Field guide · packaging
Read the label. Then look at the serving.
Compare similar packaged foods using per-100g figures, then check whether the labelled serving matches the amount you actually eat.
Read with sources
A nutrition label describes a packaged product. Start with the per 100g or per 100ml column when comparing similar products, then check the per-portion column against the amount you will actually eat. A dish photo cannot replace either piece of information.
Find the common measure
On UK prepacked food, the nutrition panel shows energy in kilojoules and kilocalories, plus fat, saturates, carbohydrate, sugars, protein and salt. The figures are given per 100g or 100ml; a manufacturer may also show them per portion. The shared 100g/100ml measure lets you compare similar products even if their suggested servings differ. Source: NHS Food labels.
Ask whose portion it is
The maker's portion may be smaller or larger than yours. If a label says "per portion," read the stated portion size before treating that number as your meal. If you need an amount for your own serving, measure it rather than estimating its weight from a photograph. The NHS explicitly cautions that a manufacturer's idea of a portion may differ from yours. Source: NHS Food labels.
Use front-of-pack colour as a prompt, not the whole answer
Some UK packs use red, amber and green front-of-pack labels for fat, saturates, sugars and salt. These are quick cues. Turn the pack over for the full values and the basis they use. If a dietary decision matters to you, read the full label and seek qualified advice when appropriate. Source: NHS Food labels.
Keep the kinds of evidence separate
A product label can tell you what the manufacturer reports for that product. Food Says Hi may offer a rough nutrition estimate for a submitted dish only when the available portion details support one; it shows the assumption beside that estimate. It cannot read the actual weight, recipe or package label from a dish photo. If the food is packaged, use the pack for that product. If it was prepared for you, ask about ingredients and serving details when those matter.