Calorie Deficit: Is Weight Loss Really As Simple As ‘Calories In’ vs Calories Out’?

Achieving weight loss, weight gain, or maintenance…

Is often described as a simple balance of ‘Calories In vs Calories Out’.

The theory says…

More ‘calories in’ = weight gain...


More ‘calories out’ = weight loss.

Its a simple equation.

And it’s seemingly easy enough to put into practice...

…If your goal is to decrease your bodyweight, you can either;

  • decrease ‘Calories In’

  • increase ‘Calories Out’

  • or a combination of both

...until you tip the equation in your favour.

Calorie Deficit: Lower Calorie Intake vs Calories Burned

We often use this strategy to achieve weight loss, as it’s relatively easy to explain, and to implement.

But it can get confusing, when you apply what you believe to be a calorie deficit/surplus, and your results aren't what you expect.

The explanation reveals a very easy, and very common mistake to make…

That mistake... is assuming that ‘calories in’ and ‘calories out’, refers solely to the food that you eat, and the amount of exercise that you do.

'Calories In': Trying To Measure & Record What You Eat

A ‘calorie’ is a unit of measurement, used to describe the energy contained within food. As a general rule, the following numbers apply to the 3 macronutrients;

Fat: 9 calories per gram

Carbohydrate: 4 calories per gram

Protein: 4 calories per gram

However… understand that measuring calories is not an exact science

Traditionally, the calories contained within foods, are measured using a bomb-calorimeter. A bomb calorimeter allows fuel (food in this case) to be burned, and for the energy that is released (calories) to be accurately measured. (eg. if you burned 10 grams of pure fat, you would produce the equivalent of 90 calories worth of energy, hence the 9 calories per gram of fat figure).

The obvious problem with this method, is that it’s observing the effect of burning fuel in a perfectly controlled environment, creating a 100% efficient process.

This does not reflect what is happening in reality.

Your body is a VERY complicated machine. And the process of digesting food and producing energy is NOT a perfect system.

(Some calories (contained within high-fibre foods, for example), may not be digested at all).

Also if you are monitoring your calorie intake, you will usually be relying on information provided on food packaging.

Do you trust this information?

You probably shouldn’t (at least not entirely)...

Food labelling in the UK IS regulated. And deliberately misleading consumers with inaccurate information is illegal.

However, the regulations do allow a certain margin for error

The legislation allows for different methods of calculating the nutrient values. It does not necessarily require laboratory analysis and it may be possible for a food business operator to calculate the values themselves depending on the type of product.
Declared values must be based on:
manufacturer's analysis of the food
calculation from the known or actual average values of the ingredients used
calculation from generally established and accepted data
The declared values in the nutrition table are average values to take into account of the natural variation in foods”.

In other words, while nutrition labels must give you a fairly accurate description of what you are eating, they may not be as precise as you think.

EU law requires nutrition data reported on food packaging to be within 20% of the real figures.

For example, a product that is labelled as containing 10 grams of sugar per 100g serving, could actually contain between 8-12g of sugar. Multiply that discrepancy over your entire diet, and you could be eating a significantly different amount of carbs, sugars, fats, total calories etc compared to what you think. And don’t forget, that's allowed within the law...

On top of that, investigations have shown that foods are often labelled incorrectly to an even greater extent, with labelled data falling outside of those legal limits.

Nonetheless, measuring calorie intake according to labels is probably still the most accurate method we realistically have…

Even so... in the real world… how many people are doing this?

And if you are, how accurate is your tracking?

Relying On An ‘Educated Guess’

  • Some people choose to measure their calorie intake very carefully; weighing out foods and recording the calorie and nutrient intake based on the labels. This can be time consuming and has been discouraged in people who suffer from eating disorders (you could argue that being so meticulous when it comes to eating, encourages an ‘unhealthy relationship with food’). On the other hand, this is an effective way of actually understanding what you are eating. Whether this approach works for you would depend on your goals and circumstances.

Often, when clients are asked to record their food/calorie/nutrient intake for the first time, they will immediately identify their mistakes themselves, without any input from somebody else/me. When your habits are spelled out on paper, they will often seem blindingly obvious. You no longer have the option of ‘moving on and forgetting’ about the packet of chocolate biscuits you ate at lunchtime.

  • MANY other people have absolutely no idea what the nutritional profile of their food is. Some don’t care. Some don’t/won’t take the time to worry about it. Others wouldn’t know what their nutrient intake should look like in the first place. Diet becomes a guessing game, and more often than not, consistent bad habits lead to undesired results.

  • Then there’s the people who do have a decent level of interest in their diet. And possibly even pay attention to the labels on their food packaging and engage in a certain amount of planning. However, most people do not accurately measure their calorie intake. They take an educated guess based on the nutrition labels and portion guides included on food labels… and then come to a rough estimate at the end of the day. has been shown that, on average, UK adults UNDER-ESTIMATE THEIR DAILY CALORIE INTAKE, BY APPROXIMATELY 500 CALORIES PER DAY! Based on rough estimates, that could lead to weight gain at a rate of 1lb per week. That’s almost 4 stones of weight gain per year!

Consider recording your calorie intake. "If you're not assessing, you're guessing".

How Many Of Those Calories To WE ACTUALLY Absorb: Digestion & The Thermic Effect of Food

So it’s clear that measuring/estimating calorie intake is rarely precise…

But what happens after those calories have been eaten is also complicated. And a significant variation exists between individuals, affecting the ‘end result’ of those calories...

The Thermic Effect Of Food (TEF): EVERY movement and process that your body performs, requires energy. This includes the digestion process…

  • energy used to chew

  • energy used by muscle contractions to move food through your digestive system

  • energy to produce digestive chemicals & enzymes

  • & much more…

On average, you will burn approx’ 10% of your daily calorie output, digesting and absorbing nutrients*.

But between individuals, there may be a large variation…

Different nutrients are easier, or more difficult, for the body to digest & absorb.

For example, digesting protein requires a greater amount of energy (has a greater ‘Thermic Effect’) than digesting carbohydrate. So in terms of net calorie intake, eating 100 calories of protein, or 100 calories of carbohydrate, are actually two very different scenarios.

And for various reasons, some intentional, some not, different people will eat diets made up of different proportions of each macronutrient. This means that some people’s diets will have a greater Thermic Effect than others

*Imagine if that '10%' rose to '15%' in one person compared to the average. On a daily intake of 2500 calories, that’s an extra 125 calories burned simply digesting food (325 calories compared to 250).

Chewing: Imagine two people eating a meal together…

They both have exactly the same plate of food in front of them…

Same food, same ingredients, same calories, same protein etc.

Also imagine that they are physically identical... same physiology, same size etc.

Person A is eating ‘mindfully’… taking their time to chew thoroughly.

Person B is stressed, in a rush and having a text conversation on their phone. Without realising, they are trying to eat as quickly as possible and NOT chewing thoroughly.

Would you be surprised to find out that Person A & Person B are going to digest the meal very differently?

Research shows that chewing until food is ‘liquefied’, significantly increases digestion efficiency. (Fairly obvious).

But this also affects the quantity of nutrients that are absorbed by the body. (eg. If you specifically aimed to eat 25g of protein in a meal, and did not chew properly, you may only be obtaining 20g of that protein).

Also, it has been shown that chewing correctly, encourages your body to ‘feel full’ at the correct time. You essentially get time to recognise that you’ve eaten ‘enough’ before you continue to eat to excess. (People who chew more, eat less).

Ultimately, it has been proven that chewing food up to 30 times improves fat loss (or helps to prevent fat gain), via improved digestion and nutrient absorption.

So again, it is not quite as simple as looking at a food package label and counting the ‘number of calories’ that you are eating.

Among MANY lifestyle factors, something as simple as how you chew can influence the actual effect of those calories.

Again, this illustrates how the 'Calories In' part of the energy equation can be be complicated.

'Calories Out': Measuring ‘Calories Burned’ During Exercise

If you want to measure the calories that you are burning during exercise, you have 3 broad options;

  • use the built-in calorie counter on exercise machines

  • use your own tech (Smartwatches etc)

  • estimate using existing data (online, books etc)

Just like measuring your calorie intake, none of these can possibly be precise…

Exercise Machines & Smartwatches: Firstly, the information is clearly an estimate. Factors such as exercise efficiency and body composition will affect how many calories are actually being burned by different individuals, even if the workouts appear to be identical. Secondly, you’re relying on the equipment manufacturer (who have a financial incentive to make the equipment appear to be effective) providing an accurate method of measuring those calories. This may or may not be the case.

Scientific Data: based on averages, data does exist and can be used to provide some insight into the calorific expenditure of various exercises. But again, this is based on ‘averages’ and various assumptions. There will be many people who lie significantly outside of the ‘average’ data ranges. Exercise efficiency, will cause a very significant difference in energy expenditure between individuals. Imagine swimming for example… a smooth technique is going to dramatically reduce energy expenditure compared to a relative novice with an inefficient technique.

It's extremely difficult to accurately measure your calorie expenditure. Keep a workout/activity diary to monitor your activity levels.

Metabolic Rate

You probably know somebody who seems to able to get away with eating whatever they want… apparently never seeming to gain any excess fat. Whereas you might feel that you only have to look at something sweet to gain weight.

There’s probably more going on there than simply a difference in metabolism. But that is certainly a major factor.

So again, when it comes to calories, there's more to think about than simply ‘how many’ calories.

Different metabolic rates in various individuals, means that the way that those calories are processed will vary.

Most metabolic rate calculations take into consideration your age and activity level. But not much else.

In reality, a number of other variables will affect how much of your calorie intake you ‘burn off’ or store as fat...

  • type of exercise

  • muscle mass

  • plus much more

Non Exercise Activity Thermogenesis

You have a 24 hour opportunity to ‘burn’ calories everyday. Even if you are exercising regularly, your workouts would still only account for a small percentage of that time…

In terms of time, simple activities such as walking, climbing stairs, cleaning, even just standing (with correct posture preferably), will make a bigger contribution to your daily routine.

The difference between an active person and inactive person in this sense, makes a huge difference to your calorie output. Don’t make the error of thinking that you are only burning off energy when you are ‘intentionally’ exercising. If you are trying to measure your 'calories out', take your full 24 hours into account.

Bodyweight 'Set-Point'

Most of the conditions within your body are kept at a relatively constant level…

  • body temperature

  • fluid balance

  • blood sugar

  • pH levels etc…

These levels must be kept within specific ranges to ensure optimal bodily function. Significant deviations can cause serious illness and in extreme cases... death.

There is a theory that the body also has a set-point for body-fat.

There is no doubt, that a genuine calorie deficit, over time, WILL produce fat loss (and overall weight loss).

But the set-point theory suggests that the body is designed to make adaptations in the event of sudden, significant weight gain or loss, in an effort to maintain equilibrium, as best as possible.

Don’t forget, from an evolutionary/survival point-of-view, this makes perfect sense. Only relatively recently, have humans made a conscious effort to “lose weight”. For most of our existence, we have had to survive relative food shortages. And even more recently, have we understood the need to maintain a ‘healthy weight’. So the human body is much better adapted to ‘storing’ energy.

It’s plausible that changes in metabolic rate, appetite and energy levels may contribute to a relative maintenance of the ‘norm’.

(You could even argue that the classic yo-yo dieting routine is an example of this).

“Does This Mean That Calories Don't Matter?

Calories absolutely do matter… and you SHOULD, of course, be aware of the amount that you are eating…

The 1st law of thermodynamics dictates that energy cannot be created or destroyed. It can only be transferred from one form to another...

Your body cannot create or destroy energy.

Ultimately, this means that if you consume more calories than you ‘burn off’… you WILL gain weight...

And vice versa…

If you consume less calories than you ‘burn off’… you WILL lose weight.

This is an underlying principle of many (probably most) weight gain/loss programmes.

However, be aware that the equation is not simply a case of the calories that you (think) you are ingesting, versus the number of calories that you (think) you are burning through exercise.

There is a lot more going on...

While some of this is measurable/observable,

Some of it isn’t.

The answer…

Ensure that you have a clearly defined plan.

(Otherwise you're just guessing!)

Monitor your results closely…

Set clear & effective goals, and make sure that you are progressing towards them.

If, for whatever reason, that progress stalls, realise that you probably miscalculated your calorie deficit/surplus based on the limited data that you actually have available.

Make your adjustments accordingly.