Mass gainers are the most expensive way to consume calories per kilo on the UK supplement shelf in 2026. They're also the most convenient. This guide ranks the best UK mass gainers by calorie density, protein per 100g, and cost per serving, so you can decide whether you actually need one and which one earns its place.
What is the best mass gainer in the UK in 2026?
Optimum Nutrition Serious Mass is the best overall UK mass gainer in 2026. 1,250 calories and 50g protein per serving with the widest UK retail availability of any mass gainer on this list. Applied Nutrition Critical Mass Professional is the highest-protein option at 42g protein per 100g and Informed Sport certified. Warrior Mass Gainer is the price leader at the lowest cost per 100g.
What a mass gainer actually is
A mass gainer is a high-calorie protein blend. The base is usually whey protein concentrate or a whey-casein-egg blend. The bulk of the calories comes from carbohydrates - maltodextrin in cheaper products, rolled oats or oat flour in better ones - and a smaller fraction from fats (medium-chain triglycerides or flaxseed). Some mass gainers add creatine, vitamins, or digestive enzymes; most of these extras are cheaper bought separately.
The honest job of a mass gainer is to make it easier to hit a calorie surplus when food alone isn't getting you there. Two scoops in a blender with milk delivers 600-1,250 kcal in 90 seconds. That convenience is what you're paying for, not the ingredients themselves.
The 5 best UK mass gainers in 2026
1. Optimum Nutrition Serious Mass - Best overall
The benchmark mass gainer on UK shelves. 1,250 calories and 50g protein per 334g serving, the highest serving-size and one of the most balanced protein-to-carb ratios in the category. Available in 2.7kg and 5.4kg bags from every major UK retailer including supermarkets. Trustpilot taste scores sit around 4.3/5 across UK reviewers.
Best Overall
Optimum Nutrition Serious Mass 5.4kg
5.4kg bag
One of the most affordable protein powder options in the UK. Strong cost efficiency.
See cheapest price →Best Overall
Optimum Nutrition Serious Mass 5.4kg
5.4kg bag
One of the most affordable protein powder options in the UK. Strong cost efficiency.
See cheapest price →Quick verdict
Pros
- + 50g protein per serving
- + Added vitamins and minerals blend
- + Trusted established brand
- + Creatine included in formula
Cons
- – Enormous 334g serving size
- – High sugar and maltodextrin
- – Pricier than budget gainers
Quick verdict
Pros
- + 50g protein per serving
- + Added vitamins and minerals blend
- + Trusted established brand
- + Creatine included in formula
Cons
- – Enormous 334g serving size
- – High sugar and maltodextrin
- – Pricier than budget gainers
2. Applied Nutrition Critical Mass Professional - Best for protein
The highest protein density mass gainer on this list - 42g protein per 100g, well above the 15-25g/100g that's typical in the cheap end of the category. 6kg bag, Informed Sport certified, and the lean-mass formula keeps carb-to-protein ratio tighter than Serious Mass for people who want calories without the maltodextrin spike.
Highest Protein
Applied Nutrition Critical Mass Professional 6kg Powder
6kg bag
Applied Nutrition Critical Mass Professional is the highest-protein UK mass gainer at 42g per serving. Organic oats keep sugar to 2.9g per 150g shake. Loaded ingredient deck: HMB, dual creatine, probiotics, AstraGin.
See cheapest price →Highest Protein
Applied Nutrition Critical Mass Professional 6kg Powder
6kg bag
Applied Nutrition Critical Mass Professional is the highest-protein UK mass gainer at 42g per serving. Organic oats keep sugar to 2.9g per 150g shake. Loaded ingredient deck: HMB, dual creatine, probiotics, AstraGin.
See cheapest price →Quick verdict
Pros
- + 42g protein per serving - among the highest in the UK mass-gainer category
- + Only 2.9g sugar per 150g serving thanks to organic oats over maltodextrin
- + Loaded with HMB, dual creatine matrix, AstraGin and LactoSpore probiotics
- + Lean Mass Professional formula targets muscle gain over fat gain
Cons
- – £59.99 for 6kg sits above the budget tier
- – 150g serving size is large to consume in one shake
- – Complex ingredient deck overwhelms beginners shopping for a simple gainer
Quick verdict
Pros
- + 42g protein per serving - among the highest in the UK mass-gainer category
- + Only 2.9g sugar per 150g serving thanks to organic oats over maltodextrin
- + Loaded with HMB, dual creatine matrix, AstraGin and LactoSpore probiotics
- + Lean Mass Professional formula targets muscle gain over fat gain
Cons
- – £59.99 for 6kg sits above the budget tier
- – 150g serving size is large to consume in one shake
- – Complex ingredient deck overwhelms beginners shopping for a simple gainer
3. Warrior Mass Gainer - Best on price
The cheapest credible mass gainer on UK shelves at around £0.52 per 100g for the 5kg bag. Protein density is lower than the Applied or ON picks (closer to 20g per 100g) but the calorie density is solid and the ingredient list is honest. If budget is the constraint and you just need calories in, this is where to start.
Best Value
Warrior Mass Gainer Protein Powder - 5kg
5kg bag
Warrior Mass Gainer delivers up to 61g protein and 1,000+ calories per serving from a whey-casein-milk blend with glutamine. 4.4 stars across 1,752 Team Warrior reviews. Salted Caramel is the standout flavour.
See cheapest price →Buy direct from Warrior →Best Value
Warrior Mass Gainer Protein Powder - 5kg
5kg bag
Warrior Mass Gainer delivers up to 61g protein and 1,000+ calories per serving from a whey-casein-milk blend with glutamine. 4.4 stars across 1,752 Team Warrior reviews. Salted Caramel is the standout flavour.
See cheapest price →Buy direct from Warrior →Quick verdict
Pros
- + 4.4 stars across 1,752 Team Warrior customer reviews
- + Up to 61g protein per serving from whey + casein + milk blend
- + Peptide-bonded glutamine included in formula
- + Salted Caramel and Double Chocolate flavours consistently praised
Cons
- – 1,000+ kcal per serving is intense for non-hard-gainers
- – Contains sucralose and maltodextrin alongside oats
- – Some flavour variants score notably lower than salted caramel
Quick verdict
Pros
- + 4.4 stars across 1,752 Team Warrior customer reviews
- + Up to 61g protein per serving from whey + casein + milk blend
- + Peptide-bonded glutamine included in formula
- + Salted Caramel and Double Chocolate flavours consistently praised
Cons
- – 1,000+ kcal per serving is intense for non-hard-gainers
- – Contains sucralose and maltodextrin alongside oats
- – Some flavour variants score notably lower than salted caramel
4. Mutant Mass - Best for volume eaters
Mutant Mass uses some of the largest serving sizes in the UK market - 322g per scoop delivering well over 1,000 calories. Suited to genuine hard-gainers who struggle to eat enough whole food. The trade-off is taste fatigue: a 6.8kg bag at 322g servings runs out in ~21 days, which is a lot of the same shake.
Hard Gainer
Mutant Mass 6.8kg Powder
6.8kg bag
Mutant Mass 6.8kg delivers 1,100 kcal and 56g protein per serving from a five-source Pro-Matrix protein blend. Cookies and Cream flavour praised on UK Amazon. Built for hard gainers who need the volume.
See cheapest price →Hard Gainer
Mutant Mass 6.8kg Powder
6.8kg bag
Mutant Mass 6.8kg delivers 1,100 kcal and 56g protein per serving from a five-source Pro-Matrix protein blend. Cookies and Cream flavour praised on UK Amazon. Built for hard gainers who need the volume.
See cheapest price →Quick verdict
Pros
- + 1,100 kcal and 56g protein per serving for genuine hard-gainers
- + Pro-Matrix blend: whey concentrate + hydrolysed + isolate + micellar casein + milk protein
- + Cookies and Cream rated 'delicious' by UK Amazon reviewers
- + 6.8kg bag lasts ~3 weeks of daily double-serves
Cons
- – 192g carbs per serving is heavy on digestion
- – Taste fatigue real over a 3-week solo bag
- – Around £68 RRP for 6.8kg is a serious upfront spend
Quick verdict
Pros
- + 1,100 kcal and 56g protein per serving for genuine hard-gainers
- + Pro-Matrix blend: whey concentrate + hydrolysed + isolate + micellar casein + milk protein
- + Cookies and Cream rated 'delicious' by UK Amazon reviewers
- + 6.8kg bag lasts ~3 weeks of daily double-serves
Cons
- – 192g carbs per serving is heavy on digestion
- – Taste fatigue real over a 3-week solo bag
- – Around £68 RRP for 6.8kg is a serious upfront spend
5. MyProtein Hard Gainer Extreme - Best on Impact Week sales
MyProtein's mainline mass gainer rarely competes on RRP but becomes the cheapest UK mass gainer on Impact Week sales (typically -50 to -60% off). Best approach: wait for the sale, buy in bulk, store dry. Off-sale it's mid-pack on value.
MyProtein Hard Gainer Extreme
2.5kg bag
MyProtein Hard Gainer Extreme. 34.9g protein per 100g and sensible 250-500 kcal serving size. Mint Choc Chip mixes well even in water. Wait for Impact Week sales for genuine value.
See cheapest price →MyProtein Hard Gainer Extreme
2.5kg bag
MyProtein Hard Gainer Extreme. 34.9g protein per 100g and sensible 250-500 kcal serving size. Mint Choc Chip mixes well even in water. Wait for Impact Week sales for genuine value.
See cheapest price →Quick verdict
Pros
- + 34.9g protein per 100g - balanced ratio vs maltodextrin-heavy rivals
- + Mint Choc Chip mixes well even in water alone
- + Affordable during Impact Week sales (-50 to -60% off RRP)
- + Sensible 250-500 kcal serving range vs 1,000+ kcal monsters
Cons
- – Sweetness can be 'sickly' in Vanilla and Cookies and Cream variants
- – Full RRP poor value vs Warrior Mass on cost per 100g
- – Mixed flavour reviews - taste varies more than competitors
Quick verdict
Pros
- + 34.9g protein per 100g - balanced ratio vs maltodextrin-heavy rivals
- + Mint Choc Chip mixes well even in water alone
- + Affordable during Impact Week sales (-50 to -60% off RRP)
- + Sensible 250-500 kcal serving range vs 1,000+ kcal monsters
Cons
- – Sweetness can be 'sickly' in Vanilla and Cookies and Cream variants
- – Full RRP poor value vs Warrior Mass on cost per 100g
- – Mixed flavour reviews - taste varies more than competitors
Calorie density vs protein density: which wins?
The two metrics often pull in opposite directions. A 1,250-calorie mass gainer like Serious Mass leans heavier on carbs (maltodextrin + oats) and lighter on protein-per-100g. A lean mass gainer like Applied Nutrition Critical Mass Professional pushes protein density up and total calorie density down.
The right pick depends on your bottleneck. If you struggle to eat enough food but already hit 1.6-2g protein per kg, prioritise calorie density. If your diet is already calorie-dense but protein-poor, prioritise protein density. For most lifters in a normal bulk, the difference is smaller than the price gap suggests.
Best mass gainer by budget tier
- Under £25 / 2-3kg bag: Warrior Mass Gainer or Mutant Mass 2.27kg. Lowest cost per 100g but lower serving counts.
- £25-£40 / 5-6kg bag: Optimum Nutrition Serious Mass 5.4kg. Sweet spot for value plus brand reliability.
- £40-£60 / 5-6kg bag: Applied Nutrition Critical Mass Professional. Highest protein density, Informed Sport certified.
- £60+ / 6.8kg bag: Mutant Mass 6.8kg. Largest serving sizes, lowest cost per 1,000 kcal in the volume tier.
When to skip mass gainer and DIY
A DIY mass gainer made from cheap whey concentrate, instant oats, and peanut butter consistently beats commercial mass gainers on cost per calorie. Rough numbers:
- Commercial mass gainer: £2-£4 per serving for 600-1,250 kcal.
- DIY: 30g whey + 100g oats + 1 tbsp peanut butter: ~£1-£1.50 per serving for ~700 kcal.
The DIY route saves around 40-60% per shake. The trade-off is time and texture - blending oats takes longer than mixing maltodextrin and the result is gritter. If you have a blender and 90 seconds, DIY usually wins. If you need to mix with water in a shaker bottle at the gym, commercial wins.
To go DIY, start with the cheapest whey concentrate in the UK, add 80-100g oats and a tablespoon of peanut butter for a 500-700 kcal shake.
For a fuller breakdown see affordable mass gainer UK and cheapest mass gainer UK by ingredients.
Ingredients that actually matter on the label
- Protein per 100g: Anything below 15g/100g is mostly carbs with a sprinkle of protein. 20-30g/100g is mid-pack. 35-42g/100g is the lean mass gainer tier.
- Carbohydrate source: Oat flour and waxy maize are slower-digesting and steadier. Pure maltodextrin spikes blood sugar harder. Cheaper bags lean maltodextrin.
- Fat content: 5-10g per serving is normal. Anything above 15g per serving is either MCT-loaded (fine but expensive) or padded with cheap oils.
- Added creatine: Nice-to-have at 3-5g per serving. Don't pay a price premium for a mass gainer just because it includes creatine - it's £4 for a year's supply bought separately.
- Sugar per serving: Most mass gainers carry 20-60g sugar per serving. That's the calorie point, not a defect. If you want a clean bulk, lean mass gainer formulas keep this in the 5-15g range.
Cost per serving and per 1000 kcal
The fair value comparison for mass gainers is cost per 1,000 kcal, since brands manipulate serving sizes to hit eye-catching numbers on the front of the bag. As of May 2026:
- Warrior Mass Gainer 5kg: ~£0.52 per 100g, ~£1.20 per 1,000 kcal. Cheapest credible.
- Optimum Nutrition Serious Mass 5.4kg: ~£0.65 per 100g, ~£1.65 per 1,000 kcal. Best overall value.
- Applied Nutrition Critical Mass Professional 6kg: ~£0.85 per 100g, ~£2.10 per 1,000 kcal. Premium for the protein density.
Prices rotate weekly. The UK mass gainer comparison table ranks every product by cost per 100g, refreshed weekly across 85+ retailers.
Frequently asked questions
How much mass gainer should I take per day?
One serving on training days, half a serving on rest days, with both timed between meals or post-workout. Use a TDEE calculator to find your maintenance calories, add 250-500 kcal for a lean bulk or 500-1,000 kcal for a fast bulk, and fill the gap with mass gainer only if whole food doesn't get you there.
Are mass gainers bad for fat gain?
Calories cause fat gain, not the source of those calories. A 1,250-calorie mass gainer plus your maintenance diet will absolutely add fat alongside muscle if the total surplus exceeds your training's ability to drive growth. The mass gainer isn't the problem; the unmonitored surplus is.
Can women use mass gainers?
Yes. The branding leans heavily male but the formulas are sex-neutral - they're just high-calorie protein blends. A female lifter trying to add weight uses the same product with smaller serving sizes proportional to bodyweight.
Does Serious Mass cause bloating?
Common reports of Serious Mass bloating trace back to two things: lactose (it's a whey-based product so lactose-intolerant lifters will react) and the 334g serving size hitting digestion harder than smaller protein shakes. Splitting into two 167g servings 4 hours apart usually resolves it.
