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Whey Protein Side Effects

As arguably the most popular type of bodybuilding supplement, its invariable that individuals will run into some type of side effects from time to time when using a given whey protein supplement. While whey protein consumption is not associated with any outright major adverse side effects, there a few common mild symptoms that can arise from time to time depending on the individual. Mild gastrointestinal complaints are the most common side effects experienced by users of whey protein supplements. Generally speaking, these are caused by either a lactose or protein intolerance.

Whey Protein Types & Side Effects

The degree to which a whey protein will elicit symptoms in an individual is often dictated by the type of whey protein.

Whey Protein Concentrate Side Effects

For example, whey protein concentrate (WPC) is the cheapest and most basic type of whey protein. This is because it undergoes the least amount of processing/filtration and therefore retains the most amount of fat and carbohydrate (mainly in the form of lactose). As such, WPC is the least preferred option for lactose intolerant individuals.

Whey Protein Isolate Side Effects

Whey protein isolate (WPI) on the other hand has much lower levels of fat and lactose, with some varieties claiming to have zero carbs and fat. Naturally, these type of WPI’s are ideal for individuals with lactose intolerance.

Guy Making protein shakeWhey Protein Hydrolysate

Whey protein hydrolysate is a rather peculiar one when it comes to side effects. While most whey protein hydrolysates contain background levels of fat and lactose (and therefore are not suitable for lactose intolerant individuals), on the other hand, they can be ideal for individuals with a degree of protein sensitivity and/or intolerance. Whey protein hydrolysates contain whey protein that has been pre-digested or broken down with specific enzymes to yield smaller peptides. However, whey hydrolysates vary in the degree to which they are broken down (dependant on the enzymes used), which in turn impacts their protein digestibility. This degree of breakdown is measured using a term called ‘degree of hydrolysis’. As such, individuals with relatively mild protein intolerance may be able to tolerate whey protein hydrolysates with a low degree of hydrolysis, while individuals with more severe or clinical protein intolerance/allergy may actually require specific whey protein hydrolysates with a high degree of hydrolysis. Cow’s milk allergy

In fact there are medical grade whey protein hydrolysates that are prescribed for children and adults with diagnosed protein intolerance. Such products typically contain protein that has been digested down to the point that it exists predominantly as dipeptides and tripeptides. In this form, protein requires virtually no digestion and passes straight into the small intestine. There are only a couple of whey protein hydrolysate supplements that specifically advertise the fact that they contain appreciable levels of dipeptides and tripeptides. But for individuals with medically diagnosed protein intolerance, it is best they seek advice from a qualified health care practitioner as to what protein supplements are most appropriate.

Whey Protein Hydrolysate and Cow’s Milk Protein Allergy

Cow’s milk protein allergy is a common issue in infants1-3 but can also occur in adults. While the symptoms of cow’s milk protein allergy are unspecific, they most frequently involve the skin (such as atopic dermatitis), the gastrointestinal tract (vomiting, diarrhea, constipation), the airways (wheezing, sneezing) are more general (colic)1,4. Extensively hydrolysed whey proteins are the preferred form of treatment for infants and adults suffering from cow’s milk allergy. While such products are typically of medical grade and only available through prescription from a suitably qualified healthcare practitioner, it does highlight the potential use of high grade whey protein hydrolysates by individuals with a mild to moderate degree of protein intolerance/allergy. It is always best, however, to get medical advice before trying a whey protein powder that has the potential to evoke an adverse reaction.


Protein Intolerance vs Lactose Intolerance

One of the confusing issues when it comes to common side effects of whey protein is discerning the difference between a sensitivity to protein or lactose. Often one is mistaken for the other and vice versa, which is probably part to blame on self diagnosis propagated by the internet.

One of the important, but lesser known aspects of lactose intolerance is that individuals vary widely in their degree of intolerance5. Some may be surprised to learn that most individuals with lactose intolerance actually have some ability to produce lactase (the enzyme required for breakdown of lactose) and as such digest a certain amount of lactose naturally occurring in dairy products or whey protein supplements. Given that the typical amount of lactose in a standard serve of a whey protein supplement will almost always be below 5g, the average individual with mild lactose intolerance should be able to tolerate a standard serve of most protein powders. This becomes even less of a concern when a lactose intolerant individual is consuming a high grade whey protein isolate, which characteristically contains less lactose than concentrates. Likewise, your typical whey protein hydrolysate will only contain 1-2g of lactose at best and therefore should not pose a problem for a typical lactose intolerant individual who is still able to produce some background lactase.

Excessive Whey Protein Intake

So what side effects can one expect if consuming excessive amounts of whey protein in the order of greater than 100-150g per day. This level of protein intake can pose a risk to kidney function. As such, any individual with a family history or suspected kidney disease should exercise extreme caution with the level of whey protein supplements they use. The liver is another major organ that can be adversely stressed when protein intake is very high. The liver detoxifies a by-product of protein intake called ammonia, which can be very toxic to the body if levels greatly exceed the normal physiological range. As such, any individuals with a family history or suspected liver disease need to exercise extreme caution with the amount of whey protein supplements they use.


When all is considered, your average whey protein supplement is one of the safest types of bodybuilding supplements on the market when used reasonably and according to the manufacturer’s directions. Most individuals with a mild degree of lactose intolerance should still be able to withstand a serve of whey protein each day due to the relatively low levels of lactose in your typical whey protein powder. However, individuals with known gastrointestinal disorders or allergies should consult with a suitable health care practitioner before using a whey protein powder. There are instances though where individuals with cow’s milk protein allergy may be able to tolerate a whey protein hydrolysate that is extensively hydrolysed. However, such decisions are again best made by a suitably qualified health care practitioner.


1. Koletzko S, et al. Diagnostic approach and management of cow’s milk protein allergy in infants and children: a practical guideline of the GI-committee of ESPGHAN. J Pediatr Gastroenterol Nutr 2012; 55: 221–9.
2. Sicherer SH. Epidemiology of food allergy. J Allergy Clin Immunol 2011; 127: 594–602.
3. Rona RJ, et al. The prevalence of food allergy: a meta-analysis. J Allergy Clin Immunol 2007; 120: 638–46.
4. Vandenplas Y, et al. Guidelines for the diagnosis and management of cow’s milk protein allergy in infants. Arch Dis Child 2007; 92: 902–8.
Mattar R, et al. Lactose intolerance: diagnosis, genetic, and clinical factors. Clin Exp Gastroenterol. 2012;5:113-21.


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