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Myths about Calories

cartoon joke about calories

One of the most misleading dietary rules is “count the calories and you’ll lose weight”. Calorie calculations are based on experiments made over a century ago that even then were acknowledged as “broad brush”.

Quite how a unit of measurement originally applied to steam engines and then adapted by nutritionists who stuck people in copper cells for a week at a time to measure their food, breathing and faeces, became the mainstay of so many diets is peculiar.

And focusing on ‘calorie counting’ distracts from the difference between ‘food like substances’ (such as ultra processed, mass produced chocolate) and ‘real foods’ (like craft chocolate). Calorie counting isn’t a path to healthy eating or even losing weight.

Chocolate is demonised for being high in calories. It is indeed true that a craft dark chocolate bar will contain more calories than a bar of ultra processed, mass produced chocolate that is packed full of additives, preservatives and sugar (sugar is not calorically dense). But this certainly doesn’t mean that ‘low calorie’ snacks (including confectionery and chocolate) are ‘healthier’ or good for your waistline.

To unwrap these misconceptions, it’s worth understanding the history of calories and unpicking the challenges posed by over focusing on calories, low fat foods, etc.

The History of The Calorie … France

Given France’s culinary tradition, it’s appropriately ironic that the man credited with first coining, and then defining, the calorie was a Frenchman: Nicolas Clément. Nicolas was not a chef or nutritionist. Rather he was an entrepreneur who also held one of the first chairs in industrial chemistry at the Conservatoire des Arts et Metiers in Paris. And his students record him using the term calories to measure how steam engines convert heat into work, specifically defining a calorie as the quantity of heat needed to raise the temperature of 1 kg of water by one degree.

Whilst Clement is now credited with inventing the term calories another French chemist, Antoine Lavosier, laid the groundwork that enabled it’s rapid adoption. Back in 1780 Lavoisier designed a tool to measure how guinea pigs’ breathing would heat up ice. He called this device a “calorimeter” and then adapted it to measure the heat from various mechanical experiments and chemical reactions.

In the late 19th century scientists in Germany, keen to improve farming efficiency, used calories and calorimeters to measure how different animal feeds impacted cattle’s weight gain by weighing them, and monitoring their respiration. Note the link between nutrition and respiration is key; we lose weight and burn calories via breathing (yes, that’s right; we lose weight almost entirely via breathing and Lavosier was definitely onto something).

…The USA

Turning this work on cattle and animal feeds to modern calorie counting and diets involved a couple of extraordinary hops.

The man generally credited with putting calories at the heart of human nutrition and dieting is an American, Wilbur O. Atwater, who studied in Germany (and Atwater generously credits these scientists, especially: Voit, Rubner, Henneberg and Stohmann, in much of his work). Atwater’s work was designed to inform people to spend their “hard earned wages” on more “calorifically and nutritionally effective foods”; as far as can be understood, dieting wasn’t on his agenda.

Atwater first experiments were with a ‘bomb calorimeter’; basically a chamber-like device where food samples are burned, heating up the surrounding water. The amount of food that needed to be burnt to raise the temperature of the surrounding water by one degree gave Atwater a benchmark to calculate the calories of different foods (this is where the phrase “burning calories” comes from) and come up with some general rules.

But measuring food energy in a bomb calorimeter is obviously different from the way a human body digests, and uses, food. Basically we don’t ‘consume’ everything we eat; some foods we can’t digest and we will ‘excrete’ (mainly via our bowels). Atwater called the difference between what we consume and excrete “available energy” (nowadays known as metabolisable energy). And he calculated it through simple arithmetic; taking the total energy produced by burning the food sample and subtracting this from the energy not used by the body (i.e. excreted matter).

To measure this excreted matter, and to control for other variables, Atwater performed thousands of experiments on volunteers on over 500 different foods in what he called a “respiration chamber”. The respiration chamber sounds somewhat like a prison, and not much fun. Volunteers were asked to spend a week in a “box of copper incased in walls of zinc and wood [where] he lives – eats, drinks, works, rests, and sleeps. …the temperature is kept at the point most agreeable. …in the chamber are a small folding cot-bed, a chair, and a table. …[the chamber is] 7 feet long, 4 feet wide, and 6 feet high. Food and drink are passed into the chamber through an aperture which serves also for the removal of the solid and liquid excretory products, and the passing in and out of toilet materials, books, and other things required for comfort and convenience“.

Armed with the results of the bomb calorimeter and the respiration chamber Atwater could work out the ‘calorie count’ of different foods. And in 1894 Atwater published his findings in the USDA Farmer’s Bulletin under the title “Foods: Nutritive Value and Cost”. In this he categorised three basic food types; protein, fats and carbohydrates. And to each of these food types he assigned different calorie counts. The basics for the calculation have been tweaked, but have remained basically the same ever since; proteins and carbohydrates are assumed to contain 4 kCals per gram and fats and lipids to have 9 kCals per gram. And even today when you look at the calorie count on any food, it will be based on a simple calculation on the amount of protein, carbohydrates and fats in the food multiplied by these Atwater’ factors.

The simplicity of the calorie system proved irresistible. It was used during the first world war to help work out what agricultural crops to plant and animals to rear. And after the war, authors started to write articles and books to help people diet. One of the most famous of these was by Dr Lulu Hunt Peters, titled “Diet & Health”, and from 1922 to 1926 it consistently was in the NY Times Top 10 best seller list. Read it today and it’s hard to believe it isn’t an article (or blog) from any current dietary magazine (or website).

Why a calorie may not really be a calorie…

From the get go, the problems of Atwater’s calculations were apparent (and to be fair, he acknowledged many of them). And his calculations were NOT designed for dieting. They were designed to help people generally, and farmers specifically, figure out which foods were better nutritional value for their hard earned dollars.

In no apparent order, here are some examples of the problems with “calorie counting” to diet:

  • The way protein is metabolised by the body is radically different to the way carbohydrates and fats are metabolised. To quote Dr Giles Yeo: “Atwater’s calculations never took into account the energy it takes our cells to metabolise food in order to use it. …a calorie of protein makes you feel fuller than a calorie of fat, because protein is more complex to metabolise. For every 100 calories of protein you eat, you only ever absorb 70”.
  • And it’s not just protein calories that work differently; in 1973 Merill and Watt of the USDA revised the Atwater Factors noting that variations of digestibility in carbohydrates could mean you can absorb between 32% to 98% depending on which carbohydrate you ate (i.e. for some carbohydrates, only 32g of a 100g portion will be digested, for others it’s 98g).
  • How food is cooked (and prepared) also radically alters how it can be metabolised, as is what you cook together (e.g., making it more digestible and therefore higher in calories).
  • Your genes also make a massive difference to how you absorb foods too, and again, Giles Yeo’s book is eye opening here; he has some pretty sobering studies from Professor Clare Llewellyn of UCL showing how socio-economic status impacts the heritability of body weight varies from 40% for middle class families to 70% for those who are “food insecure”.
  • Your microbiome similarly makes a huge difference (read any of Tim Spector’s books for more on this).

So basically, the nature of the protein/carb/fat, the way the are cooked, what else you eat it with, your genes, your socio-economic circumstances, and your microbiome, all mean that the effective calories you eat mean that a food listed as having 100 calories could effectively be metabolised by you to generate anywhere from 20 to 99 calories.

But because almost all packaged foods list their calculated calories and because it seems so simple, many people do ‘count the calories’. Counting calories can convey an impression of control. But counting calories is also very misleading and may encourage people to believe that a low calorie, ultra processed snack (or chocolate bar) is better for them.

So What to Do?

It is very clear that some foods (and drinks) are unhealthy. And fattening. But you won’t be able to work this out by looking at their calorie count.

A far better approach would be to avoid ultra processed foods, including almost all mass processed chocolate and confectionery with their additives, preservatives, hydrolyzed added fats, sugars, etc.

The best advice is to first check the ingredients. If there is an ingredient listed that you don’t have in your kitchen and/or if your grandmother wouldn’t recognise the ingredient, why are you considering eating this? And please, please, try to ensure you know where the bars are made and beans are sourced.

And don’t fixate on calories. The listed numbers need to be adjusted by so many factors that they are effectively as useful as the proverbial chocolate tea pot.

Far better to follow the simple advise of Michael Pollan: “Eat food, not too much, mostly plants“; and in particular focus on the first two words: “eat food“. Not low calorie food stuffs that are ultra-processed and mass produced.

Chocolate and Calories

Gram for gram, sugar is lower in calories than chocolate (and many artificial ingredients and additives are lower still). So mass produced chocolate appears ‘better’ than craft chocolate in terms of calorie count; for example:


Maltesers (37g)187
Creme Egg187
Kit Kat (4 finger)233
Mars Bar (58g)260
Bounty (57g)268
Snickers (58g)296


Menakao 45% Milk and 72% Dark (70g)391-451
Standout Coconut Milk (50g)316
Amaro Piura Peru, 75% Dark (70g)390

Gram per gram, craft chocolate bars contain more chocolate, which is far more filling (and nutritious) than sugar and all the other additives, flavouring agents, e-numbers, etc. in low calorie, mass produced chocolate snacks. So, craft chocolate has a higher calorie count (note: the bars are also bigger in most of the cases above). But (normally) you savour a few squares of craft chocolate at a time. In contrast, ultra-processed, mass market chocolate is also designed to be scoffed. So you end up eating the whole bar and, depending on the time, mess up your appetite for lunch, dinner, etc.

So, check the ingredients (and ideally, identify where the bar has been crafted, and the source of the beans). Don’t get distracted by calories. And please see below for a few very different craft chocolate bars that you can savour (and ignore the calorie counts).

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