Are mass gainers bad for your gut?

January 10, 2026 •

4 min read

Many mass gainer users report experiencing digestive discomfort, including bloating, gas, and cramps, especially during the first week of use. This reaction is often not a sign that mass gainers are inherently harmful but rather that certain ingredients or the high caloric load can pose a challenge to the digestive system.

Quick Summary

Mass gainers can lead to digestive issues like gas and bloating due to high calorie density, rapid consumption, lactose content, low-quality carbs, and artificial additives. These side effects can be managed by choosing clean formulas, opting for digestive enzymes, and adjusting serving sizes.

Key Points

Not Inherently Bad: Mass gainers are not automatically bad for gut health, but their specific ingredients and concentration can cause problems for some individuals.
Common Culprits: Digestive issues often stem from high calorie loads, lactose content (in whey/casein), low-quality carbs like maltodextrin, and artificial additives.
Choose Quality: Opt for mass gainers that include digestive enzymes, complex carbohydrates, and minimal added sugars to promote better digestion and nutrient absorption.
Adjust Your Intake: Start with smaller serving sizes and gradually increase as your body adapts to reduce initial digestive shock and discomfort.
Improve Habits: Mitigate side effects by staying well-hydrated, mixing your shakes thoroughly, and continuing to incorporate fiber-rich, whole foods into your diet.
Lactose-Free Alternatives: If you are lactose intolerant, choose mass gainers made with plant-based protein or whey protein isolate/hydrolysate to avoid bloating and gas.

The Ingredients Causing Gut Issues

Not all mass gainers are created equal, and the ingredients are a major determining factor in how your gut will react. The side effects are typically a result of the formulation rather than the concept of a mass gainer itself. By understanding the common culprits, you can make a more informed choice.

High Concentration of Macronutrients

Mass gainers are designed to pack a large number of calories into a single, often substantial, serving. This concentrated influx of protein and carbohydrates can overwhelm your digestive system, which is unaccustomed to processing such a high volume of nutrients at once. This can lead to a feeling of fullness, indigestion, and heaviness in the stomach. Your body needs time to adapt to this new intake level, which is why discomfort is common for beginners.

Lactose Content

One of the most frequent causes of digestive distress from mass gainers is lactose intolerance. Many formulas are built on dairy-based proteins, such as whey protein concentrate and casein. For individuals with a sensitivity or intolerance to lactose, this can result in significant bloating, gas, stomach cramps, and diarrhea. It's crucial for those with dairy sensitivities to read the ingredient list carefully and opt for a lactose-free or plant-based alternative.

Low-Quality Carbohydrates

To drive up the calorie count cheaply, some mass gainers rely on simple, low-quality carbohydrates like maltodextrin. While effective for adding calories, these simple sugars can cause rapid blood sugar spikes, which can interfere with the body's glucose-insulin metabolism over time. Furthermore, the large quantity of easily fermentable carbs can feed bad bacteria in the gut, leading to increased gas and discomfort. Choosing a formula with complex carbohydrates like oats, quinoa, or sweet potato offers a cleaner and more gut-friendly energy source.

Artificial Additives

Mass gainers often contain artificial sweeteners, colors, and preservatives to enhance flavor and shelf life. These additives can disrupt the delicate balance of the gut microbiome, potentially leading to long-term digestive issues. Many consumers prefer products with natural ingredients or minimal additives to reduce this risk.

How to Choose a Gut-Friendly Mass Gainer

Mitigating potential gut issues involves a proactive approach to selecting your supplement. Look for a mass gainer that prioritizes quality ingredients and digestive health.

Check for Digestive Enzymes: Many quality mass gainers now include a blend of digestive enzymes, such as Digezyme®, to help break down the protein and carbohydrates more efficiently. This can significantly improve nutrient absorption and reduce the likelihood of bloating and gas.
Prioritize Complex Carbohydrates: Opt for gainers that list complex carb sources like oats, barley, or quinoa instead of maltodextrin as the primary carb source. These provide sustained energy and are gentler on the digestive system.
Be Mindful of Added Sugars: A good mass gainer should have minimal added sugars, preferably less than 10 grams per serving. Excessive sugar can cause digestive upset and unwanted fat gain.
Consider Lactose-Free Options: If you are lactose intolerant, choose mass gainers with alternative protein sources, such as soy, pea, or hemp protein. Whey protein isolate or hydrolysate are also better-digested forms of dairy protein, containing less lactose than concentrate.


Feature	Typical Mass Gainer	Gut-Friendly Mass Gainer
Protein Source	High in whey concentrate (high lactose)	Whey isolate, plant-based protein, or casein
Carbohydrates	Often primarily maltodextrin or simple sugars	Complex carbs like oats, quinoa, or barley
Added Sugar	Often high to increase calorie count	Low added sugar, natural sweeteners
Digestive Aids	Rarely included	Fortified with digestive enzymes like Digezyme®
Fillers	May contain artificial colors and sweeteners	Minimal to no artificial additives

Tips for Minimizing Digestive Discomfort

If you're already using a mass gainer and experiencing issues, or want to prevent them from the start, here are some actionable tips:

Start Small and Go Slow: Begin with a half serving and gradually increase the amount as your body adjusts. This allows your digestive system to adapt to the higher volume of nutrients.
Stay Hydrated: Consuming a lot of protein and fiber requires more water. Increased hydration can help with nutrient absorption and ease digestion.
Blend It Better: Proper mixing can help avoid lumps, which can be tough on the stomach. Use a quality blender to create a smooth, easily digestible shake.
Split Your Intake: Instead of consuming one large shake, split your daily serving into two smaller shakes spread throughout the day. This reduces the load on your stomach at any one time.
Add Fiber: Increase your fiber intake from whole food sources to promote better digestion and regular bowel movements.
Pair with Whole Foods: Remember that mass gainers are supplements, not meal replacements. Always combine them with a balanced diet of whole foods to ensure you get a full spectrum of nutrients.

Conclusion

Mass gainers are not inherently bad for your gut, but they can cause digestive issues for sensitive individuals due to their concentrated formula and certain ingredients like lactose, maltodextrin, and artificial additives. However, these problems can be effectively managed by choosing a high-quality product with digestive enzymes and complex carbohydrates. By being mindful of your body's tolerance, starting with smaller servings, and pairing the supplement with a balanced diet and adequate hydration, you can safely use mass gainers to reach your muscle and weight gain goals without compromising your gut health. For those with specific digestive conditions or intolerances, consulting a healthcare professional is always the best course of action before starting a new supplement regimen.

An excellent resource for understanding how enzymes aid digestion can be found here: How to Use Digestive Enzymes for Weight Gain.

Frequently Asked Questions

Mass gainers can cause bloating and gas for several reasons, including a high volume of calories overloading the digestive system, high lactose content from dairy-based proteins like whey concentrate, or low-quality carbohydrate sources like maltodextrin that are difficult to digest.

Yes, look for mass gainers that contain digestive enzymes, use complex carbohydrate sources (like oats), and are made with whey isolate or a plant-based protein if you are lactose intolerant.

To prevent issues, start with a smaller, half-serving dose to let your body adjust. Ensure you are drinking plenty of water, as hydration aids digestion. You can also split the daily serving into smaller shakes throughout the day.

For those with lactose intolerance, the best options are mass gainers that use plant-based protein sources like soy, pea, or hemp protein. Alternatively, whey protein isolate and hydrolysate are also much lower in lactose than whey concentrate.

Yes, digestive enzymes like amylase, protease, and lactase can significantly improve the digestion and absorption of nutrients from mass gainers, helping to minimize gastrointestinal discomfort such as bloating and gas.

Mass gainers that are loaded with artificial additives and high amounts of simple sugars can potentially disrupt the balance of the gut microbiome. Opting for cleaner formulas with natural ingredients can help mitigate this risk.

While mass gainers offer convenience, getting a significant portion of your calories and nutrients from whole foods is generally better for overall health and gut function. Mass gainers should be used to supplement, not replace, a balanced whole-food diet.