What is a calorie deficit?

A calorie deficit is when you consume fewer calories than you burn. If you consume 2000 calories and your Total Daily Energy Expenditure (TDEE) is 2500 calories, you will be in a 500 calorie deficit. A calorie deficit is a fundamental underpinning to any effective weight-loss strategy – if you're in a calorie deficit, you will, indubitably, lose weight/body fat over time.

Why is a calorie deficit important for weight loss?

One can implement many dietary strategies to shed body fat; keto, vegan, calorie counting, intuitive eating, IIFYM (if it fits your macros), IF (intermittent fasting), and many more. But they will all need to adhere to a calorie deficit to elicit a fat loss response. 

A calorie is a unit of measurable energy, defined as the amount of heat needed to raise the temperature of one gram of water by one degree Celsius. When the word "calorie" regarding food, people are usually referring to the number of kilocalories a specific item has listed on food labels – one large kilocalorie (kcal) is the equivalent of 1,000 small calories.

Total Daily Energy Expenditure (TDEE)

The calories you burn or expend throughout the day – also known as Total Daily Energy Expenditure (TDEE) – include the following components:

• Basal Metabolic Rate (BMR)

  This is the sum of all bodily functions needed to keep the body alive. Things like breathing and the processes our organs go through each day.

• Thermic Effect of Food (TEF)

  The thermic effect of food or TEF refers to the number of calories needed by your body to digest, absorb and metabolise the food you eat.

• Exercise Activity Thermogenesis (EAT)

  EAT refers to the number of calories burned through planned exercise, such as; running, resistance training, HIIT, etc. 

• Non-Exercise Activity Thermogenesis (NEAT)

  NEAT accounts for all your subconscious physical activity – activities such as fidgeting, walking to work, typing, gardening, etc. 

If you provide your body with fewer calories than it needs to support these components of TDEE, you put your body into a calorie deficit. Doing so consistently for long periods results in weight loss [1]. 

Conversely, you will gain weight if you regularly provide your body with more calories than it needs to support these functions – this is known as a calorie surplus.

Creating a calorie deficit

To create a calorie deficit, you'll need to know how many calories you need to consume to put you in the appropriate caloric deficit. 

I've done an in-depth article on how many calories you should eat and created a free online calorie calculator to do the work for you. This online calculator will provide you with the most accurate possible estimation. But remember, this is just an estimation, and an estimated calorie deficit isn't necessarily a true deficit. You'll need to monitor your weight for a week or two. If the scales are heading in the right direction at a good rate – losing between 0.5% and 1% of your body weight per week, without too much hunger, then it's a good amount of calories. If you weigh 100 kg you're aiming for between 0.5 to 1kg per week loss. Suppose you're losing weight rapidly (consistently over 2% of your body weight per week), along with an insatiable appetite and low energy levels. Then you'll likely need to increase the calories – the deficit needs to be sustainable. Suppose the scales aren't moving after a few weeks, and you don't notice your body changing (visually shedding fat). In that case, you'll likely need to reduce the calories further – remember that an estimated deficit isn't necessarily a true deficit. 

Exercise and stay active

Nutrition is, in my opinion, the most important thing to focus on when it comes to fat loss, specifically being in a calorie deficit, which you now know. But, remember that to lose weight, we need to nail both sides of the energy balance equation – calories in and calories out, so we need to ensure we maintain appropriate activity levels. If you are pretty sedentary, I recommend having a daily step target to hit, something realistic but effective; 5000 steps per day are good, 10,000 steps per day are awesome! You can use step tracker apps to track your daily steps and ensure you're burning a lot of calories each day. Many people who reduce their calories also subconsciously reduce their movement. We can avoid this by having a daily step target. I also recommend regular resistance training – if you're in a caloric deficit and not stimulating your muscles regularly, you have a good chance of breaking down muscle tissue and using it as an energy source. We avoid this and prioritise the loss of body fat rather than muscle mass by stimulating the muscles frequently via resistance training [1, 2, 3] and consuming a decent amount of protein – you want to consume between 1.6 to 2.4 grams per kg of body weight.

One caveat here when looking into exercise to burn more calories is that exercise doesn’t burn as many calories as many of us believe [4, 5, 6, 7]. So, it’s imperative that one primarily focuses on their diet.

Can you lose weight without being in a calorie deficit?

Yes and no, but mostly no. You can lose 'weight' without being in a deficit, but not fat. Many things impact your body weight, which are not related to body fat, such as your body's fluid levels fluctuating; it’s been shown that individuals undertaking low carb diets can lose up to 3kg of water weight alone [8, 9]. Food in transit is another one to consider – you can weigh in at 100kg, pop to the toilet, and then weigh in at 99kg, good effort, sir! Conversely, you could gain 1 kg by simply drinking a litre of water. But these situations are impacting your weight, not your body fat, and it's important to differentiate between the two. Okay, can you lose fat without being in a deficit? No, sorry, that's not how the body works. Anyone tells you otherwise – then they're possibly uneducated on nutrition, human physiology and the laws of physics, or perhaps they're intentionally providing misinformation to sell their service – claiming they "have the answer to fat loss". 

Summary 

A calorie deficit is required to shed body fat – if anyone states otherwise, then they know how to defy physics (specifically the first law of thermodynamics). Perhaps they're a wizard? Or they live in a Peter Pan style fairy tale world where the laws of physics don't apply. If someone state that you can lose weight over time without adhering to a calorie deficit – then ask them if they can show you some magic tricks, as you are undoubtedly speaking to a wizard. 

During your fat loss journey, you do, of course, need to control your calories, but you also need to take a sustainable approach by finding the right diet for you. Working with clients worldwide for almost a decade, I have found that sustainability is the key to any effective fat loss strategy. This is also shown heavily in scientific research – check out this 2018 review done by Chrysi Koliaki and colleagues [10].

If you'd like me to accompany you on your fat loss journey and provide you with a bespoke training and nutrition plan, then please get in touch.