I don’t agree with Layne on many topics (e.g. NEAT, metabolic damage) but he does a good job here:
"The fallacy being that plant protein and animal protein are really no different and if anything, plant protein is better. That is a flat out misrepresentation of scientific data. There are several reasons why plant protein may be inferior to animal protein. The first being that most plant proteins are far less bioavailable than animals proteins on the average of about 10-40% depending upon the source. [21] Further, most plant proteins are limiting in various essential (meaning we need to get them from the diet) amino acids. Rice protein is deficient in lysine, pea contains about half of the minimum methionine content, and soy, while low in methionine, has just enough not to be considered deficient. [22] Further, most plant proteins are low in leucine, the essential amino acid responsible for stimulating muscle protein synthesis. [23] Now, if you eat enough total protein from a variety of plant sources you can make up for these limitations. For example, in my PhD thesis, we found that consuming a diet containing 30% of calories from wheat protein was sufficient to maximize protein synthesis, whereas at 10% & 20% of calories from wheat protein, animal protein was superior compared to wheat. [24][25] So you CAN get maximal anabolism from vegan protein sources, but you will need more total protein, and a much more well thought out diet to do so. However, keep in mind that on average, vegans only get about 14% of their calories from protein. At these low levels of protein, the quality of protein becomes even more important. Do we need animal protein? No. But is it a superior source of essential amino acids? No question, especially when total protein in the diet is low.”
As we have already established, meat eaters tend to eat more calories, gain more weight, and be more prone to heart disease, but as we demonstrated with the data on inflammation, this is a problem of excess energy intake and its associated weight gain, not because animal protein is somehow inherently inflammatory. What about CVD? While fatty meats are associated with increases in total cholesterol and LDL, lean meats do not have the same effect of increasing blood lipids. [44] There is also evidence that fish, even fatty sources of fish such as salmon which contain the essential fatty acid omega 3, may decrease CVD risk. [45] Further, consumption of lean beef (113g per day) as part of a healthy overall diet has been demonstrated to decrease cardiovascular risk and improve blood lipids.”
Menno Henselmans also wrote a nice review here:
"While plants offer certain health benefits and nutrients, animal foods do too. While plants shine in terms of vitamins, anti-oxidants and phytochemicals, animal foods have a higher protein quality and are typically richer in bioavailable minerals, especially iron, beneficial fatty acids like omega-3s (EPA and DHA specifically) and B-vitamins.
Plant protein sources are not as high quality as animal protein sources and vegan diets are not optimal for our health. So if you’re not a vegetarian for ethical reasons, there’s absolutely no incentive to turn vegetarian for your health or physique.
If you’re an ethical vegetarian, you’ll have to put in a bit more work than omnivores to get the same results from your efforts in the gym. It’s a sacrifice you’ll have to make to stand up for your beliefs. Lacto-ovo vegetarian diets and pescatarians have it much easier. However, with meticulous attention to the diet and strategic supplementation, you can likely achieve equivalent results as meat eaters."