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The "Real" Side Effects of Protein

Protein powder is arguably the most popular sports supplement, and it makes sense. Protein is made up of individual amino acids responsible for multiple different roles within the body -the most commonly discussed roles amongst the fitness community include muscle growth, recovery, and regulating other cellular functions.

Protein is the most taken dietary supplement on the market, but how safe is it?

But let’s face it, there’s an elephant in the room when it comes to protein powder, and it seems like no one wants to talk about it, which is understandable. Depending on your tolerability to dairy products, a few protein forms may leave you with what the fitness community so eloquently puts as “protein farts,” as well as other stomach issues.


If you respond well to dairy, you can go ahead and let out a sigh of relief -you won’t run into any negative side effects, just positive ones like increased gains and workout recovery. Even if you are slightly sensitive to lactose, many companies are now starting to throw in lactase to ingredient formulas to combat lactose intolerance.

Here’s a quick look at some of the most common protein powders found in sports supplements, so you can better understand protein powder side effects:


Whey protein takes the cake as the one of the most recognized protein powder in sports supplements, and that is mainly due to its ability to provide effective amounts of protein per serving and also its price. Whey protein is derived from cow’s milk –a byproduct from the process of making cheese.

Unless otherwise specified, most whey protein comes from cow's milk and is a by-product of making cheese.

Whey Protein Concentrate

Despite the discrepancy, one fact agreed upon is protein is important for everyone -from the gym bros clad in their muscle stringers and sweatbands down to the new girl at the gym looking to improve her physique and overall health. Keep in mind, however, everyone’s protein requirements differ depending on several life factors such as age, sex, and physical activity.

Lifestyle Choices and Health Conditions

Whey concentrate contains higher amounts of lactose compared to other whey protein powders. The lactose content in whey concentrate may be hard for some individuals to digest, causing bloating, cramps, and gas. 1,2

If you don’t respond well to lactose, check and see if the protein powder you are interested in is formulated with lactase, because if not, the last thing you’ll want to do is throw down 1-2 scoops of concentrate and then head over to the squat rack for some nice deep squats.

Whey Protein Isolate

Whey isolate is a more filtered whey form; consequently, it is slightly more expensive, but a higher quality protein powder nonetheless. Whey isolate undergoes a filtration process to remove the base component, making this whey form almost lactose- and cholesterol-free.

If you are only mildly sensitive to lactose, whey protein isolate is definitely a better option than concentrate, especially if lactase added to the protein powder formula.


Casein protein comes from cow’s milk, and is a very popular protein powder to take before bed due to its slow digesting property. This essentially means you get a prolonged protein digestion while you sleep.

However, casein protein does contain lactose as it is derived from milk. So, if you are severely intolerant to lactose or have an allergy to casein, you’ll want to avoid this protein powder, as supplementing with it, as well as other dairy products may cause some significant side effects like swollen lips and hives.2

If you are only slightly sensitive to lactose, casein might not cause many side effects, if any.
Most protein side effects are mild and extremely temporary and varies person to person.


Milk Protein Concentrate

Milk Protein is a concentrated milk protein form that contains whey and casein protein. This means that there are also trace amounts of lactose, which may cause some digestive discomfort for lactose-intolerant individuals.

Milk Protein Isolate

Much like whey protein isolate is a filtered form of whey concentrate, milk protein isolate is the filtered version of milk protein concentrate. Milk protein isolate undergoes a filtration process to remove large amounts of lactose.

If you are severely intolerant to lactose, you’ll probably want to steer clear of milk protein in general, or at least make sure that the milk protein isolate powder is also formulated with lactase to help combat the lactose.


In a word, yes. Protein can have some negative side effects on the gastrointestinal tract but it really depends on a individual basis. You may see some unappealing gas and maybe an upset stomach but this only happens to a small percentage of the population. But here is another example of the pros far outweigh the cons. Protein is a great supplement for putting on lean muscle. Take in moderation and with a good diet and you’ll be just dandy.

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Stefan R. Wilson
Stefan R. Wilson is a marketing professional, as well as a freelance author for nutritional supplements. He is based out of Salt Lake City, Utah and holds a BS from Brigham Young University. Stefan's expertise resides in the field of supplements to be used by athletes and bodybuilders while training.


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