Whey protein is used by some athletes to help improve muscle growth and training recovery with few side effects. However, more research is needed to fully understand its long-term effects.

Whey protein is a popular supplement among athletes and people looking to build muscle mass.

In addition to its many health claims, there’s also some controversy surrounding its safety.

Some claim that too much whey protein can damage the kidneys and liver and even cause osteoporosis.

This article provides an evidence-based review of whey protein’s safety and side effects.

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Whey protein is a popular fitness and dietary supplement.

It’s made from whey, which is the liquid that separates from milk during the cheese-making process. The whey is then filtered, refined and spray-dried into whey protein powder.

There are three main types of whey protein. The key difference between them is how they are processed (1, 2, 3).

  • Whey protein concentrate: Contains roughly 35–80% protein. It also contains lactose, fat, and minerals from milk.
  • Whey protein isolate: Contains 90-96% protein. It contains very little lactose or fat.
  • Whey protein hydrolysate: This form is pre-digested, which may help your body absorb it faster.

Whey protein is a popular choice among athletes, fitness enthusiasts and people wanting to build muscle or lose weight.

Studies show it may help athletes recover from exercise, build muscle, and gain strength as part of a resistance training routine, particularly for young adults without health conditions (2, 4)

In addition, some research suggests whey protein may aid weight loss for people with overweight and obesity. Consuming more protein may help people feel fuller, which could help with weight loss (5, 6).

Whey protein is also a complete source of protein, meaning it contains all the essential amino acids. Your body cannot make essential amino acids, so it’s important to get enough of them from your diet (NEW3).

Eating foods high in protein, such as lean protein, seafood, eggs, and nuts, can help you increase protein in your diet. If dietary approaches are not enough to meet your training goals, whey protein supplements are an option to increase your protein intake.

While whey protein has several reported health benefits, some people are concerned about its safety.

Based on current research, whey protein is generally considered safe for athletes who wish to add more protein to their diet. However, the National Institutes of Health advise caution when consuming high amounts of protein. Experts say more data is needed on potential adverse effects of high protein intakes (7).

It’s always a good idea to talk with a doctor before adding any supplements to your diet.


Whey protein is generally believed to be safe for athletes who want to increase their protein intake, though more studies are needed. It may help you build muscle and strength, lose weight, and reduce your appetite.

Several of whey protein’s reported side effects are related to digestion.

For some people, these side effects may be related to lactose intolerance.

Some people have problems digesting lactose, which can cause symptoms such as bloating, gas, stomach cramps and diarrhea (8).

Lactose is the main carb in many whey protein supplements.

People who are lactose intolerant don’t produce enough of the enzyme lactase, which your body needs to digest lactose. Lactose intolerance is incredibly common and can affect up to 65% of people worldwide (8).

If you are lactose intolerant, you might consider using a whey protein isolate supplement instead of whey protein concentrate.

Whey protein isolate is more refined, with a significantly smaller amount of fat and lactose than whey protein concentrate. People with lactose intolerance can often safely take whey protein isolate (9).

Non-dairy protein powders are also available, such as soy, pea, egg, rice or hemp protein. Read the label to check whether a product is free of lactose, and to see if it meets your nutritional goals.

You can also prevent digestive side effects from protein supplements by avoiding supplements, and eating protein-rich foods instead.


Whey protein supplements may cause digestive symptoms in people with lactose intolerance. If you experience uncomfortable symptoms, consider eating high-protein foods instead, or try switching to whey isolate powder or a non-dairy protein powder.

Because whey protein comes from cow’s milk, people with a cow’s milk allergy can be allergic to it. People with a cow’s milk allergy are typically advised to avoid milk products such as whey protein (10).

Cow’s milk allergy is relatively common among children, affecting 2-3% of children younger than 3 years old. However, it’s less common in adults. About 80% of people with cow’s milk allergy outgrow the condition by the age of 16 (8).

Symptoms of a cow’s milk allergy may include hives, rashes, facial swelling, throat and tongue swelling and a runny or stuffy nose (11).

In some cases, a cow’s milk allergy may trigger anaphylaxis, a severe, life-threatening allergic reaction. Signs of a severe allergic reaction include swelling in your lips, tongue, or throat, or difficulty breathing. If you suspect a severe allergic reaction, get medical attention right away.

Again, it’s worth remembering that a cow’s milk allergy is relatively rare in adults, but it can have severe consequences.

Moreover, an allergy to whey protein should not be confused with lactose intolerance.

Most allergies occur when the body produces an immune response to a protein. Lactose intolerance is different from an allergy. It is caused by an enzyme deficiency (12).

If you have a cow’s milk allergy, try a non-dairy protein powder, such as soy, pea, egg, rice or hemp protein. Be sure to read labels carefully to check whether a product is safe for people with cow’s milk allergy. Instead of supplements, you can also increase the amount of protein in your diet by eating more protein-rich foods.

If you are unsure whether your symptoms are due to an allergy or intolerance, it’s best to check with your doctor.


Those who are allergic to cow’s milk may also be allergic to whey protein, and are typically advised to avoid milk products such as whey. Cow’s milk allergy is rare in adults, but reactions can be potentially be severe.

Whey protein supplements may cause digestive problems for people with lactose intolerance. In some cases, lactose intolerance may cause constipation by slowing the movement of the gut (13, 14).

Constipation may also happen if people eat fewer fruits and vegetables in favor of whey protein, especially when they’re on a low-carb diet.

Fruits and vegetables are a great source of fiber, which helps form stool and promotes regular bowel movements (15).

If you suspect that whey protein makes you constipated, check whether you are eating enough fruits and vegetables. It’s also a good idea to talk with your doctor, who can help diagnose the cause of constipation.

In theory, replacing other foods with protein supplements could increase your risk for nutrient deficiencies. Many whole foods are nutrient-rich and contain a variety of vitamins and minerals necessary for optimal health. Protein supplements may not provide the same nutrition.

Major changes to your diet should always be discussed with your doctor or a registered dietitian first.


You may be at risk of constipation and nutrient deficiencies if you replace whole foods such as fruits and vegetables in your diet with whey protein. Talk with your doctor or a dietitian before making major changes to your diet.

A high-protein diet may cause your kidneys to work more to filter your blood. Over time, this increased workload could cause kidney damage or make kidney disease worse (16, 17).

However, the evidence is mixed. Some research suggests that the increased filtering work is not actually harmful for your kidneys. For people who do not have other health conditions, a high protein diet may not increase the risk of kidney damage (18, 19).

For example, a review of 74 studies on protein’s effects on the kidneys concluded that there is no reason to restrict protein intake in healthy people (20).

That said, there is evidence that a high-protein diet can be harmful for people with kidney disease.

Studies show that a high-protein diet in those with kidney disease may further damage the kidneys (21, 22).

If you have an existing kidney condition or another health condition, it’s important to check with your doctor before trying whey protein supplements.


It’s unknown whether high protein intake could damage your kidneys. Some experts suggest it’s unlikely to cause harm in people without health conditions. However, there appear to be greater risks for people with kidney conditions. Ask your doctor if whey protein is right for you.

In an older 2001 statement, the American Heart Association suggests that eating more protein than your body needs could create extra work for your liver. In turn, it’s possible that this extra workload could lead to liver damage (23).

However, others have suggested there is little evidence that too much protein can damage the liver in healthy people (24).

Your liver uses some of the protein you eat to repair itself and convert fats to lipoproteins, which are molecules that help remove fats from your liver (25).

In a small study of 11 obese females, taking 60 grams of a whey protein supplement helped reduce liver fat by approximately 21% over four weeks.

Moreover, it helped reduce blood triglycerides by approximately 15% and cholesterol by about 7% (26).

One case report suggested that a 27-year old male could have suffered liver damage after taking whey protein and creatine supplements (27).

However, more evidence is needed to understand the potential connection between whey protein and liver damage.

A high protein intake may harm people who have hepatic encephalopathy. This condition is a potential complication of severe liver disease (28, 29).

Your liver helps remove harmful substances such as ammonia from your blood. Ammonia is produced when your body digests protein (27).

With severe liver disease, the liver cannot filter very well. In such cases, a high protein intake may lead to high levels of ammonia in the blood, which can potentially damage the brain (29, 30).

If you have liver disease or another health condition, be sure to check with your doctor before taking protein supplements, including whey protein.


Some experts suggest that too much protein could lead to liver damage in healthy people, while others say there is no reason for concern. However, people with liver disease or other health conditions should check with their doctor about whether whey protein is safe for them.

The relationship between protein intake and bone health has created some controversy.

There is some concern that too much protein may cause calcium to leach from the bones and increase the risk of osteoporosis, a condition characterized by hollow and porous bones (31).

This idea came from earlier studies that showed a higher protein intake made urine more acidic (32, 33).

In turn, the body would release more calcium from bones to act as a buffer and neutralize the acidic effects (33).

However, newer research has shown that the body counters the effects of calcium loss by increasing calcium absorption from the gut (34, 35).

In an analysis of 36 studies, scientists found no evidence that eating too much protein was bad for bone health.

In fact, they came to the conclusion that eating more protein was actually beneficial for bone health. These benefits were found to affect an area of your back called the lumbar spine (36).

Furthermore, several studies suggest that older people, who are prone to osteoporosis, should eat more protein to help maintain strong bones (37, 38).


Some early research indicates that high protein intake may lead to osteoporosis. But more recent studies suggest eating a high protein diet may not affect bone health, or may even promote healthy bones.

You can take whey protein powder simply by mixing it with water or a liquid of your choice.

It’s important to follow the serving instructions on the package. Taking more than the listed amount is not recommended. Also, be sure to follow any additional directions that may be provided by your doctor or dietitian.

In general, it’s a good idea to talk with your doctor before adding supplements to your diet.

If you have lactose intolerance, you may find whey protein isolate or non-dairy protein powders easier to tolerate. Non-dairy protein powders may come from sources such as pea, egg, rice or hemp.

People with cow’s milk allergy should not take whey protein, because it is a milk product.


When taking a whey protein supplement, be sure to follow the serving instructions on the package. Do not take more than the recommended amount.

Whey protein is a popular supplement. It’s claimed to have benefits for athletes who wish to increase muscle mass or recover faster when training, with few side effects. Some suggest it may also aid weight loss.

However, research suggests both potential benefits and some risks related to whey protein and high protein diets in general. More studies are needed to understand the possible long-term effects of high protein intake, and the effects of whey specifically.

If you’re interested in trying whey protein supplements, it’s a good idea to talk with your doctor first. This is especially important for people with health conditions, including liver or kidney conditions.

Some people may wish to try eating more protein-rich foods instead of using supplements. If you experience digestive side effects from whey protein supplements, you might consider trying whey protein isolate or a non-dairy protein alternative.

Whey protein is not appropriate for people with cow’s milk allergy because it could cause an allergic reaction.