This also has to do with a conversion “glitch” and the United States’ relative reluctance to adopt the metric system. In US food labels, there’s a technical distinction between little-c calories and big-C Calories. What we see in FDA nutritional labels are big-C Calories, which are technically **Kilo**calories. Since the US is always weird about the metric system, they decided to just avoid that Kilo altogether and make it even more confusing.
So, combine that with fast-and-loose rounding and you get 0 big-C Calories =< 999 little-c calories.
>What is the difference between calories and kilocalories?
> The “calorie” we refer to in food is actually kilocalorie. One (1) kilocalorie is the same as one (1) Calorie (upper case C). A kilocalorie is the amount of heat required to raise the temperature of 1 kilogram of water one degree Celsius.
https://www.nutrition.gov/expert-q-a#:~:text=The%20%22calorie%22%20we%20refer%20to,of%20water%20one%20degree%20Celsius.
You have two things going on here.
1. The label can round down. So if there are 0.499 Calories in a serving it can list 0. Bonus: Serving sizes for a lot of items are arbitrary so they adjust the serving size to hit the 0 Calorie rounding sweet spot
2. Artificial sweeteners are in there in very small amounts. I forget the numbers but an easy way to explain it is that the artificial sweeteners are thousands of times sweeter than regular sugar, so you only need very tiny amounts to make something very sweet.
Obviously number two has a lot of nuances and complicated things going on, but that doesn’t belong on ELI5.
Simple: They (or at least most food) can’t.
The amount of vitamins in food is usually small enough that it doesn’t matter, so their caloric value might as well be 0 although they’re considered nutrients. And most artificial sweeteners really have 0 or close to 0 caloric value. Table salt is edible (in small amounts) and has 0 caloric value, and of course plain water is drinkable and also has no calories.
But carbohydrates have calories pretty much by definition, as do amino acids. If you’re eating any of those, you’re eating calories.
They can’t really have 0 calories, but they could theoretically have 0 *net* calories. This means that the amount of energy you get from the food is equal to the amount of energy it takes your body to digest it. So, effectively, it does nothing for you.
Imagine you’re buying and selling items at a market. If you sell an item for the same price you bought it, you have a profit of £0 even though someone gave you money for it. This is like the net calorific value.
They can not:
Carbs have 4.5 calories a gram.
Protein has 4.5 calories a gram.
Fat has 9 calories a gram.
Calories are allowed to be rounded on labeling in the U.S.; but unless something has so little macro-nutrients that it has less than 0.5 calories, it will have calories to have any nutritional value (nutritional value is not the same as supplemental value – like the zero calorie multi-vitamin that has lots of micro nutrients).
However, they are some chemical sweeteners that do not have calories, but the health damage from them is vast, and they are best to be avoided. There are natural and lower calories sweeteners that are acceptable (honey, stevia, coconut sugar, etc.), but the zero cal sweeteners are generally carcinogenic (cancer causing) and best completely avoided.
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