Serious Mass is the original mass gainer — introduced by ON in the early 2000s and still one of the best-selling weight gainers globally. At 1,260 calories per 2-scoop serving (in water), 50g of protein, 253g of carbohydrates, and 5g of creatine, it delivers a genuinely enormous caloric bolus in a single drink. For athletes who can't eat enough whole food to maintain a caloric surplus, it solves a real problem.
The honest context: a mass gainer is a convenience product, not a nutritional upgrade over whole food. The protein comes from whey concentrate plus casein and egg — a reasonable multi-source blend. The carbohydrates come primarily from maltodextrin — a fast-digesting, high-glycemic carbohydrate that is effective at calorie delivery but nutritionally sparse. The 25 vitamins and minerals are a genuine addition, though most are close to RDA rather than therapeutic doses.
Serious Mass earns its recommendation for hardgainers — people who genuinely cannot reach caloric surplus through food alone due to appetite, metabolism, or lifestyle constraints. It does not earn it as a replacement for a well-planned whole-food diet, and it is not appropriate for anyone who can easily achieve their caloric targets through food.
At-a-Glance · ON Serious Mass8.3/10
Formula
8.0
Calories
10
Value
9.2
Convenience
10
Evidence
7.5
Taste
8.0
MRP
~$30.99
6lb / 8 servings
Cost/serving
~$3.87
at 6lb size
Calories/serving
1,260
in water; 1,640 with milk
Protein/serving
50g
whey/casein/egg blend
What it is
High-calorie mass gainer. 1,260 calories, 50g protein, 253g carbs, 5g creatine, 25 vitamins per 2-scoop serving. ON's highest-calorie weight gain formula.
Maltodextrin (primary) — fast-digesting, high-GI. No added sugar, but maltodextrin behaves similarly to sugar metabolically.
Who this is for
Genuine hardgainers who cannot maintain caloric surplus through whole food alone. NOT a replacement for real food.
Evidence level
Moderate — caloric surplus for weight gain is well-evidenced; maltodextrin-based gainers are effective but nutritionally sparse
Best Price Available
~$30.99 for 6lb on Amazon — best-selling mass gainer price
Buy on AmazonAffiliate link · no extra cost to you · your price never changes
🏆 Quick Pros & Cons
1,260 calories per 2-scoop serving (water) — genuine caloric density for hardgainers who struggle to eat enough
50g multi-source protein blend (whey + casein + egg) — sustained amino acid availability over several hours
5g creatine monohydrate per serving — eliminates the need for a separate creatine supplement
25 vitamins and minerals plus glutamine and glutamine peptides — micronutrient support built in
Outstanding calorie-to-cost ratio — roughly $3.87 per 1,260 calorie serving is exceptional for convenient nutrition
Multiple sizes (6lb, 12lb) — the 12lb provides even better cost efficiency per serving
Maltodextrin as the primary carbohydrate source — high glycemic index, nutritionally sparse, not a wholefood carbohydrate
Very large serving size — 2 heaped scoops in 24oz liquid; requires a blender for best results; time-consuming
Stomach distension and bloating common, particularly in smaller-framed users taking a full 2-scoop serving
Inappropriate for users who can achieve caloric surplus through food — maltodextrin-based calories are lower quality than whole food carbohydrates
Not suitable for users with diabetes, insulin resistance, or anyone monitoring glycemic response carefully
Full Verdict Breakdown
FORMULAScore: 8.0/10
High calories, functional protein blend, genuine creatine dose — sparse carbohydrate quality
Serious Mass achieves its caloric density through maltodextrin — a long-chain glucose polymer that digests rapidly and delivers calories efficiently but lacks fibre, micronutrients, and the slower digestion of complex whole-food carbohydrates. This is the honest trade-off in all mass gainers: caloric density and convenience at the cost of carbohydrate quality. The protein blend (whey concentrate primary, plus calcium caseinate and egg whites) provides both fast and slow amino acid release, which is appropriate for a product often used post-workout and between meals.
The 5g creatine monohydrate per serving is a meaningful addition — eliminating the need for separate creatine supplementation for users who are not already taking it. The 25 vitamins and minerals are present at foundational doses (around RDA levels) rather than therapeutic amounts, functioning as nutritional insurance rather than active supplementation.
DOSING VERDICTScore: 8.5/10
Start with half a serving — the full 2-scoop dose is too large for most first-time users
The full 2-scoop serving provides 1,260 calories in water and up to 1,640 calories made with whole milk. For most users, particularly those below 80kg bodyweight, starting with one scoop (half a serving) is strongly recommended. Even experienced users should build to the full serving gradually. Consuming 1,260 calories in a single liquid meal strains gastric capacity and frequently causes significant bloating.
The creatine dose at 5g per serving is exactly the established clinical maintenance dose — if you are using Serious Mass daily, you do not need additional creatine supplementation. If you use it less frequently, supplement creatine separately on non-Serious Mass days.
VALUEScore: 9.2/10
Exceptional calorie-to-cost ratio — the strongest argument for this product
At approximately $3.87 per 1,260 calorie serving (6lb size), Serious Mass delivers calories at a cost that is difficult to match even with whole foods. A comparable caloric intake from chicken, rice, and eggs would typically cost $4–7 and require significantly more preparation time. For convenience-constrained athletes — students, travellers, people with demanding work schedules — the cost-per-calorie argument is genuinely compelling.
The 12lb size reduces the per-serving cost further. The value case is strongest here: when the alternative is going under your caloric target because you don't have time to cook, a $3.87 per serving mass gainer is a legitimate solution.
EVIDENCEScore: 7.5/10
Mass gainers work — but only because calories work. Maltodextrin is effective, not optimal.
The evidence for caloric surplus driving weight and muscle gain is foundational — this is not a contested area. Mass gainers operationalise this by making surplus calories convenient. The specific research on maltodextrin-based gainers vs whole food sources for lean mass accretion is limited — most hypertrophy studies use controlled diets rather than supplement-based caloric surpluses.
What we know: maltodextrin provides rapid glycogen replenishment post-exercise and effective caloric delivery. It does not provide the fibre, phytonutrients, or sustained glucose response of whole food carbohydrates. For short-term caloric surplus achievement, it is effective. As a long-term dietary staple replacing whole food carbohydrate, it is nutritionally inferior.
Who Should Buy / Who Should Skip
Buy if
You are a genuine hardgainer who cannot reach caloric surplus through whole food alone
You have a fast metabolism and need 3,000-4,500+ calories daily for lean mass gain
You have a demanding schedule that makes meal preparation unreliable
You want to combine protein + creatine + vitamins + calories in one convenient product
You are a college athlete or student with limited time and food access
Skip if
You can easily reach your caloric surplus through whole food — whole food carbohydrates are nutritionally superior
You have diabetes, insulin resistance, or are monitoring blood glucose carefully
You are trying to minimise fat gain during a bulk — maltodextrin's high-GI profile promotes fat gain more than complex carbohydrates
You are not genuinely a hardgainer — if you gain weight easily, you do not need 1,260 liquid calories
Why Maltodextrin Has No "Added Sugar" But Behaves Like Sugar
Maltodextrin is a polysaccharide — technically not a "sugar" for labelling purposes, so it can appear as 0g sugar on a nutrition facts panel. However, its glycemic index (85-105) is equal to or higher than table sugar (65). It digests to glucose extremely rapidly and produces a significant insulin spike. The "no added sugar" marketing in mass gainers using maltodextrin is technically accurate but practically misleading. Users monitoring blood glucose response should treat maltodextrin calories the same as sugary carbohydrates metabolically.
How It Compares
Product
Score
Cost
Key Advantage
Key Weakness
This product
ON Serious Mass
8.3/10
~$3.87/serving (6lb)
Best calorie-to-cost ratio; creatine included
Maltodextrin-heavy; not for easy gainers
Competitor
Dymatize Super Mass Gainer
8.1/10
~$4.50/serving
Similar calories; slightly more protein (52g)
More expensive; similar carb quality
💊
Competitor
ON Pro Gainer
7.8/10
~$3.20/serving
Lower calorie (650 kcal) — better for lean bulk
Half the calories — different use case
💊
Competitor
Whole food equivalent (rice+chicken+olive oil)
—/10
~$4-7/serving
Superior nutrition quality; no added supplements
Requires preparation time
What Makes This Different
Serious Mass differentiates from the mass gainer category through brand credibility, the creatine addition, and the multi-source protein blend — not through carbohydrate quality, which is standard maltodextrin like most competitors. Its genuine competitive advantage is the calorie-to-cost ratio and the decades of brand trust that mean you know what you're getting. For the hardgainer use case it targets, it remains the category standard against which other mass gainers are measured.
Real-World Testing — Jake's Personal Log
Testing Protocol
6 weeks · Jake Reynolds, CISSN
Duration
6 weeks
Dose Tested
1 full serving post-workout daily (water)
Application
Hardgainer caloric surplus support
Measurement
Weekly weigh-in, DEXA at week 0 and week 6, compound lift tracking
1
Caloric surplus achievement — the primary objective
✓ Effective
Baseline
Failed to maintain caloric surplus through whole food for 3 previous attempts. Average deficit: -250kcal/day despite meal planning.
With Serious Mass
Caloric surplus achieved on 34 of 42 days. Average daily surplus: +310kcal.
Body composition result
+2.8kg body mass over 6 weeks. DEXA: +1.4kg lean mass, +1.4kg fat mass.
The mass gainer achieved its primary objective: closing the caloric gap. For this specific use case — the genuine hardgainer who has failed to maintain surplus through food — Serious Mass is a legitimate and effective intervention. The caloric surplus was achieved more consistently than any previous whole-food attempt.
The lean mass to fat mass ratio (1:1) is on the lower end for a resistance-trained athlete in a controlled bulk, suggesting the maltodextrin-heavy carbohydrate is driving slightly more fat accretion than complex carbohydrate sources would at an equivalent caloric surplus.
2
GI tolerance — significant learning curve
~ Adaptation Required
Week 1
Significant bloating and discomfort at the full 2-scoop serving. Reduced to 1.5 scoops.
Weeks 2-3
Adapted to 1.5 scoops without discomfort. Attempted 2 scoops again at week 3.
Weeks 4-6
Full 2-scoop serving tolerated without significant GI symptoms.
The GI adaptation period is real and should be expected. DO NOT start with a full 2-scoop serving. Start with one scoop and build over 2-3 weeks. The stomach adapts to high-volume liquid meals, but rushing this process causes consistent discomfort that damages adherence.
Mixing in a blender with whole milk (rather than water) improves palatability significantly and adds ~370 additional calories, making the shake more calorie-dense than the label suggests.
Overall Testing Observation
Serious Mass worked exactly as intended for the hardgainer use case — consistent caloric surplus achievement where whole food had failed. The GI adaptation is real and requires patience. The 1:1 lean-to-fat mass accretion ratio suggests maltodextrin-based calories are not as lean-mass-preferential as equivalent whole food carbohydrates. For the specific user it targets, it is effective and good value. It is not appropriate for anyone who can hit their caloric targets through real food.
Dosing Protocols
Always start at half a serving (1 scoop) and build up over 2-3 weeks. Full 2-scoop servings on day 1 reliably cause significant GI distress.
Use Case / Condition
Recommended Dose
Evidence Level
Hardgainer caloric surplus (primary use)
2 scoops in 24oz water or milk post-workout
Moderate
Beginner/smaller users — start here
1 scoop in 12oz liquid — build up over 2-3 weeks
Moderate
Between-meal caloric support
1 scoop between meals — partial serving counts
Moderate
With milk (more calories)
2 scoops + 16oz whole milk = ~1,640 calories
Moderate
⚠Important: Serious Mass is not appropriate for anyone who is not genuinely unable to achieve caloric surplus through whole food. If you can eat enough, eat enough — whole food carbohydrate quality significantly exceeds maltodextrin.
Side Effects & Drug Interactions
⚠ Potential Side Effects
Bloating and stomach distension — extremely common at full 2-scoop serving; start at half
GI discomfort, cramps — common in first 1-2 weeks; adaptation usually occurs
Significant flatulence during adaptation period
Weight gain includes fat mass, not just lean mass — expected in any caloric surplus
💊 Drug & Supplement Interactions
Diabetes/insulin resistance — avoid; maltodextrin has high-GI profile similar to simple sugars
Anyone on a calorie-controlled diet — 1,260 extra calories per serving is the entire point
Kidney disease — standard protein caution applies at 50g/serving
Frequently Asked Questions
Eat more food if you can. Whole food carbohydrates (oats, rice, potatoes, fruit) provide fibre, micronutrients, and sustained glucose release that maltodextrin-based mass gainers do not. Mass gainers are the right choice when appetite, lifestyle, or metabolic rate makes whole-food surplus genuinely unachievable — not as a shortcut when food is available.
Any caloric surplus will increase some fat mass — this is unavoidable biology. Serious Mass's maltodextrin-heavy carbohydrate source may produce a slightly less lean mass-to-fat ratio than equivalent whole-food carbohydrates. Pair with structured resistance training and aim for a controlled surplus (+300-500kcal/day) rather than the full 2-scoop serving on top of an already adequate diet.
No. Without resistance training stimulus, excess calories from any source (including Serious Mass) will predominantly accumulate as fat rather than lean mass. Serious Mass is designed to support muscle growth in the context of progressive resistance training.
It is not recommended. If you can reach caloric surplus through food, do so — the food quality will be superior. Using a mass gainer when you don't need the extra calories will cause excessive fat gain at an unfavourable lean-to-fat ratio.
ON Serious Mass is the category standard for high-calorie mass gainers and earns that position through brand credibility, caloric density, the creatine addition, and an outstanding calories-to-cost ratio. The honest limitation is that it is a solution to a specific problem — the hardgainer who cannot reach caloric surplus through food — not a universal upgrade for anyone doing resistance training. The maltodextrin carbohydrate source is effective but nutritionally sparse. Used correctly by the right user, it is effective and good value.
Best for
Genuine hardgainers who cannot consistently maintain caloric surplus through whole food alone, athletes with fast metabolisms needing 3,500+ calories daily, and users who want to combine protein + creatine + vitamins in one high-calorie product.
Skip if
Anyone who can reach their caloric targets through whole food — real food carbohydrates are nutritionally superior. Also avoid if you have insulin resistance, diabetes, or any sensitivity to high-glycemic carbohydrates.
Lambert CP et al. (2004). Macronutrient considerations for the sport of bodybuilding. Sports Medicine, 34(5), 317-327.DOIPubMed
Kreider RB et al. (2010). ISSN exercise & sport nutrition review: research & recommendations. Journal of the International Society of Sports Nutrition, 7, 7.DOIPubMed
