From celebrity-endorsed eating plans to influencer-led weight loss programmes, we can’t escape elaborate diets promising miraculous results. Whatever the latest weight loss trend – intermittent fasting, celery juice, or cabbage soup – most regimes focus on entering a calorie deficit to lose weight.
But the ‘calories in, calories out’ approach is a little restrictive – not just because we’re all different in size, shape, and age, but also because we all have different activity levels.
So, if you’re calorie counting and still not losing weight, perhaps it’s time to rethink your method. And that’s where BMR and TDEE come in.
What is a calorie?
Firstly, let’s cover the basics: What is a ‘calorie’? A calorie measures the amount of energy in food and drink.
The NHS recommend men consume around 2,500 calories and women consume 2,000 calories daily to fuel normal bodily functions and support optimal health (1).
However, these needs vary based on factors like your age, height, weight and how much exercise you do, as we explore below with BMR and TDEE.
What is BMR?
BMR stands for basal metabolic rate (basal means ‘base’). BMR is the number of calories you need to sustain life with minimal movement.
It’s the energy your body requires to support vital functions like breathing, nutrient processing, circulation and cell production – not the calories required for daily activities like moving, walking and exercising.
What is TDEE?
TDEE, on the other hand, stands for total daily energy expenditure.?It estimates the number of calories you burn over 24 hours based on three major factors: your basal metabolic rate, activity levels and the thermic effect - the rate at which your body burns calories, of food.
To calculate your TDEE, you first need to find out your BMR. Then, you can set an achievable calorie deficit goal.
How to calculate BMR
Strictly speaking, you can only measure BMR in a clinical setting using a process called indirect calorimetry, which calculates how much oxygen you use and carbon dioxide you produce (2).
Since most people don’t have access to sophisticated devices, researchers have developed a more convenient way to calculate BMR with an equation.
Technically, this calculation determines your RMR (resting metabolic rate), which gauges the calories you burn with minimal movement. BMR is more restrictive and measures calories with zero movement, but RSR should give you a close enough estimate.
You can calculate your BMR/RMR rate using the Mifflin-St Joer equation below (3).
Women: 10 x weight (kg) + 6.25 x height (cm) − 5 x age (years) − 161
Men: 10 x weight (kg) + 6.25 x height (cm) − 5 x age (years) + 5
For instance, a 28-year-old, 69kg, 180cm female would have a BMR/RMR of 1,514. At rest, she’ll burn 1,514 calories.
Although you can’t change your gender, height, and age, studies suggest building muscle through resistance training can also boost BMR levels (4).
TDEE calculator
Now you know your BMR, you can work out your TDEE. To determine your TDEE, you need to add an activity factor.
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1.2: sedentary (little to no exercise)
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1.375: lightly active (light exercise 1 to 3 days per week)
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1.55: moderately active (moderate exercise 6 to 7 days per week)
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1.725: very active (hard exercise every day, or exercising twice a day)
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1.9: extra active (very hard exercise, training, or a physical job)
The TDEE calculator looks like this: BMR x activity factor. To use the example above, a 28-year-old female who is moderately active has a TDEE of 2,346.7 calories.
TDEE provides a reasonable estimate of your daily calorie needs to maintain your current weight. And if you want to lose weight, you'll need to consume fewer calories each day.
Using TDEE for weight loss
In the context of using TDEE for weight loss, you might be wondering: how low can I go? Theoretically, any number of calories below your TDEE will lead to weight loss, though a greater calorie deficit will result in faster weight loss.
One method is the 500-calorie-a-day deficit (TDEE minus 500), which should see you losing a steady 1lb a week. However, many experts recommend reducing your calories by 10 or 20 per cent of your TDEE, which is a healthier and more sustainable approach to weight loss.
For instance, if you have a relatively low BMR and TDEE, subtracting 500 calories from your TDEE could mean your calorie goal will be lower than your BMR, risking putting your body into ‘starvation mode’.
‘Starvation mode’, also known as nutrient deficient mode, is where your body doesn’t get what it needs to function normally. As a result, it will conserve energy by reducing the number of calories it burns.
If your body is burning fewer calories than it would normally, it can be even harder to lose weight, debunking the myth that eating fewer calories always leads to faster weight loss.
Restricting too many calories can also make you lethargic, hungry, and irritable – the main reason many diets fail.
Want to learn more?
Calculating your BMR and TDEE can be useful tools for weight loss. However, it’s also important to recognise their limitations. BMR and TDEE don’t consider underlying health conditions, muscle-to-fat mass, hormone levels, and other metrics.
Moreover, striking the right nutritional balance is more important than obsessing over calorie counting, which may even lead to disordered eating in some cases.
The take-home message is to use BMR and TDEE as a guide to support your health and wellbeing goals but avoid fixating on them.
For more information on supporting weight loss in a healthy, sustainable way, explore the rest of Nutrition Buzz. Alternatively, contact our team of expert Nutrition Advisors, who provide free, confidential advice.
References:
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NHS (2019) "What Should My Daily Intake of Calories be?" NHS. Available online: https://www.nhs.uk/common-health-questions/food-and-diet/what-should-my-daily-intake-of-calories-be/.
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Kenny GP, Notley SR, Gagnon D. (2017) "Direct calorimetry: a brief historical review of its use in the study of human metabolism and thermoregulation." Eur J Appl Physiol. 117(9):1765-1785.
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Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. (1990) "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 51(2):241-7.
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Stavres J, Zeigler M, Bayles M. (2018) "Six Weeks of Moderate Functional Resistance Training Increases Basal Metabolic Rate in Sedentary Adult Women." Available online: https://digitalcommons.wku.edu/cgi/viewcontent.cgi?article=2051&context=ijes.
Christine
Christine Morgan has been a freelance health and wellbeing journalist for almost 20 years, having written for numerous publications including the Daily Mirror, S Magazine, Top Sante, Healthy, Woman & Home, Zest, Allergy, Healthy Times and Pregnancy & Birth; she has also edited several titles such as Women’ Health, Shine’s Real Health & Beauty and All About Health.
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