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

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Male & female bodybuilders who use mass gainers

In this “Mass Gainer 101” overview article I provide answers to several of the most common questions asked about mass gainer supplement powders, including:

  • what are they,
  • what do they do,
  • how to use them,
  • do they even work or not,
  • what are their possible side effects,
  • & more.
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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 is a mass gainer?

A mass gainer is a supplement powder that is designed to help you gain weight by providing you with a lot of calories in a drinkable form.

When you see the word mass on a fitness supplement label, the implication there is almost always that it’s about building muscle mass versus just gaining weight, fat & all.

Thus a mass gainer is a supplement usually associated with the athlete/weightlifter looking to get bigger through muscle growth.

And one of the main (and critical) contributing factors to adding muscle mass is the presence of a sufficient amount of additional high-quality calories, which is what a mass gainer product aims to provide you.


What’s in a mass gainer?

There are many mass gainers on the market and so their formulas vary, but the majority of the biggest sellers all share a few common traits.

Most mass gainers contain (per serving):

  • a ton of carbohydrates;
  • a lot of protein, but less than the carbs;
  • not very much fat in comparison.


What do mass gainers use for the carbs

In most cases, manufacturers of the popular mass gainers rely on maltodextrin to supply the big dose of carbs for a couple of reasons I’ll get into in a bit.

Maltodextrin’s a starchy food additive that is commonly used as a thickening agent in processed foods. (1)

A financial reason it’s used in weight gain powders is because maltodextrin is cheap to cook up in a food plant, and it’s usually made out of corn, wheat, rice, or tapioca. (2)


On the nutrition side of things, maltodextrin delivers a lot of carbohydrate calories in a powdered form that mixes easily with liquids so you can drink it, which can be a convenience for some people.

Maltodextrin is technically classified as a complex carbohydrate, but it has an absorption rate as fast as glucose & other simple sugars, and a high glycemic index to boot.

This means it can spike blood sugar levels soon after taking it, which is bad for diabetic & pre-diabetic people.

However, sports science studies have found that post-workout, a state of raised insulin levels — thanks to consuming high GI carbs like maltodextrin — plus some rapid-absorption protein can enhance muscle recovery & growth. (3)

What mass gainers use for the protein

With many mass gainers it is also very common is for its protein formula to be a blend of milk proteins like whey isolate, whey protein concentrate, & casein, and some contain egg whites as well.

There are very few vegan mass gainers on the market at the present time — more on that in a bit — but the ones that do exist lean on plant-based protein sources like pea, rice, quinoa, peanut, chia, etc.


What type of fats are in a mass gainer

There isn’t a lot of fat in the majority of mass gainers (I’ve read the Supplement Facts labels of 20+ brands), and in those cases I’d guess most of the fat is naturally occurring in the casein & whey protein concentrate that’s in their “protein blends”.

A few of the brands I’m familiar with use small amounts of MCTs (medium chain triglycerides) which is often derived from coconut oil, and that’ll add a gram or two of fat per serving too.


How many extra calories are needed to build muscle?

Numbers are all over the board on this one, just poke around online and you’ll come across the differing opinions amongst weight management physicians, dieticians, nutritionists, and strength & conditioning coaches.

This isn’t too unexpected or surprising, considering there’s no “one size fits all” when it comes to fitness since we’re all different.

We all have unique:

  • bodies
  • life & health situations
  • fitness goals
  • current dietary habits
  • etc.

There also haven’t been an extensive amount of research studies dedicated to trying to come up with the “ideal” number of additional calories per day (or per week) you need to eat in order to gain X amount of weight.

That said, the ISSA (International Sports Sciences Association) notes that there is some consensus that somewhere in the neighborhood of 2500 calories above normal per week will likely add between a half a pound to a pound of mass per week.

They note that that is a very general guideline, given all those lifestyle differences we each have I mentioned earlier.


And in an article on gaining weight safely, Medical News Today states that

“consuming 300–500 calories more than the body burns on a daily basis is usually sufficient for steady weight gain.”

That comes out to 2100-3500 extra calories per week, putting it in the same ballpark as other weight management expert opinions on the subject.


What do mass gainers do?

The positive things mass gainer powders can provide include:

* high glycemic carb loading immediately post-workout, which has been shown to aid in muscle recovery & growth; (4)

* daily calorie enhancement that’s pretty convenient to use (just need that blender);

* high quality protein, and some brands include vitamins, minerals, & performance enhancers like creatine too;

* helping you gain quality weight, as long as you’re working out hard enough.


Do mass gainers make you fat?

By itself, a high-calorie weight gain product is not going to make you fat, that has more to do with how many calories a day you’re consuming above normal, and what the quality of those calories is.

Keep in mind though, that if you’re not eating enough to put your body in a calorie surplus state each day, you won’t even gain weight. (5)


Mass gainers a have a lot of calories in them, so you’ll want to consider training with enough intensity so that any weight you gain is in the form of muscle not fat.

And since mass gainers also get the majority of their calories from carbs, whatever you don’t use while exercising will be converted to fat & stored by your body. (6)


What’s the difference between a mass gainer & whey protein?

Lil Boji with ON's whey protein & mass gainer best-sellers - heydayDo image

Optimum Nutrition’s whey powder on the left, and their mass gainer product on the right.


There are several things that distinguish a mass gainer product from a whey protein product, and I discuss them in detail in the following article:

Whey Protein vs. Mass Gainers: 7 Important Differences to Know

Check it out if you’re interested in learning more, but for now I can share that these two types of supplement powders have big differences in their ingredients, calories, & macronutrient profiles, among other things.


How to use a mass gainer?

The manufacturers that make the best-selling mass gainer powders are all pretty clear in laying out what the intended use of their respective mass gainer powders ought to be: post-workout & “between meal” calorie boosts.

On the back label of the tub of O.N.’s Serious Mass I bought it says

“Serious Mass is designed to provide serious calories, protein, & carbohydrates – making this a convenient way to get extra calories throughout your day.”

Optimum Nutrition Serious Mass directions for use - heydayDo image

“Extra” being the operative word, meaning your diet should already be solid…you just want to create a calorie surplus so you can gain some (hopefully muscular) weight.

Optimum Nutrition says the same thing again — with a couple of more clues — on their website’s Serious Mass product page:

“Use post-workout and/or between meals to add calories, carbs and protein to your healthy, balanced diet.”


Mass gainer user tips

Use a blender vs. a shaker bottle if possible

Protein powders — especially those that are whey-based — mix pretty easily in a shaker bottle, but gainers are different.

Remember that the main ingredient(s) in a mass gainer is the carbohydrate source, whether that’s maltodextrin or starch from peas, quinoa, etc.

Those things aren’t as easy to blend in a shaker bottle, and you could end up with those “fun” clumps…so use a blender.

If you look at the pic I took of Serious Mass’ instructions above, you’ll see they’re recommending a blender too.


Use more water than you would with a pure protein powder

Again due to all the carbs, a mass gainer needs more water than your whey or vegan protein powder would.


Best time to take a mass gainer

As Optimum Nutrition recommends with their Serious Mass & Pro Gainer products, these types of weight gain powders are best taken post-workout &/or between meals as a daily calorie booster.

It’s not nutritionally complete so replacing a regular meal with it isn’t a good idea (in my opinion anyway).

However if you’re in a pinch time-wise and can’t wolf down a sufficient amount of food-based calories, drinking a gainer is a convenient substitute.


Do mass gainers work?

It is up to the person trying to gain muscular weight to create a daily caloric surplus that includes sufficient amounts of quality protein and a weightlifting program of suitable intensity.

A mass gainer can help by supplying additional calories via extra carbs for workout energy & protein for post-workout muscle repair & growth, but only if the person’s diet & training plan are on point will lean mass gains be achieved.


Are mass gainers worth it?

If you are:

* trying to add lean muscle weight quickly,

* and are weight training with sufficient intensity & volume,

* and just can’t hit your daily caloric surplus requirements with solid food, whether due to your busy schedule or slow digestive system,

then adding a mass gainer to your diet could help you achieve your goals.


If you can get your daily calorie needs from high-quality solid foods &/or from making your own weight gain shakes (see below), buying a mass gainer is a waste of your money, in my jaded yet humble opinion…


What is the best mass gainer?

I have evaluated over 20 mass gainer products, and have written up detailed reviews of about a dozen of them spread across these three articles:

7 Best of the Cheapest Mass Gainers

Top 4 Vegan Mass Gainers

Serious Mass vs. Pro Gainer: Comparing 2 Weight Gain Powders

So given that background I can say fairly confidently that as of now, the best-selling mass gainer in the world is Optimum Nutrition Serious Mass.

At a rough glance it looks like it currently has more buyer reviews than all other mass gainers combined, and there are well over 40,000 Serious Mass buyer ratings across all of the internet retailers I could track down.


Best mass gainer for skinny guys

This section will provide a list of the highest-rated mass gainer powders, according to their buyers’ opinions across the internet.

Part of my product review process is to figure out buyer ratings (meaning how many stars), by combining all online sellers’ numbers.

(I often exclude using the manufacturer website reviews when tallying them though, since some of them simply never show a buyer review/rating under 4 stars. 😳)

Here are the mass gainer powders with the best buyer ratings at this time, and you can click on their blue names or pics to check price & reviews on Amazon:


Highest buyer-rated mass gainers

Rivalus Clean Gainer 4.6⭐ 4,000+ reviews

Rivalus Clean Gainer


Optimum Nutrition Serious Mass 4.6⭐ 40,000+ reviews

Optimum Nutrition Serious Mass


BSN TRUE-MASS 1200 4.6⭐ 6,000+ reviews

BSN True Mass 1200


Optimum Nutrition Pro Gainer 4.6⭐ 4,000 reviews

ON Gold Standard Pro Gainer



How to make your own mass gainer

All you need to build your own weight gain shakes is a solid protein source, a handful of high-quality high-calorie foods, a blender, & a little culinary creativity.

I share several of my own mass-building recipes — plus provide the caloric & macro numbers for each shake — in this article:

Make Your Own Protein Shakes for Weight Gaining


In a perfect world I’d be able to eat all my necessary calories whenever I’m on a mass-building training cycle, but I can’t: my digestive system is much slower now that I’m older.

(I feel full for longer, so my appetite is smaller now at 60+ than it was when I started lifting in my 20s…)


So for me the next best thing is to be able to drink all those natural, whole-food calories — and that’s why I’m a big fan of DIY mass gainers.

Plus you avoid ingesting all those processed & synthesized ingredients most of them use.😉


Mass gainer side effects

Far & away the most likely side effect from drinking a thousand calorie beverage in one sitting — if you experience anything at all — is temporarily feeling bloated or real full.

Yet for many people (and I’m in this camp too) drinking those calories has less of a “stuffed” feeling than if those calories came in the form of a big meat-filled or otherwise bulky meal.

Note though that in rare situations certain ingredients often used in mass gainer supplements pose a potential health risk, and I discuss this below.


Is a mass gainer safe?

The FDA (U.S. Food & Drug Administration) has undoubtedly approved each of the main food-based ingredients found in the popular mass gainers for safe human consumption, but that doesn’t mean you’re automatically good to go.

For one, the FDA doesn’t regulate products it considers as dietary supplements…like a mass gainer for instance. (7)


There are quite a few different mass gainer products on the market and they don’t all use the same ingredients, so relative safety of these types of products ought to be done on a case-by-case basis.

And since a weight gainer powder is delivering a whole bunch of calories at once, you can bet that there’ll be at least one or two ingredients found in large amounts in a single serving.

Like maltodextrin for example, which is responsible for the majority of the calories in several of the best-selling mass gainer products.


A much rarer possible side effect for a few people

Anyone with blood sugar issues better avoid a mass gainer powder made with maltodextrin or glucose — or check with the doc first before taking it — given their high glycemic index and insulin-spiking ability.


But assuming you’re healthy, if anything unpleasant came up it’d most likely be some form of digestive discomfort.

(Though poking around the internet I found very few buyer complaints in that regard actually, considering how many people have written online about their experiences using a mass gainer supplement.)


Are there vegan mass gainers?

There are a lot more vegan protein powders on the market these days compared to 10-15 years ago, which is nice if you’re vegan or lactose intolerant, or just want a little variety in your protein sources.

Unfortunately there are very few vegan mass gainers being made by fitness supplement companies at this time.

I went on a hunt for them recently and only came up with a small handful worth writing about, which I did in the review article below:

4 Best Plant-Based Vegan Mass Gainers

The two most popular vegan gainers are Naked Mass Vegan and IronVegan Athlete’s Gainer, and both use pea & brown rice as their main protein sources.


Wrapping up

Related articles here on heydayDo

7 Best of the Cheapest Mass Gainers

The Hunt For The Best Optimum Nutrition Flavor

I hope that this overview article on mass gainer supplement powders is useful to you, and I wish you well on your fitness journey.

– greg

About The Author

heydayDo author Greg Simon

Hi, I’m Gregory 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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