Serious Mass Review: Have Optimum Nutrition Created the Best on the Market?

Image of a weight-gain powder mixed into water in a glass

Optimum Nutrition is a part of the Glanbia Global Nutrition Group, and for the last 30 years, have been creating a whole range of sports nutrition supplements, some of which are extremely popular.

After recently trying out their Gold Standard Whey, I decided to go back to my hardgainer roots, and give their signature weight gainer another go, to see how the formula is years on.

My full Optimum Nutrition Serious Mass review covers everything you need to know about this heavyweight supplement. Overall, we rated it as the best budget mass gainer currently available.

And you'll soon find out why.

Optimum Nutrition Serious Mass Nutrition Facts

Optimum Nutrition takes calorie density to the next level. Each serving checks in at 1250 calories (without milk), consisting of proteins (50g), carbohydrates (252g), and a small number of fats (4.5g), of which only 1.5g are saturated. Only a tiny 8% of the carbs come from sugar. However, it does contain maltodextrin which is great for gaining weight, but a tad controversial.

More on that later.

In addition to 25 vitamins and minerals, ON pack in a decent amount of l-glutamine (500mg), glutamine peptides (500mg), creatine monohydrate (1g) for recovery and strength. There's also some choline bitartrate (250mg), inositol (250mg), and para-aminobenzoic acid, which we'll talk more about in the next section.









High Calorie




Making up the rest of the ingredients are medium chain triglycerides, which are a fast-acting fat source used to fuel exercise. The final nutrients are lecithin — used to keep the components from separating, and acesulfame potassium, which is an artificial sweetener.

Optimum Nutrition Serious Mass Ingredients

4-Protein Mixture

Whey concentrate, calcium caseinate, egg albumen, and sweet dairy whey, are the four protein sources included in the Serious Mass mix. The greatest thing about the protein mixture is that it consists of both fast and slow-digesting sources, supplying the body with amino acids more consistently.

Egg Albumen

Being almost fat-free and highly bioavailable, egg albumen (more commonly known as egg whites) is popular among bodybuilders seeking a reliable protein source with all the amino acids needed for muscle growth.

Sweet Dairy Whey

During the process of making cheese, the liquid is separated from the curds, which results in pasteurized whey. This whey is then dried, creating what is known as sweet dairy whey, a type of protein which is a little less protein dense than the regular whey we buy at the store. While not ideal for maximum muscle growth, it's not the primary protein source in Serious Mass, so there's no need to panic.

Whey And Calcium Caseinate

The bulk of the formula consists of whey and calcium caseinate, which are two quality protein sources of varying digestion speeds. Research shows that a combination of fast and slow protein sources might well be even better for growing muscle mass than whey alone.

Image of a supplement shaker cup

Carbohydrates — 252g

Maltodextrin is a complex carbohydrate designed to release energy for the body rapidly, to fuel workout performance, and create a calorie surplus for muscle growth. The popular glucose polymer is listed very high in the glycemic index, which is why not everyone likes to drink a bunch of it.

When taken with protein and fats, like in Serious Mass, the glycemic response can be reduced, and unlike dextrose, there is no sickly sweet taste, making it easy to consume in large quantities and trigger a weight gain spurt.

Creatine And Glutamine

Creatine monohydrate is a remarkable supplement for busting through strength plateaus. As 95% of creatine is found in the muscles, it can also make our muscle bellies appear fuller and rounder.

However, at a measly 1g dose, it is not going to do much for your body in the way of strength. To enjoy its best effects, take an extra 2-4g of creatine on top of the 1g in Serious Mass.

On the recovery side of things, we get 1000 mg of glutamine in total, which is split into regular l-glutamine, and also glutamine peptides. It's what is known as a conditionally essential amino acid, meaning that under certain circumstances, it becomes necessary because the body's natural stores become depleted.

The best example of this is strenuous and exhaustive exercise. As you train progressively harder, heavier, and for longer, recovery doesn't come as easy as it once did when you were bench pressing an empty barbell.

Not only do you have DOMS to contend with, but you also have to battle CNS fatigue, which can significantly impact your strength if it's not managed.

Glutamine contributes towards reducing muscle soreness, as well as keeping your body's amino acid supplies topped up, and ready for training. But what's so special about the glutamine in Serious Mass?

Unlike regular l-glutamine, glutamine peptides are bonded with other amino acids, giving them more stability. This makes them more desirable for bodybuilders due to having better absorption into the location they need to be in— your muscle tissue.

image showing a supplement scoop

Choline, Inositol, And PABA

I bet there's a good chance your thinking the following:

What on earth are these 3 weirdly named ingredients? And will they help me gain weight?


According to Healthline, choline is an essential nutrient used to maintain brain and liver functioning, metabolism, and muscle contractions. Within the diet, you can get it from whole foods such as eggs, salmon, and broccoli. Those who are at risk of deficiency include endurance athletes and pregnant women.


This is a type of sugar tasked with giving structure to your bodies cell membranes. It also helps the body to use insulin better and may be beneficial for mental health and metabolic syndrome, although more research is needed to be sure.

Para-aminobenzoic Acid

Naturally found in eggs, milk, and grains, PABA is taken orally to treat skin conditions and is also used in sunscreen. It won't help you gain weight and is a rather bizarre ingredient to have in a mass gainer.

Who Can Benefit From Using It?

Anyone who is seeking significant weight and muscle mass can enjoy the benefits of ON Serious Mass, by taking it after weight training and between meals.

However, some users will naturally enjoy better weight gain effects than others. Gym goers or those who are skinnier than average, training more intensely and have a higher metabolic rate, which increases calorie requirements significantly.

Those who will get the most from Serious Mass, are those who are natural hardgainers, and who have high-calorie requirements that are difficult to meet through whole foods. If you don't have such problems with budging the scale, then you may want to give it a miss, seen as it well over 1,000 calories per serving.

On the other side of the coin, if you desire a bulkier physique and more impressively developed muscles, that make you feel proud of your body, then you may well benefit from taking Serious Mass daily.

If this sounds like a goal of yours, go ahead and give Optimum Nutrition's weight gainer a try, to supplement all your hard work in the gym.

Image of a muscular man stood next to a slim man

Are There Any Serious Mass Side Effects?

Fat Gain

I won't sugar coat it, bulking up isn't a straight road to looking like a chiseled Greek God. Even with strict macro tracking, weight gain isn't going to be pure muscle, you're going to gain some fat mass too.

How to avoid: you can minimize this side effect by using Serious Mass sensibly, and not eating in a ridiculous calorie surplus, as I did on my first bulk.

Gas & Bloating

Protein farts are a real thing. And with 50g of the stuff per serving, it can increase the likelihood that you (and your significant other) have to suffer this gassy side effect.

How to avoid: Don't consume more protein than you need. Anything more than 1.8g/kg or 0.8g/ lb is likely too much. You don't have to hit these number accurately, but a good reference point.

How To Use Serious Mass

  • Fill a blender without around 24 oz of cold water or milk
  • Add 2 heaping scoops (334g) into the liquid
  • Add in calorie-contributing ingredients (optional)
  • Blend for between 45-60 seconds

Tip: if you are new to the world of weight gain supplements, you may want to begin with half a serving, then work your way up to the full dose.

Best Time To Take

Here are some of the most effective times to ON Serious Mass:

  • After Training: give your muscles the proper fuel to grow by drinking Serious Mass after weight training. By replenishing lost muscle glycogen and stimulating protein synthesis, you can make sure you hit your next workout heavier, and stronger than before.
  • Between Meals: while others are able to get all the calories they need in 3 meals, not everyone has it that easy. Take Serious Mass as an extra meal to bump up your daily calories and grow.
  • Before Bed: don't have another disappointing morning weigh in, wake up heavier by drinking Optimum Nutrition's heavyweight mass gainer before going to sleep.

Sizes, Servings, And Scoop

It is available for purchase in a 6 lb tub which has 8 servings, or you can buy it in a 12 lb resealable bag for 16 servings. The scoops are more like shovels, with a standard heaping scoop weighs around 165g. The full dose is 2 heaping scoops, which checks in at 334g.

Container And Bag

The smaller size serving option comes in a protein powder-style tub, which is really convenient to screw on and off and store in a kitchen cupboard. The problem is, you only get 8 servings, which is not a lot.

The larger 12 lb bag has a resealable zip which admittedly, has been a little fiddly for me in the past, but with a little bit of patience, sealing up the goods shouldn't cause any issues.

Whichever size you go for, be prepared to fish for the scoop, which could be right at the bottom of your tub or bag.

Which Flavor Tastes The Best?

Out of the 5 available flavors, I've tried 2 of them over the years. Being almost obsessed with strawberries as a kid, that was the first flavor I tried. Although it got repetitive drinking 1250 strawberry calories a day in day out, it wasn't too sweet or intense, unlike a few other mass gainers I'd tried.

Chocolate flavor

Strawberry wasn't my favorite flavor through. I much preferred chocolate, which reminded me more of a milkshake than a protein shake. Again, it was not that sweet, but it did taste delicious when I added in some milk (I used half milk and half water).

All the calories and protein made me feel really full and satisfied, so I wouldn't drink it more than once a day.

How Does It Compare To Other Weight Gainers?

If you want to see how ON Serious Mass stacks up against the competition, then check out our chart below to see which mass gainer you should take.


Our Rating

Best For




Naked Mass

Best of the Best



Serious Mass

Best Value



Pro gainer

Lean Bulking



Overall Review

Overall, Serious Mass is a genuinely great weight gainer for those seeking a more bulked up physique. As a hardgainer answer that uses high-quality protein and complex carbs, we rank it highly among the best on the market.

On my first bulk, I gained 7 lbs using it alongside my diet.

Considering that Optimum Nutrition supplies the formula with such a high-calorie density, there is a good chance you could make sizeable weight progress like I did if your training and diet are good too.

Optimum's success in the supplement industry is a testament to their quality ingredients and simple, yet useful products. This mass gainer is capable of pushing past weight gain plateaus, increasing strength, and improving your confidence, which comes from building an impressive physique.

I hope that you enjoyed our Optimum Nutrition Serious Mass review. Hopefully, it helps you to decide which gainer to go for in the future.

ON Serious Mass | Best Value Weight Gainer

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Jonathan Abbott
Jonathan Abbott
Jonathan is a long time fitness enthusiast who specializes in helping others reach their goals faster with the most up to date sports science. When he's not working, you'll find him challanging his body with heavy squats and deadlifts.

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