Best Mass Gainer UK 2026: Calories, Protein and Cost Per Serving Compared
Best UK mass gainer 2026: Optimum Nutrition Serious Mass at 1,250 kcal and 50g protein leads. Applied Nutrition Critical Mass Professional is highest protein. Warrior wins on price.
Kevin, founder of WheyWise
Quick answer
Optimum Nutrition Serious Mass is the mass gainer to beat in the UK, delivering around 1,250 calories and 50g of protein per serving, which is the entire point of a gainer: a calorie surplus you can drink rather than chew. Warrior Mass Gainer does much the same job at a lower price if cost is the priority. That said, a gainer only earns its place once you have genuinely tried and failed to hit your calories from food, since it is largely maltodextrin, whey and oats you could blend yourself for less.
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 Gainer
5.45kg bag
Competitively priced protein powder from Optimum Nutrition. Good balance of quality and value.
Buy Serious Mass Gainer →See the price on AmazonBest Overall
Optimum Nutrition Serious Mass Gainer
5.45kg bagPros
- + Competitive pricing
- + Widely available in the UK
Cons
- – Lower protein ratio
- – High serving size
●Nutrition per scoop · 50.3g protein in 335g▼
Protein makes up 15%
of this 335g scoop · 1263 kcal total
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 Lean Mass Gainer
6kg bag
One of the most affordable protein powder options in the UK. Strong cost efficiency.
Buy Critical Mass Professional Lean Mass Gainer →See the price on AmazonHighest Protein
Pros
- + Strong value per 100g
- + Widely available in the UK
Cons
- – High serving size
●Nutrition per scoop · 42g protein in 150g▼
Protein makes up 28%
of this 150g scoop · 557 kcal total
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 bag
One of the most affordable protein powder options in the UK. Strong cost efficiency.
Buy Mass Gainer Protein Powder →See the price on AmazonBest Value
Pros
- + Strong value per 100g
- + Widely available in the UK
Cons
- – Lower protein ratio
- – High serving size
●Nutrition per scoop · 61g protein in 280g▼
Protein makes up 22%
of this 280g scoop · 1047 kcal total
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 Weight Gainer
2.2kg bag
Competitively priced protein powder from Mutant. Good balance of quality and value.
Buy Mass Weight Gainer →See the price on AmazonHard Gainer
Mutant Mass Weight Gainer
2.2kg bagPros
- + Competitive pricing
- + Widely available in the UK
Cons
- – Lower protein ratio
- – High serving size
●Nutrition per scoop · 56g protein in 280g▼
Protein makes up 20%
of this 280g scoop · 1101 kcal total
5. MyProtein Impact Weight Gainer - 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 Impact Weight Gainer
2.5kg bag
Competitively priced protein powder from MyProtein. Good balance of quality and value.
or compare all UK prices →MyProtein Impact Weight Gainer
2.5kg bagPros
- + Competitive pricing
- + Widely available in the UK
Cons
- – High serving size
●Nutrition per scoop · 50.4g protein in 180g▼
Protein makes up 28%
of this 180g scoop · 693 kcal total
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: ~£0.93 per 100g, ~£1.20 per 1,000 kcal. Cheapest credible.
- Optimum Nutrition Serious Mass 5.4kg: ~£1.37 per 100g, ~£1.65 per 1,000 kcal. Best overall value.
- Applied Nutrition Critical Mass Professional 6kg: ~£0.97 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 every UK retailer we track.
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.
What is the best mass gainer in the UK?
Optimum Nutrition Serious Mass leads overall with 1,250 calories and 50g protein per serving from a well-trusted UK brand. Applied Nutrition Critical Mass Professional is the highest-protein option at 42g per 100g. Warrior Mass Gainer is the budget pick at the lowest price per 100g on UK shelves.
Are mass gainers worth it?
Mass gainers earn their place only when you genuinely can't eat enough whole food to gain weight. For most people, oats plus whey plus peanut butter delivers the same calories at half the cost. The mass gainer wins on convenience when meals get skipped, not on raw value.
How many calories should a mass gainer have?
300-500 kcal per serving suits a lean bulk. 700-1,250 kcal per serving suits hard-gainers or off-season volume. The number on the front of the bag is usually the largest scoop size - check the calories per 100g instead, which is the fair comparison metric.
When should you take a mass gainer?
Between meals or post-workout, never as a meal replacement during a bulk. Your goal is to add calories on top of your existing diet, not displace whole food protein and nutrients.
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