Whey protein is one of the most popular supplements on the planet.
But despite its many health benefits, there’s 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.
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 ().
- Whey protein concentrate: Contains roughly 70–80% protein. It’s the most common type of whey protein and has more lactose, fat and minerals from milk.
- Whey protein isolate: Contains 90% protein or more. It’s more refined and has less lactose and fat, but it also contains fewer beneficial minerals.
- Whey protein hydrolysate: This form is pre-digested, allowing your body to 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 can help you recover from exercise, build muscle and strength and even lose weight by reducing your appetite and boosting your metabolism (, , ).
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.
You can take whey protein simply by mixing it with water or a liquid of your choice.
Despite its health benefits, some people are concerned about its safety.
That said, whey protein is safe for most people and a convenient way to increase your protein intake.
Summary: Whey protein is generally safe and can help you build muscle and strength, lose weight, reduce your appetite and boost your metabolism.
Most of whey protein’s side effects are related to digestion.
Some people have problems digesting whey protein and experience symptoms such as bloating, gas, stomach cramps and diarrhea (5).
But most of these side effects are related to lactose intolerance.
Lactose is the main carb in whey protein. People who are lactose intolerant don’t produce enough of the enzyme lactase, which your body needs to digest lactose (5).
Moreover, lactose intolerance is incredibly common and can affect up to 75% of people worldwide ().
If you are lactose intolerant, try switching to a whey protein isolate powder.
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 ().
Alternatively, try a non-dairy protein powder, such as soy, pea, egg, rice or hemp protein.
Summary: Whey protein may cause uncomfortable symptoms in people with lactose intolerance. If you experience uncomfortable symptoms, 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 may be allergic to it.
Nevertheless, cow’s milk allergies are very rare in adults, since up to 90% of people with cow’s milk allergies outgrow them by the age of three ().
Symptoms of a cow’s milk allergy may include hives, rashes, facial swelling, throat and tongue swelling and a runny or stuffy nose (9).
In some cases, a cow’s milk allergy may trigger anaphylaxis, a severe, life-threatening allergic reaction.
Again, it’s worth remembering that a cow’s milk allergy is 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. However, an intolerance is caused by an enzyme deficiency and does not involve the immune system (10).
If you have a cow’s milk protein allergy, try a non-dairy protein powder, such as soy, pea, egg, rice or hemp protein.
If you are unsure whether your symptoms are due to an allergy or intolerance, it’s best to check with your doctor.
Summary: Those who are allergic to cow’s milk may also be allergic to whey protein. Nevertheless, cow’s milk allergies are very rare in adults.
Constipation is not a normal side effect of whey protein.
For a few people, a lactose intolerance may cause constipation by slowing the movement of the gut (, 12).
However, constipation is more likely caused when 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 ().
If you suspect that whey protein makes you constipated, check whether you are eating enough fruits and vegetables. You can also try taking a soluble fiber supplement.
Another reason why replacing whole foods with whey protein is a bad idea is because it may increase your risk of nutrient deficiencies.
Whole foods, especially fruits and vegetables, are nutrient-rich and contain a variety of minerals necessary for optimal health.
Therefore, it’s important to keep eating a balanced diet while you’re taking whey protein.
Summary: You may be at risk of constipation and nutrient deficiencies if you replace fruits and vegetables in your diet with whey protein. Eating a balanced diet can help counter these effects.
Eating a high-protein meal can raise the pressure inside the kidneys and cause them to filter more blood than usual (14, ).
However, this does not mean that a high-protein meal harms the kidneys.
In fact, studies show that this is a normal bodily response and not usually a cause for concern (, ).
Moreover, there is no evidence that too much protein can damage the kidneys of healthy people (, ).
For example, a detailed review of 74 studies on protein’s effects on the kidneys concluded that there is no reason to restrict protein intake in healthy people ().
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 (, ).
If you have an existing kidney condition, then it’s best to check with your doctor about whether whey protein is fine for you.
Summary: There is no evidence that too much protein can damage the kidneys in healthy people. However, people with an existing kidney condition should check with their doctor about whether whey protein is right for them.
No evidence shows that too much protein can damage the liver in healthy people ().
In fact, the liver needs protein to repair itself and convert fats to lipoproteins, which are molecules that help remove fats from the liver ().
In a study of 11 obese women, 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% ().
One case report implied that a 27-year old male could have suffered liver damage after taking whey protein supplements ().
However, he was also taking a variety of other supplements. Doctors were also unsure if he was taking anabolic steroids, which can damage the liver (24).
Considering that thousands of people take whey protein without liver problems, this single case provides insufficient evidence that whey protein can damage the liver.
Although, a high protein intake may harm people who have cirrhosis, a chronic liver disease (, ).
The liver helps detoxify harmful substances in the blood like ammonia, which is a by-product of protein metabolism ().
In cirrhosis, the liver cannot function properly. So a high protein intake may increase ammonia levels in the blood, which may damage the brain (, ).
If you have liver disease, check with your doctor before taking whey protein.
Summary: There is no evidence that too much protein can damage the liver in healthy people. However, people with liver disease should check with their doctor about whether whey protein is safe for them.
The relationship between protein intake and bones 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 disease characterized by hollow and porous bones (29).
This idea came from earlier studies that showed a higher protein intake made urine more acidic (, ).
In turn, the body would release more calcium from bones to act as a buffer and neutralize the acidic effects ().
However, newer research has shown that the body counters the effects of calcium loss by increasing calcium absorption from the gut (, ).
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 ().
Furthermore, several studies suggest that elderly people, who are prone to osteoporosis, should eat more protein to help maintain strong bones (, ).
Summary: There is no evidence that whey protein can cause osteoporosis. In fact, whey protein may help prevent the disease.
Whey protein is generally safe and can be consumed by many people without side effects.
A commonly suggested dose is 1–2 scoops (25–50 grams) per day, but it’s recommended that you follow the serving instructions on the package.
Taking more than this is unlikely to offer more benefits, especially if you already eat enough protein.
If you experience uncomfortable symptoms like bloating, gas, cramps or diarrhea after taking whey protein, try switching to a whey protein isolate powder.
Alternatively, try a non-dairy protein powder, such as soy, pea, egg, rice or hemp protein.
Summary: The recommended daily dose of whey protein is 1–2 scoops (25–50 grams). If you suffer from digestive symptoms, try a whey protein isolate or non-dairy protein alternative.
Whey protein is safe and many people can take it without adverse effects.
However, it may cause digestive symptoms in those with lactose intolerance, and those allergic to cow’s milk may be allergic to it.
If you experience side effects, try a whey protein isolate or non-dairy protein alternative.
Despite these exceptions, whey protein is one of the best supplements on the market. It has a variety of research to support its beneficial roles in strength and muscle building, recovery and weight loss.