WTF is a calorie deficit?
Heard of a calorie deficit but not sure if that’s good, bad, or just another fad? It’s actually the fundamental of weight loss, so let’s see what it means.
No wonder weight loss feels like a minefield when there are so many different approaches and so much jargon to wade through. But this one is different, and it’s worth taking the time to understand it.
You’ve probably heard of a ‘calorie deficit’, but if you’re not a PT or someone with extensive experience of weight loss, you might not know what it means.
What is a calorie deficit?
To lose weight, you need to eat and drink fewer calories than you burn. When you do that, you’re creating a calorie deficit – where the number of calories from food and drink is smaller than the number of calories you’ve burned through activity and body processes.
But how do I know if I’m eating fewer calories than I burn?
There are two ways you burn calories – through the activity you do every day (which includes exercise and other movement like walking around) and through the necessary things your body does to stay alive (which includes things like breathing, your heart beating, cell production, etc.).
The number of calories your body uses is known as your basal metabolic rate (BMR). It’s influenced by a lot of things, like your age, height, weight, gender, and even the temperature of your environment.
As well as your BMR, for weight loss you need to figure out your total daily energy expenditure (TDEE) – yep, another bit of lingo for you.
While your BMR is how many calories your body needs to stay alive and kicking, your TDEE also includes the activity you do (both exercise sessions and general activity). It’s an estimate of how many calories you burn in a day in total, which includes your BMR.
Confused? It’s a lot to take in, but once you figure your own BMR and TDEE numbers out it gives you a great start for counting calories, which will lead to weight loss.
The most accurate way to get your BMR is to be monitored in a lab, fasting beforehand and breathing into a special mask for an entire day and night to see how many calories you burn when resting.
Since we’re guessing you don’t have access to a lab and a team of scientists, you can use a widely accepted equation that has been found to be pretty spot on. It’s called the Mifflin-St Jeor equation and will give you your individual number based on all the variables we mentioned above.
Don’t fret about the maths! This free online calculator will work it out for you.
Your TDEE is how many calories you’d need to eat to maintain your weight. For weight loss, you need to eat fewer calories than your TDEE. It’s usually recommended that you subtract 500 from your TDEE to lose weight at a safe pace.
If you’re thinking the number seems higher than what MyFitnessPal gives you, remember that MyFitnessPal tends to give everyone a 1,200 calorie goal based on sedentary, smaller people. Your TDEE and subsequent calorie goal is personalised to you.
An example
Let’s take Bob as an example. He’s 36, weighs 280lbs (that’s bang on 20st) and is 5ft 10. He does little to no exercise.
Using the calculator mentioned above, his TDEE is 2648. To lose weight, he should subtract 500 and start off by eating 2148 calories a day.
How to eat in a calorie deficit
The number you end up with after subtracting 500 from your TDEE is how many calories you should aim to eat every day. You can track calories using an app like MyFitnessPal (free with a paid premium version) or NutraCheck (paid), or you can do it the old school way and use pen and paper, although apps make it way easier.
How to eat for weight loss is personal preference, but in general you should aim to increase your fruit and veg intake, cut down on processed foods and booze, and eat plenty of foods high in protein and fibre.
Your calorie needs will change as you lose weight, so it’s a good idea to recalculate after you’ve lost a chunk of weight or if you feel your weight loss has stalled.