The Sneaky Reason Your Plant Protein Isn't As Good As You Think

We're living in prime time for protein powders, with whey, hemp, soybean, and pea protein all readily available for your sipping pleasure.

All protein powders look alike and taste at least vaguely similar, so it can be easy to think that their benefits are also comparable. But don't be fooled: Animal protein powders (like whey) and plant powders (like soy and pea) don't always have the same impact on lean muscle mass.

In general, plant proteins are lower in the amino acid building blocks needed to spur muscle growth. Let's unpack that further: Here are a few reasons you may not be getting the results you want with a plant protein.

Plant proteins are lower in leucine

The biggest difference between plant and animal proteins comes down to their leucine content. Leucine is the amino acid in protein that's most directly implicated in muscle growth.

The branched-chain amino acid activates the body's mTOR pathway1, which controls the anabolic (growth) and catabolic (breakdown) signaling of skeletal muscle. "You can think of the BCAA leucine as a trigger or 'its go-time' button for muscle protein synthesis (i.e., the critical cellular process for building muscle)," explains mindbodygreen's former vice president of scientific affairs, Ashley Jordan Ferira, Ph.D., RDN.

You need to consume around 2.5 to 3 grams of leucine at a time to trigger this muscle growth, Don Layman, Ph.D., a leading amino acid researcher, previously explained on the mindbodygreen podcast.

Animal proteins are naturally higher in leucine, so it's reasonable to reach this 2.5-gram threshold in just one serving. That's not the case with plant proteins. While whey protein powder typically has about 8 to 10% leucine content, soy is 7.8%, while hemp is 5.1%2. This means it would take 25 grams of whey protein to trigger muscle growth (a standard one- to two-scoop serving size) but up to 50 grams of hemp (which could take up to four scoops or more).

Beyond leucine, animal proteins also contain all the other essential amino acids in the amounts we need for muscle growth, maintenance, and repair. Plant proteins (except for soy) are considered incomplete proteins; they don't contain adequate amounts of all the essential amino acids to meet the minimal human requirements.

Because of these differences, whey protein has proved to be more effective for muscle growth than plant proteins in many clinical trials. In one scientific literature review, whey protein was found to be better at increasing lean body mass3 than soy protein. When put head-to-head against pea protein in a controlled trial, whey was also better at decreasing muscle soreness4 following prolonged exercise.

This isn't to say that taking plant protein won't support your muscle health at all. It will just likely be less effective than whey, and you may need to consume a much larger serving5 to see the same benefits.

Plant proteins aren't digested as efficiently

Soy protein isolate is the only plant protein with a PDCAAS of 1.0—others, like pea, fall closer to the 0.78 to 0.91 range. So, you may need to consume even larger portions of them to ensure that you're getting the amino acids your body needs and can put to use for muscle growth.

Plant proteins are more likely to contain heavy metals

Finally, plant proteins are more likely to contain heavy metals like lead than animal proteins—which makes eating them in large quantities less appealing.

A highly cited report from the watchdog group Clean Label Project tested 53 brands of protein powder and found that, on average, plant proteins contained twice the amount of lead per serving as animal proteins.

They found measurable levels of lead in 75% of plant protein powders tested (including organic varieties).

The takeaway

Plant protein powders can be a convenient tool for reaching your daily protein quota while getting some fiber, healthy fats, and phytonutrients along the way. That said, they likely won't be as helpful for strength goals as animal proteins, which are higher in essential amino acids like leucine and more efficiently digested.

At the end of the day, the best protein powder is the one that works for you—plant or animal. But if you're looking to choose one over the other for enhanced muscle health, go with an animal protein like whey. Just be sure to look for one that's low in sugar and other funky additives.