Isolate, whey, casein: which protein powder is best for building muscle?

A nutritionist shares his insight

protein powdet shaker with a scoop of protein next to it
(Image credit: Getty Images)

If your goal is to build muscle then, as well as supplementing with creatine, making sure you consume enough protein is key to help your muscles repair and recover. Although consuming whole foods is always best, adding a protein powder to your diet is one of the easiest ways to up your intake. 

But apart from having to choose from the hundreds of flavours out there, you need to make sure you’re picking the best type of protein to support your muscle-building goals.  

Whey concentrate, whey isolate and casein are three common types of protein powders you’ll encounter, but which is best in helping you secure gains? We spoke to Dr Mark Evans, a Nutrition Consultant at Optimum Nutrition to find out.

Whey, isolate and casein: what’s the difference?

Before we jump into which protein is best for building muscle, let's take a look at each protein more closely. While there are differences that set the three apart, there are similarities too. 

Dr Evans points out that whey, isolate and casein are all derived from milk during the cheese making process. “Every gram of protein in these powders provides four calories, so any calorie differences between them is due to protein content, serving sizes or the presence of other nutrients such as carbohydrates and fats,” he says. "They all also contain the nine essential amino acids that are essential for muscle growth and recovery."

Ok, now for the differences...

Man putting a scoop of protein powder into a protein shaker

(Image credit: Getty Images)


Whey: This is by far the most popular protein supplement on the market. “Whey is a fast-digesting protein that is quickly absorbed by the body, making it an ideal choice for fast delivery of amino acids to the muscle during the post-workout recovery period, or any time during the day to help you hit your daily protein target,” explains Dr Evans. 

Whey isolate: Isolate contains a higher protein purity than both whey concentrate and casein. “It undergoes a filtration process to remove most of the fat, carbohydrates, and lactose,” says Dr Evans. “Isolate can be particularly useful for people who may have digestive sensitivities to other types of whey powders.” It’s also typically more expensive because of the extra step in processing and its higher protein purity. 

Casein: The main difference with casein protein is that it takes longer for the body to digest, which means a more sustained supply of amino acids to the body over a longer period. “This makes it an excellent protein choice between meals, during extended periods of fasting, or before bed,” says Dr Evans. “Casein powders are also slightly higher in carbohydrates compared to whey protein, but are higher in calcium and phosphorus, which are important minerals for bone health.” 

Which type of protein powder is best for building muscle?

Out of the three proteins, Dr Evans recommends whey protein if building muscle is your goal, whether that be concentrate or isolate. He says this is because of its fast absorption rate to deliver amino acids to the muscles quickly after a workout, but also because it has higher levels of leucine, than casein. “Leucine is an essential amino acid and is a key trigger of the muscle-building process, so these two things combined make it the ideal choice for muscle-building efforts,” he says.

Not sure how much protein you should be consuming a day? Check out Optimum's Nutrition protein calculator, it will also recommend your carb, fat and calorie intake.

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Bryony Firth-Bernard
Staff Writer, Active

Bryony’s T3’s official ‘gym-bunny’ and Active Staff Writer, covering all things fitness. In her spare time, you will find her in her natural habitat - the gym - where her style of training is a hybrid of bodybuilding and powerlifting. Bryony loves writing about accessible workouts, nutrition and testing innovative fitness products that help you reach your fitness goals and take your training to the next level.