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?

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.

There are 20 amino acids, four of which are "nonessential" because they can be synthesized by the human body and therefore don't need to be consumed in the diet.

Nine aminos are "essential amino acids" (EAAs) since the body can't produce them and they must be consumed in the diet. Three of the EAAs contain chemical side branches and are called branched-chain amino acids (BCAAs): leucine, isoleucine, and valine. Leucine is often studied for its ability to increase muscle protein synthesis via the mTOR pathway1.

Eight amino acids are "conditionally essential," meaning our bodies produce them but we may be depleted of them during times of illness or stress.

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.

"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.

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. 

Lots of research has found that whey protein supplementation can build muscle when combined with resistance training. A recent Clinical Nutrition ESPEN review3 found that whey protein supplements had the greatest effects on body composition when combined with resistance training and a reduction in calorie consumption.

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."

A review of 112 trials6 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 dangerous7.)

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 oxide8, which is a vasodilator that allows more blood flow to muscles during exercise), two to three times more glutamine (important for rebuilding cells9) and double the glycine (has antioxidant properties10) content compared to whey protein.

Although there may be a greater improvement in lean body mass11 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 review12 supports the notion that plant protein has positive outcomes on metabolic health compared to animal protein.

According to a Nutrients meta-analysis13 of 16 studies, animal protein results in more lean mass, regardless of resistance training status, whereas muscle strength was similar between groups. Another meta-analysis14 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. You also don't need to choose one over the other—both can be a part of a diet with adequate protein.