The short answer (prices checked 30 October 2026)
- Cheapest protein: Warrior RAW Oat Flapjack, £9.71 for 12 · 75g, which is 4.05p per gram of protein.
- Cheapest per bar: Nature Valley Protein Peanut & Chocolate, £16.58 for 26 · 40g, which is 63.8p a bar but 6.38p per gram of protein.
- The chart pick: Grenade Chocolate Chip Salted Caramel, £20.47 for 12 · 60g, sitting at number 7 in Amazon UK's Health & Personal Care chart on 30 October 2026, at 8.53p per gram of protein.
- The spread across our six picks is 4.05p to 10.41p per gram of protein, a difference of 2.57 times. None of the 20 listings we read states a figure like it.
- Audit finding: "high protein" is a legal claim about the share of a food's energy, not the grams on the front. Of the first 20 unsponsored listings, 16 make the claim and only 4 publish the nutrition panel you would need to check it.
Protein bars are having a moment in the Amazon UK charts. On 30 October 2026 the Health & Personal Care best sellers had a Grenade bar at number 7, a kilo of whey powder at number 12 and a meal replacement shake at number 16. Three formats, three brands, all selling the same promise in the same month.
The promise is printed as a number of grams. Twenty grams, eighteen grams, fifteen grams. That number is what the packs compete on and it is what the listings put in the title. It is also not the number the law uses, and the gap between the two turns out to explain a lot about which bars are worth buying.
Prices in this table come from Amazon and are refreshed at least once a day, with the date of the last update under the table. The cost-per-use and running-cost figures on this page use prices Look Into read on 30 October 2026, so they can differ from today's price.
As an Amazon Associate, Look Into earns from qualifying purchases. Product prices and availability are accurate as of 30 October 2026 11:13 am and are subject to change.
Prices and specs last checked by Look Into on 30 October 2026 · next check 25 December 2026 · how we picked
What "high protein" actually means in law
The conditions for protein claims sit in the Annex to Regulation (EC) No 1924/2006, which we read on legislation.gov.uk on 30 October 2026. There are two of them, and neither mentions grams per bar.
- A source of protein claim "may only be made where at least 12 % of the energy value of the food is provided by protein".
- A high in protein claim "may only be made where at least 20 % of the energy value of the food is provided by protein".
So the test is a proportion, not a quantity. A bar can carry a big gram number and still fall short, because fat and sugar push up the energy figure that sits underneath the fraction. Working it out needs two numbers from the pack: the protein in grams and the energy in kcal. Protein counts as 4 kcal per gram, which is set out in Annex XIV to Regulation (EU) No 1169/2011, also read on legislation.gov.uk on 30 October 2026. Multiply the protein by four, divide by the kcal, and you have the share.
Of the first 20 unsponsored results for "protein bars" on amazon.co.uk, only four publish a structured per 100g nutrition panel. Those four are the only ones where a shopper can do that sum at all. Here is what they come to.
| Listing | Per 100g | Protein share of energy | Clears 20%? |
|---|---|---|---|
| Fulfil Vitamin and Protein Bar | 357 kcal, 37g protein | 41.5% | Yes |
| Warrior RAW Oat Flapjack | 340 kcal, 28.52g protein | 33.6% | Yes |
| Nature Valley Protein Peanut & Chocolate | 492 kcal, 25.5g protein | 20.7% | Yes, by 0.7 points |
| Trek Protein Flapjack Cocoa Oat | 455 kcal, 18.4g protein | 16.2% | No |
The last row is worth sitting with. The Amazon listing title for that product reads "Trek High Protein Flapjack Cocoa Oat". Its own bullet points on the same listing claim something narrower: "9g of plant-based protein" and "SOURCE OF FIBRE". We checked the product at Waitrose on 30 October 2026, where it is sold as TREK Protein Flapjacks Cocoa Oat, the panel reads 454 kcal and 18g protein per 100g, and the nutritional claims section lists one claim only, source of fibre. On either set of figures the protein share lands near 16%, which clears the 12% bar for a source of protein claim and falls short of the 20% needed for a high protein one. The words "High Protein" are in the listing title, not on the maker's claim list.
We are not saying the bar is badly made, and a flapjack at 16% protein is still a source of protein by the legal test. The point is narrower and it applies to the whole category: the number shoppers are sold on is not the number the claim rests on, and on most listings you cannot get at the second number at all.
How we picked these
We read the first 20 unsponsored results for "protein bars" on amazon.co.uk on 30 October 2026, opened every product page, and confirmed each one by its title on the page rather than trusting the search tile. Six made the final list on a mix of cost per gram of protein, sugar per bar and a role the others do not fill. Every pick was open in a browser on the day, in stock, with a buy box price we have quoted as read.
Cost per gram of protein is our own arithmetic: the pack price in pence, divided by the number of bars multiplied by the protein grams the maker states for one bar. Where a nutrition panel exists we also give the protein share of energy. Where it does not, we say so instead of guessing.
Look Into has not handled these products: every figure comes from the maker, the listing or a named source, read on the date shown.
How the six compare
| Bar | Pack | Price on 30 Oct 2026 | Protein a bar | Per gram of protein | Per bar |
|---|---|---|---|---|---|
| Warrior RAW Oat Flapjack | 12 · 75g | £9.71 | 20g | 4.05p | 80.9p |
| SCI-MX High Protein Brownie | 12 · 65g | £12.99 | 20g | 5.41p | 108.2p |
| Nature Valley Protein Peanut & Chocolate | 26 · 40g | £16.58 | 10g | 6.38p | 63.8p |
| Snickers Protein | 12 · 57g | £16.99 | 20g | 7.08p | 141.6p |
| Grenade Chocolate Chip Salted Caramel | 12 · 60g | £20.47 | 20g | 8.53p | 170.6p |
| Barebells Official Mix Box | 12 · 55g | £24.99 | 20g | 10.41p | 208.2p |
Put the same amount of protein through each one and the gap stops being abstract. Thirty grams costs £1.21 from the Warrior flapjacks and £3.12 from the Barebells box.
The six we would buy
Warrior RAW Protein Bars, 12 · 75g
£9.71 on 30 October 2026, which works out at 4.05p per gram of protein and 80.9p a bar. Nothing else on the first page of results came close. The panel reads 340 kcal and 28.52g of protein per 100g, so protein supplies 33.6% of the energy and the high protein claim on the listing stands up to the legal test.
The catch: these are oat flapjacks, so a 75g bar carries roughly 255 kcal, the most of any pick here. If you are counting calories rather than hunting protein, the cheap protein comes attached to a bigger snack.
SCI-MX Nutrition High Protein Brownie Box, 12 · 65g
£12.99 on 30 October 2026, or 5.41p per gram of protein, second cheapest here. The listing states 20g of protein and 0.5g of sugar per brownie, the lowest sugar figure of the six, and the texture is closer to a cake than a nougat bar.
The catch: there is no nutrition panel on the listing, so the 20g sits on the maker's word and the high protein claim cannot be checked from the page. You are also buying one flavour, chocolate, twelve times over.
Nature Valley Protein Peanut & Chocolate, 26 · 40g
£16.58 on 30 October 2026 for 26 bars, so 63.8p each, the cheapest single bar of the six by a wide margin. It is also the only pick whose own panel puts it right on the legal line: 492 kcal and 25.5g of protein per 100g gives a protein share of 20.7%, which clears the 20% condition by seven tenths of a point.
The catch: 10g of protein a bar is half what the others give you, so matching one Grenade means eating two of these and 394 kcal. Sugars run at 15.5g per 100g, the highest of our picks bar none.
Snickers Protein Bar, Milk Chocolate, 12 · 57g
£16.99 on 30 October 2026, 7.08p per gram of protein. The listing states 20g of protein and 2g of sugar a bar. If the reason you abandon protein bars is that they taste like protein bars, this is the one that tastes like a chocolate bar, because it broadly is one.
The catch: no nutrition panel on the listing again, and at 7.08p a gram you pay 75% more for your protein than the Warrior flapjacks ask.
Grenade Chocolate Chip Salted Caramel, 12 · 60g
£20.47 on 30 October 2026, 8.53p per gram of protein. This is the bar sitting at number 7 in Amazon UK's Health & Personal Care chart on the morning we read it, and the listing claims over 20g of protein with 1.4g of sugar. It is also Informed Sport certified, which matters if you compete under anti-doping rules.
The catch: it is more than twice the cost per gram of protein of the cheapest pick, and like most of the category it publishes no nutrition panel on the listing, so the claim in its own first bullet point cannot be verified from the page it is printed on.
Barebells Protein Bars Official Mix Box, 12 · 55g
£24.99 on 30 October 2026. Four flavours in the box, cookies and cream, caramel cashew, salty peanut and hazelnut nougat, each stated at 20g of protein. If boredom is what stops you finishing a box, variety is a real feature and not a gimmick.
The catch: 10.41p per gram of protein makes this the dearest of the six, 2.57 times the Warrior flapjacks for the same gram of protein. No nutrition panel on the listing either.
What the 20 listings actually state
On 30 October 2026 we read the first 20 unsponsored results for "protein bars" on amazon.co.uk, which came from 12 brands, and counted what each listing states. Two scopes, because they give different answers and the difference is the finding. The first scope is the product title, the bullet points and the product description, which is the part a shopper reads. The second is the whole listing page, nutrition panel included.
| What we counted | Title, bullets and description | Whole listing page |
|---|---|---|
| Makes a high protein claim | 16 of 20 | 16 of 20 |
| States protein in grams | 13 of 20 | 13 of 20 |
| States energy in kcal | 6 of 20 | 14 of 20 |
| Publishes a structured per 100g nutrition panel | 0 of 20 | 4 of 20 |
| States any cost per gram of protein | 0 of 20 | 0 of 20 |
| Mentions the 20% of energy condition behind the claim | 0 of 20 | 0 of 20 |
Sixteen listings make the claim. Four publish the panel that would let anyone check it. That leaves twelve listings where the central selling point cannot be tested against the condition that governs it, using only the page the shopper is standing on.
Not one of the twenty states a cost per gram of protein, which is the figure that actually decides whether a box is good value. When we worked it out ourselves across the seven packs we priced, the ranking moved. The Trek flapjacks are the third cheapest pack at £14.67 and the second dearest protein at 10.19p a gram, because the pack price buys 16 bars of 9g rather than 12 bars of 20g. The cheapest box on the shelf and the cheapest protein are not the same purchase, and nothing on the listings tells you which one you are making.
What this audit does not measure
It counts what the listing text and the published panel state on one morning. It does not measure what is physically in a bar, it does not test anyone's protein content, and a listing that states nothing may still be a perfectly good product. Several listings put their nutrition table inside a product image, where it cannot be read as text, and those count as not stated here.
Questions people ask
Is a bar with 20g of protein automatically high protein?
No, and that is the whole point of the Annex wording. Twenty grams in a small, lean bar is a large share of its energy. The same twenty grams in a bar loaded with fat and sugar can drop below the 20% the condition asks for. You need the kcal figure as well as the grams before the words mean anything.
How do I work out the share myself?
Take the protein in grams per 100g, multiply by 4, divide by the kcal per 100g, then multiply by 100. The 4 is the energy conversion factor for protein in Annex XIV to Regulation (EU) No 1169/2011. A bar at 455 kcal and 18.4g of protein gives 73.6 divided by 455, which is 16.2%.
Which is better value, a big box or a small one?
Work in pence per gram of protein rather than pence per bar, because bar weights and protein loads vary by more than two to one across this category. Our cheapest pick per bar, at 63.8p, sits in the middle of the table once you measure the protein it carries.
Do protein bars count towards my daily protein?
They count the same as any other food containing protein. Whether you need the extra is a separate question and depends on what you already eat, and it is worth raising with a GP or a registered dietitian rather than a product listing.
Sources
- Annex to Regulation (EC) No 1924/2006, nutrition claims and conditions applying to them, legislation.gov.uk, read 30 October 2026, for the 12% and 20% conditions.
- Annex XIV to Regulation (EU) No 1169/2011, conversion factors for the calculation of energy, legislation.gov.uk, read 30 October 2026, for protein at 4 kcal per gram.
- TREK Protein Flapjacks Cocoa Oat product page, Waitrose, read 30 October 2026, for the product name, the per 100g panel and the nutritional claims list.
- Amazon UK Best Sellers in Health & Personal Care, read 30 October 2026, for the chart positions quoted.
Prices and nutrition figures were read from each product's own Amazon UK listing on 30 October 2026 and are quoted as read on that date. Look Into earns a commission on qualifying purchases made through the links above, at no extra cost to you, and the commission does not change what we pick or what we say about it.