ON Pro Gainer Review: Best Ingredients for Lean Bulking?

Image of a shirtless man drinking a weight gainer

Optimum Nutrition is a giant in the supplement industry, and are perhaps most well-known for their Gold Standard line of products. Aside from their famous protein powder, they also make 3 different mass gainer supplements.

After trying out Serious Mass with great results, we decided to create a detailed Optimum Nutrition Pro Gainer Review, to see how effective it really is for sizing up.

Boasting more protein than weight gainers double its size, this is a bulking supplement that is quickly becoming one of our favorites.

And you'll soon learn why

Pro Gainer Nutrition facts

One Pro Gainer serving includes a moderate 85g of carbs, a remarkable 60g of protein, and only 8g of fats, which checks in at 650 calories overall. Only 8% of the carbohydrates are from sugars, and only 4g of the fats are saturated, making it an excellent lean gainer.

There's also a heap of vitamins and minerals, including an impressive 40% of the RDI for calcium, iron, and magnesium, which all play vital roles within the body.






Vitamins & Minerals



Whey Isolate, concentrate, calcium caseinate, egg whites




The other ingredients are maltodextrin and Aminogen®. Maltodextrin is the primary carb source while the latter is a relatively new type of digestive enzyme, and is especially useful during a weight gain or bulking phase for absorbing all the nutrients.  

Rounding off the ingredient label are common supplement sweeteners acesulfame potassium and sucralose, both of which a little controversial, but quite hard to avoid in products like these.

How Do The Ingredients Work?

True to form, ON Pro Gainer utilizes maltodextrin as it's primary carbohydrate source, which is by far the most common ingredient in modern-day weight gain supplements, and for a good reason, as you're about to find out.

Having a naturally high glycemic index, it provides the body with energy incredibly fast. However, unlike dextrose, maltodextrin is not sweet. But despite its rather bland taste, it can comfortably be consumed in large quantities without any real stomach distress.

But it gets better.

This rapid energy is used for muscle glycogen replenishment after training, and for creating a growth-triggering calorie surplus between meals, the holy grail of any weight gain goal.

Boasting a solid 60g protein dose for every 85g of carbs, ON Pro gainer has an excellent lean-gaining nutritional profile for those who don't want to spend half their calorie budget on a single shake.

Image of a shirtless man drinking a weight gainer

Who Can Benefit From Drinking It?

Whether you are seeking to gain a healthy amount of body weight, find the right supplement for your lean bulk, or even become a bodybuilder, Pro Gainer can help you along your weight gain journey.

However, those who will enjoy its best effects, are those who are seeking a gainer with a carefully matched carbs to protein ratio, or those who require only a moderate amount of calorie assistance from supplements.

It is not uncommon for weight gainers to contain five times more carbs than it does protein. While this certainly has its place in hardcore bulking diets, ratios like these are unfit for those who do not need an extraordinary amount of carbs.

Based on our Pro Gainer review, we rate it as the current best lean gainer on the market.

Offering more protein than many mass gainers twice its size, it is a top choice for sustainable weight gain and lean-bulking regimes. If you've been searching for a high protein weight gainer, go ahead and give Pro Gainer a try.

Side Effects And Disadvantages

Bloating Or Gas

Whether you like to admit it or not, if you're into working out, you've probably experienced protein farts at some point in time. Although they're not harmful, they're not exactly pleasant either. And with 60g of protein per scoop, this supplement may contribute to your gas problem, especially if you're overall protein intake is excessive.

How to avoid: don't eat more protein than is necessary. You won't build any more muscle by eating over the odds, and it may actually make you gain less weight, by decreasing your appetite.

Insufficient calories

Being engineered for lean gaining, Pro Gainer may be a little bit too tame for those with superhuman calorie needs. Of course, you could just take another scoop, but then you'll burn through the bag really fast.

How To Use Pro Gainer properly

  • Prepare 16 oz of cold water or milk in a shaker bottle
  • Add 1 heaping scoop (165g)
  • Shake until the powder is thoroughly mixed, then drink
  • Use a blender instead of a shaker cup to add in other calorie-contributing ingredients like nut butter, berries, and avocado (optional)

For best results use alongside a healthy, whole foods diet, with regular exercise.

When To Take

Image of a clock face

It can be taken anytime throughout the day to meet your calorie and macronutrient requirements. In particular, you may want to use it after training because it is a critical time for muscle repair and recovery.

You may also want to consider taking it before sleep. Although sleep is a restful time where recovery takes place, weight gain requires a surplus of calories, which Pro Gainer can contribute towards.

Sizes, Serving, And Scoop

It is available to buy in either a 5 lb tub that has 14 servings or in a resealable bag, which consists of 28 full dose servings.

The scoop is enormous in size and looks more like a shovel if you're used to just taking regular protein shakes. The total dose is around 165g of powder.

The Available Flavors

We went for Double Rich Chocolate this time around, but it's also available in Banana Cream Pie, Strawberry Cream, and Vanilla Custard if you're not much of a chocolate fanatic.

Image of a bar of chocolate

How Does It Compare To Other Mass Gainers?

If you want to see how Pro Gainer compares to some of Optimum Nutrition's other mass gainers, then you can check out our comparison chart below. Or, for more information on buying a weight gain powder, feel free to head over to our mass gainer reviews page, and see what other products take your fancy.


Our Rating

Best For




Naked Mass

Best of the Best



True Mass

The Tastiest



Pro Gainer

Lean Bulking



Overall Review

Overall, during this review, we were very pleased with this supplement and its protein to carbs ratio. With more protein per scoop than mass gainers twice its size, ON Pro Gainer packs a lot of punch considering its moderate 650 calorie mixture.

This weight gainer will help you add lean muscle and overall mass by replenishing lost muscle glycogen and contributing to a calorie surplus. If you are looking for one of the best mass gainers, but don't want a ton of carbs, we highly recommend this supplement.

We hope that you found our optimum Nutrition Pro Gainer review helpful, and hopefully, it makes deciding which brand to go for, a little bit easier.

Optimum Nutrition Pro Gainer | Best For Lean Bulking

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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.