Measuring REE and AEE with devices and estimating TEF:

Kcal / day:  REE + AEE + TEF

3. This option would be possible if the person carries any of the previously mentioned devices during 24 hours, and its software calculates the daily Kcal consumed.

How much energy is necessary each day?

The necessary daily energy will depend on the goal pursued. In a quantitive way, the relationship between calorie intake and energy expenditure, i.e. energy balance. 

Hence there can be a positive energy balance or caloric surplus, a balanced energy balance or a negative energy balance or calorie deficiency. 

Caloric surplus

Normally pursued when the goal is to increase body mass, usually searching for muscle increase. Fat increase is pursued in certain times, when it’s too low. 

An ESSENTIAL aspect is increasing calorie intake.

• Calorie intake is calculated to be higher than energy expenditure
• The new diet must increase protein intake up to 2,5-3 g per kg body weight per day
• Carbohydrates are prioritised when workouts are moderate or highly intense
• Healthy fats are prioritised when workouts are low intensity

Maintenance calories

When someone intends to maintain body mass, a nutritional strategy must be designed to cover the daily energy consumed, i.e. intaking and expending the same daily calories, which is commonly known as maintenance calories. 

Calorie deficiency, until when?

Finally, the following strategies to pursue a calorie deficiency or negative energy balance, aiming to decrease fat mass, would be:

a) Increasing resting metabolic rate: 

• Avoiding high calorie restrictions so the RMR doesn’t decrease
• Increasing muscle mass. Muscle is what consumes the energy

b) Increasing daily energy expenditure (training): 

• Increasing the workout quality or quantity. Coaches are responsible for this commitment

c) Following an active lifestyle:  climbing stairs instead of using lifts, moving around without using motorised vehicles (whenever possible), etc.

But be careful because a programme which goal is to lose weight and is based on strict calorie restriction, could cause certain problems both in men and women:

• Oligospermia / amenorrhoea
• Osteoporosis
• Physiological and metabolic changes: fatigue, immunosuppression, anaemia, loss of capacity to restore tissue, etc.

This set of alterations is known as the RED-S syndrome ‘Relative Energy Deficiency in Sport’. The key to preventing it is to avoid an excessive calorie deficit.

But how much is excessive?

Hence, to establish and guarantee a minimum calorie intake by an athlete, carry out a body composition study that indicates the kilograms of fat free body mass and multiply it by 30. 

For example, for a 75 kg athlete with 19.2% fat, 14.4 kg are fat. Free fat mass would be 75 – 14.4 = 60.6 kg

• For example, for a 75 kg athlete with 19.2% fat, 14.4 kg are fat. Free fat mass would be 75 – 14.4 = 60.6 kg
• Hence, the necessary energy availability world be: 60.6 x 30 = 1,818 Kcal / day

Not everything are maths

Lastly, indicate that not everything is so mathematical, since each person’s metabolism is very different and is influenced by many factors, but these calculations can serve to have more precise initial references, that can be tweaked with a good follow up and evaluation program.