We can't even measure calories accurately, never mind predicting how much your specific body will actually absorb. Maybe we could be more accurate with vitamins and stuff, but I dunno.
The only way to get an accurate reading on calorie count is to burn it. 1 kilocalorie (nutritional calorie) can increase the temperature of 1kg of water by 1 C°
What? Calorie is a perfectly accurate method of measurement. Just because your body might absorb more or less than the next person doesn't change the amount of calories in a food.
But for relatively unprocessed foods, seems completely reasonable to me at first glance. The relative sugar content of, say, an apple, is dependent on all sorts of parameters (sun, water, soil...). The gluten content of wheat, iron content of vegetables, all of these things are variable. The more "natural" a food is, the higher the variability (as opposed to, say, artificial candy --- that should be pretty uniform).
Actual reason? Not sure because I wasn't around for the comment period.
Likely reason? People are terrible at making decisions based on ranges or anything more complex than a single number. They aren't even that good at a single number.
Since mixed things like trail mix can have some variety in ratio from bag to bag, going with an average and some variance means having some kind of flexibility. Then there are vegetables and other plants that can vary wildly too.
But what about something like gummy bears where the whole thing is very consistent? Can't have different rules for different foods, because companies will tie the whole thing up in court.
So the end result is a rule that allows flexibility for the things that actually need it that is also applied to everything else for simplicity.
It makes sense though. Say you claim there's 10g per 100g of something in your product. Any random scoop of 100g is not always equal. The 20% range means that any random scoop of 100grams must contain between 12 and 8 grams of something.
Due to personell shortages, this will obviously not be tested enough. But ideally it is and when an average of a dundred tests comes out at something other that 10grams per 100 gram, than they'll have to change it. I gues... I'm don't know the procedures.
I don't know if people look that closely at the nutritional values that it if worth it to manipulate them for advertising. I think the bigger effect is that they don't have to quality check that hard and can have a little more of this or that. Producing consistently is hard. But maybe it's a little bit of both.
Well, that's kinda besides the point right? The composition of "natural" food has huge variation. There is no "nutritional content of a banana." There's the nutritional content of this banana, of that banana, of an unripe banana, of a ripe banana, of an overripe banana...but these can be hugely different. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8266066/
I mean, just eat the occasional cookie. Don’t worry about the macros in it. Tracking macros is never going to be precise but you can get a general idea if you’re getting the right amounts. But, if you’re getting most or a lot of your nutrition from processed food, you’re probably tracking the wrong thing.