First off I think you might be under a few misconceptions. Don't feel bad - almost everyone is.
Lets back up quite a bit and talk about protein in general. I go to the gym and strength train too. Most of the guys at the gym have some very inflated ideas of what is the proper amount of protein they need in a day. (1) A lot of the guys at the gym talk about a factor or coefficient or multiple for calculating how much protein you need. Usually expressed as X times the number of pounds you weigh (or want to weigh) which then equals the number of grams of protein you need each day.
At my gym X is usually a number greater than 1.0. But that is easily twice the amount you actually need. All the medical scientific research puts the number somewhere between 0.44 and 0.48.
Why is that misconception so prevalent you might ask. The supplement industry is a billion dollar industry. They spend millions to get people to think they need more protein and must spend bucks on supplements. Meat, Dairy, and Egg companies are in on it too.
The gyms too are part of it. They make money selling the supplements.
I'll throw some references in at the bottom that will validate my point. but for now, I'm going to move on to another idea.
Although the coefficient is a pretty good rule of thumb a better one is based on the percent of the calories you eat. This takes a bit more math but does provide a much better picture of what a person's diet should be. I've seen articles call for as much as 60% of your calories should come from protein. This again is about twice what is healthy. Probably no more than 30% is necessary or healthy. If i remember right an athlete should try for 30% protein, 30% fat and 40% carbs. Regular people should aim for 20/20/60.
Another number thing is how many grams of protein are absorbable at any one time. Our bodies do not store protein very well. Any protein we consume that is not needed ends up getting broken down and flushed out in our urine. This is not good for anyone. One of the byproducts of protein decomposition is nitrogen which is poison and must be removed from our bodies. Many studies have shown that we can absorb between 20 and 30 grams of protein per meal. And this actually fits in with the other calculations that most of us need between 60 and 90 g of protein a day.
Next myth is the myth of the complete protein. This myth got started by accident like 60 years ago and it is amazing how persistent it is. Proteins are made of amino acids and it is true that different foods have different amounts or percentages of different amino acids. but it is not true that in order to get all your amino acids you have to carefully combine your protein sources. This is an extreme example but if you got all your caloric requirements from iceberg lettuce you would meet all your amino requirements. and then some. Ok, you would have to eat something like 20 heads of lettuce. but I'm just using this example to make a point. (2)
If you meet your calorie requirements you will meet your protein requirements. The best way to meet all your nutritional requirements is to eat a large amount and a large variety of foods. No one food is better than another. Eating lots of different food is best.
Sorry, that took so long. but with that said.
A. No one vegetable is best. They are all good. Maybe a good strategy is to eat lots of different kinds.
B. All vegetables are a good source of protein. Earlier I mentioned that you should be trying to get 20 -30% of your calories from protein. Most vegetables are 20 - 30% protein.
That said, beans are really really important. First off they are around 30% protein. Plus they are really good sources of iron. And soybeans are the best. over 40% protein. There is a reason that Tofu is vegan's mascot. And there is no reason to be wary of soy. Everything you heard bad about soy is either a misrepresentation or just false.
Soy milk is great for adding protein to your diet. but if you would rather, pea milk is almost as good.
Oh, and lentils are also a good alternative.
I know I promised you some references. but I gotta get going... but hers is a great article and it has 20 references.
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1. Please please forgive me if i was just guilty of some stereotyping and generalizations.
2. I even checked in Cronometer.