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Optimum Nutrition Serious Mass Review: Is It Safe and Effective?

By Gavin Van De Walle, MS, RDN, LN

Published on March 10, 2022

Medically Reviewed by Natalie Olsen, MS, RDN

Dietitian Rating:


About This Rating
The average rating of this product is calculated based on the evaluation of the following factors:
  • Support for Claims:4.0
  • Ingredient Safety:4.0
  • Value for the Price:4.0
  • Brand Transparency:4.0

Optimum Nutrition Serious Mass is a mass gainer supplement packed with calories, protein, and carbohydrates. Using this product after your workout or in between meals can help boost calorie intake and support muscle building and weight gain.

Written by
Gavin Van De Walle, MS, RDN, LN
Registered Dietitian Nutritionist, Human Nutrition and Exercise Physiology
Gavin P. Van De Walle obtained his master's degree in human nutrition and exercise physiology, during which, he researched the impact of nitrate supplementation on exercise performance and published in findings in the Journal of Strength and Conditioning Research.
Medically Reviewed by
Natalie Olsen, MS, RDN, LD, ACSM-EP
Registered Dietitian, Certified Exercise Physiologist
Natalie is a registered dietitian, functional medicine practitioner and certified exercise physiologist with over 15 years experience in the health and wellness industry and holds a Master's degree in Human Nutrition and Functional Medicine through a collaborative program provided by the University of Western States and the Institute of Functional Medicine.
Optimum Nutrition Serious Mass Review: Is It Safe and Effective?
Photo credit: iStock.com/glegorly


  • Contains 1,250 calories and 50 grams of protein per serving to support muscle building and weight gain.
  • Contains 25 essential vitamins and minerals as well as ingredients that can improve exercise performance like creatine monohydrate.
  • It's a great value compared to similar weight gainer supplements.


  • There is the potential for digestive problems, particularly in people with food intolerances.
  • An increase in fat gain is likely if you routinely take this product without exercising.

What Is Optimum Nutrition Serious Mass?

Manufactured by Optimum Nutrition, Serious Mass is a mass gainer supplement that provides plenty of calories, carbohydrates (carbs), and protein to support muscle building and weight gain.

Each serving provides:

  • Calories: 1,250
  • Fat: 4.5 grams
  • Carbs: 252 grams
  • Protein: 50 grams

Glanbia Performance Nutrition owns Optimum Nutrition and other leading sports and lifestyle nutrition brands, including SlimFast, Amazing Grass, and Bio-Engineered Supplements and Nutrition (BSN), among others.

Due to its high calories content, Serious Mass can be a good option for people who struggle to eat enough calories from food alone to either maintain their weight or gain weight.

Consistently eating more calories than your body needs to support normal bodily functions and physical activity levels is necessary to gain weight.

Serious Mass is best taken when combined with an exercise program that incorporates weight training to promote weight gain primarily from muscle rather than fat.

Taking this product after an intense workout can support muscle recovery and building processes, but it can also be taken in between meals or before bed.

Serious Mass isn’t intended to be used in place of eating whole foods, but rather as a supplement to your current diet.

To make a Serious Mass shake, add one serving to a blender filled with 24 ounces of cold water, milk, or other beverage, and blend for 30–45 seconds until dissolved.

A serving size is two scoops, but Optimum Nutrition recommends that new users start with one scoop, or half of a serving, for the first week and then gradually increase to the full, two-scoop serving.

This can help prevent or reduce stomach discomfort that new users may experience.


Optimum Nutrition Serious Mass is a high-calorie weight gainer supplement that supports muscle building and weight gain.

Is It Effective?

Serious Mass claims to support muscle building and weight gain goals.

Although there are no published studies on Serious Mass directly, it provides plenty of nutrition to support these claims when taken in combination with an exercise routine and used to supplement your usual diet.

Muscle Building

Building muscle requires a combination of weight training and good nutrition.

Weight training is the driving force behind building new muscle, while good nutrition provides the building blocks and fuel to support the process.

Protein is necessary for repairing and building new muscle, while carbs provide the energy you need to train long and hard.

With 50 grams of protein and 252 grams of carbs, Serious Mass provides plenty of nutrition to support muscle building and replenish your energy stores to ensure you're ready to tackle the next workout.

Serious Mass also provides three grams of creatine monohydrate.

Creatine monohydrate is one of the most studied and effective sports supplements for increasing muscle, size, strength, and power. (1)

However, unless you plan to take Serious Mass every day, it's best and more cost-effective to purchase creatine monohydrate and supplement with it alone on days that you don't use Serious Mass.

This is because creatine monohydrate has no immediate performance-enhancing effects.

Its benefits are only realized once your muscle creatine stores are fully saturated with creatine, which can take up to 28 days with a daily 3-gram dose. (1)

Along with creatine, Serious Mass contains 25 vitamins and minerals to support immune health and fluid balance, as well as help convert food to energy.

Weight Gain

While many people desire to lose weight, others can benefit from gaining weight.

Gaining or regaining weight can be beneficial for people who are:

  • recovering from a serious illness
  • below a healthy body weight and want to feel better
  • athletes who want to perform betters at their sports
  • older adults who have lost weight unintentionally

Providing 1,250 calories per serving, Serious Mass can easily promote weight gain when consumed with your normal diet.

For reference, a 2,000-calorie diet is considered standard and a general guide for nutrition advice.

Of course, calorie needs are based on various factors like age, gender, body weight, and physical activity level, but understanding that Serious Mass supplies more than 60% of most people's calories in one serving is pretty impressive.

But it's not just the significant number of calories supplied by Serious Mass that can make it effective for weight gain, it's also how those calories are delivered.

Liquid calories tend to have less impact on fullness than calories from solid foods. (2)

In other words, it's much easier to drink an additional 1,250 calories per day than it is to eat them.

This can make the Serious Mass particularly beneficial for people who struggle to eat enough to maintain or gain weight due to a poor appetite or early satiety.


Serious Mass provides the calories and nutrients necessary to support muscle building and weight gain when used in combination with an exercise routine and when taken in addition to your usual diet.

Verdit on Claimed Benefits

Below is our summary of the evidence for the claimed benefits of Optimum Nutrition Serious Mass based on the available research:

Helps promote muscle gain4/5
Helps promote weight gain4/5

Side Effects and Safety

Serious Mass is likely safe for most people.

But because it contains eggs, milk, and soy, it may be unsuitable for people with certain food allergies and intolerances or vegetarians.

It may also be unsuitable for people with diabetes or congenital sucrase-isomaltase disease (CSID), a digestive disorder caused by the inability to digest and absorb certain carbs, due to its high content of maltodextrin, a highly-processed, fast-digesting carb.

All 252 grams of carbs that Serious Mass provides come from maltodextrin.

Serious Mass uses the artificial sweeteners sucralose and acesulfame potassium. Artificial sweeteners have been shown to disrupt gut health, increasing the risk of disease. (3)

Stomach problems are also possible, even in people without a food intolerance, with the use of Serious Mass, so it's best to start with half of a serving to assess your tolerance as recommended by the directions.

And although most people use a weight gainer supplement to gain size and weight, it's a good idea to monitor your weight when using this product to make sure you’re not gaining weight too fast, which is likely due to water retention and bloat and could be a sign you are not tolerating the product.

A good rate of weight gain to aim for is 0.025%–0.05% of your body weight each week, which equates to 0.4–0.8 pounds (0.2–0.4 kg) for a 150-pound (68-kg) person. (4)

Depending on your rate of weight gain and overall goals, you can adjust your calories accordingly.


Serious Mass may be unsuitable for vegetarians or people with allergies or intolerances to eggs, milk, soy, or maltodextrin. It may also cause minor stomach upset in new users who take a full serving.

Consider monitoring your weight when using Serious Mass to prevent excess fat gain.

Cost and Where to Buy

Serious Mass is one of the most popular weight gainer supplements on the market, so it's usually easy to find.

You can purchase it directly from Optimum Nutrition's website or from other online retailers like Amazon or Bodybuilding.com.

Popular sports supplement store chains like GNC and Vitamin Shoppe also carry Serious Mass in-store and online.

Serious Mass comes in a 6-pound tub or 12-pound bag, and you can choose from banana, chocolate, chocolate peanut butter, strawberry, or vanilla flavor.

Servings Cost
6-pound tub 8


($4.48–$6.25 per serving)

12-pound bag 16


($3.94 to $4.75 per serving)

The price ranges depending on where you buy and the flavor you choose.

Serious Mass costs more when you purchase it directly from Optimum Nutrition's website compared with the other channels. However, you’re provided with a 30-day money-back guarantee if less than 75% of the product has been used, which the other retailers might not offer.


Owing to its popularity, Serious Mass is widely available. However, the price can vary significantly depending on where you buy and the flavor. Purchasing directly from Optimum Nutrition's website guarantees you a 30-day return policy.

How Serious Mass Compares to Alternatives

Weight gainer supplements have long been in the cupboards of athletes and bodybuilders, but they are becoming increasingly popular among those looking to regain weight or just maintain their weight.

As such, more supplement companies have entered the weight gainer product category to meet the growing demand.

But not all weight gainer products are created the same, especially when it comes to their nutritional profile and price.

Here's a look at how Serious Mass stacks up in comparison with other popular mass gainers, including a different one from Optimum Nutrition:

Weight Gainer Calories


Carbs Protein Servings Price Other Ingredients
Optimum Nutrition Serious Mass 1,250 4.5 g 252 g

50 g

16 About $65 ($4.06/serving) 3 g creatine
Optimum Nutrition Pro Gainer 650

8 g

85 g

60 g

28 About $110 ($3.93/serving) 25 vitamins & minerals
Dymatize Super Mass Gainer 1,280

11 g

245 g

52 g

16 About $70 ($4.38/serving) 1 g creatine
BSN True Mass 1,220

17 g

215 g

50 g

15 About $60 ($4/serving) 3 minerals
MuscleTech Mass Tech Extreme 2000 2,050

6 g

440 g

60 g

18 About $140 ($7.78/serving) 10 g creatine
Naked Mass 1,250 2.5 g 252 g

50 g

11 About $70 ($6.36/serving) 5 vitamins & minerals

These prices were pulled from Amazon for consistency.


Comparatively, Serious Mass offers the best price point based on calories, macronutrients, and other ingredients.

Frequently Asked Questions

Is it good to take a mass gainer?

Mass gainers like Serious Mass are neither good nor bad. They are simply a tool to help you increase your calories and promote muscle building and weight gain.

However, you shouldn't rely solely on them as you want to get most of your nutrition from whole food sources when possible.

Does a mass gainer help build muscle?

Taking a mass gainer without regular training won't result in any muscle gain. Remember that training is what drives the muscle-building process, and nutrition is what fuels it.

Do mass gainers expire?

Mass gainers supplements like traditional protein supplements are best used within two years of their manufactured date, which you can find stamped on the tub or package.

Are mass gainers bad for the kidneys?

High-protein diets are thought to strain and damage the kidneys. And because mass gainers are high in protein, some people may be concerned that they can cause kidney damage.

The amount of protein in mass gainers is safe to take (around 50 grams per serving). The total amount of protein taken in a day over time is what matters most when it comes to kidney health. (5) (6)

Are mass gainers a waste of money?

While mass gainer supplements aren't needed, they can be a very helpful and relatively inexpensive way to increase your caloric intake and promote weight gain.

The Bottom Line

Optimum Nutrition Serious Mass is a high-calorie, -protein, and -carb supplement that supports weight gain when combined with weightlifting muscle building.

It can be a good option for people who struggle to eat enough calories from food alone to either maintain their weight or gain weight.

Serious Mass contains egg, soy, and milk, so it may be unsuitable for certain individuals. It can also cause stomach discomfort in new users, so it's best to start with half of a serving if you decide to try it.

While Serious Mass can be a convenient and relatively inexpensive way to increase your calorie and protein intake, make sure that you consume most of your calories from whole food sources, when possible, to best support your health and goals.

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At WellnessVerge, we only use reputable sources, including peer-reviewed medical journals and well-respected academic institutions.

  1. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine - PubMed:
  2. Effects of Solid versus Liquid Meal-replacement Products of Similar Energy Content on Hunger, Satiety, and Appetite-regulating Hormones in Older Adults:
  3. Artificial sweeteners induce glucose intolerance by altering the gut microbiota - PubMed:
  4. Nutrition Recommendations for Bodybuilders in the Off-Season: A Narrative Review:
  5. Changes in Kidney Function Do Not Differ between Healthy Adults Consuming Higher- Compared with Lower- or Normal-Protein Diets: A Systematic Review and Meta-Analysis - PubMed:
  6. The Effects of High-Protein Diets on Kidney Health and Longevity: