Nutrition labels look like straightforward measurements and are in fact regulated documents with specific conventions. Several of the numbers people rely on most are shaped by those conventions rather than by the food.
Serving size governs everything above it
Every figure on the panel refers to a stated serving, and that serving is often smaller than the portion a person would actually eat.
Serving sizes are set by reference to typical consumption categories rather than to the package, which is why a single container can hold two or three servings.
Comparing two products therefore requires checking that the servings match, and the per-hundred-gram column exists precisely because the per-serving one is not comparable across products.
Rounding creates real gaps
Small quantities may be rounded down to zero under labelling rules, so a product can declare none of a nutrient while containing a small amount per serving.
This matters most where a small per-serving quantity is multiplied by the number of servings people actually consume, which is common in spreads, oils and drinks.
The ingredient list is the check, since anything present must be listed there regardless of what the rounding permits on the panel.
The ingredient order carries information
Ingredients appear by weight in descending order, which tells you more about the composition than most of the panel does.
Sugars appearing under several different names distribute the same category across multiple lower positions, so no single sugar sits near the top.
Reading the list for categories rather than for individual items is the way around that, and it requires no arithmetic.
Claims on the front are separately regulated
Phrases such as light, reduced or a source of a nutrient have legal definitions, and they are comparative rather than absolute.
Reduced means less than a reference product, which may still leave a substantial amount, and a source of a nutrient means meeting a defined threshold rather than being a notable contributor to a diet.
Front-of-pack claims are therefore best read as pointers to check the panel, since they describe compliance with a rule rather than the character of the food.
Reference intakes are a benchmark, not a target
Percentage figures are calculated against a standardised reference diet that does not correspond to any particular person's requirements.
They are designed for comparing products against a fixed yardstick, which they do well, rather than for telling an individual what proportion of their needs a food supplies.
Anyone managing a condition where a specific nutrient matters clinically needs individual guidance rather than the panel, since the reference figures are not built for that purpose.