How to Read UK Food Labels (and What 'per 100g vs per serving' Really Means)
A no-nonsense guide to UK supermarket food labels — the traffic-light system, per 100g vs per serving, hidden sugars, and the three numbers that actually matter when you're trying to slim.
Walk down any UK supermarket aisle and you'll see the same label on almost every packet — that little colour-coded panel showing calories, sugar, fat, saturated fat and salt per portion. It's traffic-light labelling, and once you know how to read it properly, you can do most of your slimming work in five seconds at the shelf instead of an hour at home.
The three numbers that actually matter
If you read nothing else on a label, read these:
- Energy (kcal) — the calorie count. This is the only number on the panel that tells you anything about weight change.
- Sugars — broken out as a sub-line under "Carbohydrate". Anything red on the traffic-light scale (over 22.5g per 100g) is dessert pretending to be food.
- Saturates — saturated fat. Red here means it's calorie-dense without being filling.
Per 100g vs per serving — the trick of the trade
This is the single biggest source of "I thought I was doing well" disappointment in the UK. Manufacturers know that per serving sounds smaller, so they print that one in big bold type. But "per serving" is whatever portion size they chose — sometimes a third of the bag, sometimes a tenth.
Always do the maths in your head:
- Pick up the bag, look at the back panel.
- Find the "per 100g" column (it's there by law in the UK).
- Compare apples to apples — a "low calorie" cereal at 380 kcal per 100g is roughly the same as a chocolate digestive at 470 kcal per 100g.
The traffic-light cheat sheet (per 100g)
| Per 100g | 🟢 Green | 🟡 Amber | 🔴 Red |
|---|---|---|---|
| Sugar | ≤ 5g | 5–22.5g | > 22.5g |
| Fat | ≤ 3g | 3–17.5g | > 17.5g |
| Saturates | ≤ 1.5g | 1.5–5g | > 5g |
| Salt | ≤ 0.3g | 0.3–1.5g | > 1.5g |
Sneaky names for sugar
If "sugar" isn't on the ingredients list, it's been renamed. Common UK label disguises: glucose syrup, fructose, dextrose, maltodextrin, invert sugar syrup, fruit juice concentrate, agave nectar, honey, treacle, corn syrup. Same effect on your waistline, different name on the box.
The 30-second supermarket rule
If you're in a rush, just check three things on the back panel:
- Look at the kcal per 100g. Anything over 400 is energy-dense — fine occasionally, not for an everyday food.
- Glance at the traffic lights. If sugar and saturates are both red, it's a treat, not a staple.
- Read the first three ingredients. They're listed in order of weight, so if sugar shows up there, the product is mostly sugar.
That's it. You don't need a degree in nutrition to slim — you just need to read the back of the box, not the marketing on the front.