Energy 101

What do you need to know about energy?

“How much energy do I need every day?” This is one of the most fundamental questions to be asked on a health and fitness journey – and it may be more complicated to answer than you might think.

Energy is defined as “the capacity to do work”, and is obtained from carbohydrates, proteins, fats and alcohol. Vitamins and minerals do not provide energy but help with metabolic reactions to provide energy.

It’s actually amazing how the body takes the energy that is in food and uses it to fuel our everyday activities. How you fuel, is how you live.

Before we dive into individual energy needs, let’s start with the fundamentals:

The standard measuring unit for energy is a calorie, which is the amount of heat energy required to increase the temperature of 1ml water at 15⁰C by 1⁰C. The amount of energy in metabolism is very large, and that is why we use kilocalories (kcal) to measure it.

Another way to measure energy is in kilojoules. 1 Kcal = 4.2 kilojoules.

• 1g of protein = 17kj or 4kcal
• 1g of carbohydrate = 17kj or 4kcal
• 1g of fat = 38kj or 9kcal
• 1g of alcohol = 29kj or 7kcal

“Energy requirements” are how much energy a person needs to take in for growth or maintenance of a certain age, gender, weight, height and physical activity.

Basal metabolic rate (BMR) is the minimum amount of energy needed to maintain life; in other words, how much energy you expend at rest.

Basal energy expenditure (BEE) or resting energy expenditure (REE) is the energy expended in the reactions in the body necessary to sustain normal bodily functions and homeostasis. It is used interchangeably with BMR.

What does your daily energy requirements consist of?

Your total energy expenditure (TEE) consists of:

• Your BMR, which is affected by age, body composition (how much muscle/fat you have), body size, temperature/climate, gender (males tend to have a higher BMR than females), hormones, and other factors like caffeine, nicotine and alcohol.

It is important to know that fat-free mass (muscle mass) makes up most of the metabolically active tissue in the body and contributes to about 80% of the differences in BMR, which is why athletes tend to have a higher BMR than non-athletes.

• Activity thermogenesis (AT) which is comprised of two components: energy expended during physical activity (PA) as well as non-exercise activity thermogenesis (NEAT). Energy expended during physical activity can be as little as 100kcal per day for sedentary people up to 3000kcal per day for athletes. NEAT represents the energy you use in a typical day that is not directly exercise, like working, walking, shopping, fidgeting and even gum chewing. This might be why the energy expenditure between people is so different.
• Thermic effect of food (TEF): this is the energy you use to consume, digest and absorb food and accounts for about 10% of your total energy use.

THUS: TEE = BMR + PA + NEAT + TEF

Estimations of BMR and total energy

There are various scientific ways to measure energy expenditure, like direct and indirect calorimetry, using the respiratory quotient, doubly labelled water and traxial monitors – but let’s be realistic, most people do not have the means or access to these types of tests.

That is why we turn to estimations. But it is very important to remember that they are exactly that – estimated values of how much energy you use. They do, in many cases, not account for various individual factors like hormones, temperature, and diet history or in some cases even body composition. It is important to educate yourself about the strengths and limitations of different equations and devices estimating energy and not get too caught up in absolute numbers. A sports dietitian or registered sports nutritionist who consults you in person has the background in science to look at an athlete holistically, compare the athlete’s diet history, biochemistry, clinical signs and anthropometry with the equations and come up with a much more realistic estimate of an athletes energy expenditure, which is why they are such a vital part of an athlete’s personal medical team.

• The Harris Benedict equation:
  Most websites, personal trainers and some apps use the Harris Benedict equation, which to determine BMR, which looks like this:
  For men: BEE = 66.5 + (13.8 x W) + (5.0 x H) – (6.8 x A)
  For women: BEE = 655.1 + (9.6 x W) + (1.9 x H) – (4.7 x A)
• Mifflin-St. Jeor equations:
  The popular calorie-counting app, MyFitnesspal, uses this specific equation to estimate BMR.
  For Men: 10 x weight (kg) + 6.25 x height (cm) – 5 x Age + 5
  For Women: 10 x weight (kg) + 6.25 x height (cm) – 5 x Age – 161
  
  • After the BMR is calculated, this amount is then multiplied with an activity factor which is determined by how active you are, ranging from “sedentary” (1.2) to very heavy/2 training sessions per day (1.9).
  • Although it is handy to have a broad idea of your intake, the limitations of these equations are that they don’t take into account all the factors that have an impact on energy expenditure, like muscle mass, hormones, environmental changes, individual differences in diet history or metabolic reactions to food, which means that it can overestimate or underestimate how much energy you really need. In fact, many research papers report inaccuracies in estimated vs. actual energy needs for many equations.
  • There are equations that take into account your fat percentage and total amount of lean body mass, which may be a more accurate way to determine your BMR. The Cunningham equation is an example of this. It looks like this: BMR = 500 + 22 x LBM (Lean body mass – your body mass minus your fat mass). Still, some over/underestimation may still occur.

What about fitness devices?

Fitness devices uses age, weight, activity and heart rate to determine the amount of calories expended per day.

It is handy to compare one day’s activity or one week’s energy expenditure in the same person with the same device.

However, in a paper where a series of experiments where done on several fitness tracking devices, including two models of Fitbit, a Garmin smartwatch, and an Apple Watch, data collected on the number of steps taken, distance travelled and calories burned by each subject for 14 days showed that these numbers “could vary significantly when devices of different manufacturers are compared side by side”. In other words, these devices could under- or overestimate energy expenditure. Once again, getting too caught up in the numbers of fitness devices is not necessarily the best way to reach your goals.

The takeaway

In order to really elevate our health and fitness, we need to make sure we get into the habit of obtaining our energy from high-quality food sources. Our focus should not be on absolute numbers from fitness devices, apps or meal plans from the Internet or someone who is not able to look at holistically at you as an individual and consider every factor that may affect energy needs. Learn to listen to your body – eat when you are hungry, and stop when you are full. Trust your body’s hunger and satiety mechanisms. Eat foods that make you feel good, not only while eating it but also while you go on with your day and use the energy from the food to fuel your daily activities. And remember that it is okay to have fun foods once in a while, if it forms part of an overall healthy diet. I’d even argue that it is necessary to do so to really stick with a healthy lifestyle long-term.

Remember, health elevation is about having a lifestyle and making healthy habits stick and not going to the extremes that only end up giving you short-term results.

References

• Bender, C.G., Hoffstot, J.C., Combs., B.T., Hooshagi, S., Cappos, J. 2017. Measuring the Fitness of Fitness Trackers. 2017 IEEE Sensors Applications Symposium (SAS). DOI: 10.1109/SAS.2017.7894077
• Mahan, L. K., Raymond, J.L. 2017. Krause’s food and the Nutrition Care Process. 14th ed. Canada: Elserevier. Pp 17-27.