The topic of calories is a controversial one, with many suggesting that calories are important to be aware of for health, and other’s advising that calories don’t count. So, which is it?

In this article, we will bust some of the common myths around calories.

Firstly, what are calories?

The definition of a calorie is the amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius. In simple terms, calories are a unit of measurement describing the amount of energy that a food or drink provides us.

When calories are displayed on food labels, they state the energy in terms of kilocalories (kcals). The terms ‘kilocalories’ and ‘calories’ are used interchangeably and refer to the same amount of energy (1).

However, in certain countries, energy may be expressed as kilojoules (kJ) rather than kilocalories.  Kilojoules are a different unit of measurement and require conversion to calories. One calorie (kcal) equates to 4.18kJ, so for example, 100 kcal is 418kJ.

Calories are also used to describe the energy needs of our body. It is common to overhear people talking about the amount of calories they burn through exercising, but our day-to-day tasks from breathing and thinking, to digesting food and even the functioning of systems, like our reproductive system, all require energy too.

Calories are not the same as nutrients

The amount of calories in a food gives us an insight as to how much energy that food can provide us. This does not tell us how nutritious a food is.

Even when a food or meal provides the same amount of calories as another, they can have very different impacts on our energy levels, our health and how we feel. This is often where the phrase “calories are not created equally” comes from.

For example, a donut may have a similar amount of calories to a pot of muesli and yogurt. Having the muesli is likely to provide us with more protein and fibre than a donut would, which will help to keep us fuller for longer. This doesn’t make the donut “bad” for you, or the muesli “better”, but it highlights that just because foods are similar in calories, they can offer a different range of nutrients.

Whilst our body does need energy, it requires specific nutrients for optimal functioning too. Focusing solely on quantity of calories rather than quality of nutrients could lead to not getting enough of the nutrients we need, like protein and essential fatty acids, or having too much of the nutrients we may want to limit, such as trans fats.

It’s not as simple as ‘calories in vs. calories out’

When it comes to weight management, the phrase “calories in vs calories out” is thrown around a lot. This concept implies that if the amount of calories we consume equates to the amount we burn, our weight will remain stable.

Whilst in theory this makes sense, our bodies are not robots.

Here are a few reasons as to why this notion is flawed:

1. Our body’s energy requirements vary

Fitness trackers and calorie tracking apps estimate the amount of energy that your body burns, and depending on your goals, may suggest that a certain number of calories are required.

Our energy requirements are not just dictated by how active our lifestyles are, but will also be influenced by our sleep, if we have any illnesses, and based on our individual body composition and genes. Fluctuations in hormones can also influence our energy requirements. For example, various studies have found that during the luteal phase of the menstrual cycle, women can experience up to a 20% increase in their metabolic rate as a result of the increase in progesterone (2, 3, 4).

When apps dictate a figure to follow, it is often based on population averages, with most of them only asking a limited number of lifestyle questions, making it difficult to accurately recommend the energy requirements of an individual. This can be dangerous, as consuming significantly less calories than your body requires can lead to drastic weight loss, muscle loss and nutritional deficiencies.

The most accurate way of measuring the amount of energy that an individual requires is through a technique known as direct calorimetry, which measures the rate of heat loss using a calorimeter (5). This is very rarely used due to its high cost, but also because knowing the amount of calories required by the body is not a requisite to living a healthy life.

The body is capable of accommodating for changes in energy requirements through hunger and fullness signals. Calorie counting doesn’t allow for fluctuations in the body’s requirements, and over time, if hunger and fullness cues are ignored, it can lead to a distrust between an individual and their body.

2. Not all calories consumed are absorbed

In order to obtain calories from the foods we eat, they need to go through the process of digestion so that the nutrients can be absorbed. All foods are broken down differently, and things like processing and cooking can change the digestibility of foods (6).

Certain foods, particularly ones high in fibre, may not get completely broken down which means that not all of the energy can be extracted from them. For example, research suggests that only about 70% of the calorie content of almonds is absorbed (7), whereas the calories from almond butter are more likely to be absorbed as it is simpler to digest.

Digestion itself is a process that costs energy, which on average, accounts for approximately 10% of the calories that our body requires each day. This is referred to as the thermic effect of food, which is a measure of how much different foods increase energy expenditure, due to the energy required to digest, absorb and metabolise the nutrients (8).

For example, proteins are expected to require up to five times more energy to digest in comparison to carbohydrates (9), and even more than fats (6). Food labels and calorie counting apps do not account for this.

3. The calories listed on the back of packets are not always accurate

The only way to confirm the amount of calories a food can provide is to put it in a bomb calorimeter, which is a container that measures the heat generated by a food when it is burned. So, the figures on the back of packets are based on averages, rather than actual individual measurements for each food.

There is a legal allowance for calories on packets to be up to 20%  inaccurate (10). This means that the energy that the food may actually provide can be 20% more or less than the number of calories listed on the packet.

Calorie counting can be helpful for many to create an awareness of whether they are supporting their energy requirements, but focussing on the exact numbers may not be helpful due to inaccuracy, and can also lead to viewing food as numbers, which can impact an individual’s relationship with food.

Low calorie does not mean ‘healthier’

Diet culture perpetuates a narrative that low calorie foods are “better” or “healthier” than their original counterparts, but this is not always the case.

Reduced calorie or low calorie variations of foods are achieved by reducing a certain nutrient within the food, like the fat or sugar content, and usually replacing it with an artificial sweetener or other agents to improve the texture and taste. Certain artificial sweeteners can cause digestive discomfort for some individuals, and there is research emerging that high intakes of artificial sweeteners within the diet may alter our gut microbiome (11, 12, 13), which is the collection of “good” bacteria in our digestive system that are important for our digestion, our immunity and absorption of nutrients. However, the research on this is still inconclusive and most of the studies have been in animals (14).

Removing or reducing certain nutrients in a food can mean that it is less satiating too, both physically and psychologically. For example, fat is a highly satiating nutrient and low-fat variations of things like yogurt are thought to be less filling than their original products. Low-calorie versions of foods can taste differently too, which may result in the eating experience being less enjoyable, leaving an individual dissatisfied. 

Calorie counting may not be in your best interest

Calorie counting can be a helpful tool for some individuals and can create an awareness around the amount of calories being consumed. This doesn’t necessarily help people to make healthier food choices, as calories are different to nutrients but it may guide an individual to fuel their body appropriately.

Calorie counting is not recommended as a long term strategy for health or weight management. It can make other aspects of eating such as socialising and celebrations involving food more difficult and may take the pleasure out of eating as it becomes a tedious and time consuming task. This can impact an individual's relationship with food and quality of life.

There is evidence that calorie counting can increase the likelihood of developing a disordered relationship with food (15, 16, 17). Disordered eating increases the risk of developing a clinical eating disorder which carries serious health consequences.

Takeaway

Calories are often spoken about in the context of weight management, but it is important to be aware that there is so much more that impacts our weight than just the food we eat, like genetics and illness. It is certainly not as simple as “calories in and calories out”!

Calories are not the same as nutrients, and the quality of our diet plays a large role in relation to our overall health (18). Counting calories alone can detract from ensuring that we are getting the right balance of nutrients that our body needs to function optimally.

This doesn’t mean that calories don’t count, because it is important to ensure that we are supporting our body’s energy requirements appropriately. However, we don’t necessarily need to be counting our calories; our body can regulate our energy intake on its own.