Best Whey Protein Isolate UK 2026: What It Is and What It Costs per 25g of Protein
What whey protein isolate is, how it differs from concentrate on protein, fat and lactose, and what five UK isolates cost per 25g of protein at matching bag sizes, checked at each brand's own site on 23 September 2026.
Kevin, founder of WheyWise
Quick answer
If you want whey isolate for the least money, buy Peak Supps Whey Protein Isolate 90% in Unflavoured. It has 87.2g of protein per 100g and cost £1.11 per 25g of protein in the 5kg bag (£192.99) on peaksupps.co.uk, checked 23 September 2026, which beat every other isolate we priced at the brand's own site. Only pay for isolate if lactose or tight macros are a problem for you: on the same brand and flavour, isolate costs about 30% more per 25g of protein than ordinary whey.
Whey protein isolate is whey that has been filtered until the protein makes up at least 90% of the dry powder, with most of the fat and lactose removed. It costs more than ordinary whey concentrate. This guide explains what isolate is, compares it with concentrate in one table, and prices five UK whey isolates per 25g of protein at matching bag sizes. Every price was checked on the brand's own website on 23 September 2026, as a one-off price with no discount code.
What is whey protein isolate?
Whey protein isolate is whey that contains at least 90% protein on a dry basis, according to the American Dairy Products Institute (ADPI) product definition. It is made by filtering liquid whey, the by-product of cheese making, through membranes or by ion exchange until most of the lactose and fat is removed. The ADPI lists typical values for whey protein isolate of 0.5% to 1.0% lactose and 0.5% to 1.0% fat.
The number on a tub is lower than 90% because the 90% is measured on dry matter before anything is added. Isolate powder still holds around 4% to 5% moisture, and flavoured products add cocoa, flavouring, sweetener and lecithin. That is why most flavoured UK isolates show between 80g and 88g of protein per 100g on the label. If a product called isolate shows much less than 80g per 100g, check what else is in it.
How much does whey isolate cost per 25g of protein in the UK?
The cheapest whey isolate we could verify was Peak Supps Whey Protein Isolate 90% Unflavoured, at £1.11 per 25g of protein in the 5kg bag (£192.99) on peaksupps.co.uk, checked 23 September 2026. In a bag of about 1kg it was also the cheapest, at £1.29 per 25g. The table below compares five isolates at two bag sizes, using each brand's own price and its own label.
| Whey isolate | Protein per 100g | About 1kg bag | Largest bag |
|---|---|---|---|
| Peak Supps Whey Protein Isolate 90% (Unflavoured) | 87.2g | 1kg £44.99: £1.29 | 5kg £192.99: £1.11 |
| Bulk Pure Whey Isolate | 81g on the bulk.com panel, 80g minimum across flavours | 900g £43.99: £1.51 | 5kg £199.99: £1.25 |
| Applied Nutrition ISO-XP | About 88g, worked out from 22g per 25g serving | 850g £51.95: £1.74 | 1.8kg £85.95: £1.36 |
| Myprotein Impact Whey Isolate (Vanilla) | 82g | 900g £48.99: £1.66 | 4.5kg £217.49: £1.47 |
| Optimum Nutrition Gold Standard 100% Isolate (Chocolate) | 83g | 930g £58.00: £1.88 | No larger bag on the UK site |
Cost per 25g of protein in bold. One-off prices with no code, checked 23 September 2026 on peaksupps.co.uk, bulk.com, appliednutrition.uk, myprotein.com and optimumnutrition.com/en-gb. Bulk prices were Bulk Week sale prices. Myprotein shows its prices as reductions from a higher RRP. Bulk's 5kg bag comes in flavours only, so it is worked out at the 80g minimum Bulk states for its flavoured range.
Bulk Pure Whey Isolate came second on price: £1.25 per 25g of protein in the 5kg bag at £199.99, a Bulk Week sale price down from £209.99, and £1.27 per 25g in the 4kg Unflavoured bag at £164.99, down from £167.99, both checked 23 September 2026 on bulk.com. Applied Nutrition ISO-XP cost £1.36 per 25g of protein in the 1.8kg tub at £85.95, using about 88g of protein per 100g, which we worked out from the 22g of protein in each 25g serving because Applied Nutrition does not print a per-100g figure in text. Myprotein Impact Whey Isolate Vanilla cost £1.47 per 25g in the 4.5kg bag at £217.49. Optimum Nutrition Gold Standard 100% Isolate was the most expensive we checked, at £1.88 per 25g of protein in the 930g tub at £58.00.
Bag size changes the answer more than brand does. Myprotein Impact Whey Isolate Vanilla costs £1.66 per 25g in the 900g bag and £1.47 in the 4.5kg bag, an 11% saving for buying bigger. Prices change weekly, so check the cheapest whey isolate prices across UK retailers before you order.
Which whey isolate should you buy?
For most people, Peak Supps Whey Protein Isolate 90% is the one to buy, because it had the lowest cost per 25g of protein of the five isolates we checked on 23 September 2026, with 87.2g of protein per 100g on its Unflavoured label. The others each earn a place for a specific reason, listed below.
Cheapest verified isolate
Peak Supps Whey Protein Isolate 90%
500g bag
The best-value whey isolate we could verify at a brand's own site: 87.2g of protein per 100g and £1.11 per 25g of protein in the 5kg bag.
Buy Whey Protein Isolate 90% →See the price on AmazonCheapest verified isolate
Pros
- + £1.11 per 25g of protein in the 5kg Unflavoured bag, checked 23 September 2026
- + 87.2g of protein per 100g on the Unflavoured label
- + Under 0.5g of lactose per 30g serving, according to its label
- + Stevia-sweetened flavours alongside the standard range
Cons
- – Flavoured versions carry less protein: 80g per 100g in Chocolate
- – The best price needs the 5kg bag
●Nutrition per scoop · 26.2g protein in 30g▼
Protein makes up 87%
of this 30g scoop · 110 kcal total
Runner-up on price
Bulk Pure Whey Isolate
2kg bag
A plain, well-priced isolate from a big UK brand: £1.27 per 25g of protein in the 4kg Unflavoured bag, checked 23 September 2026.
or compare all UK prices →Runner-up on price
Bulk Pure Whey Isolate
2kg bagPros
- + £1.25 per 25g of protein in the 5kg bag at a Bulk Week sale price, 23 September 2026
- + 81g of protein and 1.0g of fat per 100g on the bulk.com nutrition panel
- + Unflavoured sold in 450g, 900g, 2kg and 4kg bags
Cons
- – The 5kg and 2.5kg bags come in flavours only
- – The sale saving was small, £1 to £10 depending on bag size
●Nutrition per scoop · 24.3g protein in 30g▼
Protein makes up 81%
of this 30g scoop · 101 kcal total
Informed Sport tested
Applied Nutrition ISO XP
850g bag
The pick for tested athletes who want an Informed Sport isolate at a mid-range price of £1.36 per 25g of protein in the 1.8kg tub.
Buy ISO XP →See the price on AmazonInformed Sport tested
Applied Nutrition ISO XP
850g bagPros
- + Listed as Informed Sport tested on appliednutrition.uk
- + Whey protein isolate makes up 97% of the Vanilla powder
- + £1.36 per 25g of protein in the 1.8kg tub, checked 23 September 2026
Cons
- – 22g of protein per serving, less than the 25g many isolates give
- – £1.74 per 25g of protein in the 850g tub
●Nutrition per scoop · 22g protein in 25g▼
Protein makes up 88%
of this 25g scoop · 89 kcal total
Most flavours
MyProtein Impact Whey Isolate Powder
900g bag
The widest flavour choice in UK whey isolate, at £1.47 per 25g of protein in the 4.5kg Vanilla bag on myprotein.com.
or compare all UK prices →Most flavours
Pros
- + 82g of protein per 100g and 25g per 30g scoop in Vanilla
- + 0.9g of fat and 1.9g of sugars per 100g in Vanilla
- + A wide flavour range on myprotein.com, including Salted Caramel and Chocolate Peanut Butter
Cons
- – £1.47 per 25g of protein even in the 4.5kg bag, checked 23 September 2026
- – Bag sizes and protein content vary by flavour, so compare carefully
●Nutrition per scoop · 24.6g protein in 30g▼
Protein makes up 82%
of this 30g scoop · 108 kcal total
Premium isolate
Optimum Nutrition Gold Standard 100% Isolate Protein
930g bag
A premium isolate you pay extra for: £1.88 per 25g of protein in the 930g tub on optimumnutrition.com, 70% more than Peak Supps in its 5kg bag.
Buy Gold Standard 100% Isolate Protein →See the price on AmazonPremium isolate
Pros
- + 83g of protein per 100g and 25g per 30g scoop in Chocolate
- + Made from whey protein isolate and hydrolysed whey protein isolate
- + A long-established brand, widely stocked in the UK
Cons
- – £1.88 per 25g of protein in the 930g tub, the dearest we checked on 23 September 2026
- – Only 450g and 930g tubs on the UK site
●Nutrition per scoop · 24.9g protein in 30g▼
Protein makes up 83%
of this 30g scoop · 109 kcal total
How is whey isolate different from whey concentrate?
Whey isolate has more protein, less fat and less lactose than whey concentrate, because it is filtered further. The clearest way to see it is one brand and one flavour side by side. Myprotein Impact Whey Isolate Vanilla has 82g of protein, 0.9g of fat and 1.9g of sugars per 100g. Myprotein Impact Whey Vanilla, a concentrate, has 72g of protein, 5.9g of fat and 5.1g of sugars per 100g. Both labels were checked on myprotein.com on 23 September 2026.
| Per 100g of powder | Impact Whey Isolate (Vanilla) | Impact Whey (Vanilla) |
|---|---|---|
| Protein | 82g | 72g |
| Fat | 0.9g | 5.9g |
| Carbohydrate | 6.1g | 8.9g |
| Sugars | 1.9g | 5.1g |
| Energy | 361 kcal | 379 kcal |
| Typical lactose of the whey ingredient (ADPI) | 0.5% to 1.0% | 4.0% to 10.0% (80% concentrate) |
| Cost per 25g of protein, 2.7kg bag | £1.53 (£135.49) | £1.18 (£91.49) |
Labels and one-off prices from myprotein.com, checked 23 September 2026. Lactose ranges are for the raw whey ingredients, from the American Dairy Products Institute standards for whey protein isolate and 80% whey protein concentrate.
On the same Myprotein pair, isolate costs about 30% more per 25g of protein: £1.53 against £1.18 in the 2.7kg Vanilla bags, checked 23 September 2026. Bulk shows a similar gap. Bulk Pure Whey Isolate costs £1.25 per 25g in the 5kg bag, against 99p for Bulk Pure Whey Protein in the 5kg bag at £139.99 (a Bulk Week sale price with 71g of protein per 100g), so the isolate costs 27% more. For the full side-by-side, read whey isolate vs concentrate and the Myprotein Impact Whey vs Impact Whey Isolate review.
Is whey isolate worth paying more for?
Whey isolate is worth the extra money if lactose gives you trouble, or if you are on a strict diet and want the fewest calories per gram of protein. It is not worth it just to build muscle. Both isolate and concentrate are complete dairy proteins, and how much protein you eat across the day matters far more than which form it comes in.
Pay for isolate if concentrate bloats you. The whey protein isolate ingredient typically holds 0.5% to 1.0% lactose, against 4.0% to 10.0% in an 80% whey concentrate, according to the American Dairy Products Institute. For people with mild lactose intolerance that difference is often enough. Our protein powder for sensitive stomachs guide covers other options.
Pay for isolate if you track every calorie. The Myprotein pair above shows a gap of about 22 kcal and 1.8g of fat per 25g of protein. Over two shakes a day that is about 44 kcal. It is real but small, and a cheaper concentrate that fits your budget is often the better trade. The best protein powder for weight loss guide goes further.
Skip isolate if you just want cheap protein. Protein Works Whey Protein 360 Black costs 65p per 25g of protein in the 4.8kg bag at £73.49 on theproteinworks.com, checked 23 September 2026. It has 59g of protein per 100g, so the scoops are bigger, but it is still the lower cost per gram of protein: the cheapest isolate we found, Peak Supps at £1.11, costs about 70% more per 25g. If lactose is not a problem for you, compare the whey concentrate prices first.
If you do not need isolate
Protein Works Whey Protein 360 Black
1.2kg bag
The cheaper route for anyone who tolerates normal whey: Protein Works Whey Protein 360 Black at 65p per 25g of protein, against £1.11 for the cheapest isolate.
or compare all UK prices →If you do not need isolate
Protein Works Whey Protein 360 Black
1.2kg bagPros
- + 65p per 25g of protein in the 4.8kg bag, checked 23 September 2026
- + About 40% less per 25g of protein than the cheapest isolate we priced
- + WW12 takes 12% off at Protein Works
Cons
- – Not an isolate: 59g of protein per 100g
- – Not the one to choose if lactose upsets you
●Nutrition per scoop · 17.7g protein in 30g▼
Protein makes up 59%
of this 30g scoop · 109 kcal total
Is whey isolate OK if you are lactose intolerant?
Whey isolate is low in lactose but not lactose free, so it suits mild lactose intolerance better than a milk allergy. Peak Supps Whey Protein Isolate 90% Unflavoured lists under 1.5g of lactose per 100g and under 0.5g per 30g serving, checked on peaksupps.co.uk on 23 September 2026. A milk allergy is a reaction to milk proteins, and whey isolate is a milk protein, so anyone with a milk allergy should avoid it entirely. For a dairy-free option, see the dairy-free protein powder guide.
How do you check a whey isolate label?
Look at two things: protein per 100g, and the first ingredient. A whey isolate should show at least about 80g of protein per 100g, and whey protein isolate should be the first, and ideally the only, protein listed. Applied Nutrition ISO-XP Vanilla lists whey protein isolate at 97% of the powder. Optimum Nutrition Gold Standard 100% Isolate lists a 94% whey protein isolate blend of whey protein isolate and hydrolysed whey protein isolate. Both labels were checked on 23 September 2026.
Be careful with products that say "isolate" on the front but list whey concentrate or soy first. They may still be good value, but you are not getting the lower lactose and fat you are paying for. Clear whey is also usually made from isolate, but it is a different drink. The clear whey protein guide covers it, and the types of whey protein explainer covers hydrolysate. To line up any two isolates on cost per 25g of protein, use the protein comparison tool, or read the Myprotein vs Bulk whey isolate review.
Frequently asked questions
Is whey protein isolate better than whey concentrate?
It is purer, not better for muscle. Whey protein isolate has had more fat and lactose filtered out, so Myprotein Impact Whey Isolate Vanilla carries 82g of protein per 100g against 72g for Myprotein Impact Whey Vanilla, checked 23 September 2026. Both are complete dairy proteins. Isolate is the better choice if lactose upsets you or you are counting every calorie, and concentrate is the better value otherwise.
How much protein is in whey isolate?
The whey protein isolate ingredient is at least 90% protein on a dry basis, under the American Dairy Products Institute definition. A finished, flavoured powder usually shows 80g to 88g per 100g on the label because of moisture, flavouring and sweetener. Peak Supps Whey Protein Isolate 90% Unflavoured lists 87.2g per 100g, checked 23 September 2026.
Is whey isolate lactose free?
No, but it is low. The American Dairy Products Institute gives typical lactose of 0.5% to 1.0% for whey protein isolate, against 4.0% to 10.0% for an 80% whey concentrate. Peak Supps Whey Protein Isolate 90% lists under 0.5g of lactose per 30g serving. People with mild lactose intolerance often manage isolate, but anyone with a milk allergy should avoid all whey.
Which whey isolate is the best value in the UK?
Peak Supps Whey Protein Isolate 90% Unflavoured, at £1.11 per 25g of protein in the 5kg bag on peaksupps.co.uk, checked 23 September 2026. Bulk Pure Whey Isolate was next at £1.25 per 25g in the 5kg bag, at a Bulk Week sale price. Prices move weekly, so check the live whey isolate comparison before you buy.
Is whey isolate good for weight loss?
It helps a little at the margins. 25g of protein from Myprotein Impact Whey Isolate Vanilla comes with about 110 kcal and 0.3g of fat, against about 132 kcal and 2.0g of fat from Myprotein Impact Whey Vanilla, worked out from the labels on 23 September 2026. That is about 22 kcal a shake. Your total daily calories matter far more than which whey you choose.
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