One of the most common subject in exercise physiology consist to assess or estimate caloric consumption during and after both physical activity and physical exercise. It’s a complex massive topic that gather a lot of subjects, like math, physic, physiology; each of them are a part of a complex mechanism which is human body that might be compared to a big watch, where if all the components are not in balance with each other the whole system collapse.
First to immerge ourselves into the magic world of the human physiology it is important to understand some physical concept; that’s why I will talk about the Calorie.
A Calorie is Defined as the energy needed to raise the temperature of 1 gram of water through 1°C (now usually defined as 4,1868 Joules). It’s important talking about calories because regardless of ours goals, that may be losing weight, body weight maintenance, or just know our daily energy consumption to check our well-being, counting calories is still considerate the main tool to manage these components properly.
It is inevitable that talking about calorie may lead to the concept of the Total Energy Expenditure (TEE).
TEE is the total number of calories expended each day and reflects the amount of the energy required to carry out all metabolic process within the body, like growth of new cells, maintaining the functions of the body tissues, and providing fuel for movement of the body, including exercise. There are three components to determine TEE:
- Resting Energy Expenditure (REE) or Resting Metabolic Rate (RMR) or better known like Basal Metabolic Rate (BMR), which consist of the energy required to maintain normal regulatory balance and body functions at rest like breathing, blood flow, growth of the new cells etc. It might be defined like the amount of calories a person uses doing nothing throughout the day, and it takes into account the 60% to 70% of the TEE
- Thermic effect of food, which is an increase of the metabolic rate after ingestion of a meal, where the highest value is given by proteins, and it takes into account the 10% of the TEE.
- Physical Activity Expenditure, which is the energy used to perform a physical activity.
The resting energy expenditure can be calculated using the fallow Harris-Benedict Formula:
Male: 66,47 + 13,75 (body mass in Kg) + 5 (stature in cm) – 6,8 (age in years)
Female: 665 + 9,6 (body mass in Kg) + 1,8 (stature in cm) -4,7 (age in years)
Harris-Benedict’s formula was revised in 1984 by Roza and Shizgal through studies conducted on 239 healthy subjects by evaluating the relationship between measured energy expenditure, age, sex, and estimated cell mass (BCM); The standard error of estimation and 95% confidence limits are similar to the original equations. The equation evaluates the energy expenditure of a normal subject with a precision of 14%
Male: 88.362 + (13,397 x body mass in Kg) + (4,799 x stature in cm) – (5,677 x age)
Donna: 447,593 + (9,247 x body mass in Kg) + (3,098 x stature in cm) – (4,330 x age)
For obese adult might be useful use a different equation; Mufflin and St. Jeor thanks their work have developed a formula to assess REE for this population:
Male: 10 (body mass in Kg) + 6,3 (stature in cm) – 5 * age +5
Female: 10 (body mass in Kg) + 6,3 (stature in cm) – 5 * age -161
REE is the largest component of TEE and there are several factors that influence it; to some degree, everyone’s metabolism is determined by their genes, ethnicity, age, gender, and body composition, in particular lean body mass that has a major influence on REE because brain, liver, and other organs (even fat cells) contribute to one’s metabolism. Considering the control that Lean body mass has on one’s metabolism I thought it was necessary introduce another one formula to calculate REE.
Fat mass can be estimate using several ways: skinfold caliper, BIA, DEXA, Hydrostatic weighing etc. I won’t talk about these methods because it’d require another article, but, once we have calculate body fat percentage, we can get fat mass values and using these methods, it’s easy to estimate fat free mass.
Fat Mass= Body Mass * (percentage of body fat/100)
Lean mass or fat free mass can be predicted using the follows formula:
Lean Body Mass=Body mass – Fat Mass
We always have to take into account the standard deviation during these calculation, so, they can’t be 100% reliable.
Once get the predicted lean mass, the fallowing formula will give us the theoretical REE:
REE: 370 + (21,6 * Lean body mass).
REE can also be measured using indirect calorimetry, which measures an individual’s oxygen consumption.
Physical activity has a big influence on TEE; The institute of Medicine (IOM), has developed a physical activity level that takes into account TEE and BEE, independent of gender:
When calculating energy needs for weight loss, first determine REE with either indirect calorimetry or the appropriate predictive equation.
An example might be useful to figure out how these calculation can help us. So, let’s try to calculate a TEE of a low active 40 years old man who perform two training sessions per week, who is tall 175cm, and has a body mass of 100 kg, using the first and the second Harris-Benedict’s Formula.
REE= 66,47 + 13,75 (100) + 5 (175) – 6,8 (40) = 1984 kcal
REE * PAL = TEE
1984 * 1,375 = 2728 KCal
So TEE is 2728 Kcal x day.
If we use the second equation, values will be a bit different:
REE= 88,362 + (13,397 x 100) + (4,799 x 175) – (5,677 x 40) = 2041 kcal
REE * PAL = TEE
2041 * 1,375 = 2806 Kcal
As we can see, there is a difference of 78 Kcal between the first and the second formula, a difference that won’t affect customer’s results, so the only alternative we have is to try and see how our client reacts.
Now, let’s presume that this client wants to lose weight; regardless of which diet a person fallows it’s vital to understand that Body weight is Dependent on energy balance; this one in turn, is dependent of two factors:
- Energy intake (the amount of calories consumed during the day).
- Energy expenditure (the amount of calories consumed thanks the REE and the PAL).
To reduce body weight energy expenditure must exceed energy intake, thus to generate a negative energy balance, so, regardless of which kind of diet a person fallows, that become useless if there isn’t a negative energy balance, that’s why counting calories is important if we want to manage the body weight.
Once we get the TEE is important to generate a negative energy balance if we want to lose weight (we don’t have to do that if we use mufflin formula).
Guidelines for body weight management recommend a rate of weight loss in adult of 1 to 2 lb*week, which is equal to a daily caloric deficit of 500 to 1000 calories. Studies have shown that a weekly energy deficit from 3500 kcal to 7000 kcal is enough to reduce body weight of 1lb to 2lb; that’s because 1 lb of fat is equal to 454 grams and fats have 9 calories per gram; human fat tissue has approximately 87% of lipid (this is a widely accepted conversion, but it is also an estimate).
Putting these together, we can derive the sum that 454 grams of body fat tissue has approximately the calorific energy of 395 grams of pure fat (454 grams x 87%), that is 3,555 calories (395 grams x 9).
We always have to take into account that while we lose weight we don’t never, ever lose just fat cells so it’s important to take these numbers as guideline.
Let’s presume that ours 40 years old man wants to lose weight, we know that his TEE is 2728/2806 kcal per day, at this point we just have to cut 500 to 1000 kcal per day on his TEE:
2728 – 500 = 2228 Kcal * day
2806 – 500 = 2306 Kcal * day
At this point, we learned how to calculate someone’s TEE, now it’s time to understand how we can estimate exercise energy consumption using some metabolic formulae.
About the author:
Dott. Mucedola Francesco
ACSM Certified Exercise Physiologist
Training Lab Certified Personal Trainer
M.Sc. Adapted Physical Activity
B.Sc. in Sport and Exercise Science
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