The words ‘being in a calorie deficit’ are very common in the world of health and fitness, much like ‘burpees’ (shudder) and ‘five more reps’ (double shudder).

And, whilst a calorie deficit is a relatively simple idea – eating fewer calories than you expend, its meaning can sometimes get lost in the noise of health trends and eating fads. Anyone remember, the Pegan diet?

So, if you’re looking for some answers to explain the phrase used by everyone from doctors to PTs and dieticians, look no further, we’ve got you covered. (We’ve even included a handy calorie deficit calculator to get you going.)

Scroll on for our full guide to what a calorie deficit is, how to accurately calculate yours and what role exercise and nutrition play in it all.

Who should avoid being in a calorie deficit?
First things first, there are some caveats. Not everyone who goes looking for information about calorie deficits should be thinking about trying to be in one. If you’re already at a healthy weight for your height and are still trying to lose weight, consider reaching out to a medical professional or registered dietician.

They’ll be able to work with you on creating a healthy body image and moving away from unnecessary weight loss.

If you identify with any of the following medical concerns, you should speak to your GP thoroughly first.

  • You are pregnant or breastfeeding
  • You are taking prescription medication
  • You have an adrenal-related medical condition, like Addison’s disease
  • You are a teenager or a child

What is a calorie?
Taking it right back to basics, let’s brush up on what a calorie is.

A unit of measurement, 1 calorie is the exact amount of energy it would take to raise the temperature of 1 kilogram of water by 1 degree Celsius. Basically, it’s a unit of heat, hence why we ‘burn’ them during exercise and general being alive-ness.

What is a calorie deficit?
Ok, so it’s often thrown around but what does being in a calorie deficit actually mean?

To put it simply, it refers to eating fewer calories than your body needs to maintain its weight, by anywhere between 300 and 500 calories. Eating like this is how you lose weight well.

‘A calorie deficit means consuming fewer calories than your body expends,’ explains GP, Dr Mishkat Shehata, lifestyle physician and founder of The Lifestyle Code Clinic. ‘A calorie deficit of 500 calories is usually recommended and is an effective strategy for weight loss.’

Is it possible to lose weight without being in a calorie deficit?
Short answer, no. Long answer, no.

Being in a calorie deficit is the only way to lose weight no matter which eating protocol you choose – e.g. keto, vegan, standard or paleo diet. It all comes down to intake vs. expenditure when your body determines whether it needs to tap into adipose body tissue (fat) for fuel.

How do I calculate my calorie deficit?

To calculate a calorie deficit, you first need to work out how many calories your body uses to maintain your current weight and body composition.

1. Calculate your BMR
That’s your Basal Metabolic Rate – the number of calories your body burns each day without doing anything. If you were to lie flat in bed all day, not lifting a finger (the dream), this is the amount you’d burn through.

To find your BMR, use the Mifflin-St Jeor equation:

BMR(women) = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161

2. Multiply your BMR by your daily activity level
Then you need to decide your daily activity level to multiply your BMR by. This will work out how many calories you need with everything you do during the day. This is your TDEE (total daily energy expenditure).

  • Little or no exercise, desk job: 1.2
  • Little exercise 1-3 times per week: 1.375
  • Moderate exercise 3-5 times per week: 1.55
  • Heavy exercise 6-7 times per week: 1.75

3. Subtract to find your calorie deficit
Then, subtract 300–500 calories from this to find the number of calories to eat per day to remain in a deficit. Voila!

Is being in a calorie deficit bad for you?
According to the experts, it’s not unsafe when it’s done properly and when other factors are taken into account.

‘It is safe to be in a calorie deficit, provided you’re not restricting calorie intake further than necessary without medical supervision,’ advises Dr Shehata.

‘It’s also important to make sure that food consumed is nutrient-dense with mindful consumption of saturated fats and processed sugars and grains.

‘Foods such as vegetables, fruits and whole grains are minimally processed, usually lower in calories and more nutritious. It’s imperative to not just focus on calories but rather the nutritional value of foods consumed and exercise as integral to sustainable weight loss, too.’

Signs you’ve been in a calorie deficit for too long
‘When we consume fewer calories over a prolonged period of time, it makes it harder to get what we need for both energy and optimum nutrition,’ explains Dr Shehata. ‘This can lead to anaemia and nutritional deficiencies of certain vitamins and minerals, such as folate.’

Signs it’s time to stop eating in a calorie deficit:

  • Extreme fatigue
  • Poor concentration
  • Vitamin deficiencies
  • Unshakeable brain fog
  • Persistent irritability

What should I eat in a calorie deficit?
‘If you’re cutting back on calories, it is really important to prioritise nutritious foods that contain protein and vitamins and minerals,’ explains Leading dietitian and Director of CityDietitans, Sophie Medlin.

‘You could achieve a calorie deficit by just eating chocolate but you’d get ill quickly because of nutritional deficiencies. Choose high protein foods such as meat, fish, eggs, Soya, tofu and pulses and try to have three portions of vegetables at each meal.

‘Fruit and vegetables are much lower in calories than other foods which means you can eat a lot more of them, feel full and still achieve a calorie deficit.’

More… WH Explains: Here’s Exactly What a Calorie Deficit Is & How to Calculate Yours – Womens Health via MSN