ON Pro Gainer vs Serious Mass: Know the Differences

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Andy Williams
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If you’re looking for a weight gainer that will help you put on muscle mass, then this Optimum Nutrition Pro Gainer vs Serious Mass comparison is for you.

Even though these two mass gainers are made by the same supplement company, they’re very different products indeed.

So, is Serious Mass a good weight gainer? Absolutely, it’s the most popular choice for a reason. But as I said in my ON Pro Gainer review, not everyone needs a 1000+ calorie shake to maximise their results.

What Are The Difference Between Pro Gainer and Serious Mass?

A Serious Mass vs Pro Gainer comparison to illustrate the differences

Here are the main differences between Optimum Nutrition Serious Mass and ON Pro Gainer:

  • Serious Mass provides 1263 calories per 334g serving, while Pro Gainer gives you 650 calories per 165g serving.
  • Serious Mass has 251g of carbs and 50g of protein, whereas Pro Gainer has 85g of carbs and 60g of protein.
  • Serious Mass has 5.5g of fat and 26g of sugar, and Pro Gainer has 8g of fat and 4g of sugar.
  • Serious Mass has 3g of creatine per serving, whereas Pro Gainer is creatine-free.
  • Serious Mass has 25 added vitamins and minerals, while Pro Gainer has 22 different vitamins and minerals.
  • Pro Gainer mixes easier and, in my opinion, tastes better than Serious Mass.
  • Serious Mass is cheaper than Pro Gainer.

If you just want as many calories as possible for gaining large amounts of weight, then Serious Mass is the way to go.

But if you’re taking a more measured approach to bulking and want a gainer with a better carbs-to-protein ratio, then Pro Gainer is the superior choice.

It’s interesting to note that Pro Gainer has significantly more protein than Serious Mass despite having around half the calories!

As much as I like Serious Mass, it can sometimes feel like you’re just paying for carbs, which are naturally cheaper than protein. But with Pro Gainer, you’re getting loads of protein as well as—for most people—a sufficient amount of carbohydrates.

Pro Gainer vs Serious Mass: Ingredients and Nutrition

A Pro Gainer vs Serious Mass comparison

One way in which Serious Mass and Pro Gainer are very similar is that they both use maltodextrin as the sole carbohydrate source.

While I do prefer weight gainers that use oats, maltodextrin has the advantage of being easy to consume, relatively neutral in flavour, and, depending on your point of view, providing rapid energy, which may help to speed up protein absorption.

Of course, the downside of maltodextrin-only weight gain formulas is that they can lead to more of an energy crash than supplements that have oats and the like.

In terms of protein, Serious Mass uses whey concentrate and calcium caseinate, so you’re getting a good mix of fast-acting and slow-digesting protein here.

But Pro Gainer goes a step further. In addition to whey concentrate and calcium caseinate, Pro Gainer utilises whey isolate, whey peptides, whey glutamine peptides, and egg whites, which will likely result in more essential amino acids.

Now, the 50g of protein provided by Serious Mass is more than enough for most people, but the fact that you have to drink over 1200 calories just to get that 50g of protein can be quite annoying if you’re not an extreme hard gainer.

I personally like that Pro Gainer has fewer calories and more protein than Serious Mass. It’s the ideal choice for those who want to eat in a calorie surplus without going overboard and gaining unwanted body fat.

Finally, both supplements use MCTs for fat, but Pro Gainer also contains high oleic sunflower oil, which probably explains why it has more overall fat than Serious Mass.

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Serious Mass vs Pro Gainer: Weight-Gaining Effectiveness

Optimum Nutrition Serious Mass positioned next to Pro Gainer

It’s not a particular supplement that makes you gain weight; it’s your overall calorie surplus, to which a mass gainer can certainly contribute.

As I noted earlier in this Serious Mass vs Pro Gainer comparison, since it has roughly double the calories of Pro Gainer, Serious Mass obviously makes it easier to eat in a calorie surplus and gain weight. However, not everyone needs a 1200+ calorie shake to put on muscle mass.

Also, Serious Mass has a 5:1 carbs-to-protein ratio, which doesn’t suit everyone because some people don’t need loads of carbohydrates to gain weight, and instead do better with a leaner supplement like Pro Gainer.

My view is that a weight gainer should be a supplement to your wholefood meals, which is where you should get most of your calories, carbs, protein, and fats.

So if you only need 2500 calories per day to gain weight, then Serious Mass is probably too calorie-dense for you.

On the other hand, if you’re bulking on 4500 calories, then Pro Gainer might be too lean, and Serious Mass could be ideal because it enables you to fuel up on carbs without consuming too much protein.

Which Tastes Better, Pro Gainer or Serious Mass?

This one’s easy for me; Pro Gainer Tastes better than Serious Mass because the flavour is more authentic (more like actual chocolate) and has a smoother texture.

Also, Pro Gainer tastes good with plain water, whereas Serious Mass, I find, only tastes good when you mix it with milk.

To be fair, I do like the taste of Serious Mass, it’s just that Pro Gainer really does taste good.

I think as well, when you’re drinking a 1200-calorie shake, it’s always going to seem more effortful and less enjoyable than when you’re sipping on a tasty 650-calorie weight gainer.

One advantage that ON Serious Mass does have over Optimum Nutrition Pro Gainer is that it has a bigger selection of flavours to choose from, which can be useful for keeping your shakes exciting during a prolonged bulking phase.

Obviously, taste is the most subjective part of this Serious Mass vs Pro Gainer comparison, so I can’t guarantee that you’ll feel the same way. This is why I like buying different supplements and trying the flavours for myself.

Pro Gainer vs Serious Mass: Mixing and Digestion

The biggest mixability difference between ON Pro Gainer and Optimum Nutrition Serious Mass is that Pro Gainer is mixable in a standard shaker bottle, whereas Serious Mass requires a blender.

So if convenience is important for you, you’ll definitely find Pro Gainer less of a hassle.

However, making Serious Mass in a blender doesn’t take that long, and it’s the best way to ensure a smooth consistency. Plus, you can add things like peanut butter to increase the fat and calorie content, giving your shake a more balanced macronutrient profile.

When using Serious Mass in the past, I did sometimes split the full serving across two shaker bottles if I didn’t want to use a blender, which can be useful if you’re bringing your mass gainer to work with you.

In terms of digestion, Pro Gainer doesn’t sit as heavy on your stomach as Serious Mass, so you won’t feel too full after drinking it.

Still, I suppose that feeling full after drinking Serious Mass is actually a good thing because it means that you’re getting lots of calories!

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Optimum Nutrition Pro Gainer vs Serious Mass: The Verdict

So, should you get Pro Gainer or Serious Mass? Well, as you’ve probably guessed by now, it depends on your goals and how much weight you want to gain.

If you’re trying to bulk very aggressively, are a hardgainer, or have a fast metabolism, then Serious Mass is the better choice because it has twice the calories of Pro Gainer and has been used successfully by tens of thousands of people.

On the other hand, if you want to gain good quality weight and would prefer a supplement with more protein and fewer carbohydrates, then Pro Gainer is the way to go because it has 650 calories, 85g of carbs, and 60g of protein.

As I’ve said throughout this Optimum Nutrition Pro Gainer vs Serious Mass comparison, both supplements have been proven to work well, and it pretty much boils down to whether you want a bit more protein (Pro Gainer) or a lot more carbs and calories (Serious Mass).

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Andy Williams
Andy Williams is a UK-based personal trainer and bodybuilder who coaches gym-goers of all levels using proven evidence-based techniques in strength training, nutrition, and supplementation. He’s tested over 70 different mass gainers for their ingredient quality and muscle-building effectiveness and regularly shares his findings in his mass gainer reviews.
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