Are the amount of calories you burn accurate?

Posted in Nutrition
29/07/2020 Mikey

Are the amount of calories you burn accurate?

A 60 minute experiment - plus the science!

On the surface I cycled for 60 minutes, covered 33.4 km and burnt 289 calories. Does this seem right to you?

Alongside 60 minutes on the bike with me, the following post talks about energy expenditure estimations, how we can use them, but why we should most definitely approach them with caution.

The 60 minute experiment begins…

Roughly 10 minutes in (the timer counts down from 60:00) and according to the bike I’ve already burnt over 250 calories! Strange that I only burn 31 calories in the next 50 minutes…

How many calories do you burn during exercise?

Of course this question is littered with confounding variables. How old are you? What’s your weight? How much muscle mass do you have? How “fit” are you? What exercise are you doing? How intense is the exercise? How long are you exercising for? What environment are you in?

All of these factors, and many more, are going to directly affect how many calories me or you burn during exercise. This is the fundamental problem with any energy expenditure calculation. Yes, the estimations are reliable and produce consistent results repeatedly. These estimates do roughly indicate the amount of calories you have expended and subsequently how hard you have worked. However these amounts are not valid. They do not provide an exact, accurate representation of how many calories you’ve actually burnt. Energy expenditure calculations would be represented by the top left dart board – reliable but not valid. An ideal test/measurement is both reliable and valid – bottom right dart board. Everyone is unique and will burn a different amount of calories when completing exactly the same amount of exercise which is why we should approach these estimations with caution and not compare results against one another.

Roughly 20 minutes in and I’ve burnt over 600 calories… clearly something isn’t right if I only burnt 289 calories throughout the whole 60 minutes. Maybe I defy the laws of physics and suddenly create energy… 

So what is a calorie?

A calorie (kcal) is a unit of energy. 1 kcal = 4.184 kJ and is the amount of heat energy needed to raise the temperature of 1kg of water by 1°C. Around the world we use calories to denote the amount of energy found in food and drinks. But it is also used to determine how much energy we burn during exercise.
Approximately halfway through it now makes sense as to why the end summary said I only burnt 289 calories. The display only has three digits and after 999 it ticks over, reverting back to 0 calories.
Indirect calorimetry is considered the gold standard method of measuring energy expenditure. By comparing the volumes and concentrations of gasses inhaled and exhaled we can accurately measure the amount of energy used/calories burnt during exercise. The issue with indirect calorimetry is that it requires all gasses that are inhaled and exhaled to be analysed. This can be done in a variety of different ways but none that are easily accessible or feasibly used outside of a laboratory setting. Hence it not being used in the general public for energy expenditure estimations during exercise. This is where the prediction equations are bought in, along with the inaccuracies associated with them.

Prediction equations are usually based on age, sex, height, weight, MET value, and sometimes heart rate. MET stands for metabolic equivalent of task and identifies how intense a task or exercise is in relation to your resting metabolic rate. So resting, sitting doing nothing, is equal to 1 MET, and for example cycling at an average of 30-50 watts is equal to 3.5 METs.

With approximately 20 minutes to go I was over the peak, became a sweaty mess, and had burnt nearly 1600 calories.

The science

In 2017 a study by Shcherbina et al., compared energy expenditure estimations from five different wrist worn exercise devices against energy expenditure measurements via indirect calorimetry. Across a diverse cohort and different exercise modalities, none of the devices had a mean measurement error less than 20% of energy actually expended. Meaning, the devices that told you how many calories you’d burnt were inaccurate by at least 20%.

With 10 minutes left I was nearing a second tick over and the 2,000 calorie mark.

So despite their inaccuracies do energy expenditure estimations have a role in the health and exercise world?

Of course they do! Although they’re not the most accurate, the estimations are reliable and reproducible, giving you a comparative measure to compare the intensity of one exercise to another that you complete. They’re certainly more accurate than you or I at guessing how many calories you’ve burnt, just not as accurate or valid as indirect calorimetry.

So in a practical sense you can use these figures to compare one workout to another by how hard you’ve worked. But don’t rely on them in absolute terms that you’ve burnt that exact amount of calories, you could be at least 20% out!

At the end of the workout I was done. A tired sweaty mess!

The final display read 289 calories, plus the two times it ticked over 999. [999+999+289 = 2287]

According to the bike I’d burnt 2287 calories, now that’s a lot of snacks!!! But seriously, read the bikes manual. It even tells you it’s a “rough guide for comparison of different exercise sessions which can not be used in medical treatment.”

So what’s the take home message from this little journey and experiment?

Use energy expenditure estimations to compare the intensity of workouts you’ve completed yourself, but don’t compare them against each other. Besides, health and exercise is a competition against yourself, not against others.

Also don’t think because you’ve burnt 600 calories, you can go and eat 600 calories worth of snacks and not put on any weight. You could be more than 20% out on the calories burnt, not to mention the inaccuracies of energy intake on food packaging – that will have to wait for another blog!
So yes, energy expenditure estimations do have their place and role, but please use them with caution and don’t use them to justify eating something, particularly if your goal is to lose weight.

Relative Energy Deficiency in Sport (RED-s)

Just one thing to bear in mind is a syndrome called relative energy deficiency in sport (RED-s).
RED-s is a syndrome whereby consuming insufficient energy (calories) leads to long term performance and health issues such as osteoporosis. It’s vital to remember that exercise is catabolic and causes the body to breakdown. Meanwhile rest and recovery are anabolic, allowing the body to rebuild itself. If there isn’t enough energy available (food and drink consumed) for recovery the bodily functions begin to be compromised and can lead to long term health issues. So if you are training to lose weight, just ensure you’re still maintaining adequate calories to remain healthy and fulfill normal bodily functions.

Mikey is one of our expert Corporate Wellbeing Advisors who spends his time helping clients employees be the best they can.