For skinny guys with a fast metabolism, eating enough to build muscle can feel like a nonstop chore. You train hard, but the scale barely moves. That’s where calorie-dense, protein-packed mass gainers step in to fill the gap, delivering the extra fuel your body needs for serious size and strength.
I’m Mohammad — the founder and writer behind ProteinJug. I’ve spent years analyzing supplement labels, comparing protein blends and carb sources, and digging through clinical data to find what actually works for hardgainers.
After comparing hundreds of options, I’ve narrowed down the top choices to help you pick with confidence. Here are the best weight gain supplements for skinny guys on the market today.
How To Choose The Best Weight Gain Supplement For Skinny Guys
Not all mass gainers are built the same. Some are loaded with cheap sugars that spike insulin without building muscle, while others provide a balanced blend of complex carbs and quality proteins. Here’s what to look for.
Protein Blend and Bioavailability
A fast-acting protein like whey isolate kicks in right after your workout, while slow-digesting casein feeds your muscles for hours. Look for a combination of both to cover the entire recovery window. A 50g protein serving is ideal for serious gains.
Calorie Density and Carb Sources
You need surplus calories, but the source matters. Complex carbs like oat flour or maltodextrin provide steady energy without the crash. Avoid formulas where sugar is the first or second ingredient — you want mass, not fat gain.
Quick Comparison
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| Model | Category | Best For | Key Spec | Amazon |
|---|---|---|---|---|
| Optimum Nutrition Serious Mass | Premium | High-calorie bulking | 1250 calories, 50g protein | Amazon |
| Optimum Nutrition Gold Standard Pro Gainer | Premium | Clean calories, lower sugar | 650 calories, 60g protein | Amazon |
| GNC AMP Mass XXX | Premium | Clinically studied formula | 780 calories, 50g protein | Amazon |
| MuscleMeds CARNIVOR Mass | Mid-Range | Lactose-free option | 700 calories, 50g protein | Amazon |
| MHP UYM XXXL 1350 | Mid-Range | Milkshake taste, high carbs | 1350 calories, 50g protein | Amazon |
| Dymatize Super Mass Gainer | Mid-Range | Fast + slow protein blend | 1280 calories, 52g protein | Amazon |
| Animal M-Stak | Budget-Friendly | Non-powder anabolic support | 21 packs, pill form | Amazon |
In‑Depth Reviews
1. Optimum Nutrition Serious Mass
Optimum Nutrition Serious Mass is the gold standard for skinny guys who need a massive calorie surplus. Each two-scoop serving delivers over 1,200 calories and 50 grams of blended protein, including whey and casein, to support sustained muscle growth all day long. The chocolate flavor mixes smoothly with a blender and has a rich, dessert-like taste that makes hitting daily goals feel effortless.
With more than 250 grams of carbohydrates per serving, mostly from maltodextrin and oat flour, it provides steady energy without the sugar crash. It also packs over 20 vitamins and minerals, including vitamin C and zinc for immune support — crucial when you’re eating at a big surplus and training heavy. The 6-pound bag provides around 8 servings, so it’s best to buy the larger sizes for value.
Users report gaining 5 pounds in as little as two weeks when adding it as a post-workout or nightly shake. The powder is fine and can be messy to scoop, but a quick spin in a blender eliminates clumps. If you’re a hardgainer who struggles to eat enough, this is the most reliable tool to push past your plateau.
Why it’s great
- Massive 1250 calories per serving; easy to hit surplus
- Blended protein with whey and casein for sustained release
- Loaded with vitamins and minerals for immune support
Good to know
- Only 8 servings per 6-pound bag; large size is more economical
- Fine powder can be messy; blender recommended for smooth consistency
2. Optimum Nutrition Gold Standard Pro Gainer
If you want serious muscle without the heavy calorie load of a 1250-calorie shake, the Gold Standard Pro Gainer hits the sweet spot. At 650 calories and 60 grams of protein per serving, it delivers more protein than almost any other mass gainer while keeping carbs moderate. The Vanilla Custard flavor is rich and creamy, mixing easily without clumps.
With less than 8 grams of sugar per serving, this is a cleaner option than many gainers that rely on cheap sweeteners. The protein blend includes whey isolate, whey concentrate, and egg white, giving you fast absorption right after training. It also contains over 80 grams of carbohydrates to replenish glycogen stores without unnecessary fillers.
The serving size is 14 scoops per container, so check the label before buying — but for a premium protein-first mass gainer, this is a top-tier choice for skinny guys who want lean mass, not bloat.
Why it’s great
- 60g protein per serving — highest in this guide
- Only 8g of sugar; cleaner carb profile
- Rich, creamy taste that blends easily
Good to know
- Fewer servings per container than some competitors
- Lower calorie count may require additional shakes for extreme hardgainers
3. GNC AMP Mass XXX
GNC AMP Mass XXX is one of the few mass gainers backed by clinical research. It features MyoTOR and BETAPOWER, which are clinically proven to improve muscle strength in as little as two weeks and enhance stamina during resistance training. Each shake delivers 780 calories and 50 grams of protein with added creatine and micronized amino acids.
What sets this formula apart is its focus on muscle quality, not just weight. It includes naturally occurring EAAs and is designed to help you get 40% more out of your training sets. The brand also bans over 220 substances per WADA testing standards, making it a trusted choice for serious athletes.
The vanilla flavor mixes well and tastes decent for a mass gainer, though some users find it slightly thick. With 13 servings per 6-pound tub, it’s a premium pick that delivers measurable strength gains alongside your weight. If you want a gainer that doubles as a performance supplement, this is your pick.
Why it’s great
- Clinically proven ingredients for strength and endurance
- Includes creatine and betaine for performance
- Third-party tested for banned substances
Good to know
- Thicker consistency; blender recommended
- Fewer servings per container compared to budget options
4. MuscleMeds CARNIVOR Mass Gainer
For skinny guys who are lactose intolerant or prefer to avoid dairy, the CARNIVOR Mass Gainer is a game-changer. It uses beef protein isolate — the world’s first and most popular beef protein brand — delivering 50 grams of protein and 700 calories per serving with zero fat and zero sugar. The Chocolate Peanut Butter flavor tastes like a milkshake with a faint beef undertone that most users adjust to quickly.
The formula is designed for rapid absorption, spiking amino acid levels faster than traditional dairy blends. It also contains 125 grams of carbohydrates for quick glycogen replenishment. Because it’s free from whey and casein, it won’t cause the bloating or digestive issues that some users experience with milk-based gainers.
Users report that it mixes easily even in a shaker cup, something rare for mass gainers. The high-protein, zero-sugar profile makes it ideal for those watching insulin spikes. If dairy upsets your stomach, this is the best mass gainer to keep your progress on track.
Why it’s great
- Zero fat, zero sugar — cleanest carb profile
- Lactose-free and Halal certified
- Mixes easily in a shaker without clumps
Good to know
- Noticeable beef smell that some dislike
- Blender recommended for best consistency with water
5. MHP UYM XXXL 1350
MHP UYM XXXL 1350 is built for hardgainers who need extreme calorie density without sacrificing taste. Each serving packs 1,350 calories and 50 grams of protein from a fast- and sustained-release blend designed to optimize insulin response for maximum muscle growth. The Milk Chocolate flavor is consistently praised as one of the best-tasting mass gainers on the market.
Its carbohydrate matrix uses a mix of waxy maize starch and maltodextrin for rapid glycogen replenishment without excessive sugar. The formula also includes 11 grams of BCAAs and added leucine to kickstart muscle protein synthesis. Users note that it digests easily with no artificial aftertaste, which is rare in this calorie range.
Counting scoops matters here — some users found slightly fewer than advertised in each tub. But for sheer calorie density and flavor, this is a standout. If you have trouble choking down big shakes, MHP makes the experience palatable without needing extra mix-ins.
Why it’s great
- 1,350 calories per serving — extreme density
- Excellent taste with no chemical aftertaste
- Digests easily despite high carb content
Good to know
- Some tubs have slightly fewer scoops than listed
- Very high carb content may not suit all goals
6. Dymatize Super Mass Gainer
Dymatize Super Mass Gainer combines fast- and slow-digesting proteins — whey isolate, concentrate, and casein — to provide sustained protein delivery for up to 8 hours. Each serving delivers 1,280 calories, 52 grams of protein, and 245 grams of carbohydrates, plus 1 gram of creatine to boost strength and power output.
The Gourmet Vanilla flavor mixes well with milk or water and has a clean, sweet profile that doesn’t get old. It also includes 14 essential vitamins and minerals, including vitamin C, E, and calcium, to support overall recovery. Users appreciate that it blends with minimal lumps compared to other thick gainers.
One thing to note: the serving size is 5 scoops (about 2.5 cups), which is a lot of powder per shake. Some users found the scoop size confusing at first. But for a gainer that covers immediate post-workout needs and overnight recovery, this is a well-rounded option for skinny guys who train intensely.
Why it’s great
- Fast + slow protein blend for all-day delivery
- Includes creatine for power and strength
- Packed with essential vitamins and minerals
Good to know
- Large serving size may be hard to finish in one drink
- Some find the scoop sizing confusing
7. Animal M-Stak
Animal M-Stak takes a different approach — it’s not a powder shake but a 21-pack of pills designed to improve nutrient partitioning and nitrogen retention. This means your body shuttles more calories into muscle and less into fat, making it ideal for skinny guys who eat plenty but can’t keep the weight on.
The formula includes 6 different complexes, including ingredients to boost energy, reduce cortisol, and prevent muscle breakdown. Users take one pack 30-45 minutes before training on workout days and between meals on rest days. Reviews consistently report gains of 10-15 pounds of dense muscle over a cycle, along with improved sleep quality and appetite.
The pills are large — some users recommend splitting the dose. It also contains caffeine, so skip the red energy pill if you’re sensitive. If you hate drinking shakes or want an anabolic edge alongside your regular diet, M-Stak offers a unique non-hormonal path to breaking plateaus.
Why it’s great
- Promotes nutrient partitioning for lean gains
- Convenient pack system, no mixing required
- Non-hormonal, safe for consistent cycles
Good to know
- Large pills; may be difficult to swallow
- Contains caffeine; not ideal for evening use
FAQ
How many times a day should a skinny guy take a mass gainer?
Are mass gainers just fat and sugar?
Final Thoughts: The Verdict
For most users, the best weight gain supplements for skinny guys winner is the Optimum Nutrition Serious Mass because it delivers the perfect balance of calories, blended protein, and proven brand trust for hardgainers. If you want a cleaner, protein-dominant option, grab the Optimum Nutrition Gold Standard Pro Gainer. And for a dairy-free, zero-sugar alternative, nothing beats the MuscleMeds CARNIVOR Mass Gainer.