Mass Gainer
1250kcal Per Serving
Optimum Nutrition Serious Mass Gainer - 2.7kg / Banana
Optimum Nutrition

Serious Mass Gainer

★★★★★
4.85 | 277 reviews |  16 Servings
£32.99 £39.99 £2.06/serving
More Calories On Demand Built to push daily intake up
Protein + Carbs Together All-in-one weight-gain shake
5.4kg Pack Made for repeat use
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Banana
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Next Day · 30-Day Returns · UK Made
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Food supplements should not be used as a substitute for a varied and balanced diet and healthy lifestyle. If you are pregnant, breastfeeding, taking medication, or under medical supervision, consult your doctor before use. Do not exceed the recommended daily intake. Store out of reach of children.

Banana
Chocolate
Chocolate Mint Out of stock
Chocolate Peanut
Cookies & Cream
Strawberry
Vanilla
Banana
Chocolate
Chocolate Mint
Chocolate Peanut
Cookies & Cream
Strawberry
Vanilla

Mass gainer for easier calorie intake

Optimum Nutrition Serious Mass Gainer is a higher-calorie shake option for people who want an easier way to push calorie intake higher when food falls short. It uses a simple powder format, making it a better fit for regular use than overcomplicated, stop-start supplementation. An easier way to support a surplus across longer phases.

Each serving provides 50g of protein and 1260 (335.0g serving), with 250g of carbohydrates and 6.3g of fat. This macro profile suits anyone looking for a lean protein source that supports daily intake without excessive calories.

Each pack contains 16 servings, with a 335.0g serving size. Mix with water or milk as part of a daily routine around training or between meals. Consistent use tends to deliver better results than sporadic intake.

Ultimate Weight Gainer for Fast Muscle Growth, Strength Gains & Post-Workout Recovery

Trusted by bodybuilders, athletes and hardgainers, this delivers 1,250 premium calories per serving with 50g protein, 250g carbs, and 25 essential to help you:

Serious Mass Gainer is manufactured by Optimum Nutrition. Contains milk (whey, casein), egg and gluten (wheat). May contain traces of soy, nuts and peanuts. Full ingredient and allergen details are listed on this page and on the product packaging.

Key Benefits

1250kcal Calorie Surplus

1250 calories per serving gives hard gainers the calorie surplus required for muscle mass gain - difficult to achieve through whole food alone when appetite is limited.

50g Multi-Source Protein

Whey Concentrate, Calcium Caseinate, and Egg Albumin combine to deliver 50g of protein per serving with both fast and slow-releasing amino acid profiles for extended muscle support.

Creatine & Glutamine Included

Creatine Monohydrate for strength and power, L-Glutamine and Glutamine Peptides for recovery - both included in every serving so you don't need to add separate supplements.

Full Vitamin Complex

A comprehensive vitamin blend including A, C, E, and the full B group ensures micronutrient needs are met during calorie-surplus phases where food variety may be reduced.

Frequently Asked Questions

Who should use Serious Mass and who should avoid it?

Serious Mass is designed for hard gainers who struggle to eat enough calories from food to gain weight. This includes naturally thin individuals, people with fast metabolisms, and athletes in sports that demand high calorie expenditure. It is not suitable for people trying to lose weight, those who gain fat easily, or anyone who can already meet their calorie targets through normal meals. At 1250 calories per serving, it adds significant energy that will lead to fat gain if total intake exceeds what your body needs.

Can I use half a serving of Serious Mass instead of a full serving?

Yes, and many people find this is the better approach, especially when starting out. A half serving gives you roughly 625 calories, 25g protein and 126g carbohydrates, which is still a substantial addition to your daily intake without the digestive challenge of the full 334g scoop. You can gradually increase toward a full serving as your appetite and tolerance allow. Using milk instead of water for a half serving adds roughly 150 to 250 extra calories depending on milk type.

What is the best time to take Serious Mass?

The two most popular times are post-workout (when your body is primed to use the calories for recovery and glycogen replenishment) and between meals (to bridge gaps when eating enough solid food is not practical). Avoid taking it right before training, as the high volume and calorie density can cause discomfort during exercise. If you use a full serving, spacing it at least 90 minutes from your next solid meal gives your digestion time to process the shake.