I know we all burn energy differently but just after an idea of how we got to those averages used in the formulas when working out our daily requirements.
I know we all burn energy differently but just after an idea of how we got to those averages used in the formulas when working out our daily requirements.
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We put it in an enclosed chamber with lots of oxygen and see how well it burns.
It’s super dodgy. It really doesn’t tell us much about how much energy the human body can extract from food, but… it’s the measure we have, and if we don’t think too much about it, we can sort of convince ourselves that it works.
Finding the raw energy is the easy part. You put a food in a sealed box and burn it. Chemistry is conservative – if the inputs and outputs are the same, the energy is the same, and what happens in the middle doesn’t matter. Burning sugar, for example, releases energy just like it would when our body ‘burns’ it.
But calories alone don’t tell you that much. Some calories can’t be processed by your body, so it is important to separate out these things ahead before burning.
Then, beyond that, calories in protein are handled differently than carbs or fats. We can identify how much of each of these are in food, too, but that’s not reflected in “energy” or calorie counts.
These days, we know exactly how much energy is in each component of a food, so we don’t have to test much.
Old way to evaluate calliries in food – to literally burn it and measure released energy.
Then take same food and feed 100 people for month with similar physical activity and find ammount off food which is nessesary to maintain their weight.
Then repeat same while they have no physical activity and when yhey have exccesive one.
From this scientist deducted aproximate base amount of calories which are nessesary to maintain live process and aproximations of how much you need to eat for various life style.
If you looking for personal diet use those numbers as starting points and adjust over time according to your observations
Food calories were originally literally embrasured by burning the food.
Of course the chemical reactions that our bodies use to turn food into energy are not quite the same as burning it and lots of stuff can be burned but not digested by humans, but it is close and consistent enough to work with.
Fun additional fact about calories:
The calories we usually measure the energy of food in are actually kilocalories. It is sort of like calling a kilogram a Gram for short and not helpful, but at least it is consistent. Any time you hear calories mentioned in the context of food those are actually kilocalories.
Another fun fact about calories.
When expressing the power of explosions in Tons of TNT equivalent, the measurement is not actually based real TNT which can vary a lot, but on calories.
It was decided that 1 gram of TNT equivalent would be defined as one food calorie (kilocalorie) of energy.
This means you can easily visualize how big of a boom your food would make if its energy was released all at once.
1 BicMac has 545 kcal which equates to 545 gram of TNT
The smallest yield of the USDavy Crockett tactical nuclear weapon system was 10 tons of TNT.
This means, that if you eat a BicMac a day for 50 years (or 5 a day for ten year) you will have consumed enough energy to be the equivalent of a very small nuke. (It gets faster if you include fires and the drink.)