[0:00]I weigh about 80 kg. Most of that, let's say 64% is water, though you can't tell by looking. I mean as organisms go, I like to think that I look fairly solid. After water, the next largest proportion of me is protein, about 16%, not just in my muscles, but also in things like the tiny sodium, potassium, pumps in my neurons, and the hemoglobin in my blood, and the enzymes driving the chemical reactions in every one of my 37 trillion cells. And another 16% of me is fat, which I'm totally okay with. 4% of me is minerals, like the calcium and phosphorus in my bones and the iron in my blood and 1% is carbohydrates. Most of which is either being consumed as I talk to you or is sitting around as glycemic waiting to be used. But here's the thing. It's not like I just ate 80 kg of food and then all this happened. Instead my body like yours is constantly acquiring stuff, extracting some of it to keep burning some of it for energy and getting rid of the rest. But even the stuff that my body does hold on to doesn't last forever. Some of the chemicals that I absorbed in my food eventually become a part of me, but enzymes wear out and membranes break down and DNA get oxygen, so they get discharged. And then I need more of those chemicals to reconstruct the material that I've lost. As a result, over the course of my lifetime, my cells will synthesize somewhere between 225 and 450 kg of protein. That's like three or four or five separate mees, just made of protein. And all the protein and fat and carbohydrates and nucleoic acids that make up me, of course, come from food. Every organism has to keep taking in and breaking down food to keep replacing itself with the raw materials it needs to And all that activity requires energy which we also gain from food. So how do our bodies actually convert what we eat into energy and raw materials? The answer is a never ending series of reactions that are dedicated to doing two vital and totally contradictory things. One set of chemical reactions destroys the reactants that you give them reducing big complex substances into molecular ruble. And the other set reassembles that ruble into new and bigger products that are put together again to make you. So our bodies are constantly re-inventing them in a perpetual state of loss but also always rebuilding. And even though all of this is happening at the cellular level, its consequences could hardly be larger. These two sets of reactions are where everything that we've learned so far about the digestive endocrine circuitary and respiratory systems really starts to come together. Together, these processes make up your metabolism.
[2:31]Now the science word metabolism has come to have a meaning in popular speech, but metabolism isn't just one thing. People talk about metabolism is meaning like how fast your body burns the fuel in your food or how high your personal energy level is. And that's fine for use by personal trainers and fitness magazines. But physiologically, metabolism really describes every single biochemical reaction that goes on in your body. And maybe more importantly, it recognizes two conflicting chemical processes that are always simultaneously underway inside of you. One of those chemical forces is anabolism. Anabolic reactions and construct things and consume energy. These are the processes that take the small monomer building blocks in your food like monosacharides and fatty and amino acids and build them into bigger more complex polymers like carbs and fats and proteins that are used in your cells. Then when you need new building blocks or you need to release some energy, those polymers in your body or new ones in your food get broken up by catabolic reactions. The processes of catabolism break down bigger molecules and then break their bonds release the energy you need to stay warm and move around and provide yourselves with fuel to build those polymer back up again. To be honest, you're metabolism is a lot like cis. It works really hard, but it is never finished. And the builder that your inner cis is always pushing up hill and watching fall back down, that's nutrients. The molecules that your body is forever breaking up and then rebuilding only to have them break apart again. And these nutrients, the materials that your body needs to build, maintain and repair itself come in six major groups. volume, the majority of what we consume and what makes up our bodies is water. So that's maybe the most vital nutrient. Then there are vitamins, compounds that come in either fat soluble or water soluble forms. They aren't used as building blocks or for energy, but they're essential in helping the body make use of other nutrients that do do those things. Vitamin C for example helps improve iron absorption while vitamin K is crucial to blood clotting and some B vitamins are important in the production of ATP from glucose. Minerals like vitamins don't provide fuel, but they have all sorts of other functions. magnesium and phosphorus, hardened bones and teeth while iron is of course crucial in hemoglobin plus potassium, sodium and chloride help maintain your body's pH balance and are used in action potential. So water, vitamins and minerals are all necessary. But the three major nutrients that everyone always talks about, the ones you find on food labels from oatmeal to pop tarts are carbohydrates, lipids and proteins. Most of the carbohydrates you've ever eaten with the exception of lactose in milk originally came from plants. Mono and diassharide come from fruits, honey, sugar and sauce while pollen starch come from veggies and grains. The main thing you need to know is that the monosodium glue is the B all and all molecular fuel that your cells need to make ATP. ATP being the molecule that your cells use to drive anabolic reactions when they need to make new polymer or get anything else done whether that's operating a sodium potassium pump or detaches the head of a myosin to contract a muscle. But ATP is too unstable to store so cells often store energy in the form of glucose which they can then and convert to ATP when they need it. Now some of your cells can get their energy from fats. But many of the most important ones like your neurons and red blood cells feed exclusively on glucose. So most of the carbs that your intestines absorb are converted to glucose for that reason. But if it's not needed right away that energy can also get stored as glycogen in your liver and muscles or converted to glycogen and fatty acids to make triglyceride fats. And even though there seems to be some kind of marketing war going on against dietary fats, we most definitely need them. The fats in your adipose tissue store energy. of course, but they also store fat soluble vitamins and cushion your organs. Lipids also form the milin that insulate the neurons in your brain and throughout your body as well as the oil in your skin and they provide the vital calorie content found in breast milk. But there are other important lipids like cholesterol, which is the precursor to things like testosterone and estrogen. And of course, phosphorus lipids which form the cell membrane and every single one of the three dozen or so trillions cells you have. Now, if you're into eating meat, a lot of the fat you ingest might come from that, but guess what? Plant have fat too. Plant use for energy storage just like we do, except they do it in fruits and nuts and seeds, which when you think of it are kind of like plant-based milk. It's food for their growing babies. Either way though, when you eat lipids, your body breaks down triglycerides into glycogen and fatty acids. Those molecules can then be processed in used in the making of ATP or they might be converted into other kinds of fatty acids which your cells can then reassemble into your very own triglycerides or phosphate. And your liver happens to be great at converting one fatty acid into another, but there are some it just can't synthesize For example, Omega 6 and 3 fatty acids are called essential fatty acids because your body can't make them, so they have to be ingested. They get turned into all kinds of useful molecules like the ones used for napkins formation in the brain and for signaling inflammation during the healing process. But if carbohydrates provide energy and fats insulate and store energy, then just about everything else is done with proteins. They form the bulk of your muscle and connective tissue, but they're also what the ion channels and pumps are made of in your neurons and muscle cells and they make up your enzymes which are responsible for pretty much every chemical reaction in your body. In other words, your body runs on protein and pretty much is protein. Nutritionally speaking, meats, dairy products, eggs, legumes, nuts, cereals are all particularly high in protein. But because everything we eat was once alive and every cell of every living thing contains protein. As long as you're eating whole foods, you're at least partially restocking your protein supplies. So, that might seem like you'd have to eat muscle to make muscle or eat enzymes to make enzymes, but that's not how it In all your proteins are made up of just 20 amino acids, the difference between the thousands of unique proteins are simply in the sequence of those amino acids. And of course, you have a specialized molecule that knows just which amino acids to put together in what order to make a certain protein is called DNA. When you consume some hamburger, for example, the protein act in the meat gets catabolized into its component amino acids, which gets mixed up with all of the amino acids from all the other proteins in the meat like the collagen, and elastin, and Titan, and myasin, as well as all the protein from the bun and the tomato and the. Those amino acids then get re-assembled using anabolic reactions into your very own but somewhat different proteins as defined by your DNA. It cell is like a picky little Gordon Ramsey and it has to have every amino acid needed, every ingredient present before it will even think about starting to make a protein. And just like with your lipids, your cells can improvise and convert some amino acids into others if they're missing an ingredient. However, there are nine essential amino acids that you cannot make from others and have to eat. Now lots of foods don't provide every essential amino acid, but when you combine foods like beans and rice or pasta and cheese, you do get all of the essential amino acids, which is important because remember after water, you are mostly made of protein on the order of 16%. But what about the 1% of you? The carbohydrates. How that tiny fraction of you ends up creating all of the energy is what we'll discover next time. But for now, you've learned all about the vital nutrients including water, vitamins, minerals, carbs, fats, and proteins as well as how anabolic build structures and require energy while cata- edited by Blake Depayino and her consultant is Dr. Brandon Jackson. It was directed by Nicholas Jenkins, edited by Nicole Sweyne, our sound designer is Michael Aranda and the graphics team is Dot Cafe.
