How to Read Food Labels for Prediabetes: A UK Supermarket Guide

Start with carbohydrate — not just sugar

One of the most useful numbers for anyone thinking about blood sugar is carbohydrate.

UK labels show carbohydrate and “of which sugars” separately.

For example:

The important point is that this food contains 58g of total carbohydrate per 100g, not 6g.

That 6g tells you how much of the carbohydrate comes from sugars. The remaining carbohydrate can include starches and other forms of carbohydrate.

Diabetes UK is clear on this: look at total carbohydrate rather than only the “of which sugars” figure, because starchy carbohydrates affect blood glucose too. Front-of-pack traffic lights don't usually show total carbohydrate, so you'll normally need to turn the packet over to find it.

That's why a “low sugar” label doesn't automatically mean low carbohydrate.

Bread, rice, pasta, potatoes, breakfast cereals and plenty of other everyday foods can be fairly low in sugar while still containing a substantial amount of carbohydrate.

What does “of which sugars” actually mean?

Here's where it gets a bit more confusing.

The “of which sugars” figure isn't the same as “added sugar”.

It includes sugars from different sources together — including sugars that occur naturally in foods as well as sugars that may have been added during manufacturing.

Plain yoghurt, for example, can contain naturally occurring milk sugar even when no sugar has been added.

So two products with identical sugar figures aren't necessarily the same nutritionally.

The ingredients list can help fill in the gaps. Ingredients are listed in order of weight, so whatever's near the top makes up more of the product.

Watch out for sugar appearing under other names too — sucrose, glucose, fructose, syrups, honey and molasses are all forms of sugar.

So the sugar number alone rarely tells the full story.

Check the fibre too

Fibre is genuinely useful when you're comparing carbohydrate-containing foods side by side.

Diabetes UK recommends choosing higher-fibre carbohydrates. Its current guidance for prediabetes includes choosing options such as brown rice, wholemeal pasta and wholemeal bread instead of more refined versions where that's realistic for you. Comparing loaves is a good place to practise — see our guide to wholemeal and higher-fibre bread and our guide to snacks for prediabetes.

Adults in the UK are generally advised to aim for around 30g of fibre a day, and the NHS describes foods containing 6g or more of fibre per 100g as high-fibre.

Fibre often doesn't make it onto the front of the pack, so you'll need to check the back.

When two similar products are otherwise neck-and-neck, the higher-fibre option may be worth considering.

Why saturated fat still matters

Prediabetes isn't only about sugar.

Your heart health matters too, which is why it's worth glancing at saturated fat when you're comparing similar products.

UK health guidelines recommend that the average man has no more than 30g of saturated fat a day and the average woman no more than 20g a day.

On a label, you'll often see saturated fat written as “saturates”.

And a product being high in total fat doesn't tell you everything about the type of fat inside it — so it's worth checking the saturated-fat number separately.

Don't forget the salt

It's easy for salt to fade into the background while you're busy focusing on carbs and sugar.

But much of the salt we eat is already present in packaged and everyday foods before they reach the table.

The NHS recommends adults have no more than 6g of salt a day.

Ready meals, sauces, processed meats, soups and bread can vary considerably in salt content, so it's often worth comparing similar products.

The easiest way to compare products: use the per 100g figure

Manufacturers love their own portion sizes.

One cereal box calls 30g a serving, another says 45g. A ready meal might describe half the pack as “a portion” even though you may actually eat the whole thing.

That can make comparing products confusing.

Nutrition information on pre-packed foods is provided per 100g, or per 100ml for drinks, which makes similar products much easier to compare.

Diabetes UK also recommends using the per-100g column when you're weighing up similar foods.

Once you've worked out which product looks better per 100g, circle back and think about how much of it you'll actually eat.

Both numbers matter — one for comparing, one for reality-checking.

Portion size can completely change the picture

Picture two supermarket ready meals.

At a glance, Meal B looks lower in carbohydrate because it has 10g per 100g rather than 12g.

But if the whole pack is the portion you actually eat, it provides slightly more carbohydrate overall than Meal A.

Diabetes UK points out that a manufacturer's idea of a portion may be different from yours.

So think of per 100g as your comparison tool, and your actual portion as the reality check.

What do the red, amber and green labels actually mean?

Lots of UK supermarkets use front-of-pack traffic lights.

It's a voluntary system, usually covering energy plus:

fat, saturated fat, sugars and salt.

Green means low, amber means medium, red means high.

For food, the NHS uses this general per-100g guide:

Drinks are judged using slightly different criteria.

Traffic lights are handy for a quick comparison between similar foods, but there's one thing they leave out that matters a lot here:

total carbohydrate isn't part of the traffic-light system.

So treat the front of the pack as a quick glance, and save the fuller comparison for the back.

Take front-of-pack claims with a pinch of salt

Manufacturers know that words like “protein”, “natural”, “light” and “no added sugar” catch the eye.

Some of these come with specific rules attached — but none of them lets you skip reading the rest of the label.

“High protein”

In Great Britain, “high protein” is a regulated nutrition claim. At least 20% of the food's energy must come from protein before the claim can be used.

Useful to know — but it tells you nothing about carbohydrate, sugar, fibre or saturated fat.

Check those separately.

“Reduced fat”

For a “reduced fat” claim, the fat content generally has to be at least 30% lower than a comparable product.

That doesn't mean the product is actually low in fat — and it certainly doesn't automatically mean it's lower in carbohydrate or calories.

Diabetes UK also points out that reduced-fat or reduced-sugar versions aren't automatically the healthier overall choice.

“No added sugar”

This is probably one of the easiest claims to misunderstand.

A “no added sugars” claim has specific rules governing when it can be used.

It can still contain naturally occurring sugars.

And it can still contain plenty of carbohydrate.

So “no added sugar” is never a reason to ignore the rest of the nutrition label when you're thinking about blood sugar.

“Natural”

“Natural” does not tell you how much carbohydrate, sugar, fibre, saturated fat or salt a product contains.

Check the nutrition panel rather than relying on the word on the front of the pack.

A supermarket example: why sugar alone can mislead you

Here are two fictional breakfast cereals, based on the kind of nutritional profiles you might genuinely find on a UK supermarket shelf.

Look only at carbohydrate, and the first cereal seems very slightly lower.

Look only at sugar, and the second one looks much lower.

Bring in fibre and saturated fat, and the picture shifts again.

There's rarely a single magic number to chase.

What actually helps is looking at the whole combination — carbohydrate, sugars, fibre, saturated fat, salt, and how much of it you'll genuinely eat.

These figures are illustrative examples rather than current values from specific supermarket products. Recipes and nutrition information change, so always check the current label.

One red light doesn't make a “bad” basket

A red traffic light means the food is high in that particular nutrient; it does not make the food automatically off-limits. The overall pattern of what you eat matters more than one colour on one product.

PrediabetesBasket follows the same principle by looking at the shop as a whole rather than judging one item in isolation.

A simple rule for next time you're in the supermarket

When you're comparing two similar packaged foods, start with the per 100g or per 100ml column.

Look at total carbohydrate rather than leaning on “of which sugars”. Check the fibre. Then weigh up saturated fat, salt and the ingredients list.

Finally, be honest with yourself about the portion you'll actually eat.

That will tell you far more than any claim printed on the front of the box.

And remember — supermarket shopping doesn't need to turn into a hunt for the “perfect” food.

Small, realistic changes across your regular shop go a lot further than worrying over one red traffic light.