Then how did they build muscles if they are vegan?
Vegetables have protein too.
One of the biggest misconceptions is that you need to eat a lot of protein to put on a lot of muscles. If that were true, then why aren't bodybuilders who eat more animal proteins than others putting on even more muscles?
Or even just regular people - I know some guys who eat a ton of animal protein and they don't appear to be very muscular at all. I have a friend who drinks protein shakes but doesn't work out - she's flabby despite consuming a lot of animal protein.
So the link between the more animal protein you eat, the more muscles you get is misleading.
When I was bodybuilding, I knew a few bodybuilders and we would always discuss our diets because it's paramount in the bodybuilding world. I would look at the physique of a vegetarian bodybuilder and the physique of a meat eater - visibly, there's no difference. None.
It's total calories that makes the difference in building muscles, not protein. And nutrition coaches of say olympic athletes - they put a lot more focus on carbs than protein. Carbs is what gives you energy, carbs is what delivers protein to the muscles. When bodybuilders start getting ready for a competition, they start eliminating carbs from their diet in order to get more lean but they also lose a bit of muscles too. So, what they would do is eat as much as possible - the term for this is carb-loading - they eat and eat and eat to put on as much muscles as possible to offset any muscle loss when they start cutting out carbs pre-competition. This proves carbs is what's more important for muscle building and more essential to preventing muscle loss, not protein.
That's not to say protein is not essential for building lean muscles. It is but not in great quantities. You would not put on more muscles if you had a huge steak instead of one egg. your body can only utilize so much protein from a meal. the rest is either burned off or stored as fat depending on how fit you are.
A human only needs about 0.7 grams of protein per body pound to put on muscles. that means if you are 150 lbs, in order to gain more muscles than you have, you would need about 105 grams of protein a day.
Here are some facts: Lentils, beans and peas are loaded with protein. Almonds and pistachios have 7 grams of protein per serving (1/4 cup) and both pumpkin and hemp seeds have 11 grams per serving. One potato has 3 grams of protein, 2 cups of yams have about 5 grams of protein People usually only count protein grams from animal sources but this is a huge mistake. Vegetables have protein, brown rice has protein and even your morning bowl of oatmeal has 10 grams per cup.
So, as long as a vegan eats a well rounded diet containing the above, they will have no problems putting on muscle mass.