Here’s Why Mass Gainer Makes You Feel Sick

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Andy Williams
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There are various weight gainer side effects that you can experience, and feeling sick (or actually being sick) is the most common one. But why is that?

Well, as you’re about to learn, there are many reasons why mass gainers might make you feel sick, and it could be a combination of these factors that does the real damage.

So, in addition to illuminating the causes of mass gainer sickness, I’ll also explain how you can stop weight gainers from making you feel sick. Of course, these tactics won’t work for everyone, especially if you’re lactose intolerant. 

However, many gym-goers have successfully used these tips and tricks to make their mass gainers much less distressing for their stomachs, so hopefully, you can do the same.

Can Mass Gainer Make You Sick?

Mass gainer scoops positioned side by side

Yes, mass gainers can make you sick, both in terms of making you nauseous and actually making you vomit. 

Unlike protein shakes, mass gainers are loaded with calories, and when you add these additional calories into an already high-protein, high-carb bulking diet, your stomach can easily become overloaded, especially if you’re not used to eating so much food.

On the other hand, your body may be able to cope with the caloric volume, but the lactose from the whey and casein could be upsetting your stomach and making you feel sick. I’ll talk more about this in a second.

You may also be allergic to other, less well-known ingredients in your mass gainer formula. So, for this reason, I always recommend getting a weight gainer that uses natural ingredients that you can easily identify. This way, you know precisely what foods and nutrients you're putting inside your body.

Mass Gainer Makes Me Feel Sick, Why Is That?

Here are some of the most common reasons why drinking mass gainers might make you feel sick. Remember, there could be multiple reasons why weight gainers make you feel sick, so it could be a good idea to arrange a consultation with a gastroenterologist to rule out any underlying health condition that could be provoking your sickness.

Lactose Intolerance

A man rejecting a glass of milk because he's lactose intolerant

Some people struggle to break down the lactose contained within the milk proteins whey and casein, which can cause them to feel sick when they drink mass gainers and protein shakes. [1]

One way around this is to use supplements that have a 100% whey isolate formula and no whey concentrate. In other words, you’re looking for a lactose-free protein powder.

Unfortunately, most mass gainers are full of lactose. However, some aren’t, so it can be worth finding a weight gainer that doesn’t trigger your lactose intolerance.

Another option is to buy some lactose-free protein powder and then make your own high-calorie shake by adding oats, plant milk, and nut butter. This DIY option is more laborious, but it will definitely save you money and could stop you feeling sick as well.

Too Much Maltodextrin

Some maltodextrin powder

Most people agree that a bit of maltodextrin here and there won’t do you any harm. However, due to the low cost of maltodextrin, many supplement companies completely abuse it and flood their mass gainers with hundreds of grams of the stuff!

Research suggests that consumption of maltodextrin can harm your metabolic health by causing chronic low-grade intestinal inflammation. [2]

For this reason, you should stick to mass gainers that use oats (or a comparable carbohydrate) as the primary carb source. This way, you can protect your health, minimise or even eradicate nausea, and nourish your body with healthy fibre and natural carbohydrates.

While a small amount of maltodextrin is okay if it’s used to enhance the texture of a mass gainer, you definitely don’t want it to be the primary carb source in your gainer. The one exception to this could be if the maltodextrin is of the organic tapioca variety.

Drinking Your Mass Gainer Too Soon After a Workout

A muscular man drinking a mass gainer shake at the gym

After training, your digestive system isn’t as efficient at absorbing food because blood flow is diverted to your working muscles and major organs, leading to gut ischemia, which is essentially a reduction in intestinal blood flow. [3]

But what about the anabolic window?

Well, the post-workout window certainly isn’t a narrow 20-minute period in which you have to slam down a shake in order to avoid losing your gains. After all, if that were true, then the first few exercises in your workout would be in vain!

Still, to maximise muscle protein synthesis, you should probably have some kind of nutrition shortly after your workout. So, if a high-calorie mass gainer is too much, you could always have a protein shake and a banana, which should be easier to digest.

Drinking Your Weight Gainer Too Quickly

A man drinking a weight gainer

Because most mass gainers are loaded with maltodextrin and whey protein, they digest a lot faster than your whole food meals. 

As such, the rapid influx of 500+ calories can be quite overwhelming for your digestive system, especially if you’re skinny and/or aren’t accustomed to drinking high-calorie shakes.

So, try to drink your mass gainer more slowly. This is easier to do if you have a weight gainer that actually tastes good because you can actually sit back and savour the flavour rather than chug it as fast as possible while holding your nose and trying not to gag.

It Could Be The Artificial Sweeteners

Sachets of artificial sweeteners

Some people also believe that artificial sweeteners can cause stomach discomfort and make you feel sick. 

Whether this is due to the intensity of the sweetness or something else remains unclear, but if you want to play it safe, you should look for a mass gainer that uses natural flavourings rather than artificial ones.

How Can You Stop Mass Gainers From Making You Sick?

A mass gainer shake with chocolate powder

A good, practical way to stop mass gainers from making you feel sick is to rule out potential causes for your sickness and nausea by a process of elimination.

For many people, I’d say that the biggest culprit is excessive maltodextrin, so your first port of call should be to get a gainer that uses oats as the main carbohydrate source.

If this stops you from feeling sick, great! If not, you could always try a mass gainer that’s plant-based if you suspect that you’re lactose intolerant.

In general, it’s a good idea to look for a weight gainer that’s as natural as possible so that you don’t ingest any questionable ingredients that could upset your stomach and make you sick.

Learn More About Mass Gainers:

Conclusion: Is It Possible To Take Mass Gainer Without Feeling Sick?

Many people take mass gainers on a regular basis without feeling sick. However, the sheer calorie volume of your weight gainer can sometimes be overwhelming and cause you to feel sick, especially if you’re not used to drinking 500+ calories in a single sitting.

Also, some people are lactose intolerant, meaning that the whey and casein from their mass gainer can easily upset their stomach.

Similarly, most mass gainers are absolutely loaded with maltodextrin, which is well-known to cause stomach discomfort for a lot of people. This is why I always recommend selecting a mass gainer that contains oats rather than highly processed carbs like maltodextrin.


  1. Thornton, J. ". (2018, November 18). How to prevent being nauseous from protein shakes. LIVESTRONG.COM.
  2. Arnold, A. R., & Chassaing, B. (2019). Maltodextrin, modern stressor of the intestinal environment. Cellular and Molecular Gastroenterology and Hepatology, 7(2), 475–476.
  3. De Oliveira, E. P., & Burini, R. C. (2011). Food-dependent, exercise-induced gastrointestinal distress. Journal of the International Society of Sports Nutrition, 8(1).
A picture of Best Mass Gainer UK founder, personal trainer Andy Williams
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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