Detailed Optimum Nutrition Serious Mass Review

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heydayDo Rottweiler Lil Boji lying on grass next to tub of Optimum Nutrition Serious Mass

In this review article we’ll be taking a close look at Optimum Nutrition Serious Mass, the #1 selling mass gainer supplement powder in the world.

I’ll be going over its ingredients, macronutrient profile, cost per serving, Serious Mass’ buyers’ ratings & how those compare to its competitors.

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Science resources included

As is my custom here on heydayDo, I will provide links to all of the relevant sports science and medical resources, clinical studies, & nutritional data used in this article.


What’s next

Before getting into the details of all those categories I mentioned earlier, I want to provide a brief general overview of Serious Mass.

It may have whey in it but it is nothing like your typical protein powder, nor is it intended by the manufacturer (Optimum Nutrition) to be used the same either.

So let’s take a quick look at it and see what’s unique about Serious Mass compared to those hundreds (thousands?) of other protein powders on the market these days.

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What is Serious Mass?

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Optimum Nutrition (aka ON) says in their marketing material that Serious Mass is designed “for Muscle Building & Weight Gain Goals.”

And on the Serious Mass product page on their site, ON also writes that

“Serious Mass is the ultimate muscle building and weight gain formula.”


Muscle building & weight gain.

In a nutshell nutritionally-speaking, compared to typical whey-based protein powders, Serious Mass has:

* a lot more protein per serving (50 grams vs. the usual 25-30 grams), and that’s the “muscle building” part I’m pretty sure;

* a ton more calories per serving (1,250 vs. the usual 120-160), and that’s the “weight gain” part I’m definitely sure of;

* 252 grams of carbohydrates per serving that are there to “help fuel workouts”, per ON’s website.


By comparison, the #1 selling protein powder in the world, Gold Standard — also made by Optimum Nutrition — only has 3 grams of carbs in a serving:

ON Gold Standard Whey nutrition facts showing 3 gramsof carbs per serving - heydayDo image

About Optimum Nutrition

Whether you look on Amazon, in Costco’s aisles, or on bodybuilding supplement sites like and Muscle&, you’ll see how a number of Optimum Nutrition products are the most popular in their category.

Just check out how many more buyer reviews their stuff has than their competitors.


But they’re just one of a number of companies owned by an even bigger whale in the sea of fitness supplements, and their name is Glanbia.

They were originally a big dairy conglomerate based in Ireland and just moved into the fitness supplement market, which isn’t too much of a stretch when you think about all those milk-based protein powders for sale I showed you earlier.

They own a few brands you may recognize besides ON too:

Glanbia Sports Performance Product Lines - heydayDo image


About ON’s quality standards

Optimum Nutrition goes into detail on their website about how important quality is to them at each stage of their manufacturing processes, which you can read about here if you’re interested.

They also have a short, 2-minute video that speaks to that product standard of theirs too:



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Serious Mass macros

The macronutrient profile of Serious Mass is where you can really see how much different it is compared to regular protein powders, and here’s a look at its numbers:

(per serving)

Serious Mass calories: 1,250

Protein: 50 grams

Carbs: 252 grams

Fat: 4.5 grams


Serious Mass supplement facts - heydayDo image


About that Serious Mass serving size

Note that 336 gram serving size, and realize that is 12 ounces, or 3/4 of a pound.

Just my humble opinion, but that’s a massive dose of powder that I guarantee will expand in your belly like…well, like I don’t know what.

Might I also suggest you cut that in half, since that’ll still give you 625 calories in one sitting — which is definitely in “full meal” territory.


A little later on you’ll see that the directions on their label suggest you start with just one scoop, which is 1/2 a serving too.


Usefulness of knowing macros

In case you didn’t know, to get a macro profile of anything you’re eating or drinking you just need to figure the percentages of calories that the protein, carbs, & fat you’re consuming each contribute.

The math is just an approximate kind of deal, but it’s useful when comparing foods or supplements, or when trying to dial in the right daily diet for your particular training & fitness goals at any time.

The key piece of info is knowing that while one gram of fat provides roughly 9 calories of energy, one gram of both carbs & protein only have around 4 calories in them. (1)


So if I convert Serious Mass’ protein, carb, & fat grams to calories and divide them by its total calorie number (1,250), we’ll get its macro profile.

In an article I wrote called Whey Protein vs. Mass Gainers, I did just that and compared it to ON’s Gold Standard whey powder…look at the huge difference in nutrient portions:

Macro comparison between ON's Serious Mass & Gold Standard Whey - heydayDo image

This is due to the simple fact that Serious Mass’ number one ingredient is not whey protein (or any other type of protein for that matter) like it is in so many of the protein powders on the market.

And in the Ingredients section up next, we’ll take a look at what makes up over 80% of Serious Mass.

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Check current price on Amazon


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Serious Mass ingredients

Here’s a summary of what’s in the Serious Mass’ vanilla flavor that I bought, with details to follow:

  • Maltodextrin
  • Protein Blend
  • Natural & artificial flavor
  • MCTs (medium chain triglycerides)
  • Lecithin
  • Acesulfame potassium
  • Sucralose
  • Vitamin & minerals
  • Creatine
  • Glutamine

Allergens: egg, milk, & soy (the lecithin)

Serious Mass ingredients label - heydayDo image

(from my tub of vanilla Serious Mass)


Serious Mass is fortified with vitamins & more

Notice that I listed vitamins, minerals, creatine, & glutamine as ingredients, but they’re not on Serious Mass’ ingredients label?

We know they’re in there because they’re seen on an extended Supplement Facts panel, just above the ingredients label, take a look:

Serious Mass vitamins minerals & fitness supplements - heydayDo image copy

I can tell you that I know they’ve been added — as opposed to naturally occurring in one of the ingredients — simply because neither maltodextrin nor the “Protein Blend” has all those vitamins, minerals, & sports performance enhancers in them.

And the maltodextrin & the Protein Blend make up 98% of Serious Mass…remember the macros’ percentages?



* The #1 ingredient in Serious Mass, making up 82% of it.

* It’s a food-additive product made from corn, rice, or tapioca usually, and is a complex carbohydrate that acts as a simple carb like sugar, because it has a very high-glycemic index. (3)

* This makes it useful post-workout, when immediate carb intake “after exhausting exercise can rapidly stimulate replenishment of muscle glycogen”, per the International Society of Sports Nutrition in their Position Stand on nutrient timing. (4)


Protein Blend

* #2 ingredient in Serious Mass, making up 16% of it.

As you can see it’s a blend of whey & casein from cow’s milk, and egg whites…pretty straightforward stuff.

The different protein types are here (my guess) in order to provide different digestion speeds, since casein digests much more slowly than whey does, which gets absorbed pretty quickly. (5)

And egg whites — thanks to the yolk being removed — have a digestion speed that’s somewhere in the middle between casein & whey. (6)


Serious Mass has exercise performance enhancers

Creatine & l-glutamine have been added to the Serious Mass formula, which certainly tells us this is intended for people who workout, or at least know a little something about sports performance supplements.



Creatine is arguably one of the most studied exercise-enhancing supplements ever. (7)

It has also clearly demonstrated on hundreds of occasions in sports science trials that it can safely enhance exercise performance in a number of ways, aid in muscle & strength growth, & assist in post-workout muscle recovery too. (8)



L-glutamine doesn’t have the same level of proven sports science behind it to verify many of the claims you’ll come across on supplement makers’ websites & product pages.

Results from research studies have been mixed, meaning that for every clinical trial where some benefit was demonstrated, another study done showed no benefit whatsoever.

From the ISSN (International Society of Sports Nutrition):

“Although glutamine may simulate muscle glycogen synthesis, reviewers recently concluded that there is no advantage over ingestion of adequate carbohydrate alone.

Moreover, several recent studies indicate that neither short-term nor long-term glutamine supplementation has an ergogenic effect on muscle mass or strength performance.”


Ergogenic means something that enhances physical performance; in other words, l-glutamine didn’t help.


Medical publisher Healthline says just about the same thing in their glutamine article, concluding:

“In the end, there is no evidence that these (glutamine) supplements provide benefits for muscle gain or strength. There is some limited support for other effects, but more research is needed.”


L-glutamine (or just “glutamine”, they mean the same thing when you’re talking about the fitness supplement glutamine) is an amino acid you’ll see used by supplement manufacturers for boosting (some of us call it spiking) the amino acid content in their product.


I don’t think Optimum Nutrition is doing that here with using glutamine in their Serious Mass product, because nowhere in its marketing material or Supplement Facts do you see any bragging about how much amino acids are in Serious Mass. 😉


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Serious Mass taste & mix-ability

First let’s check out the mix-ability.

Optimum Nutrition recommends you use a blender for your Serious Mass beverage, and they say so right on the side of the package:

Optimum Nutrition Serious Mass directions say use a blender - heydayDo image

I totally agree with them on that one.

I’ve done dozens of protein powder reviews here on heydayDo, and I’ve taste-tested every one of them using 8-12 oz. of water and my good ol’ shaker bottle.

Well, I tried that with the Serious Mass and despite getting pretty aggressive with the shaking, I couldn’t get rid of all the clumping going on.

Not much of a surprise though, really…


Maltodextrin has a different consistency & texture compared to whey or collagen powders; it sticks together a bit, and Serious Mass is over 80% maltodextrin.


So yeah, the blender’s definitely the way to go.



Serious Mass flavors

Currently it comes in five flavors:

  • Banana
  • Chocolate
  • Chocolate peanut butter
  • Strawberry
  • Vanilla


Serious Mass sizes

It’s available in a 12 lb. bag or a 6 lb. tub and as you’d expect, it’s cheaper if you go with the bigger package.


Taste of Serious Mass

I haven’t tried all five of those flavors of Serious Mass: I only bought the vanilla, and it is definitely tolerable for me.

Consider though, that I’ve been drinking powdered supplements for 40 years and have probably built up a tolerance for downing crappy-tasting products in the name of fitness & vanity. 😄

Plus, keep in mind that taste is very subjective & unique to each of us, and genetics has a bunch to do with that. (2)


Optimum Nutrition’s taste consistency

Despite only trying one of the five Serious Mass flavors, I can weigh in on the other four, sorta…given that I’ve been drinking their stuff off & on for around 20 years now.

Optimum Nutrition maintains a pretty uniform standard when applying their flavors to their various products.

I have taste-tested a bunch of their protein powders, including about a dozen for my article The Hunt for the Best Optimum Nutrition Flavor.

And to me, this Serious Mass vanilla tastes like their Vanilla Ice Cream flavor they use elsewhere.


So I’ll go out on a limb and rank the five Serious Mass flavors from best to worst (just my opinion, o’course) based on my taste-testing experiences with the 30+ flavors Optimum Nutrition floats out on the market these days:

  • chocolate
  • chocolate peanut butter
  • vanilla
  • strawberry
  • banana (they don’t use real bananas of course, and their “exotic” flavors often just taste weird to me).


Q: Which serious mass flavor is the best?

A: Depends on the person thanks to the genetics of taste & other subjective factors as I shared earlier, but I’ll go with chocolate since Optimum Nutrition seems to have a handle on how to create a decent chocolate flavor.



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Serious Mass buyer reviews

In this section I’ll show you the results of compiling all the buyer ratings & reviews I could find online for Serious Mass, and I’ll also compare its results to a handful of its closest competitors.


A quick word about my numbers…

I gather buyer ratings for any product I’m reviewing from as many different places I find where it’s for sale and also where people leave buyer feedback.

The ⭐  rating you see reflects the combining of all reviews, and the % you see represents the percentage of buyers who left a 4 or 5-star rating.

(Anything over 80% is good, like a B in school…and 90% & up is excellent.)


Amazon has long since taken over as the internet’s #1 supplement seller, so the majority of reviews for big-name products like Serious Mass will come from Amazon shoppers, and then to a lesser extent from the manufacturer’s own website.

Other fitness supplement sellers who often do enough business to get a lot of reviewers chiming in are places like and Muscle&, and sometimes Walmart or other places like GNC, VitaminShoppe, Vitacost, etc.


(The product names in blue & the images are links to its Amazon product page if you want to check out current price or buyer reviews there. And the prices I’m quoting today may be different when you look them up.)


Optimum Nutrition Serious Mass

4.6 ⭐  88% 4&5-star ratings,  40,000+ online reviews

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Cost per oz. (12 lb. bag): 24¢

Cost per serving: $2.90

See reviews & latest price on ol’ Amazon


Note on cost: I did a cost comparison of roughly two dozen mass gainers recently, and wrote a review on the most inexpensive ones (a link to the review is at the end of this article). Serious Mass was the 3rd cheapest at that time…


Serious Mass vs. its competitors

Here’s a ranking of Serious Mass and a few of its competitor mass gainers, ranked in terms of buyer ratings.

By “competitor” I mean products that are the top sellers in the mass gainer category besides world #1 Serious Mass.


(The numbers after the stars are the total number of online reviews each product has so far that I could track down.)

ON’s Pro Gainer 4.6⭐ 2,700

Serious Mass   4.6⭐   40,000

BSN TRUE-MASS 1200   4.6⭐   3,900


Naked Mass   4.5⭐   1,600


Dymatize Super Mass Gainer  4.4⭐   5,900

Muscle Milk Gainer   4.4⭐   3,800

Mutant Mass   4.4⭐   1,800

MuscleTech Mass-Tech Elite  4.4⭐   2,700

MusclePharm Combat XL Mass  4.4⭐   1,800


MuscleTech Mass-Tech Extreme 2000  4.3⭐   2,700


Bottom line: I listed Serious Mass’ sibling, Pro Gainer — also made by Optimum Nutrition — higher than Serious Mass because it has a slight edge in percentage of 4&5-star ratings over Serious Mass, 90% vs. 88%.

I compared those two gainers head-to-head in the article Serious Mass vs. Pro Gainer.

The other thing to note is something I mentioned before: the fact that Serious Mass has several times the number of buyer reviews compared to its closest competitor in that regard (Dymatize), and at least 10x the amount of any of the others.


Wrapping up

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Related articles here on heydayDo

How to Use a Mass Gainer, How It Works, Side Effects, & More

How To Build Muscle & Gain Weight If You’re An Ectomorph

Make Your Own Homemade Protein Shake Recipes for Weight Gain


I hope that my article reviewing Optimum Nutrition’s flagship gainer powder Serious Mass is useful to you, and I wish you well on your fitness journey.

– greg

About The Author

heydayDo author Greg Simon

Hi, I’m Greg Simon. Fitness training & nutrition researching since 1982. ISSN (International Society of Sports Nutrition) Pro Member. MBA, B.Sc.

Author. Surfer. Organic food grower. Congenital heart disease survivor (so far). is my wellness blog that’s about encouraging a healthy lifestyle as we age. 

I share my fitness training experience as well as the sports science research I’ve done on the many benefits strength building, exercise, & good eating habits offer us. 

I also write review articles after product testing and evaluating home gym equipment & fitness supplements.

My hope is that you’ll find useful or encouraging information here on my website that will benefit your unique fitness journey.

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