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Calories, calories, calories and not a nutrient in sight!

Updated: Aug 7, 2023

If you are an obsessive calorie counter perhaps it is time to consider what a calorie actually is and think about whether counting calories is at all useful to helping you lose weight. After all, you don’t eat calories, you eat food!

What is a calorie?

So, what is a calorie? Here’s a dictionary definition:” the energy needed to raise the temperature of 1 gram of water through 1 °C”. In other words, it’s a unit of heat energy.

How do you measure the amount of heat energy contained in food? Well, it’s done in a device called a ‘bomb calorimeter’.

Calorimeter, "A device for measuring the heat developed during a mechanical, electrical, or chemical reaction and for calculating the heat capacity of materials."

Basically, the food to be measured is put into a bomb cell, which is immersed in a tank of water, and the food is then completely incinerated until it is ash. As it burns it gives of heat which heats the surrounding water, and the temperature increase is measured. The number of calories of heat given off is then calculated. We then say that 100g of food ‘X’ contains ‘Y’ calories. The more 'energy' in a particular food the more heat that is produced when that piece of food is incinerated and thus we day it has 'more calories'. But is that even meaningful?

Though the number of calories calculated to be in different types of food seems a logical way to assess the amount of energy each food provides, it is very flawed logic. Here’s why:

1. We don’t incinerate foods to ash in our gut, we digest it down and separate it into individual nutrients, which we absorb.

2. We don’t utilise heat energy to power our cells and metabolism, we use chemical energy in the form of ATP (Adenosine Triphosphate).

Your boiler can burn gas, releasing heat energy (calories) to heat the water that supplies your radiators, but your body doesn’t incinerate food to release heat to power your body.

Our bodies are powered, healed, grown, repaired, and maintained using a variety of nutrients, not calories. Calories are the end-product of combustion (heat), not a substrate to create the chemical energy we need – for that we need nutrients like glucose and fatty acids. We need nutrients, not calories!

What’s the problem with counting calories?

So, you want to count calories because you’ve been told that restricting calories is the best way to lose weight? You may also have been told that you need to ‘move more’ so that you can ’burn’ more calories. Burn calories? How do you burn something that isn’t a ‘thing’, it’s a unit of heat energy?

Three potential problems of counting calories:

1. You eliminate the foods from your diet that are most ‘energy dense’, which is fatty foods. Fats are necessary in the diet for absorbing a range of fat-soluble nutrients (vitamins A,E,D and K, many phytonutrients from plants, CoQ10 etc). Two fatty acids, omega-3 and omega-6 are essential nutrients i.e., they must be consumed in the diet, and are critical for correct blood clotting, immunity and other functions. Fats are needed for nerve insulation, forming functioning cell membranes and many other things. Why on earth would you cut out all fat from your diet when fat is so essential to health?

2. You stop eating once you’ve reached your daily calorie allowance, or you starve yourself all day so that you can enjoy a meal in the evening. Either way, your body is not receiving a regular replenishment of nutrients through the day. Yes, intermittent fasting can have health benefits, as long as when you do eat you are eating plenty of nutrient dense foods. This includes plenty of protein rich foods such as meat, fish and dairy, and a broad range of fruit and vegetables which will also give you the fibre you need to feed your gut microbiome.

3. You pay far more attention to how much you are eating rather than what you are eating.

An over observance of food quantity rather than food quality can lead to nutritional deficiencies. Weight loss requires you to limit your intake of ‘fuel’ foods (fats and sugars), particularly those with little nutritional value, such as sugary foods and refined carbohydrates, so that you encourage your body to metabolise its own stored fuel, i.e., body fat. However, you don’t want to restrict the amounts of micronutrients (vitamins & minerals) eaten per day because they are essential to health. So, during weight loss, food quality becomes doubly important, so you need to pay attention to what you are eating rather than just how much.

Hopefully I have convinced you that counting calories is a fairly meaningless thing to do! Our bodies don’t incinerate food and we are not powered by heat energy. Counting calories also drives your behaviour, persuading you to eat low energy-density foods at the expense of essential nutrients.

Here are some more reasons not to count calories:

Food labels may not be accurate.

The calories listed on food labels are not necessarily accurate. According to the US Food and Drug Administration (FDA), calorie counts on food packaging are permitted to be accurate to within 20%. So, something listed as having 200 Kcal could actually have up to 240 Kcal in it. A study found that the stated energy (calories) content of a range of commercially produced foods and restaurant foods where wholly inaccurate, generally underestimating the number of calories in foods (and occasionally overestimating) (1)(2)

Absorption of ‘calories’ is very variable.

The number of ‘calories’(macronutrients) you absorb from food varies considerably from person to person. Also, different nutrients have different absorbability rates (bioavailability). How much you absorb can also depend on its source, what other foods you are eating it with, and what cooking method is used. Nutrient absorbability is also dependent on the how healthy your gut is and even the time of day you are eating! (3) In other words, you can have no idea how many ‘calories’ are actually in the food you are eating or how many of those calories you are absorbing.

This is particularly true of protein where animal derived sources of protein are more bioavailable than plant sources of protein (4) and can be better utilised to build muscle, and maintaining muscle during weight loss is really important to maintain metabolic rate. It doesn’t matter what your calorie counting app says, its impossible to be accurate, yet your app may lead you to make food decisions that are harmful to your health. For example, it may lead you eat a sweet but low-calorie food with little nutritional value rather than a fattier but low sugar food containing many fat-soluble vitamins vital for health.

‘Burning calories’ is also a misnomer.

An accurate measurement of your total daily energy expenditure (TDEE) can only be done in a research laboratory using ‘double labelled water’ or other complex techniques 5). Yet every piece of gym equipment and weight loss app claims to be able to monitor how many calories you are ‘burning’ each day. How accurate can they be? The answer is – not very accurate.

These apps are based on a variety of mathematical algorithms which make a lot of assumptions about you - they particularly assume that all people of the same height, weight, sex and age will have the same metabolic rate and that these people will expend the same amount of energy for any given level of activity or energy intake.

However, we are not so similar to other people! Studies of fitness tracking apps have shown them to be widely variable in their accuracy (6). The best wrist worn tracking device was 27% inaccurate whilst the worst was 97% inaccurate (7). Is this because the devices are based on algorithms that can’t capture very individual responses to activity and exercise? Or is it because we are thinking about energy expenditure as ‘calories burned’, whereas really, energy expenditure is about the rate of ATP production in cells in order to do the body’s work – exercise more and you need to make more ATP to make your muscles do more work, hence you will metabolise more glucose and fatty acids. How do you measure that? Probably not with an app!

Is it time to put down your calorie counter and think about the quality of food you eat?

The importance of nutrient density.

Food is about nourishment, and this remains true when you need to lose weight. When you are trying to lose weight, it is even more important that you eat good quality nutrient dense foods because you will be eating less food.

The most nutrient dense foods are animal foods (meat, fish, eggs and dairy) (8). Animal foods contain more fat than plant foods but also contain a higher level of micronutrients and virtually no carbohydrates. They also suppress appetite due to the high protein and fat content which helps people to regulate their food intake better. The reduction in carbohydrates also enables the body to transition into metabolising body fat for energy, encouraging weight loss.

Plant foods contain essential nutrients such as vitamin C, magnesium and some b vitamins but are not so nutrient dense per gram of food because of the high water content of fruit and vegetables. Plants also contain a lot of carbohydrate, particularly starchy foods like cereals and potatoes, providing the body with lots of glucose for energy but making it more difficult for the body to metabolise its own body fat. However, plants do contain fibre which is important for gut health due to its positive effect on the gut microbiome.

Overall, a diet containing a combination of animal and low-starch plant foods is the best way to lose weight and restore health as it is nutrient rich and prevents over-eating. Counting calories is distracting and highly inaccurate, leading to poor food choices and ultimately nutritional deficiencies. So, is it time for you to ditch that calorie counting app and think about the quality of the food you eat?

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