Are you thinking about using mass gainers to bulk up? While these supplements can help you gain weight, you should know about mass gainer side effects before you start taking them.
Mass gainer side effects include weight gain, digestive issues, kidney problems, insulin resistance, liver damage, allergic reactions, diarrhea, breathing difficulties, dehydration, cramps, flatulence and nutrient imbalances.
In this article, I’ll walk you through the seven most common side effects of mass gainers that you should know about. Understanding these risks will help you make better choices for your fitness journey.
Table of Contents
- 1. Weight Gain
- 2. Digestive Issues
- 3. Kidney Disease
- 4. Insulin Resistance
- 5. Liver Problems
- 6. Allergic Reactions
- 7. Diarrhea
- How to Minimize Mass Gainer Side Effects
- When to See a Doctor
- FAQ’s
- Final Thoughts
1. Weight Gain
When you take mass gainers, weight gain is expected, that’s their purpose! But not all weight gain is the same.
Good vs Bad Weight Gain
Mass gainers can cause:
- Muscle weight – what most users want
- Fat weight – what most users don’t want
Many people don’t realize that mass gainers are packed with calories. One serving can contain 500-1200 calories! If you don’t burn these extra calories through exercise, they turn into fat instead of muscle.
Who Should Be Careful?
You should think twice about using mass gainers if:
- You have a slow metabolism
- You don’t exercise regularly
- You already struggle with weight issues
Quick Tip: Always check the calorie content of your mass gainer and adjust your daily food intake accordingly.
2. Digestive Issues
Your stomach might not be ready for what mass gainers bring to the table!
Common Digestive Problems
Many users report these problems after taking mass gainers:
- Stomach pain
- Bloating
- Indigestion
- Nausea
These mass gainer side effects happen because these supplements contain concentrated amounts of protein, carbs, and other ingredients that can be hard for your digestive system to process all at once.
How to Reduce Digestive Issues
Try these simple fixes:
- Start with half the recommended serving
- Gradually increase your serving size
- Make sure to drink plenty of water
- Take your mass gainer with food instead of on an empty stomach
3. Kidney Disease
This is one of the more serious mass gainer side effects that people often overlook.
Why It Happens
Mass gainers typically contain high amounts of protein. When you consume too much protein, your kidneys work overtime to filter it. Over time, this extra strain can lead to:
- Kidney damage
- Reduced kidney function
- Kidney stones
Warning Signs
Watch out for these symptoms:
- Lower back pain
- Changes in how often you pee
- Swelling in your hands, feet, or face
- Feeling tired all the time
If you notice any of these signs while taking mass gainers, talk to your doctor right away.
Who Is at Risk?
You should be extra careful with mass gainers if you:
- Already have kidney problems
- Have diabetes
- Have high blood pressure
- Are over 50 years old
4. Insulin Resistance
This is a hidden mass gainer side effect that many users don’t know about.
What Happens in Your Body
Many mass gainers contain lots of sugar and simple carbs. When you consume these regularly:
- Your blood sugar levels spike
- Your body releases insulin to manage blood sugar
- Over time, your cells may become less responsive to insulin
- This can lead to insulin resistance
Long-term Risks
If not addressed, insulin resistance can lead to:
- Type 2 diabetes
- Weight gain that’s hard to lose
- Higher risk of heart disease
Better Choices
Look for mass gainers that:
- Have complex carbs instead of simple sugars
- List a low glycemic index
- Contain less than 10g of sugar per serving
5. Liver Problems
Your liver is your body’s main detox organ, and mass gainers can put extra stress on it.
How Mass Gainers Affect Your Liver
Some mass gainers contain:
- Artificial ingredients
- Chemical additives
- High amounts of certain vitamins and minerals
All these need to be processed by your liver. When you take mass gainers regularly, especially at high doses, your liver has to work harder.
Signs of Liver Stress
Watch for these warning signs:
- Yellowing skin or eyes
- Dark urine
- Stomach pain
- Unusual tiredness
- Loss of appetite
Protecting Your Liver
To reduce these mass gainer side effects:
- Choose products with natural ingredients
- Avoid mass gainers with long lists of chemicals
- Take breaks from using mass gainers
- Drink plenty of water
6. Allergic Reactions
Mass gainers contain many ingredients, increasing the chance of allergic reactions.
Common Allergens in Mass Gainers
Be aware of these common triggers:
- Whey protein (from milk)
- Egg proteins
- Soy ingredients
- Wheat or gluten
- Artificial flavors and colors
Symptoms to Watch For
Allergic reactions can show up as:
- Skin rashes or hives
- Itching
- Swelling, especially of lips, face, or throat
- Trouble breathing
- Upset stomach
Safety First
Before starting any mass gainer:
- Read the ingredient list carefully
- Start with a small amount to test your reaction
- Stop using it immediately if you notice any unusual symptoms
- Seek medical help for severe reactions
7. Diarrhea
This unpleasant side effect is one of the most common complaints among mass gainer users.
Why It Happens
Diarrhea from mass gainers usually occurs because:
- Your body can’t absorb all the nutrients at once
- Lactose intolerance (many mass gainers contain dairy)
- Sugar alcohols used as sweeteners
- High concentration of minerals
Managing This Side Effect
If you experience diarrhea:
- Mix your mass gainer with food instead of just liquid
- Try lactose-free options
- Switch to a different brand
- Reduce your serving size
Remember: Diarrhea can lead to dehydration, so drink extra water if you experience this side effect.
How to Minimize Mass Gainer Side Effects
Follow these guidelines to reduce your risk:
- Start slow – Begin with half the recommended dose
- Stay hydrated – Drink more water than usual
- Choose quality – Look for products with natural ingredients
- Listen to your body – Stop if you notice concerning symptoms
- Consult a professional – Talk to a doctor or nutritionist before starting
When to See a Doctor
Get medical help right away if you experience:
- Severe allergic reactions
- Persistent digestive problems
- Signs of kidney or liver issues
- Unusual heart rate or blood pressure changes
FAQ’s
No, I don’t recommend taking mass gainer every day. Your body needs breaks to avoid side effects like digestive issues and kidney strain. Use it 3-4 times weekly instead.
Yes, mass gainers can help skinny guys gain weight when combined with strength training. But watch for side effects and focus on getting nutrients from whole foods too.
Avoid taking mass gainers on an empty stomach, mixing with milk if lactose intolerant, consuming before bed, and using alongside other high-protein supplements.
Final Thoughts
Mass gainers can be helpful for some people, but they come with risks. Being aware of these mass gainer side effects will help you decide if they’re right for you.
Remember that the safest way to gain weight is through a balanced diet and proper exercise program. No supplement can replace the benefits of whole foods and smart training.
Have you experienced any side effects from mass gainers? What alternatives have worked better for you? Share your experience in the comments below!
Ajay Rathod is the founder of Fitness Zain. He shares easy-to-follow tips on fitness, healthy eating, and wellness. His goal is to help people live strong, active, and healthy lives.