Protein comes from meat and dairy so you need to eat plenty of that, especially if you are an athlete, right? This is what many people think about protein, but it is not true. You're not totally off base if you think this though because animal products are an excellent source of protein. However, let's look at the rest of the story.
Protein comes from plants. Animals consume that protein and it becomes part of them, thus making them a source of protein. Therefore, plants are the real source of protein, even if you consume it as part of a cow. Animals are often considered a better source of protein, not because of quantity, but because of quality. To better understand the quality of protein, we need to understand what protein is.
From Wikipedia: "Proteins (also known as polypeptides) are organic compounds made of amino acids arranged in a linear chain and folded into a globular form" (read more). Plants can generally synthesize all of the standard 20 amino acids, but humans are unable to synthesize 8 of them and must therefore consume them from some source.
Think of amino acids as the ingredients in a recipe. If you have copious amounts of most of the ingredients, but are missing just one, you can't make the recipe. Amino acids work similarly in your body. You need to make sure the protein you consume contains sufficient amounts of each of these essential amino acids. Therefore, high quality protein is protein that contains all of the essential amino acids. Animals generally contain all of these amino acids because they need them too.
By this definition, plants are a "low quality" source of protein. But wait, most animals had to get their essential amino acids from plants! So how are they producing high quality output with low quality input? Because all of these animo acids are plants. Just not necessarily all together in one plant. Plants have tons of protein and if you eat a moderate variety of plants, you will get all the amino acids you need.
Is "high quality" protein better for you that "low quality" protein? No. Eat a variety of fruits and vegetables and you will be fine without any animal products.
PS - Most Americans get way too much protein. Even still, many athletes believe they need to consume extra protein supplements since they are building muscle. This is absurd. First of all, natural sources of protein are better than supplements anyway. Second, most people taking protein supplements already have way more protein in their diet than they need anyway. The supplements are pointless excess and a waste of money. I'm not saying protein isn't important. It is very important. But nature's got you covered on this one.
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