Overly-Vague Statements About Protein
Statement 1: You "Need" Protein
For starters, this is outright false. The human body does not require protein ingestion, it requires amino acids that are taken up by cells in the human body wherein the cell itself manufactures protein(s) to be used by the human body from the raw ingredients that it took in from the bloodstream. The body creates an "amino acid pool" that is measurable in the sera (blood) of the person in question.
The body takes in the amino acids it requires from the bloodstream for use. Although proteins are the form that amino acids typically are in when a human ingests them, protein is a product created by typically complex organization of amino acids and is not required to be ingested for most if not all humans. The breakdown of protein into its constituent amino acids is typically done by the liver (the liver can be overwhelmed by excessive protein ingestion) and the byproducts of this breakdown process--ammonia and urea--are removed by the kidneys (which can be overwhelmed as well). This is likely why a low-protein diet seems to be quite therapeutic in the management/treatment of those with kidney disorders and/or diseases.
Related: Paleo Diet Myths
Statement 2: You Need to Focus on Protein or You Will Not Get Enough
Kwashiorkor is the name of protein deficiency despite adequate calorie intake, and is almost unheard of. Have you heard of someone with this disease? It is characterized by distension of the belly and swelling of internal organs. If there is a whole plant food that does not provide adequate protein when consumed in adequate amounts to meet calorie needs, I am not aware of it.
Every single commonly-eaten produce product commonly-available at grocery stores (e.g. corn, carrots, celery, berries, and bananas) provides adequate protein. There are even elite athletes that eat a diet of almost entirely fruits with a bit of grains, two types of plant foods that are some of the lowest in protein; some of them eat almost 100% fruit, which has typically the least amount of protein per calorie of all plant products. Most plant products provide at least 8% of their calories from protein (some over 30%!). If there is a study proving that 8% of calories from protein in a calorie-sufficient diet is considered "protein deficient" (or even sub optimal) I am not aware of it. Please comment if you have a link to such a study, and I will likely promptly review said study and respond accordingly.
There are rumors that diets "low" (the 10% provided by most plants being seen as "low") in protein will lead to loss of lean muscle mass if one has a fair amount of muscle already, or, will stunt the growth of new, lean, muscle mass in a strength training regimen. Yet, there appears to be no solid proof of this that I am aware of. Again, if you are privy to such information, please let me know.
Have you met anyone with, or even heard of Kwashiorkor before today?
Statement 3: A Meal That Lacks Animal Muscle Tissue (Meat) is Nutritionally Inadequate
If anything, a meal high in animal muscle tissue is one of the least nutritionally adequate. As previously stated, merely eating enough food to meet caloric needs in almost every single case will provide sufficient amino acids to repair and build new bodily tissues as well as maintain metabolic processes, even in the case of extreme athletic strain, such as the intense amounts of training done for many hours per week by professional, endurance athletes. When one forgoes the consumption of animal products, one is merely "skipping the middleman" and going directly to the source of the 9 essential amino acids: plants!
The only reason any creature in the animal kingdom is able to acquire the 9 essential amino acids is because they either ate a plant (the things that CREATE those amino acids) or ate an animal that ate a plant. There is no known animal to my knowledge that can create one of the 9 essential amino acids endogenously (internally). Plant foods are typically higher in nutrition per calorie as well, making it easier to meet the RDA for each specific vitamin/mineral. A 3-year study done on 16,000 people showed that at least 1/3 of them did not meet the RDA for 5 nutrients. With the high prevalence of animal muscle consumption by Americans, if said foodstuff was nutritionally dense, one would expect any dietary deficiency to be almost non-existent, yet, deficiency is actually borderline ubiquitous.
Keep in mind the RDA is based on avoiding pathological states, not optimizing health. Basically, the bare minimum is not likely the best, and at least half of the people studied did not get even the bare minimum RDA for Vitamin E, and even LESS for Vitamin D. Although admittedly the latter deficiency is likely due to the distance of the US from the equator in combination with most of one's day spent indoors, since Vitamin D is more like a hormone than a vitamin and is produced by the skin when exposed to UV rays, typically from the sun.
The overarching message here is that without specific information to back up a claim, a vague claim is basically worthless. Notice how when people talk about protein, they almost never give real-world examples to back up the reasoning behind their statement? Often times something is repeated so often many believe it MUST be true and it is rarely challenged. There is a lot of misunderstanding with regards to protein, and, it is fairly obvious why: almost none of them are based on either real-world facts or observations. To put it quickly: as long as you are not eating highly-processed and/or junk foods, you are getting enough protein as long as you are getting enough calories. If there is data out there to prove otherwise, please provide it. Thanks for reading and have a great day!