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People like to say all kinds of things about protein – like, you need to eat lots of it to build muscle and lose weight. The truth is, the science of protein and how your body uses it is much more complicated than that.

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People like to say all kinds of things about protein, like, you need to eat lots of it to build muscle, and lose weight. But dietary science is way more complicated than that! You can't just eat a bunch of one thing to get buff or to be healthy. In fact, eating too much of anything can be really unhealthy.

Proteins are a group of macro-molecules that do a lot of different things, like helping with chemical reactions or immune responses, giving our tissue structure, and even sending messages between cells. And by understanding the chemical basics of protein, we can understand why we need to eat it to keep our bodies working, so let's dig in!

Chemically, proteins are made up of long chains of amino acids. These organic compounds have an amine group and a carboxylic acid group plus some other atoms that make up a side chain. These strings fold up because of interactions between the amino acids, making stable 3D structures that are ready to do things inside our bodies. And some proteins, like hemoglobin which ferries oxygen around our bloodstream are made up of more than one of these strings interacting.

Our bodies use 21 different amino acids to make thousands of distinct proteins, so it's important we have all of these building blocks for ourselves to work with. Amino acids can be broken down to three types: Essential, Non-Essential and Conditionally Essential. 

Essential amino acids are the ones that our bodies need to function but have no way of making. So that's where food comes in, like meat, beans, nuts and eggs. Your digestive system breaks down the proteins in food; first you basically untwist, or denature the 3D structure of the protein with stomach acid. Then, you chop the chains into chunks of one or two amino acids, using these specialized proteins called Proteases. These amino acids are absorbed into your bloodstream and your small intestine, and sent around your body to be assembled into new proteins.

So what about the non-essential amino acids? We still need them and we can get them from food too, but our bodies can make them out of other chemicals that are hanging around. For instance, one of the intermediates from the energy making citric acid cycle Alpha Ketoglutarate can undergo chemical reactions to make four amino acids: Glutamate, Glutamine, Proline, and Arginine.

So for the most part your body's got you covered, except when it's still developing, sick, or injured, and can't naturally produce enough of some of these amino acids. We call them conditionally essential. For example, pre-term infants can be deficient in Arginine, which causes a variety of health problems in the heart, lungs, brain, and intestines. And scientists think their still developing bodies aren't synthesizing enough of the proteins that help with those chemical reactions that make the Arginine. 

So now that we know the basics, what's up with all of these protein powders and shakes and bars and pills? Why do people have these expectations that they will build muscle? When people talk about building muscle, they're probably talking about skeletal muscle, the type that's attached to your bones and you can voluntary move around like your quads and biceps. Skeletal muscle is made up of bundles of muscle fibers, which are basically a membrane surrounding these units called Myofibrils. And myofibrils are essentially bundles of these long proteins called Actin, which are thinner, and Myosin, which are thicker. When you contract a muscle, these protein filaments slide past each other, with Myosin driving the movement.

So your muscle tissue is constantly making and breaking down proteins, and your muscle grow when there's more protein synthesis than breakdown. Exercise is just a way to stimulate chemical pathways that cause more protein synthesis. When you work your muscles harder than usual, the extra tension on the muscle fibers can cause these microscopic tears, either damage to the cell membrane, or the connections between Actin and Myosin filaments. And this damage can signal for more protein synthesis. When your body repairs muscle fibers and creates a new tissue, it makes more Actin and Myosin too. But it's not clear if you need to damage your muscle for growth. 

If you eat protein when you work out, your body mostly just has more amino acids hanging around to synthesize proteins in your muscles. And your body doesn't really store extra amino acids for later. They get converted into other organic compounds, that are used in metabolic pathways, like glucose or Acetyl-CoA, or they get broken down and eliminated in urine.

So that's pretty much the basics of protein. They're super important for all kinds of bodily functions, and you make them from amino acids, which you can synthesize on your own or get them from your food. And you cannot expect protein supplements to have magic muscle building powers. They're pretty much just another way to take in sustenance, and for your body to absorb amino acids. Thank you for watching this episode of SciShow, which was brought to you by our patrons on Patreon. If you would like to help support this show, you can go to And if you want to keep getting smarter with us, don't forget to go to and subscribe!