Who figures it out? How do they know how many calories are in there? Like when it’s printed on a restaurant menu- does a restaurant just guess? And doesn’t that depend on exact measurements? Which we know can’t be exactly the same every time a person cooks a dish?
In: Chemistry
A restaurant doesn’t “guess” when they put the calories on a menu. They know the ingredients and roughly how many calories each ingredient has. Is it going to be 100%, exactly the amount of calories that’s printed every single time? No, probably not. There’s too much potential for variance. But the idea is to give you a general sense of how many calories you’re consuming. If you order something that says 1,000 calories, it might be 950, it might 1050, but at least you know generally what you’re consuming.
We have measured the heck out of everything that a human can digest. So, when you combine things that a human can eat together, you add the calories and that’s your meal.
It won’t be exactly the same every time. Nobody cares if you have a bit more or less. There is no need for greater precision so greater precision is not used.
As for how we measured the things that a human can digest, we just burned them and measured the resulting temperature change. That’s more or less what your body does with it, but with extra steps.
Restaurants just calculate the ingredients and add up the totals. But the actual base foods need to be measured in a lab to be sold on the market. They actually burn it to measure calories. You should look up a video about it because it is pretty cool. Here is a copy-paste from Google because why not:
A sample of the food is placed in an insulated, oxygen-filled chamber that is surrounded by water. This chamber is called a bomb calorimeter. The sample is burned completely. The heat from the burning increases the temperature of the water, which is measured and which indicates the number of calories in the food.
there is some wiggle room in reported figures; but we have federal guidelines as to the calories in food.
so restaraunts can look at their menu of 8oz steak 4oz green beans 8oz potatoe 1c cream and add it all together (for example)
There is a device called [Calorimeter](https://en.wikipedia.org/wiki/Calorimeter) with that we have tables and databases for everything.
The cook just takes his recipe, adds everything up and than divided it by the mass of a portion.
That way he can also break it down to the dedicated amount of carbs or fat etc.
That is no big deal. Just adding and dividing.
I actually know a woman whose career was a food scientist. Her entire job was verifying what was on food labels. They would break things down chemically. For example, if your bottle of ranch says it has 12 grams of fat in a serving, they would break it down to verify it had 12 grams. Of course, there is some wiggle room. For example, something can be marketed as “fat free” if it has less than half a gram of fat per serving (assuming the regulations haven’t changed recently). As far as calories 1 gr fat has 8 calories, carbs and proteins it’s 4 so it becomes a mathematical equation.
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