While plant-based protein powder has its benefits, it might not be the ideal choice for everyone. Here are five reasons why plant-based protein may fall short of your needs.
1. Incomplete Amino Acid Profile
Amino acids are the building blocks our bodies use to make proteins, which are super important for muscle growth, wound healing, keeping our immune system strong, creating energy, and helping our brains function properly (3).
One of the main issues with plant-based protein sources is that they often don’t have a complete amino acid profile (the exception being soy). When your diet is missing an essential amino acid, your body might break down muscle to get what it needs.
Unlike animal proteins, which give you all nine essential amino acids, many plant proteins are missing one or more (4). For instance, grains usually lack lysine, while fruits, veggies, and legumes often don’t have enough methionine (5).
2. Lower in Leucine
Speaking of amino acids, another huge difference between plant and animal proteins is their leucine content. Leucine is a branched-chain amino acid (BCAA) in protein that's most directly involved in muscle growth.
You can think of leucine as a trigger or start button for muscle protein synthesis—the critical cellular process for building muscle. Leucine activates the body's mTOR pathway (6), which controls the anabolic (growth) and catabolic (breakdown) signaling of skeletal muscle.
You need to consume around 2.5 to 3 grams of leucine at a time to trigger this muscle growth (7). 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. Soy and hemp protein powder typically have 7.8% and 5.1% leucine content, respectively (8). This means it would take up to 50 grams of hemp (which could take up to four scoops or more) to trigger muscle growth.
3. Can Be Harder to Digest
Protein digestibility is measured by a PDCAAS, or protein digestibility-corrected amino acid score (9). This score measures how much of a protein's amino acids our bodies absorb, with the highest possible score being 1.0 (100%).
Plant-based proteins often have fibers and compounds like antinutrients (phytates and lectins) that make them harder for our bodies to digest and absorb. Plant-based protein powders, especially those with pea protein, may cause bloating and cramping—especially if you have irritable bowel syndrome.
In contrast, animal-based proteins are more easily digested and utilized by the body.
4. Limited Essential Nutrients
While plant-based protein powders offer a range of nutrients, they often fall short in delivering essential vitamins and minerals compared to their animal-based counterparts.
For instance, many plant proteins lack vital nutrients like vitamin B12, which is crucial for energy production and neurological function, and iron, which plays a key role in transporting oxygen throughout the body (10, 11). Without these essential nutrients, you might find yourself missing out on what your body really needs to function at its best.
5. May 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 report from the 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 (12). They found measurable levels of lead in 75% of plant protein powders tested (including organic varieties).
