Why calories don’t count when measuring our food – New Scientist

You often hear that weight loss is a matter of burning more calories than you consume. That is not true at all, says obesity researcher Giles Yeo in the new book Why calories don’t count. This preview of the book lifts a corner of the veil. How do you determine how many calories the body extracts from food?

At the beginning of its publication Principles of nutrition and nutritional value The American chemist Wilbur Olin Atwater wrote: “The chemicals that make up the body are very similar to those in the food that nourishes the body. They consist of the same chemical elements, and so these two can be discussed together.’ Of course, Atwater was right, he believed that food consists of five different components: water, ash, proteins, fat and carbohydrates.

For most living things, water makes up the bulk of it. Humans, for example, are actually composed of about 37 trillion little sacs of water (our cells) that are supplied with oxygen and nutrients by a water-based transport system (the circulatory system). Although the water keeps the fuel supply running smoothly, everything in contact with each other, and keeping it moving, it does not in itself provide any calories. It does not provide energy.

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Ash in the food

And what about that axle?! Which part of us is it? I admit it seems like an odd expression. Atwater refers here to the minerals in our body that, however essential to life, provide little or no energy. Take for example calcium in our bones and teeth, so important for their strength; the iron in our blood, essential for the transport of oxygen; or the innumerable other compounds of sodium, potassium or magnesium with their innumerable essential biological functions. These are the main components of the “ash” left after cremation or burning in a bomb calorimeter (which chemists use to measure the caloric density of food); hence the name.

Of course, we know the remaining components, proteins, fat and carbohydrates; these are the main fuel sources. They are called organic constituents because they are mainly found in nature; in plants, fungi and animals. They all consist of different ratios and configurations of carbon, hydrogen and oxygen, with some also containing nitrogen, phosphorus, sulfur and some trace elements.

Count calories

Atwater’s approach to determining caloric availability—the amount of calories that can actually be extracted—was inevitably labor intensive. It was divided into three phases.

Firstly, a collection of different and ‘typical’ ingredients and their composition (water, ash, fats, carbohydrates and proteins) was needed. Second, the heat of combustion of each of these foods had to be measured with a bomb calorimeter, which determined the gross nutritional value. Third, each food item had to be eaten by a human and the resulting waste had to be analyzed with a fine mesh sieve (not literally, well, literally analyzing the pee and feces, but not literally with a fine mesh sieve).

Subtract the nutritional value of the waste products from the gross number of calories in the starting material, and you are left with the caloric availability of the food. Egg. Except life is always more complicated than you can imagine. Elsie Widdowson put it best in her overview of the field in 1955: ‘The whole field is very complicated, and the attempts to determine the energy value of food can only be described as a comedy of errors.’

But I get ahead of things. What did all that sifting of poop get you? After analyzing thousands of foods, Atwater found that fat, carbohydrates, and proteins had very different availability. Atwater called this availability “metabolizable energy.” In addition, the specific conditions and their combinations, whether with a particular food or as part of a meal or diet, were also found to affect metabolisable energy.

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