Not all protein is created equal.

Some forms of protein, such as whey, are better than others.

Whey protein contains an incredible range of essential amino acids, which are absorbed quickly (1).

Numerous studies show that it can help you increase strength, gain muscle and lose significant amounts of body fat (2).

However, whey is more than just protein. It contains many other nutrients, some with potent biological effects.

In fact, it’s one of the best-studied supplements in the world.

This is a detailed article about whey protein — what it is, how it works and how it can help you achieve your fitness and health goals.

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Whey protein is a mixture of proteins isolated from whey, which is the liquid part of milk that separates during cheese production.

Milk actually contains two main types of protein: casein (80%) and whey (20%).

Whey is found in the watery portion of milk. When cheese is produced, the fatty parts of the milk coagulate and the whey is separated from it as a byproduct (3).

If you've ever opened a yogurt container to see liquid floating on top — that’s whey. Cheesemakers used to discard it before they discovered its commercial value (4).

After being separated during cheese production, whey goes through various processing steps to become what people generally recognize as whey protein — a powder that is added to shakes, meal replacements and protein bars (5).

Whey protein doesn't taste very good on its own, which is why it’s usually flavored. Chocolate-, vanilla- and strawberry-flavored powders are popular.

It's important to read the ingredients list, as some products may have unhealthy additives like refined sugar.

Taking whey protein is a convenient way to add 25–50 grams of protein on top of your daily intake.

This can be important for bodybuilders and gym enthusiasts, as well as people who need to lose weight or are simply lacking protein in their diet.

Most flavored whey proteins are also rather delicious and can be used to add an incredible taste to healthy recipes like smoothies.

Whey is generally well tolerated, though people with lactose intolerance need to be careful, and some people may even be allergic to it (6).

Summary Whey protein is a mixture of proteins in whey, which is a byproduct of cheese production. It’s usually sold as a flavored powder, which is added to shakes, meal replacements and protein bars.

Proteins are the main building blocks of the human body.

They're used to make various important things, including tendons, organs and skin, as well as hormones, enzymes, neurotransmitters and various molecules.

Proteins are also the building blocks of the contractile elements in your muscles.

They’re assembled from amino acids, smaller molecules that are linked together like beads on a string.

Some amino acids are produced by your body's cells, while others are supplied by the food you eat. The ones that you must get from foods are termed essential amino acids.

Proteins that supply all nine essential amino acids are the best, and whey protein is loaded with them.

It’s particularly high in important branched-chain amino acids (BCAAs) like leucine, and also contains a high amount of cysteine (7).

Studies show that leucine is the most anabolic (growth-promoting) amino acid, and cysteine can help boost levels of the cellular antioxidant glutathione (8, 9).

Whey protein appears to be particularly effective at stimulating growth in humans. In fact, human breast milk is 60% whey, compared to 20% in cow's milk (10).

Summary The proteins in whey are of a very high quality. They’re loaded with essential amino acids, including leucine and cysteine.

There are several popular types of whey protein.

Their main difference is in the way they have been processed.

  • Concentrate: About 70–80% protein; contains some lactose (milk sugar) and fat and has the best flavor.
  • Isolate: 90% protein, or higher; contains less lactose and fat and lacks a lot of the beneficial nutrients found in whey protein concentrate.
  • Hydrolysate: Also known as hydrolyzed whey, this type has been pre-digested so that it gets absorbed faster. It causes a 28–43% greater spike in insulin levels than isolate (11).

Whey protein concentrate seems to be the overall best option.

It’s the cheapest and retains most of the beneficial nutrients found naturally in whey. Many people also prefer the taste, which is probably due to the lactose and fat.

If you have problems tolerating concentrate, or you're trying to emphasize protein while keeping carbs and fat low, whey protein isolate — or even hydrolysate — may be a better option.

Keep in mind that even though concentrate is the most popular form, most studies have examined whey protein isolate.

Summary The main types of whey protein are concentrate, isolate and hydrolysate. They can vary in protein content, taste, digestibility and price.

The best-known use of whey protein supplements is for the purpose of increasing muscle mass and strength.

Whey protein is popular among athletes, bodybuilders, fitness models, as well as people looking to improve their performance in the gym.

The ways by which whey protein promotes muscle/strength gain include:

  1. Building blocks: It provides protein and amino acids, which serve as building blocks for increased muscle growth.
  2. Hormones: It increases the release of anabolic hormones that can stimulate muscle growth, such as insulin (12).
  3. Leucine: It’s high in the amino acid leucine, which is known to stimulate muscle protein synthesis at the molecular and genetic level (13, 14).
  4. Fast absorption: Whey protein is absorbed and utilized very quickly compared to other types of protein (15).

Whey protein has been shown to be particularly effective at increasing muscle growth when consumed right before, after or during a workout. Muscle protein synthesis is usually maximized in the time period after training (16, 17, 18, 19).

However, a recent review of the evidence concluded that total daily protein intake is the most relevant factor in muscle growth. Whether protein is consumed around the workout or not doesn't seem to matter much (20).

When compared to other types of protein, such as soy protein, whey protein has usually performed slightly better (21, 22).

When compared to casein, the evidence is more mixed. Whey appears to be effective in the short-term, but casein stimulates muscle growth over a longer period, making the net effect similar (23, 24, 25, 26, 27).

Also, keep in mind that unless your diet is already lacking in protein, supplementing with whey protein is unlikely to have a significant effect on your results.

In a 12-week study in older adults with adequate protein intake, who did resistance training, there was no difference in muscle growth when supplementing with whey protein or carbohydrates (28).

Therefore, the evidence of whey protein on muscle and strength is mixed, and the results may vary greatly between individuals.

If you're already eating plenty of meat, fish, eggs and dairy — all high in quality protein — the benefits of adding whey will probably be minimal.

Summary There is a lot of evidence that whey protein is effective at increasing muscle and strength gains, though some studies find no effect.

It’s well known that protein can aid weight loss, as it’s by far the most satiating macronutrient (29).

Protein can boost energy expenditure by 80–100 calories per day, and make people automatically eat up to 441 fewer calories per day (30, 31, 32, 33).

In one study, eating 25% of the daily calories in protein cut cravings by 60% and reduced the desire for late-time snacking by half (34).

Taking whey protein is a great way to increase your protein intake, which should have major benefits for weight loss.

Studies have shown that replacing other sources of calories with whey protein, combined with weight lifting, can cause weight loss of about 8 pounds (3.5 kg) while increasing lean muscle mass (35).

If you're trying to lose weight, a whey protein supplement can help you both lose weight and hold on to your muscle (36, 37).

Summary Protein has been shown to aid weight loss by boosting metabolism and reducing appetite. Whey protein can help increase fat loss while preserving lean muscle mass.

Whey is more than just a high-quality protein source, it also contains other beneficial nutrients.

This includes lactoferrin, beta-lactoglobulin, alpha-lactalbumin and immunoglobulins (38).

Beyond just muscle, strength and leanness, whey protein may provide numerous other health benefits.

This includes lowering blood pressure, blood sugar and reducing symptoms of stress and depression (39, 40, 41, 42).

It also protects against cancer, reduces symptoms of hepatitis, increases bone mineral density, improves immune function in HIV patients and increases the lifespan of mice (43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53).

The fact that whey protein is very high in the amino acid cysteine seems to mediate many of these health benefits. Cysteine does this by raising levels of glutathione, the main antioxidant substance in your body's cells (54, 55).

Summary Whey is high in essential amino acids and other healthy nutrients. It’s also rich in the amino acid cysteine, which raises levels of the antioxidant glutathione and leads to many health benefits.

A commonly recommended dosage is 1–2 scoops (around 25–50 grams) per day, usually after workouts.

It’s recommended that you follow the serving instructions on the packaging.

Keep in mind that if your protein intake is already high, adding whey protein on top of your current intake may be completely unnecessary.

Concerns about protein causing kidney damage and contributing to osteoporosis are unwarranted.

In fact, protein has been shown to protect against osteoporosis, while having no impact on healthy kidneys (56, 57, 58, 59).

However, people with current kidney or liver issues may want to avoid whey protein or at least consult with a medical professional before taking it.

Eating too much whey protein can cause digestive issues such as nausea, flatulence, diarrhea, pain and cramping. Some people are also allergic to whey.

If you can't tolerate regular whey protein concentrate, isolate or hydrolysate may be more appropriate. Alternatively, you could simply avoid whey protein and eat other protein-rich foods instead.

But generally speaking, whey protein has an excellent safety profile and most people can consume it without problems.

Summary Whey protein is very safe. A commonly recommended dose is 1–2 scoops (25–50 grams) per day.

Whey protein is an exceptionally healthy way to add more protein to your diet. It’s a quality protein source that is absorbed and utilized efficiently by the human body.

This is particularly important for athletes, bodybuilders or people who need to gain muscle mass and strength while losing fat.

When it comes to muscle gain and fat loss, protein is the king of nutrients. Whey protein seems to be even better than other forms of quality protein.