How to read a nutrition label: what they hide

A nutrition label does not usually hide information by lying; it hides it by making you look in the wrong place. Front-of-pack traffic lights, serving sizes and health claims can all be useful, but the real evidence is usually in the per 100g nutrition table and the ingredients list. Read those first, then decide whether the marketing claim still holds up.

Start with per 100g, not the front claim

The most useful part of the label is often the least glamorous: the nutrition table per 100g or 100ml. Per-portion numbers can help if you really eat that portion, but per 100g lets you compare one cereal, yoghurt, sauce, snack or ready meal with another.

NHS guidance explains that food labels often use red, amber and green colour coding for fat, saturated fat, sugars and salt, with green meaning low, amber medium and red high.¹ This is a quick filter, not a full judgement. Olive oil will look high in fat because it is fat. A sugary cereal may look fine if the portion is tiny. A ready meal may look acceptable until you notice it is one of two portions.

Read energy, saturated fat, sugars, salt, protein and fibre together. Calories matter for weight change, but they do not tell the whole story. Protein and fibre affect fullness. Salt affects blood pressure risk. Saturated fat and overall fat quality matter differently from total fat. Sugar matters most when it is added or concentrated, but the label usually shows total sugars, not free sugars.

NHS sugar guidance explains that free sugars are added sugars plus sugars in honey, syrups and unsweetened fruit or vegetable juices, smoothies and purees.⁷ A label's "of which sugars" line does not tell you how much is free sugar. You need the ingredients list to see whether sugar, syrup, honey, juice concentrate or puree is doing the work.

Decode the ingredients list

The ingredients list is where the story becomes clearer. GOV.UK guidance says pre-packed food must list ingredients if there is more than one ingredient, and ingredients must be listed by weight, with the main ingredient first.³ If sugar, refined flour or oil appears near the top, the food is built around it.

Look for clusters, not one villain. Sugar may appear as sugar, glucose syrup, fructose, dextrose, maltodextrin, honey, agave, fruit juice concentrate or other sweet ingredients. Fats may appear as palm oil, rapeseed oil, sunflower oil, butter, cream or coconut oil. Salt may appear as salt, sodium, soy sauce, yeast extract, stock, cured meat or cheese.

Also check the ingredient that the product is named after. If the label says "blueberry", "wholegrain", "chicken", "almond" or "high fruit", the percentage may matter. UK labelling rules can require the quantity of an ingredient when it is emphasised in the name or on the label.⁵ A product can look fruit-forward while containing very little fruit, or protein-forward while mostly being starch, oil and flavouring.

Allergens are not optional detail. Food Standards Agency information explains that the 14 major allergens must be emphasised in the ingredients list on pre-packed food, for example in bold.⁶ If you have an allergy, do not rely on front-of-pack claims or assumptions about what a food "should" contain.

Watch serving-size tricks

Serving sizes are useful when realistic and misleading when optimistic. A cereal may show calories for 30g when many adults pour 60g. A bottle may show sugar per half bottle. A sharing bag may show "per serving" when the bag is designed to be eaten in one sitting. A sauce may look low in salt because the serving is a teaspoon.

Do the quick multiplication. If the serving is half the pack and you eat the whole pack, double everything. If the packet contains 2.5 servings, multiply by 2.5. If a snack bar looks small but has high calories per 100g, it is energy dense. That does not mean forbidden; it means the portion is doing the work.

Salt is worth checking both per 100g and per pack. NHS salt guidance says adults should eat no more than 6g of salt a day, and children should have less.⁸ A single ready meal, sandwich and snack combination can use a large share of that target before dinner.

How health claims shape perception

Claims are not meaningless. They are regulated. GOV.UK guidance says nutrition and health claims must meet rules, and food businesses cannot claim or imply that food can treat, prevent or cure disease.⁴ But a legal claim can still be used to draw attention away from the rest of the product.

"High protein" can sit on a sugary snack. "Source of fibre" can sit on an ultra-processed cereal. "No added sugar" can still contain fruit juice concentrate or high total sugar from dried fruit. "Low fat" can be higher in sugar. "Gluten-free" is essential for coeliac disease, but it does not automatically mean healthier for everyone else.

Be especially cautious with disease-adjacent language: "immune support", "gut health", "hormone balance", "detox", "metabolism", "energy" or "heart healthy". Ask what nutrient, what amount, what authorised claim, and whether the rest of the label supports the halo. Use insights to challenge nutrition marketing, the health library to understand conditions, Start Here to track symptoms or goals, and the stack builder to record supplements rather than buying based on label claims.

A 60-second label check

First, check the serving. Is this one portion or half the pack? Second, compare per 100g with similar products. Third, scan the first five ingredients. Fourth, check sugar, salt, saturated fat, protein and fibre. Fifth, ask whether the front claim still feels important after the back label.

Do not ignore the non-nutrition parts of the label. The Food Standards Agency's "check the label" advice covers use-by dates, storage instructions, cooking instructions and allergen information, because those details affect whether a food is safe as well as whether it is healthy.² A ready meal with decent macros still needs correct cooking. A product that looks nutritious is not safe for someone with an allergy if the ingredients list or precautionary wording says otherwise.

For everyday foods, look for patterns rather than perfection. A useful breakfast might have meaningful protein and fibre without a lot of added sugar. A useful ready meal might have decent protein, vegetables and moderate salt. A snack might be fine if it is truly a snack, but not if it is sold as health food while acting like dessert.

The label is not a moral score. It is a tool for choosing. The aim is not to fear food, but to stop marketing from making the choice for you. That skill often gets faster with regular practice.

This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.