By Declan Hallwood, Nutrition & Supplements Editor · Updated 29 July 2026
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Mass gainers occupy an odd place in supplement shops: half the people buying them do not need one, and the half who do usually take too much of it. If you are the person who trains hard, eats what feels like a lot and still cannot shift the scale, a gainer is a legitimate tool. If you are just impatient, it is a fast route to gaining fat you will spend the winter losing. This guide covers five gainers worth buying on Amazon UK, sorted by what they are actually good at, and it is honest about which ones are mostly cheap starch.
How we chose
We compared the mass gainers currently in stock on Amazon UK on the numbers that matter: calories and protein per serving, protein as a share of total calories, carbohydrate source, whether creatine is included, and cost per 1,000 calories. Nutritional figures come from the manufacturers' own published labels. We have not run a controlled trial of these products ourselves. Prices were checked on 29 July 2026 and change often.
Serious Mass has been the default for well over a decade and the formula still holds up. One two-scoop serving brings 1,262 calories, 50g of protein, over 248g of carbohydrate and under 5g of fat, plus 25 vitamins and minerals and 3g of creatine monohydrate. That creatine is the quiet advantage over most rivals, because it is the one supplement with a genuinely strong evidence base for strength and lean mass (ISSN position stand on creatine).
Now the honest part. A full serving means mixing two big scoops into 710ml of liquid, and drinking that much thick shake is a chore rather than a treat. Plenty of owners quietly settle into half servings, which is arguably the smarter approach anyway. Six flavours are available and chocolate is the one most people stick with. The 5.45kg tub gives 16 full servings, or 32 sensible ones.
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Reflex packs 60g of protein into a serving that runs just over 1,000 calories, which is the best protein-to-calorie ratio on this list by a clear margin. The protein comes from glutamine peptides, whey concentrate, milk protein and hydrolysed whey rather than a soy-heavy blend, the carbs are complex rather than pure maltodextrin, and there is creatine plus 18 vitamins and minerals in there too.
What sets it apart for anyone who competes is the Informed Sport registered facility, which means batch testing against banned substances. It is also vegetarian, halal certified, free from added sugars and artificial colours, and contains no soy protein. The tub is 2kg, so the cost per kilo looks high next to the giant bags, but you are getting more protein and less filler for that money. Chocolate Perfection is the flavour; there is not much choice beyond it.
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Not everyone needs 1,200 calories in a glass. Serious Gainz delivers around 460 calories, 27g of protein and 74g of carbs per serving, which is much closer to the 300 to 500 calorie daily surplus that actually produces lean weight gain rather than a fat gain race. Two servings a day, or one alongside normal meals, is a realistic pattern you can sustain for a whole bulk.
The blend mixes soy protein, whey isolate, casein and oat flour, so you get both a fast and a slow amino acid release, and the oat flour makes the texture noticeably less sweet and cloying than a pure maltodextrin shake. It genuinely does mix better with milk than water. Flavours run to chocolate, cookies and cream, vanilla, strawberry and banana, and the 5kg bag at £42.85 is one of the cheaper ways to buy calories on Amazon UK. The 27g protein per serving is the weak spot, so treat it as a carb-led top-up rather than your protein source.
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Six kilos for £50 is the pitch, and USN backs it with up to 1,183 calories, 60g of protein and 7.5g of creatine per serving, along with 18 vitamins and minerals. That creatine dose is well above the 3g most gainers include and sits comfortably within the range described as effective, so a separate creatine tub becomes redundant while you are on this.
A serving is four scoops (300g) mixed into 900ml of cold water, which is close to a litre of shake. Read that number again before you buy, because it is more liquid than most people can drink in one sitting. USN reformulated the chocolate to use natural cocoa with less sugar and it is one of the better tasting gainers as a result. The size that makes it good value also makes it awkward: a 6kg tub is genuinely large and does not live in a kitchen cupboard easily.
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At £21.98 for 2kg this is the cheapest way onto this list, and SCI-MX has been a fixture in UK sports nutrition long enough to be a safe bet. A 125g serving gives 32g of protein from whey concentrate and soy protein isolate, mixed into 400ml of cold water, with oat flour and DigeZyme digestive enzymes rounding out the formula.
The label is straightforward about what it is: maltodextrin leads the ingredient list, so the calories are carb-dominant. There is no creatine and the vitamin content is not there either. What you get is a cheap, decent-tasting way to add a few hundred calories and 32g of protein to a day, in a tub small enough to actually finish before you get bored of the flavour. Chocolate, strawberry and vanilla are available, and SCI-MX caps the recommended intake at two servings a day.
Check price on AmazonIf you can already eat 3,000 calories a day without effort, put the money into food. A gainer costs roughly two to four times as much per calorie as rice, oats, milk and peanut butter, and it does nothing your kitchen cannot.
Skip them too if you are trying to gain muscle while staying lean. Adding 1,200 calories in a single shake blows past the modest surplus that favours muscle over fat, and the maltodextrin base means most of those calories arrive as fast carbohydrate. Half servings fix this, but at that point a normal protein powder plus a banana does the same job cheaper.
And if you are underweight for medical reasons rather than training reasons, a supplement is the wrong starting point. The NHS has specific advice for underweight adults that is worth reading first, and unexplained weight loss deserves a GP appointment rather than a tub of powder.
Split the serving. Two half servings between meals sit far better than one enormous shake, and they keep your appetite for actual dinner intact.
Do not let it replace protein. Total daily protein is what drives the muscle side of the equation, and around 1.6g per kilogram of bodyweight is where the returns flatten out (meta-analysis of protein supplementation and resistance training). A gainer contributing 27g of that is helpful, not sufficient, and the ISSN position stand on protein and exercise sets out the wider picture including timing and sources.
Train like you mean it. Calories with no progressive resistance work make you heavier, not bigger. Two full-body sessions a week is the floor, and our best protein powder for bulking guide pairs naturally with the lifting side. If you want the creatine separately rather than bundled, see our best creatine UK guide, and there is more supplement coverage in the nutrition section.
They work in the narrow sense that drinking 1,000 extra calories adds weight, because a calorie surplus is the whole mechanism. What they do not do is add muscle that ordinary food would not. If you can eat enough already, a gainer just makes the surplus more convenient and more expensive. If you genuinely cannot face another meal, it solves a real problem.
Around 1.6g per kilogram of bodyweight per day covers it for most lifters. A meta-analysis of resistance training studies found gains in muscle mass stopped improving beyond roughly that intake, so an 80kg trainee is looking at about 128g a day. Most mass gainers deliver 27g to 60g per serving, which is a chunk of that but rarely the whole job.
Close, but the carb source is usually maltodextrin rather than sugar. Maltodextrin is a fast-digesting starch that raises blood glucose quickly, which is fine around training and less ideal at 10pm on the sofa. Check the label: if the first ingredient is maltodextrin and there is under 30g of protein, you are paying protein prices for cheap carbs.
Most people should not, at least not to begin with. A full two-scoop serving is 1,262 calories in 710ml of liquid, which is a lot of shake and a lot of surplus in one go. Starting on a half serving is easier on your stomach, cheaper per tub and closer to the 300 to 500 calorie daily surplus that puts on lean weight rather than fat.
Several do. Serious Mass includes 3g of creatine monohydrate per serving and USN Hyperbolic Mass includes 7.5g, both within the range the International Society of Sports Nutrition describes as effective for raising muscle creatine stores. If your gainer has none, adding a separate 3g to 5g of creatine monohydrate daily costs pennies.
Yes, and it is usually cheaper. Blend 60g of oats, a banana, 300ml of whole milk, a scoop of whey and a tablespoon of peanut butter and you land near 700 calories with about 40g of protein. Commercial gainers win on speed and on not needing a blender, and lose on cost per calorie almost every time.
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