Whey vs. Plant Protein Powders: What's The Difference & Is One Better?

One of the most controversial and constantly changing topics in nutrition is protein. How much should we eat? What are the best sources? What's the best time to eat it? Is plant protein the same as animal-based protein?

What we do know is that while it's always best to meet nutritional needs using whole foods, protein powders can help fill any gaps. There are a ton of milk-derived and plant-derived protein supplements available, so picking one can be overwhelming. This deep dive into the pros and cons of plant and whey protein supplements will make choosing the right option for your needs much easier.

All proteins—plant- and animal-derived—contain amino acids. Amino acids are molecules, joined by peptide bonds, that form certain structures in the human body. They are needed for the constant breakdown and regeneration of cells.

The current Recommended Dietary Allowance for men and women older than 19 years old is 0.8 gram of protein per kilogram of body weight.

It's not that simple, though—protein needs increase depending on age, activity level, and body composition. According to Essentials of Strength Training and Conditioning2, aerobic endurance athletes require approximately 1.0 to 1.6 grams of protein per kg of body weight. Strength athletes need approximately 1.4 to 1.7 grams per kg of body weight. Emerging research shows that women may also require more protein at different points of life.

You can meet these daily requirements by consuming around 25 to 30 grams of protein during breakfast, lunch, and dinner, and eating a protein-rich snack.

While it's totally possible to fulfill these protein needs with protein-rich food sources, protein powders can be helpful for those with busy schedules who need protein fast.

Whey protein powder comes from cows or goats and has been clinically shown to help build muscle, recover from workouts, and decrease body fat across several populations.

There are different types of whey protein available, namely whey protein isolate (WPI), whey protein concentrate (WPC), and casein protein.

"Whey protein isolate is the purest form of protein on a gram-per-gram basis and will be at least 90% pure protein," says Michael Twyman, M.D., board-certified cardiologist at Apollo Cardiology based in Missouri. "WPI is produced by sending milk through a series of filters. The filters will strip out lactose and milk sugar as well as fat. WPI is generally better for those who are lactose intolerant or for people who get gastrointestinal problems from WPC."

WPI is typically more expensive than WPC due to its purity and reduced fat, sugar, and carbohydrates. "WPC is produced similarly to WPI, but the milk will be sent through fewer filters," says Twyman. "WPC is good for most of the population that can tolerate lactose. Since it has more fat, it will contain certain bioactive peptides3 that can elicit some positive health benefits, Twyman adds.

During the whey manufacturing process, milk is spun, then acid is added, which causes the soluble (dissolvable) portion (the WPC) to rise to the top. This WPC is then broken down into more peptides to form WPI.

The insoluble (less dissolvable in acid) casein protein will sink to the bottom during this process. Casein can also be consumed as a protein powder. It has a thicker consistency compared to WPC and WPI, so casein products typically require more water to go down smoothly. Casein doesn't get digested as quickly as other forms of protein, so those looking to support muscle growth usually take it before sleeping to get amino acids as they recover. There are two types of beta-casein: A1 and A2. 

Though less common, you can also find whey protein hydrolysate, which is formed when WPI is broken down even more into more peptides so that it can be absorbed even faster. The difference between hydrolyzed whey protein and WPI is small, except the hydrolyzed will taste the most bitter of all proteins.

Lots of research has found that whey protein supplementation can build muscle when combined with resistance training. A recent 4Clinical Nutrition ESPEN4 review4 found that whey protein supplements had the greatest effects on body composition when combined with resistance training and a reduction in calorie consumption.

After four weeks of resistance training three times per week, 32 males in a Medicine & Science and Sports & Exercise study saw hypertrophy (muscle growth) from taking 30 grams of whey protein before and/or after resistance training. Interestingly, the results were most notable when protein was taken post-workout or both before and after, not only pre-workout.

Whey protein supplementation can also help protect muscle mass and strength as we age. One study published in the 5International Journal of Sport Nutrition and Exercise Metabolism5 found that when women ages 60 and older took 35 grams of whey protein daily for 12 weeks, along with resistance training three times a week, they had increased strength and hypertrophy.

Whey protein can also help your athletic performance, according to research. In a study that compared protein supplementation6 to carbohydrate supplementation, the results were improved reactive strength and hamstring flexibility recovery and decreased blood creatine kinase (a biomarker for fatigue) in the protein group vs. the carbohydrate group.

Another benefit of whey is that whey naturally contains more of the amino acid leucine than plant protein. Twyman mentions there is a "meal threshold theory" in which 2.5 to 3 grams of leucine is required to trigger muscle protein synthesis.

"Whey protein has a higher concentration of leucine, whereas plant-based proteins will require a higher number of grams to reach the needed leucine threshold," Twyman says.

As leading protein and amino acid requirements researcher Don Layman, Ph.D. said on the mbg podcast, "In whey protein, leucine is about 12%, so 23 grams of whey protein isolate will trigger it. Whereas in soy protein isolate, it's about 7.8%, so now you need 33 or 34 grams."

Plant-based protein powders are also becoming increasingly common due to lactose intolerance/allergies, food preferences, and increased ecological awareness.

Plant protein powders can be made from a variety of plants—most often soy, pea, rice, hemp, sprouted seeds, and grains. Since plant proteins are incomplete, these ingredients are often blended together so a plant protein powder can cover all the EAA bases.

A review of 112 trials7 published in the Journal of the American Heart Association compared the effects of a plant-based diet intervention (mostly soy protein) vs. an animal-based intervention on LDL cholesterol (the "bad" type), non-HDL cholesterol and apolipoprotein-B (Apo-B). (Apo-B is a protein found in many lipids within the arterial walls, and too much of it can be dangerous8.)

The researchers found substituting plant protein for animal protein decreased LDL, non-HDL cholesterol, and Apo-B by about 4% each in adults with and without high cholesterol.

Plant protein does not contain lactose, like some whey powders. Lactose intolerance is due to not being able to make lactase (an enzyme) in order to fully digest the lactose (sugar) in milk, Twyman explains. The main symptoms include diarrhea, nausea, stomach cramps, bloating and gas.

Aside from heart and gut health, another reason to incorporate more plant proteins into your diet is their diverse nutrient content.

Hemp protein, for example, is a rich source of fiber (about 12 grams per serving) and contains healthy unsaturated fats.

Pea protein contains nearly as much leucine and lycine as whey protein, plus many products contain several grams of iron.

Soy protein contains nearly three times more arginine (a precursor to nitric oxide9, which is a vasodilator that allows more blood flow to muscles during exercise), two to three times more glutamine (important for rebuilding cells10) and double the glycine (has antioxidant properties11) content compared to whey protein.

Although there may be a greater improvement in lean body mass12 when comparing whey to plant protein, plant-based protein powder supplements can build muscle just like whey protein powder supplements.

A Journal of Health Sciences review of studies comparing the effects of soy and whey protein on exercise found that although whey increased muscle protein synthesis better (resulting in more muscle mass after 36 weeks), soy protein resulted in less oxidative stress. Specifically, some studies showed that soy increased antioxidant levels compared to whey protein, and that whey increased lipid peroxide levels, which can cause free radicals to damage cells over time. Another systematic review13 supports the notion that plant protein has positive outcomes on metabolic health compared to animal protein.

According to a Nutrients meta-analysis14 of 16 studies, animal protein results in more lean mass, regardless of resistance training status, whereas muscle strength was similar between groups. Another meta-analysis15 found that soy and whey protein produce similar gains in strength and lean body mass in conjunction with resistance exercise.

Overall, the theme with the comparison studies is that whey protein increases muscle size more than plant protein, but both can build strength, and plant proteins can be better for your metabolic health in the long run.

At the end of the day, they both can be helpful for filling protein needs. Just remember that whole foods are the best sources of not just protein but other nutrients as well. "While protein powders are a convenient source of amino acids, whole foods contain more fats and carbohydrates, which are key to a balanced nutrition plan," says Twyman.

Both plant and animal protein powders can help you fulfill your protein needs and build strength, so which one you choose is largely a matter of preference. Consider the pros and cons of this list and be sure to read the ingredient labels of protein supplements before purchasing. And remember: Protein powders alone don't build muscle. You'll need resistance training for that.