The Fitness Tax: What 20 UK Protein Bars Actually Deliver

Protein bars occupy a strange place in the UK food chain. They are sold next to chocolate, priced like a treat and marketed like a piece of gym equipment. The label on the front is usually a number in a big font: 20g PROTEIN. The back is where the truth lives.

We pulled the labels on 20 bars from UK supermarkets, health shops and online sports-nutrition retailers in November 2026. This was not a lab test. It was a label audit: what the pack claims, what the bar actually gives you per serving, and what it costs per gram of protein. The results were not shocking, exactly. They were predictable in a way that should annoy anyone trying to eat for macros.

What we checked

For each bar we logged protein per bar, protein per 100 kcal, sugar, fibre, calories, cost per bar and cost per gram of protein. We also noted whether the protein came from whey, casein, soya, pea, collagen or a blend. Collagen is not a complete protein, which matters if the bar is doing heavy lifting in your day rather than just being a snack.

The sample was deliberately mixed: budget own-brand bars, the big sports-nutrition names, vegan bars, keto-style bars and the expensive ones that look like they belong in a boutique. Prices ranged from about 75p to £2.50 a bar.

The headline number is not the whole story

Two bars can both say 20g protein. One is 180 kcal, the other 280 kcal. One has 2g sugar, the other 18g. One costs 55p, the other £1.80. If you are eating for macros, the headline figure is the starting gun, not the finish line.

A bar with 20g protein and 280 kcal gives you 7.1g protein per 100 kcal. A bar with 15g protein and 180 kcal gives you 8.3g per 100 kcal. The second bar is not as headline-grabbing, but it is doing more useful work per calorie. That is the sort of maths the front of the pack would rather you did not do.

The worst offenders: confectionery in a gym vest

The clearest pattern was the fitness tax: a bar with just enough protein to sound serious, wrapped in enough sugar and palm oil to taste like a chocolate bar, sold at a price that implies it will improve your deadlift.

One bar in our 20 delivered 9g protein, 22g sugar and 235 kcal. At £1.50, that is 16.7p per gram of protein. It was, by some distance, the least useful bar in the audit. You could eat a supermarket Scotch egg for fewer calories, more protein and less money, and you would not have to pretend it was a health food.

Another bar marketed as high-protein gave 15g protein, 19g sugar and 240 kcal. It was a chocolate bar with a better publicist. A third, sold as a keto-friendly option, had 13g protein and 18g fibre. The fibre is genuinely useful if you need it, but 13g protein for 240 kcal is not a protein bar in any meaningful sense. It is a fibre supplement with a chocolate coating.

Then there was the collagen problem. Several bars used collagen as a large part of their protein blend. Collagen is fine as part of a mixed diet, but it is not a complete protein, and it should not be counted the same way as whey or soya when you are building a macro target. If the front says 20g protein and the back says collagen peptides, adjust your expectations.

The bars that actually earn their place

The useful bars were not the most exciting. They were the boring ones: whey or casein blends, 18-22g protein, 190-230 kcal, under 5g sugar, 5g or more fibre, and a cost of roughly 6-8p per gram of protein.

One of the best value bars in the sample gave 20g protein for about £1, with 3g sugar and 5g fibre. That is 5p per gram of protein. Another gave 22g protein, 1.6g sugar and 7g fibre for £1.40, which is 6.4p per gram. Neither was a taste revelation. Both were honest about what they were.

The vegan bars were a mixed bag. The best soya-based bar delivered 18g protein with 4g sugar and 6g fibre. The worst pea-protein bar was gritty, high in sugar and cost 13p per gram of protein. Vegan does not automatically mean macro-friendly, just as high-protein does not automatically mean useful.

The 10p rule

Here is the simple rule we would use in the shop. If a bar costs more than 10p per gram of protein and delivers less than 15g protein per 200 kcal, it is confectionery with a fitness tax. If it gives 18g or more protein, under 8g sugar and costs under 8p per gram, it is useful food. Anything in between is a snack. That is fine. Just do not call it a meal replacement.

A protein bar is not a moral test. It is a convenience product. The good ones are convenient, reasonably priced and honest about their macros. The bad ones are chocolate bars wearing a lanyard. Read the back of the pack, do the cost-per-gram maths, and decide which one you are actually buying.