Plant protein is harder to digest than meat. Everybody who has spent five minutes reading about protein carries some version of this. The amino acids are different, the absorption is not as efficient, and somewhere in the conversation sits a vague agreement that plant sources score lower, but not by much.
The last part, "not by much," feels certain until someone asks for a number. How much worse does plant protein actually score when there is a scale designed to measure exactly this?
Are plant proteins actually harder to digest than meat?
Most plant protein sources score 40 to 70 percent lower than animal proteins on the FAO digestibility scale, a gap caused by tighter protein structures and compounds that block digestive enzymes. Despite this, a controlled trial found identical muscle growth between plant and animal protein groups when total daily intake was matched.
— Herreman et al. 2020 · Food Science & Nutrition; Hevia-Larraín et al. 2021 · Sports Medicine · n=38
There is a scale. The Digestible Indispensable Amino Acid Score rates every protein source on how completely your gut can break it down and absorb each essential amino acid. The gap between plant and animal is not the quiet 10 or 20 percent most people carry in their heads.
Corn protein scores 36. Pea protein (the base of most plant-based powders) scores 70. Soy, the best widely available plant source, reaches 91.
Pork and casein each score 117. Egg sits at 101.
A pea at 70 against pork at 117 is not "slightly worse." That is a 40% gap on a scale most people assumed was nearly even.
The reason sits in the protein itself. Plant proteins fold into tight, compact structures. More than 40% of their molecular architecture resists being broken apart by digestive enzymes, compared with under 30% for meat and dairy proteins. Your gut meets a tightly wound molecule and cannot unfold it as efficiently.
The barrier doubles from there. Plant proteins carry compounds (protease inhibitors and phytate) that actively shut down the enzymes doing the work. The protein resists opening, and the enzymes trying to do it face sabotage from the same food.
The gap is real. It is physical, chemical, and roughly three times wider than most people assumed. That gap tells half the story.
A 12-week trial compared both groups directly. One eating plant protein, the other animal, both at matched total intake, both following the same strength program. Muscle growth was identical. Thigh muscle grew the same in both groups, with no detectable difference.
The protein that scored 40% lower on the digestion scale matched the one at the top for muscle growth.
Three things explain the disconnect.
Processing strips the barriers. Soy protein isolate scores 91 because manufacturing removes the compounds that block digestion. If you use a plant protein powder, the gap has already narrowed before you measured it.
Strategic mixing closes it further. Combining pea and wheat protein at a 60/40 ratio pushes the combined score to 85. Whether you need to combine at every single meal has a simpler answer than the mixing ratios suggest.
Eating enough total protein overrides the per-gram quality difference entirely. The trial demonstrated this directly. The practical cost is real: hitting that target from whole plant foods means eating more volume and more total calories than an omnivore would need for the same protein.
One honest caveat on the numbers themselves: most of those digestibility scores come from raw feed ingredients rather than cooked food. Cooking changes protein structure. Pea protein jumps from 70 to as high as 86 after heat processing. The gap is real, but your plate probably narrows it compared with what the raw scores suggest.
The scoreboard splits down the middle. Plant protein loses on digestion by a margin three times wider than most people assumed. It draws even on muscle when total intake matches. The split shifts the question from "which source wins" to what quantity of the lower-scoring source erases the practical difference.
The evidence behind that question spans more than one experiment.