Food packaging is designed by two different departments with opposite objectives. The front is marketing. The back is regulation. Most of what confuses shoppers comes from reading the first and skipping the second.
The good news is that a small number of rules make labels genuinely useful, and they take a few minutes to learn.
The two labels on every pack
Front of pack is voluntary. The traffic light scheme — red, amber and green for fat, saturates, sugars and salt — is not a legal requirement in the UK. Most major supermarkets and manufacturers use it, but a product without it is not breaking any rule, and small producers often skip it.
Back of pack is mandatory. Nearly all pre-packed food must carry a nutrition declaration: energy, fat, saturates, carbohydrate, sugars, protein and salt, expressed per 100 g or per 100 ml.
That per-100 g figure is the single most useful number on the package, and the reason is in the next section.
Rule one: compare per 100 g, never per portion
Portion sizes are chosen by the manufacturer. Two similar products can declare different serving sizes, and a smaller declared portion makes every number on the front look better.
This is why the Food Standards Agency prefers per 100 g for comparison. It is the only way to say one cereal is sweeter than another without portion-size sleight of hand.
Use it whenever you are choosing between two things on a shelf. Two ready meals, two sandwiches, two sauces — per 100 g keeps the comparison honest.
Then use the per-portion figure for the other job: working out what you are actually going to eat. And check what the declared portion is. If a bag says “serves 4” and you and one other person will finish it, the relevant number is double what is printed.
Rule two: know the thresholds
The traffic light colours come from published FSA thresholds, per 100 g of food. Drinks have their own, lower thresholds.
Roughly, for solid food:
| Green (low) | Red (high) | |
|---|---|---|
| Fat | ≤3.0 g | >17.5 g |
| Saturates | ≤1.5 g | >5.0 g |
| Sugars | ≤5.0 g | >22.5 g |
| Salt | ≤0.3 g | >1.8 g |
Anything between the two is amber.
There is a second rule worth knowing. Where a portion is larger than 100 g — or 150 ml for drinks — a product is automatically red if one portion contains more than 30% of the reference intake for that nutrient. This catches foods where the serving is big enough to push a nutrient into the high range on its own.
Red does not mean forbidden. It means less often, in smaller amounts. Olive oil is red for fat. Cheese is red for saturates. Neither is a food to avoid; both are foods where the quantity matters.
Rule three: the ingredient list tells you more than the nutrition table
Ingredients are listed by weight, in descending order. That single fact does most of the work.
If sugar — or any of its aliases — appears in the first three ingredients, you are looking at a sweet product regardless of what the front says. The aliases matter, because splitting sweeteners across several names pushes each one further down the list: glucose syrup, fructose, invert sugar syrup, dextrose, maltodextrin, molasses, honey, fruit juice concentrate, corn syrup.
The ingredient list is also where you spot ultra-processing: emulsifiers, modified starches, protein isolates, flavourings, colourings, thickeners. Substances that do not appear in a domestic kitchen.
A short ingredient list of recognisable things is a better signal than any front-of-pack claim.
Rule four: claims are regulated, and narrower than they sound
Health and nutrition claims in the UK must be substantiated and cannot be misleading. That sounds reassuring until you notice the important restriction: a claim refers to one nutrient or one aspect of the product only.
“High in fibre” is a defined claim with a legal threshold, and it says nothing about the sugar content. “Low fat” says nothing about salt — and reduced-fat products frequently add sugar or salt to compensate for the flavour lost with the fat.
Then there are the phrases that are marketing rather than regulated claims. Natural, artisan, farmhouse, wholesome, goodness, inspired by — these carry no defined nutritional meaning.
Two specific traps worth naming:
“No added sugar” means no sugar was added. It does not mean low in sugar — fruit juice concentrate and naturally occurring sugars still count, and the total on the back can be high.
“Made with wholegrain” does not mean mostly wholegrain. Check the ingredient list to see where the wholegrain actually appears in the order.
Rule five: for salt, check the number, not the colour
Salt is where UK diets go wrong most quietly, because most of it comes from processed food rather than the shaker.
The label declares salt, not sodium. If you see a product declaring sodium — often imported — multiply by 2.5 to convert. The adult reference intake is 6 g of salt a day, and most people exceed it.
Bread, breakfast cereal, sauces and ready meals are where it accumulates, and none of them taste salty in the way that crisps do. Comparing per 100 g between two loaves takes ten seconds and can change a daily intake meaningfully.
What this is actually worth
None of this is dramatic. Reading labels will not transform your health in a month.
What it does is change hundreds of small decisions across years — which bread, which sauce, which cereal — and those decisions determine fibre intake, salt intake and the ultra-processed share of a diet. Those three things have evidence behind them measured in cohorts of hundreds of thousands.
The shortest version, if you remember nothing else: compare per 100 g, read the first three ingredients, and treat the front of the pack as an advert.
This article is for general information and is not medical advice. If you have been given specific dietary advice for a medical condition, follow that.
Sources
- Food Standards Agency front-of-pack nutrition labelling guidance, as summarised in UK technical guidance. https://nutrasafe.co.uk/uk-food-label-traffic-light-system-explained
- British Nutrition Foundation. Food labelling. https://www.nutrition.org.uk/creating-a-healthy-diet/food-labelling/
- British Dietetic Association. Food labelling: nutrition information. https://www.bda.uk.com/resource/food-labelling-nutrition-information.html
- British Heart Foundation. Food labels explained. https://www.bhf.org.uk/informationsupport/heart-matters-magazine/news/food-labels-explained
- UK Food Information Regulations 2014, as summarised in front-of-pack labelling guidance. https://foodlabelmaker.com/regulatory-hub/uk/front-of-pack-labels/
This article is for general information and is not medical advice. If a health problem is affecting your daily life, speak to your GP.
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