Quick answer
A mass gainer is a protein powder with a large dose of carbohydrate added, built to deliver several hundred calories a shake for people who struggle to eat enough to gain weight. Myprotein Impact Weight Gainer gives 378 kcal, 29g of protein and 51g of carbohydrate in a 100g serving, for £1.28 a serving in the 5kg bag, checked 3 October 2026 on myprotein.com. WheyWise read every label here on the brand's own site: buy a gainer only if food alone will not get you into a calorie surplus, because a plain whey shake plus a bowl of oats does the same job.
A mass gainer, also sold as a weight gainer, is a powder that combines protein with a large amount of carbohydrate so that one shake supplies a meal's worth of calories. Bulk Complete Mass Gainer, for example, gives 572 kcal and 43g of protein in a 155g serving, according to its label on bulk.com, checked 3 October 2026.
What is a mass gainer?
A mass gainer is a high-calorie shake designed to help you eat more than you burn. The carbohydrate usually comes from oats or maltodextrin: Myprotein Impact Weight Gainer lists ground oats at 61% to 65% of the powder depending on flavour, with a 26% protein blend of whey protein concentrate and milk protein concentrate. Bulk Complete Mass Gainer is built on ultra fine oats, milk protein concentrate and whey protein concentrate.
How is a mass gainer different from whey protein?
A mass gainer is mostly carbohydrate, while whey is mostly protein. A serving of Myprotein Impact Weight Gainer has more than three times the calories of a scoop of Myprotein Impact Whey, but only 7g more protein.
| Per serving | Serving | Calories | Protein | Carbs |
|---|---|---|---|---|
| Bulk Complete Mass Gainer | 155g | 572 kcal | 43g | 81g |
| Myprotein Impact Weight Gainer | 100g | 378 kcal | 29g | 51g |
| Myprotein Impact Whey (Vanilla) | 30g | 114 kcal | 22g | 2.7g |
Labels read on bulk.com and myprotein.com, checked 3 October 2026. Myprotein Impact Weight Gainer costs £63.99 for 5kg, £1.28 a serving, and Bulk Complete Mass Gainer £59.99 for 5kg, about £1.86 a serving, both one-off prices on the brands' sites.
How much should a mass gainer help you gain?
Slowly. A review by Iraki et al., 2019 recommends a calorie surplus of about 10% to 20% and a gain of about 0.25% to 0.5% of bodyweight a week for novice and intermediate lifters, with 1.6g to 2.2g of protein per kg of bodyweight a day. The ISSN protein position stand (Jäger et al., 2017) puts the protein need for most exercising people at 1.4g to 2.0g per kg. For a 70kg lifter who maintains weight on 2,500 kcal, a 10% surplus is 250 kcal, which is less than one 100g serving of Impact Weight Gainer.
Oat-based gainer
MyProtein Impact Weight Gainer
2.5kg bag
A moderate, oat-based gainer: enough calories to help a hard gainer, not so many that one shake blows the surplus.
or compare all UK prices →Oat-based gainer
MyProtein Impact Weight Gainer
2.5kg bagPros
- + 378 kcal, 29g of protein and 51g of carbohydrate per 100g serving
- + Mostly ground oats rather than maltodextrin, per the ingredients list
- + £1.28 a serving in the 5kg bag at £63.99, checked 3 October 2026
Cons
- – A 100g serving is easy to overshoot a modest calorie surplus with
- – Myprotein's nutrition panel does not say which flavour it is for
●Nutrition per scoop · 52.2g protein in 180g▼
Protein makes up 29%
of this 180g scoop · 700 kcal total
Who needs a mass gainer?
A mass gainer suits people who train, are trying to gain weight and genuinely cannot eat enough food, often lighter people with small appetites. Skip it if you can add a meal or a snack, if you are trying to lose fat, or if you only need more protein, because a plain whey is cheaper per gram of protein. For ranked picks, see the best mass gainer UK guide, or compare every gainer on the mass gainer price comparison.
Frequently asked questions
How much protein is in a mass gainer?
Less per scoop of powder than whey, but more per serving because the servings are large. Myprotein Impact Weight Gainer has 29g of protein per 100g, and its serving is 100g. Bulk Complete Mass Gainer gives 43g of protein in a 155g serving. Myprotein Impact Whey, by comparison, has 72g of protein per 100g. All checked 3 October 2026.
Do mass gainers make you fat?
Only if the calorie surplus is bigger than your training can use. A review of off-season bodybuilding nutrition by Iraki et al., 2019 recommends a surplus of about 10% to 20% and a gain of about 0.25% to 0.5% of bodyweight a week for novice and intermediate lifters. A 572 kcal shake on top of a full diet can overshoot that quickly.
Is a mass gainer better than whey for bulking?
Only if you cannot eat enough food. A mass gainer adds carbohydrate calories that you could get from oats, rice or bread. Myprotein Impact Weight Gainer is mostly ground oats with a protein blend, according to its ingredients on myprotein.com, checked 3 October 2026.