How to Read a UK Nutrition Label

Stand in any supermarket aisle and you'll see two people doing the same thing: flipping a packet over, squinting at the little grid on the back, and looking faintly defeated. There's a lot of information crammed into that box — and most of us were never actually taught how to read it. The good news is you don't need to absorb all of it. Once you know which three or four numbers matter for weight loss, a label takes about ten seconds to read.

So let's strip it back. Here's what's on a UK food label, what's legally required, where the sneaky bits hide, and the calm version of "what actually matters" — without turning your weekly shop into a maths exam.

The two panels on every packet

UK packaged food carries up to two nutrition displays, and they do different jobs.

Back-of-pack: the nutrition table. This is the detailed grid, and by law it has to be there on most pre-packed food. It must declare energy (shown in both kilojoules and kilocalories) plus the amounts of fat, saturates, carbohydrate, sugars, protein and salt. These figures are given per 100g (or per 100ml) — that's the mandatory basis. Manufacturers may also add a "per portion" column, but they don't have to, and you'll see why that matters in a moment.

Front-of-pack: the colour labels. The red, amber and green "traffic light" panel you see on the front is the at-a-glance version. Here's the thing most people don't realise — front-of-pack labelling is voluntary in the UK. It's not legally required, though most big retailers use a consistent scheme. When it's there, it shows energy plus fat, saturates, sugars and salt, usually per portion, colour-coded for high, medium or low.

Per 100g vs per portion (and the small-portion trick)

If you take one habit away from this article, make it this: compare products using the per-100g column, not per portion.

Per 100g is a fixed yardstick. Two cereals side by side, both shown per 100g — you can tell instantly which is higher in sugar. Easy.

"Per portion" is decided by the manufacturer, and it doesn't have to match what you'd actually eat. The NHS is blunt about this: the portion size on the pack "may be different from yours." A cereal might quote a 30g serving when most of us pour closer to double that. A tub of ice cream might call a portion two small scoops. The label isn't lying — but a flatteringly small "portion" makes the per-serving sugar and calorie figures look gentler than your real bowlful.

This is the single most common way labels mislead without breaking any rules. A snack that looks reasonable "per portion" can be quite different once you weigh out what's genuinely on your plate. So: per 100g to compare two products, per portion only after you've sanity-checked the portion against reality.

Reading the traffic lights properly

The colours aren't a verdict on whether a food is "good" or "bad" — they flag how much fat, saturated fat, sugar and salt a food contains per 100g. Green means low, amber means medium, red means high. A label that's mostly green is generally the healthier pick; amber is fine most of the time; red means "fine occasionally, just keep an eye on it."

The cut-offs are set nationally, so they're worth knowing. For food, per 100g, a nutrient is:

• Fat — green (low) at 3g or less; red (high) above 17.5g.
• Saturates — green at 1.5g or less; red above 5g.
• Sugars — green at 5g or less; red above 22.5g.
• Salt — green at 0.3g or less; red above 1.5g.

Anything between the low and high marks lands in amber. There's also a quieter rule for big portions: on packs where a single portion is over 100g, a nutrient gets a red light if that portion delivers more than 30% of an adult's reference intake (40% for salt) — so a large ready meal can earn a red even when its per-100g figure sits in amber. That's the system trying to stop oversized servings from sneaking under the radar.

One reassuring point: a few reds don't make a food forbidden. Olive oil is red for fat; a tin of oily fish might be amber on a couple of lines. Colour is a prompt to think, not a rule to obey.

Reference Intakes — the % on the label

Next to the grams you'll often see a percentage and the letters "RI" — Reference Intake. It's the share of a typical adult's daily guideline that one portion provides. The reference figures are fixed values for an average adult:

• Energy: 8,400 kJ / 2,000 kcal
• Total fat: 70g
• Saturates: 20g
• Total sugars: 90g
• Salt: 6g

Two caveats keep this honest. First, these are averages — built around a notional adult, not you. If you're shorter, taller, more or less active, or eating in a deliberate deficit, your real targets differ. Second, the 90g sugars figure covers all sugars, including the natural ones in milk and fruit; the separate recommendation to cap free (added) sugars at around 30g a day is the one that matters more for most people. Treat the RI percentage as a rough sense of scale, not a personal budget.

The ingredients list, and where sugar and salt hide

The ingredients list is the most honest line on the pack, because of one rule: ingredients are listed in descending order by weight. Whatever's first is what there's most of. If sugar (or one of its aliases) appears near the top, that tells you something the colourful front panel might soften.

The catch is that sugar wears a lot of costumes. Spread across several names, it can each sit lower in the list while adding up to a lot. Watch for: glucose, fructose, glucose-fructose syrup, dextrose, maltose, sucrose, invert sugar, molasses, honey, fruit juice concentrate, and anything ending in "-ose." Salt hides too — often listed as sodium on older or imported packs (multiply sodium by 2.5 to get salt). None of these are alarming on their own; the point is just to read past the marketing on the front and check the back.

What "high in protein" and other claims actually mean

Wording like "high in protein," "source of fibre" or "low fat" isn't free marketing language — UK law sets thresholds a product must hit before it can use them. A few worth knowing:

• "Source of protein" — at least 12% of the food's energy must come from protein.
• "High in protein" — at least 20% of its energy from protein.
• "Source of fibre" — at least 3g of fibre per 100g.
• "High in fibre" — at least 6g of fibre per 100g.

These are genuine, defined claims — useful when you're scanning shelves for higher-protein or higher-fibre options. Just remember a claim only speaks to one nutrient. A "high protein" chocolate bar can still be high in sugar and calories; the claim is true and the bar might still not be doing what you hoped. Read the rest of the panel before you trust the flag on the front.

What actually matters for weight loss

Here's the part that lets you stop overthinking. For weight loss specifically, you only really need to look at three things on a label, and ignore most of the rest:

• Calories — the number that drives weight change. Weight loss comes down to a sustained calorie deficit, so this is the figure to anchor on. Check it per 100g and per the amount you'll really eat.
• Protein — higher-protein foods keep you fuller and protect muscle while you lose fat. A useful tiebreaker between two similar products.
• Fibre — fills you up, slows digestion and is where most of us fall short. More fibre usually means a more satisfying choice for the same calories.

Fat, sugar and salt still matter for overall health — that's what the traffic lights are for — but for the scale, calories do the heavy lifting, with protein and fibre making the deficit easier to live with. You don't need to fear a red light or chase a perfectly green packet. You need foods that fit your calorie budget without leaving you starving, which is exactly the approach behind counting calories without burning out. A little label-reading at the shelf does more than rigid tracking later, and it pairs neatly with a bit of meal prep so the good choices are already in the fridge.

Frequently asked questions

Should I look at per 100g or per portion?

Use per 100g to compare two products fairly — it's a fixed yardstick. Use per portion only after checking the manufacturer's portion against what you'd actually eat, since "portions" are often smaller than real life and can make calories and sugar look lower than they are.

Does a red traffic light mean a food is unhealthy?

No. Red just means that food is high in fat, saturates, sugar or salt per 100g. Some genuinely healthy foods — olive oil, oily fish, nuts — show red on one or two lines. The colours are a prompt to think about how often and how much, not a ban.

What's the difference between sugars and "added sugar" on a label?

The UK label declares total sugars, which includes natural sugars from fruit and milk as well as added sugar. The label doesn't separate them, so the ingredients list is your clue: if sugar or its aliases appear high up, more of that total is added rather than naturally occurring.

Can I trust a "high in protein" label?

The claim itself is regulated — a food can only say "high in protein" if at least 20% of its energy comes from protein. But it only describes that one nutrient. Always check the calories, sugar and rest of the panel before assuming a "high protein" product is the better choice.

Do I need to read the whole label every time?

No. For weight loss, glance at calories (per 100g and per your real portion), then protein and fibre. Check the traffic lights and ingredients when you're trying something new or comparing two products. After a couple of weeks it becomes a few seconds of habit.

Where WeightLytic fits in

Labels are clearer once you've decoded them — but doing the per-100g maths in your head, every shop, for every product, gets old fast. WeightLytic is being built to take that friction away: log a food and see the figures that matter for your goal, not a generic average, so a label becomes a quick yes-or-no rather than a calculation. We're pre-launch and won't pretend otherwise — there are no inflated numbers here, just an app designed to make everyday food choices feel obvious. If that sounds useful, join the waitlist and we'll let you know when it's ready.

Sources & references

• NHS — How to read food labels (traffic-light thresholds, per 100g vs per portion)
• Food Standards Agency — Nutrition labelling (mandatory back-of-pack nutrients, per 100g basis)
• British Nutrition Foundation — Food labelling (Reference Intakes, ingredients order)
• Regulation (EC) No 1924/2006, Annex — nutrition claim conditions (protein and fibre)