Green Ticks, Grey Areas: A Ten-Second Way to Read a Supermarket Label

Somewhere between the cereal aisle and the checkout, most of us make a series of snap judgements about packets based on a handful of coloured squares. It is a reasonable thing to do. It is also worth knowing exactly what you are trusting.

Here is the honest version: the traffic lights on the front of UK packets are a good tool used badly, and a bad tool used well. The colours mean something specific. The label does not mean what most of us assume it means. And the supermarket around it has been rearranged, quietly, to make the difference harder to spot.

What the lights actually measure

The front-of-pack scheme is voluntary but used by nearly every major retailer and manufacturer, and the thresholds come from Public Health England's guidance. There are four nutrients plus energy: fat, saturates, sugars and salt. Green means low, amber means medium, red means high — and crucially, the judgement is made per 100g, not per portion and not per packet.

That single detail undoes half the assumptions people make in the aisle. Olive oil is red for fat and red for saturates. So is a bag of nuts. Both are perfectly good things to eat. Meanwhile a low-fat flavoured yoghurt can wear green for fat and red for sugar, which is a fair summary of the product but a strange thing to call a healthy choice. The label is not a verdict. It is a nutrient snapshot of a hundred grams of something, whether or not a hundred grams is what you would ever put on a plate.

What the lights do not show at all: fibre, protein, whether the thing is ultra-processed, or how filling it will be at four in the afternoon. Those absences matter far more than most shoppers realise.

Two labels, one disappointing product

Consider a supermarket own-brand cereal bar with 'no added sugar' printed across the front. It is very often true. The sweetness comes from dates, raisins and concentrated fruit juice, which are not 'added sugar' in the technical sense but still land in the total sugars figure — occasionally at 25g or more per 100g, which is a red light. The claim and the colour can both be accurate, and the product can still be a small, sticky disappointment nutritionally.

Now consider a breakfast cereal shouting 'high in fibre'. That claim has a legal definition — at least 6g of fibre per 100g, or 3g per 100kcal — and a cereal can meet it comfortably while carrying 20g of sugar per 100g. Fibre is genuinely good for you. It does not cancel out the sugar, and the sugar does not cancel out the fibre. They are two facts sitting side by side while the packaging invites you to read only one.

Baked beans are the counter-example worth keeping in mind. Mostly green for fat and saturates, amber for sugar and salt, and a useful source of fibre and protein that the label never mentions. If you judged solely on the traffic lights you would underrate them badly.

Someone rearranged the shop while you weren't looking

Since October 2022, larger stores in England have been restricted from putting products high in fat, salt or sugar in the places that sell hardest: checkouts, store entrances and the ends of aisles. Restrictions on multi-buy offers followed later. Scotland, Wales and Northern Ireland have their own versions of the rules, so the picture varies depending on where you shop.

The intent was good. The effect, in practice, is that the crisps and the chocolate moved into the middle of the aisle rather than disappearing. Meanwhile the end-of-aisle displays filled up with things that technically passed the test — heavily marketed 'protein' puddings, syrupy yoghurt drinks, cereal bars with a green tick and a red square. Regulation changes the layout. It does not change the incentives, and it certainly does not do your reading for you.

The ten-second shortcut

Three questions. That is all you need, and none of them require arithmetic in the aisle.

One: would I eat the whole pack? If yes, look at the per-portion column rather than per 100g. If your packet is 40g, the per-100g numbers are 2.5 times worse than what you are actually holding.

Two: what is this replacing on my plate? A red-for-salt stock cube in a stew for four is a completely different proposition from a red-for-salt ready meal for one. Context beats colour every time.

Three: what is not on the label? Look at the ingredients list instead. If there is no fibre, no protein, and a list of things you would not keep in your own cupboard, the colours on the front are not the story.

Ten seconds, three questions, and you have got more out of the packet than the manufacturer intended you to.

Use the tool, don't worship it

The traffic lights are not a con. They are one of the better things to come out of UK food policy, and used properly they help you spot a genuinely salty sauce or a cereal that is mostly sugar. But they were never designed to tell you whether a food is good for you. They were designed to compare similar products quickly, and that is a much smaller job.

The most useful label-reading habit is not a rule about colours. It is a mild, permanent suspicion of any packet making a health claim in large type. The bigger the claim, the smaller the print, and the more likely it is that something on the back of the box is doing the real talking. Turn it over. Read four ingredients. Put it back if it looks like a chemistry set with a green tick on the front.

That is not cynicism. That is just shopping.