Two products with similar labels can differ considerably in what they deliver. The figures on a package are produced by a set of conventions, and knowing those conventions changes how the numbers should be read.
Energy values come from a formula
The energy figure on most labels is not measured directly. It is calculated by multiplying the amount of each macronutrient by a standard energy value and adding the results.
Those standard values are averages derived long ago. They assume a typical digestibility that does not hold equally for all foods, particularly whole foods with intact cell structures. The convention persists because a universal alternative would be impractical to apply.
Nuts and some whole grains release less energy than the formula predicts, because part of the fat and protein remains inside cell walls that digestion does not fully break down. Processing changes this, so the same food ground finely yields more.
Serving size is chosen by the manufacturer within limits
Per-serving figures depend entirely on what the manufacturer defines as a serving, and that definition varies between similar products in the same category.
Comparing per-serving numbers between two packages therefore compares two different quantities. The per-hundred-gram or per-hundred-millilitre column is the only reliable basis for comparison.
Serving sizes also frequently differ from how much people actually consume, which is why some regions require a per-container figure alongside the per-serving one. A package presented as single-use may still declare several servings.
Rounding rules hide small amounts
Labelling regulations permit rounding to fixed increments, and amounts below a threshold may be declared as zero. A product can therefore state zero of something it contains in small quantity.
Across several servings those rounded amounts accumulate into a figure that is no longer negligible, which matters most for ingredients consumed in concentrated form.
The ingredient list is the check on this. An ingredient present in a rounded-to-zero amount still has to appear in the list, in order of quantity. Its position indicates roughly how much is present.
Regional standards differ in what is required
Which nutrients must be declared, how fibre is defined, and whether fibre contributes to the energy total all vary between regulatory regions.
The same product sold in two markets can therefore carry different numbers without any change in its composition, which makes cross-border comparison unreliable. The reference intakes used for percentage figures differ as well.
Tolerances are wider than the precision suggests
Regulations allow a margin between declared and actual content, because natural products vary between batches and analysis itself has measurement error.
A label printed to the nearest whole number implies a precision the underlying system does not provide, which is a reason to treat small differences between products as noise. Consistent differences across a category are more informative than any single pair.
