Understanding Calories In vs Calories Out

Calories in vs calories out, the calorie balance, calorie expenditure; calories are associated with many different terms, all shaping both fat and muscle loss and gain. How can we use calories to help us stay on track to our goals? And is “calories in vs out” (CICO) really the only thing to focus on?

What are calories?

A calorie is a measure of energy, just like a meter is a measure of distance. A calorie is the amount of energy it takes to raise the temperature of 1 g of water with 1 degree Celcius. Which isn’t much. Therefore we tend to speak in kilocalories or Calories with a capital C, so times 1000. These are the values you find on the back of packaged foods and say something about the energy value of food.

We eat food for both energy and nutrients. Our energy expenditure (EE) determines how many calories we need and depends on three main factors:

Your BMR (Basal Metabolic Rate)

This is the amount of calories you need at rest, not digesting any food and not moving. The energy you need to just keep your heart beating, your lungs breathing and fuelling your cells. This makes up about 60% of your energy expenditure for most people. BMR is affected by body size and composition: bigger bodies have more cells and need more energy. It also matters what your body is made of. Muscle tissue burns more calories than fat tissue, which is another reason why it’s beneficial to lift weights, even if your goal is fat loss.

TEF (Thermic Effect of Food)

This is the energy you need to digest and absorb nutrients from the food you eat. This makes up about 10-25% of your calorie requirement, depending on the type of foods you eat. Eating lots of processed foods means you’ll be at the lower end of this spectrum, and you won’t lose many calories digesting and absorbing food. The clue is in the name here: processing food does the digesting for you. If you eat a diet based on whole foods, your body needs to do all the work. Therefore TEF will be higher, which means you’re effectively absorbing fewer calories from your food. Great if you’re on a fat loss diet.

The final 30-40% is made up of your PAL: Physical Activity Level.

The more active you are, the more calories you need. This is made up of EAT Exercise Activity Thermogenesis and Non-Exercise Activity Thermogenesis, basically the exercise you do in and outside of the gym. The impact of EAT is often overestimated, and the impact of NEAT is underestimated. People tend to think that if they exercise every day, they can eat as much as they like. However, exercise doesn’t always burn as many calories as we like/hope.

Even if your spin class burns 400 calories, you need to take into account the calories you’d have burned regardless without doing anything. If you hadn’t done the class, you may still have burned 100 calories, so this class really only adds 300 calories to your Energy Expenditure. That’s only a little more than the average chocolate bar people down mindlessly with their coffee.

If you spend the rest of the day sitting at a desk and travel by tube, as many people in London working in an office job do, your NEAT is going to be low. So if this is you, when you’re making an estimation of your activity level and training every day, be conservative if you don’t do much else.

On the other hand, someone who is on their feet all day and works as a waiter, for example, but never set foot in a gym, this person can have a higher EE because their EAT may be zero, but their NEAT is high. Because we spend more time outside of the gym than inside, the effect of NEAT is often stronger.

So if your goal is fat loss, you may want to consider getting off the tube a few stops early and walking an hour every day or consider ditching the tube altogether and taking the bike.

How to work out your energy balance

There are a few ways to take all these details and put a number on them.

Several formulas have been developed to make an estimation of calories; some are more accurate than others. Here’s a handy website that I often use to make an estimation of calories.

At FFF, we use the Mifflin St. Jeor Equation to calculate your BMR. The formulas are below:


10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) + 5


10 x weight (kg) + 6.25 x height (cm) – 5 x age (y) – 161

You then need to factor in your PAL as noted above. The number that comes out of this equation is how many calories you need to sustain your body at its current weight and composition: maintenance calories. Whether you should eat this amount of calories is depending on your goal. To describe the relationship between calories burned and eaten, we use the term energy balance. If you burn as much as you eat, the balance is 0 or neutral. You’re not gaining or losing any weight.

When considering energy balance, if you are trying to lose weight, you need to be in an energy or calorie deficit – this means burning more calories than you consume or vice versa.

A calorie deficit can largely be achieved in two ways, either by increasing the amount of physical activity you do or decreasing the quantity of food you consume below your maintenance amount. Your body will then have a shortage and rely mainly on your body’s reserves: body fat, but also muscle tissue for energy.

On the other hand, if you are looking to put on weight, whether that be muscle or fat mass, you need to be in an energy or calorie surplus – thus, a positive energy balance.

As a result, calories in vs calories out is an important consideration if you have a goal of this kind in mind. However, being told to just ‘eat less and move more’, if you have a fat loss goal is a large over-simplification. This is because it can be criticised to ignore a whole host of important factors, including appetite, stress levels, sleep quality, mindset, calories absorbed (due to health status and gut microbiome), and the variations in energy burned – all of which can impact energy in and energy out.

Therefore, the calories estimated for you are a great baseline to get you going, but given the factors noted above, it is important to understand that there is no one-size-fits-all approach. You may need to tweak your approach over time to find what works best for you. We are all unique, and our nutrition should be too!

At Fresh Fitness Food, we do exactly that. We use industry-leading analytics, your individual data and advice from qualified food scientists to create a personalised meal plan, which is unique to your caloric needs, macronutrient requirements and – of course – the foods you love to eat.

If you would like to discuss a bespoke plan, book a call with one of our all-knowing nutritionists to discuss further. Have all the information you need but just don’t want to cook? Give one of our plans a go with £50 off your first 5-days with code BLOG50 – Start your trial here.

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Published by Georgia Chilton

In her teenage years, a love of food and rowing led Georgia into this field as she wanted to know how to optimise performance through nutrition. With a BSc in Nutrition and an MSc in Sports and Exercise Nutrition, she has the skill set to help you track towards your goals and maximise your potential.