How to Read Food Labels: Per 100 g, Traffic Lights, Reference Intakes and Claims

Nutrition basics · By the Plain Measure editorial team · Published 2026-11-03

A woven basket of groceries holding asparagus, avocados, a yellow pepper and a punnet of cherry tomatoes — Fresh, single-ingredient foods usually carry no nutrition label; labels matter most for packaged foods. Photo by Leonie Wise, CC0.

A packet of crackers, a pot of yoghurt and a ready meal all come with more numbers than most people have time to read in a supermarket aisle. You do not need all of them. A handful of rules, set out by the NHS and fixed in food law, are enough to compare two products in a few seconds and to spot the foods that are high in fat, saturated fat, sugars or salt. This guide explains where to look and what the figures mean.

The nutrition table on the back

Almost all pre-packed foods carry a nutrition table on the back or side of the pack. By law it must give the energy value, in kilojoules (kJ) and kilocalories (kcal), and the amounts of fat, saturates (saturated fat), carbohydrate, sugars, protein and salt. Fibre and some vitamins or minerals may be added voluntarily. Fresh, unprocessed foods made of a single ingredient, such as loose fruit and vegetables, do not need a nutrition table at all.

The figures are always given per 100 g or per 100 ml, and often per portion as well. The two columns answer different questions:

Per 100 g lets you compare like with like. Two breakfast cereals, two pasta sauces or two loaves of bread can be set side by side whatever the pack size.
Per portion tells you what you get in one serving, but the portion is chosen by the manufacturer. The NHS warns that the manufacturer's idea of a portion may be different from yours, so check the stated portion weight against what you actually eat.

A note on "sugars": this line counts all sugars in the food, including those naturally present in milk and whole fruit, not only the added and free sugars that the health limits target. Our guide to free sugars and salt explains the difference and how the ingredients list helps you tell them apart.

High or low? The cut-offs per 100 g

The NHS gives a simple set of thresholds for deciding whether a food is high or low in the four nutrients that matter most for heart health and weight. They are the same figures used for the colours on front-of-pack labels:

Per 100 g of food	Low (green)	High (red)
Total fat	3 g or less	More than 17.5 g
Saturated fat	1.5 g or less	More than 5 g
Total sugars	5 g or less	More than 22.5 g
Salt	0.3 g or less	More than 1.5 g

Anything between the two columns is medium, shown in amber. Drinks are judged against different criteria, per 100 ml. Some labels give sodium instead of salt: the NHS equivalents are 0.1 g of sodium for the low threshold and 0.6 g for the high one.

You do not need to memorise the table. Remembering the high thresholds for saturated fat (5 g), sugars (22.5 g) and salt (1.5 g) covers most decisions in the aisle.

Traffic-light labels on the front

Many supermarkets and manufacturers also put a summary on the front of the pack. It usually shows energy, fat, saturated fat, sugars and salt for a portion, the percentage of the reference intake that portion provides and, on colour-coded versions, a red, amber or green background for each nutrient. In the UK this front-of-pack scheme is voluntary, so not every product has it.

The NHS reading is straightforward. A food with all or mostly green is a healthier choice. Amber is neither high nor low, so foods with mostly amber can be eaten most of the time. Any red means the food is high in that nutrient and is best eaten less often and in smaller amounts. When choosing between two similar products, go for more greens and ambers and fewer reds.

Two cautions. First, the colours judge one nutrient at a time: a red for fat on a bag of nuts or a bottle of olive oil does not put them in the same category as biscuits, and a product that is green for fat can still be high in sugars. Second, the colours say nothing about fibre, whole grains or fruit and vegetable content, which matter just as much for a balanced diet.

Reference intakes: what the percentages mean

The percentages on labels are worked out against reference intakes set in food law for an average adult. The figures are:

Energy or nutrient	Reference intake per day
Energy	8,400 kJ / 2,000 kcal
Total fat	70 g
Saturates	20 g
Carbohydrate	260 g
Sugars	90 g
Protein	50 g
Salt	6 g

So a portion with 1.5 g of salt provides 25% of the reference intake for salt. These are not personal targets. Energy needs vary with age, sex, body size and activity, and the 90 g figure for sugars covers total sugars; it is not a recommended amount of added sugar, which the NHS and WHO limit far more tightly. Reference intakes are best used as a yardstick for how much one food contributes to a day, not as a daily allowance to use up.

The ingredients list

Ingredients must be listed in descending order of weight, so the main ingredients always come first. If the first few are cream, butter, oil or sugar, the food is likely to be high in fat or sugar. Sugars can appear under many names, such as glucose syrup, honey, dextrose or fruit juice concentrate, and several of them further down the list can add up. Allergens must be highlighted, usually in bold.

The ingredients list is also the quickest way to check for whole grains in bread, crackers and cereals: look for "wholemeal" or "whole grain" near the top, as explained in our guide to fibre and whole grains.

What claims on the pack must mean

Words like "low fat" or "high fibre" are not marketing free-for-alls: in the UK and the EU they are defined by law. A few of the most common:

Low fat: no more than 3 g of fat per 100 g for solids, or 1.5 g per 100 ml for liquids.
Low sugars: no more than 5 g of sugars per 100 g for solids, or 2.5 g per 100 ml for liquids.
Source of fibre: at least 3 g of fibre per 100 g; high fibre means at least 6 g per 100 g.
Reduced (fat, sugars and so on) and light or lite: at least 30% less than a similar product (25% for salt or sodium).

"Reduced" is relative. A reduced-fat version of a very fatty product can still be high in fat, and fat is sometimes replaced by sugars or starch, so check the per 100 g figures rather than trusting the claim alone.

A ten-second routine in the shop

Pick up two similar products and turn to the per 100 g column.
Compare saturated fat, sugars and salt, and note any figure above the high threshold.
If there is a front label, count the reds.
Glance at the first three ingredients.
Check the portion size against what you will really eat.

Most of what you eat can still come from foods that carry no label at all: vegetables, fruit, pulses, plain grains and fresh fish or meat. Labels are a tool for the packaged part of the trolley, and a balanced plate, as described in the Eatwell Guide and WHO advice, remains the bigger picture.

This page is general information from public health sources and food law, not personal dietary advice. If you have a medical condition that affects what you eat, such as diabetes, kidney disease or a food allergy, follow the advice of your doctor or dietitian.

Sources

NHS, "Food labels".
Regulation (EU) No 1169/2011 on the provision of food information to consumers, as retained in UK law, Annex XIII, Part B: reference intakes; Annex V (foods exempt from the nutrition declaration).
Regulation (EC) No 1924/2006 on nutrition and health claims made on foods, Annex (nutrition claims and conditions applying to them).