They're the health food products now found in almost every supermarket, corner shop and pharmacy in Britain.

Protein bars, made by companies like Grenade, Trek, and Fulfil, are sold as health-boosting snacks, packed, not just with the crucial muscle-boosting nutrient, but other beneficial ingredients like fibre and vitamins.

And these snacks are proving increasingly popular in the UK. The protein bar industry is now worth more than £1.3billion and is projected to keep growing in size, with more and more new brands popping up every year.

However, a growing number of experts warn that protein bars also have a dark side.

Last year, TV fitness guru Joe Wicks released a documentary, Licensed To Kill, where he accused protein bar companies of packing their products with sugar, fat and ultra-processed ingredients – artificial compounds that studies have suggested, when consumed regularly, raise the risk of cancer, heart disease and even dementia.

And research appears to back up Wicks' claims about protein bars. 

A 2025 study, published by Queen Mary University of London, found that, of more than 450 snack bars (which includes all protein bars) sold across ten supermarkets, 37 per cent were high in sugar while over half were high in saturated fat – a particularly harmful form linked to chronic health problems.

The researchers concluded that customers are being 'misled' by snack bar companies about the healthiness of these products.

It's a view shared by London-based nutritionist Pippa Campbell, author of Eat Right, Lose Weight.

'I'm not a big fan of protein bars in general and I wouldn't consider them a health food,' says Ms Campbell. 'There's a lot of marketing around protein content but many bars are still ultra–processed and low in real nutrition. They can be useful occasionally, such as when travelling or when proper food isn't available, but they should never replace a balanced meal.'

However, experts say that not all protein bars are created equal. While most nutritionists argue that natural protein-rich snacks, like seeds, nuts, eggs and yoghurt, are better for the body, they say that some bars are more nutritious than others.

Ms Campbell has given her verdict on the best supermarket protein bars, and the ones to avoid. Read on to learn more...

The healthiest protein bars

Fulfil Chocolate Salted Caramel Vitamin & Protein Bar 

£2.90 for a 55-gram bar at tesco.com

Low in sugar and high in protein, Fulfil protein bars are one of the healthier protein bars on offer, according to experts.

The brand has a number of flavours including chocolate salted caramel, peanut butter, and chocolate brownie.

Its main selling point that helps it stand out from the crowded field is that the bars are enriched with nine vitamins.

This includes folic acid, vitamins E and C as well as four different types of vitamin B.

Each bar is 204 calories, which is slightly more than other competitors. However, this is partly due to its 20 grams of protein – which is higher than many other British bars.

It is also low in sugar, containing just 1.7 grams. Ms Campbell says she was impressed by the Fulfill bar.

'It's high in protein with added vitamins and quite low in sugar,' she says. However, she does point out that it is relatively low in fibre – containing just 3.4 grams.

She also argues that the sweetness in this low-sugar snack comes from sugar alcohols – a highly processed artificial ingredient.

Fast 800 Dark Chocolate Raspberry Protein Bar

£26.99 for 12 x 45-gram bars at thefast800.com

This raspberry-flavoured bar is high in protein and fibre.

Created by specialist meal-replacement firm Fast 800, its 14 grams of protein and 9 grams of fibre come primarily from peanut paste and chicory root fibre which, while not entirely natural, are not considered ultra-processed either.

The protein level is around the average for these snacks – 14 grams – and it does have an impressively low sugar content of 1 gram.

The 10 grams of fat are higher than other bars, but experts say this is largely natural forms of fat. The bar contains 192 calories, which is lower than other competitors.

However, Ms Campbell says it's not free of ultra-processed ingredients.

She says: 'It uses good quality protein and fibres, but it has added sweeteners and includes soya protein isolate which is a highly refined ingredient'.

The Protein Ball Co Blueberry Oat Muffin

£1.85 for a 45-gram bag at healthysupplies.co.uk

An increasing feature on Britain's snack shelves are protein balls – and health experts say this particular brand wins top marks.

The Protein Ball Co has a number of flavours, which include blueberry oat muffin, peanut butter, lemon and pistachio and salted caramel.

Experts say all its products are made primarily with natural ingredients.

It's blueberry oat muffin flavour is made with dates, almonds, freeze-dried blueberries, gluten-free oats, and flax seeds.

They are also enriched with vitamins B12, vitamin C and D.

These 178 calorie balls are comparatively low on protein – containing just 6.5 grams. Its 3.6 grams of fibre are are also on the more marginal side.

Moreover, its 17 grams of sugar, combined with 7.3 grams of fat, may, at first glance, appear concerning.

But Ms Campbell says this sugar and fat comes from natural sources – such as dates, which also contain nutrients like potassium and magnesium – making it preferable for those looking to avoid ultra-processed products.

'These may be lower in protein and higher in natural sugars, but this primarily comes from the dates,' she says.

'This is one of the least processed options out there.'

Deliciously Ella Roasted Peanut Protein Ball

£1.90 for a 40-gram ball at Waitrose.com 

Another protein ball made with natural ingredients, this product also got two thumbs up from our expert.

It's made by Deliciously Ella, a food brand started by the eponymous social media influencer.

Its three main ingredients are dates, peanuts and peanut butter.

The protein ball contains 150 calories, making it one of the least calorific products available. It also has just 5.2 grams of fat.

However, it is also lower on protein – 4.6 grams – than other similar snacks. Its fibre content is also fairly unremarkable at just 5.9 grams.

And, like the other naturally-produced protein balls, its sugar content – 16 grams – is high due to the dates.

But Ms Campbell says she would prefer to eat this product over one of the less sugary, but higher in ultra-processed ingredients, bars.

'The fibre, sugar and fats are coming from whole food ingredients,' she says. 'It lacks the artificial sweeteners and refined vegetable oils you might expect to find in other similar products.'

Pip & Nut Dark Chocolate Peanut Protein Bar

£4 for 3 x 46-gram bars at tesco.com 

This natural ingredients based bar is relatively high on protein and low on sugar.

Its two main ingredients are peanuts and dark chocolate. It also contains oats.

It contains significantly more protein – 10 grams – than the other natural bars on this list. It also has less sugar – 10 grams.

However, it does contain more calories – 217 – and fat – 12 grams. It is also low on fibre – with just 2.7 grams.

Moreover, as Ms Campbell points out, it is not ultra–processed ingredients free.

'It has natural sources of protein and fibre, from the peanuts and oats, as well as no artificial sweeteners and refined vegetable oils,' she says.

'It does use agave syrup, which is more refined than people realise.'

...And the unhealthiest protein bars

Trek Power Lotus Biscoff Bar

£2.29 for a 55-gram bar at proteinpackage.co.uk 

This protein bar is high in calories, fat and sugar. It's also filled with ultra-processed ingredients too, say experts. Perhaps it's no surprise given that it is based on the flavour of a sugary biscuit snack.

The Lotus Biscoff bar is made by Trek, one of the UK's most popular protein snack brands, who also sell protein flapjacks in flavours such as cocoa oat, salted caramel, and white chocolate and raspberry.

Its 239 calories per 55-gram bar is higher than most other comparable protein snacks. Meanwhile 8.9 grams of sugar and 12 grams of fat – the majority of which comes from artificial sources – are high too.

Ms Campbell says it contains a respectable amount of protein – 15 grams – and a solid 8.6 grams of fibre.

However, she says that Lotus Biscoff bar is packed with ultra-processed ingredients. 'It contains candied sugar syrups, flavouring and refined vegetable oils, such as rapeseed oil,' she says.

'I'd put this in the very highly processed category'.

Grenade Oreo White Protein Bar

£2.70 for a 60-gram bar at tesco.com 

It may be the most popular brand of protein bar in the country, but experts have few good things to say about Grenade's products.

The UK firm has a made for itself by selling low-sugar protein bars that mimic the flavour of much-loved sweet treats. This includes a birthday cake flavour and, its most recent addition, a Creme Egg protein bar.

Its Oreo White Protein flavour is one of its best-selling products and it's certainly low in sugar – just 0.7 grams. Its 135 calories are also below average.

However, it has little-to-no fibre – 0.9 grams.

And, while it is packed with protein – 21 grams – experts say much of this comes from artificial ingredients.

Ms Campbell says the bar's long list of ultra-processed ingredients is reason enough to avoid it. 'It's only low in sugar because it contains sucralose, which is an artificial sweetener,' she says. 'Plus there are flavourings and refined vegetable oils. So it's very ultra-processed.'