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By: Paul Hough (Lead Sport/Exercise Scientist)

One of my clients, Tom, recently lost 10.9 kg and reduced his body fat from 24.7% to 9.5% in six months. He discussed his body composition transformation story here. In the previous article I discussed the difference between ‘body weight’ and ‘body composition’ and the purpose of measuring body composition.

In this article I will discuss how Tom changed his diet to reduce his body fat using a ‘calorie counting’ (CC) approach.  

Calorie counting (CC) involves recording how many calories you consume on a daily basis. This is usually done by keeping a food diary or using a food tracking app. Some people also estimate their energy expenditure (calories burnt) alongside CC by using apps and wearable activity trackers.

What is the best fat loss diet?

Many diets are effective for reducing body fat, some of these often come into and out of fashion. For example, the vegan diet and the (polar-opposite) carnivore diet are currently in vogue. When Tom originally came to see me, I advised him against an extreme diet as these are not usually sustainable in the long-term. There is some merit to the cliché ‘the best diet is the one you can stick to’. In other words, adherence is key when it comes to exercise and diet plans.

There are numerous debates on social media concerning ‘the best’ diet to reduce body fat and improve health. However, all successful fat reduction diets share a fundamental principle: creating a long-term energy deficit. The concept of creating an energy deficit is best explained using the ‘energy balance’ model.  

Energy balance

Energy balance is the relationship between energy consumed (energy from food/drink) and energy expended (energy used by the body). Energy balance is often cited as the main determinant of body composition, whereby a positive energy balance (more energy consumed than expended) leads to an increase in body fat. Conversely, a negative energy balance (more energy expended than consumed) results in a decrease in body fat.

On the surface, the energy balance equation is a very simple and is informally expressed as ‘Calories in = Calories out’ (CICO). However, this simple concept is problematic to accurately apply in practice, as both sides of the energy balance equation are monitored and regulated by a complex network of physiological systems that interact with our psychology and environment. Basically, the physiological regulation of energy balance is incredibly complex.

How is energy balanced measured?


A Calorie is a unit of heat which is often used to express the energy output of humans (energy expenditure) and the quantity of energy in food/drink. The unit ‘kilocalorie’ (kcal) is often used interchangeably with Calorie. In this case, the Calorie is always spelt with a capital c.

Food (Calories in)

It is important to recognise that the Calorie content on food labels is an approximation, particularly when different foods are combined within a meal. This study showed that 19% of the restaurant foods measured contained at least 100 kcal/portion more than the stated Calorie content.

The thermic effect of food is how much energy the body uses to digest and store the food you eat. Each macronutrient (carbohydrate, fat and protein) has a different thermic effect. Hence, the total Calorie content of two meals could be identical, but the amount of Calories available to the body, after digestion, will vary depending on the macronutrient profile of the meals.

The type of food we consume also influences how much energy the body uses. This was demonstrated in this study, which showed that a processed meal decreased postprandial (after eating) energy expenditure by nearly 50% compared with a minimally processed meal.

Physical activity/exercise (Calories out)

You’ve probably used a treadmill or cycle in the gym that displays how many Calories or kcal you’ve expended. Energy expenditure (EE) is also a standard measure on most fitness trackers and smartphones. However, these EE calculations are even more imprecise than the Caloric content displayed on food labels, as EE varies depending on various factors (e.g. body weight, age, level of fitness etc.).  

So far, I’ve briefly covered that

  • the caloric value displayed on food labels can be inaccurate
  • the energy ‘available’ to the body varies depending on the type of the food
  • the calculation of energy expenditure from gym equipment and fitness gadgets is imprecise  

These points highlight that it’s not possible to precisely calculate your energy intake or expenditure. However, from a fat loss perspective, it gets worse for the Calorie counting (CC) approach… 

Fat loss is not linear

The energy balance model suggests that fat loss is a relatively straightforward process: if you are losing body fat you are expending more energy than you are taking in. Conversely, if your body fat is increasing, you are eating/drinking too much energy (Calories), not using enough energy (low physical activity), or both.

A common rule of thumb often used to guide fat loss is ‘an energy deficit of 3,500 calories is required to lose one pound of fat’. As with many nutrition and fitness ideas, it’s difficult to establish the exact origin of this advice. However, the 3500 kcal ‘rule’ likely stemmed from the work of a scientist, Max Wishnofsky, who studied the Caloric equivalents of gained or lost weight during the 1950s. I’ve seen this formula applied literally, where people believe reducing energy intake by 500 kcal/day will result in a neat 1lb weekly reduction in body fat. Needless to say, this doesn’t usually happen.

Numerous studies have shown that losing body fat is not a simple linear process. I.e. creating an energy deficit (eating less, moving more, or both) does not result in a predictable or precise loss of body fat.Similarly, a quantified energy surplus (overeating) does not cause an exact increase in body fat, as was demonstrated in this overfeeding study.

Based on the points raised so far (and others), some people argue that the energy balance model is irrelevant or useless. These critics contend that the model is too simplistic and doesn’t account for other important factors that affect body fat levels, such as hormone imbalances, insulin resistance and other health issues that affect metabolism.

The Calorie debate: are Calories irrelevant?

The answer to this is (annoyingly) yes and no. If you are losing body fat without counting Calories (CC), then CC isn’t practically relevant to you. However, Calories are always relevant in theory. As discussed above, the Calorie is a unit of energy; therefore, suggesting that ‘Calories are irrelevant’ implies energy is also irrelevant. This is not the case, as energy balance governs fat loss or gain.

The argument against Calorie counting

People who have found the CC approach ineffective might believe the energy balance model is flawed; after all, if you’re meticulously CC and being physically active, how is possible not to lose weight? This is reasonable logic, but it ignores an important fact: the energy balance equation is dynamicif you change one side of the equation, you also change the other. You've probably experienced this phenomenon if you’ve not eaten for a long period (less energy in), you tend to feel more lethargic and move less (less energy out).

Another example of this natural energy balance flux is when the resting metabolic rate (RMR) decreases following weight loss. This means the body no longer requires the same amount of energy it did previously (when body mass was higher). Therefore, as you lose body mass, you need less energy (in). Bodybuilders and athletes who need to ‘make weight’ have understood this frustrating fact for years. As they get closer to a competition they have to continually reduce their daily energy (Calorie) intake to ensure they remain in an energy deficit and continue to lose body fat.

You might have read or heard a statement like this before: ‘I’ve been eating whatever I want on the ….. diet and I am stilling losing weight. Calories are irrelevant!’  The …. diet could be anything but is usually some take on a low carbohydrate (LC) diet, such as ketogenic, paleo or carnivore. This type of statement usually misses a crucial detail and should, more accurately, be: ‘I’ve been eating whatever I want **except for carbohydrates**.

Should you reduce Calories or carbs?

There is an abundance of evidence that demonstrates LC diets are effective for fat loss and, in the short-term, result in greater weight loss than low-fat diets. This experimental evidence often leads to the assumption that minimising carbohydrates rather than Calories is more important for fat loss. This is a fair but inaccurate assumption. Even if you’re not intentionally CC, reducing/omitting carbohydrates from the diet can indirectly reduce total energy intake, through several mechanisms:

  1. Diet clean-up effect: reducing the consumption of energy dense foods/drinks such as cake, confectionary, sugary drinks, alcohol etc.
  2. Satiety:  A LC diet naturally involves substituting carbohydrates with protein and fat based foods. These macronutrients, particularly protein, are often more satiating (make you feel fuller) than carbohydrates, so you tend to eat less Calories. 
  3. Thermic effect: protein has the highest thermic effect (more energy used to digest) compared to carbohydrates and fats, which partly explains why participants in protein overfeeding studies don’t gain the predicted amount of weight.
  4. Ketosis: a very LC (<50 g/day) diet can increase the level of blood of ketones, which can lead to appetite suppression (less energy in).

I recently published a case study where the participants’ energy intake decreased on a LC diet, even though they were not consciously trying to do this.

The advantages of Calorie counting (CC)

As discussed, CC is not an exact science. Calculating your energy intake is imprecise and it is practically impossible to accurately calculate energy expenditure.With this in mind, it might seem like CC is a waste of time.However,as demonstrated from Tom’s experience, CC can be a useful method in guiding your fat loss diet. It is better to have a rough idea of your energy intake than no idea at all. Furthermore, CC often improves dietary adherence as it is simple to implement and increases accountability. 


Although some people find the CC approach laborious, the development of apps have made the method very simple to implement on a daily basis.  Mobile apps, such as the one Tom used, allow the user to quickly record food/drink intake by scanning the bar code on the label. Tom tracked his daily food intake to ensure he remained within the caloric intake guidelines I provided him with after his initial consultation.


We’ve stablished that the caloric content of foods/drinks is approximate and the exact amount of energy the body can extract from the food varies. However, tracking food/drink intake can help to build an awareness of the energy density of different foods/drinks. In my experience, people can underestimate their energy intake, as they might not have an appreciation of the energy density of different foods/drinks. For example, a previous client was drinking around 10 pints of lager a week but had no idea this was almost 2000 kcal/week, just in beer!


It is well accepted that dietary recall (remembering what you’ve eaten) is an unreliable method of monitoring food intake. It’s very easy to forget the odd snack here and there. However, keeping a food diary, either on paper or using an app is more reliable and improves accountability.  Keeping a diet record is particularly effective for individuals who like to follow a structured routine.

Disadvantages of CC


Although apps have made CC far quicker and easier than keeping a paper record, some people can still find the process of recording food/drink intake inconvenient and, in some cases, problematic. For example, CC when dining out or if someone else has prepared the food is difficult.

Neurotic eating behaviours

The CC method could lead to neurotic eating behaviours, whereby a person can begin to obsess over his/her diet. This is especially the case amongst populations with a history of irregular or disordered eating habits. Hence, the CC approach is not recommended for individuals who may be susceptible to (or have) eating disorders.

Poor dietary choices

It is important to focus on the quality and quantity of the diet. Exclusively focussing on Calories could lead to poor dietary choices, as the caloric value of the food/drink does not represent the nutrient density. For example, a Mars Bar contains approximately the same Calories as a, nutrient dense, fillet of salmon. In this example, the caloric content is the same but the effect of the food on metabolism, satiety and health are obviously different.

Take away points

  • Energy balance is the relationship between ‘energy in’ (food/drink consumption) and ‘energy out’ (energy expended by the body). The energy balance equation is often referred to as ‘Calories in, Calories out’ (CICO).
  • It is impossible to accurately quantify energy balance in free-living (real-world) conditions. Despite this, creating an energy deficit is fundamental to losing fat (weight). I.e. you need to expend more energy than you consume.
  • Energy we take in (food/drink) and expend (bodily functions, physical activity) is usually quantified using one of the following units: Calorie or kcal.
  • Despite being difficult to quantify, the energy (Calories) taken in through the diet is relevant to weight loss. Calories are important.
  • Calorie counting (CC) is a long-standing dietary system, which is often used to reduce body fat (weight loss). You do not have to track your Calories to lose body fat, but it can help.
  • Numerous diets are effective in reducing body fat. Therefore, you should choose a diet that enables you to create a consistent, sustainable energy deficit until you achieve your desired level of body fat.
  • Although imprecise, the development of apps and wearable technology has improved the accuracy of the CC method and made it easier to implement.
  • There are pros and cons to CC. Some individuals, such as Tom, have achieved excellent results using the approach, whereas others might not. Hence, it is important to experiment with the approach to establish if it works for you.