I’ve heard they are allowed to lie by 20%. And do I have to always overestimate by 20% or can I trust the label?
This is a deeper question than anyone realizes. The short answer is no they’re not entirely accurate.
Let me give you an example of how they can be inaccurate. Take “Calories” for instance. To attain this number they use what’s called a bomb calorimeter. Essentially, they incinerate the food in an enclosed tank. The number given is the exact calories contained within that food.
Now take Person A and Person B and a 500 calorie meal. Person A has no health issues and absorbs the full 500 calories. However, Person B has an intestinal issue that alters absorption of fatty acids in the small intestine. Maybe Person B only absorbs 425 calories from the meal.
There are myriad variables that impact digestion and absorption (stress, sleep quality, latent diseases, toxins, etc). The numbers you see on the Nutrition Facts panel are from a controlled scientific experiment, not from what’s absorbed in a human body. What’s on the panel and what happens in the body are not always the same.
Additionally, I will close with this. I can’t remember the study but I remember one where they had people eat a handful of almonds and they used testing to determine calorie absorption. What was listed on the package was say 180 kcal. However, the average absorption was maybe 140 kcal (these weren’t the numbers but an example).
The panel is a guideline. There are many variables at play.
Most foods can’t be as accurately measured as, say, almonds, either. When the do the bomb calimotry on a big max for example, it depends on the person that made the Big Mac (I think they use an average of several) but you get one made by a sixteen year old that is mostly trying to get into the fry cooks pants.