I weigh about 80 kilograms. Most of that, let’s say 64 p.c, is water — although you may’t inform by wanting. I imply, as organisms go, I wish to assume that I look pretty stable. After water, the subsequent largest proportion of me is protein, about 16% — not simply in my muscle tissue, but in addition in issues just like the tiny sodium-potassium pumps in my neurons, and the hemoglobin in my blood, and the enzymes driving the chemical reactions in each one of my 37 trillion cells. Then one other 16% of me is fats, which I’m completely OK with; 4 p.c of me is minerals, just like the calcium and phosphorus in my bones, and the iron in my blood; and 1 p.c is carbohydrates, most of which is both being consumed as I discuss to you, or is sitting round as glycogen ready for use. However right here’s the factor: It’s not like I simply ate 80 kilograms of meals after which all this occurred. As a substitute, my physique, like yours, is consistently buying stuff, extracting a few of it to maintain, burning a few of it for power, and eliminating the remainder. However even the stuff that my physique does maintain onto doesn’t final eternally. A number of the chemical substances that I take in in my meals ultimately turn out to be part of me. However enzymes put on out, and membranes break down, and DNA will get oxidized. So, they get discarded. After which I want extra of these chemical substances to reconstruct the fabric that I’ve misplaced. In consequence, over the course of my lifetime, my cells will synthesize someplace between 225 and 450 kilograms of protein … That’s like 3, or 4, or 5 separate me’s — simply made from protein. And all the protein and fats and carbohydrates nucleic acids that make up me, in fact, come from meals. Each organism has to maintain taking in and breaking down meals, to maintain resupplying itself with the uncooked supplies it must survive. And all that exercise requires power, which we additionally achieve from meals. So, how do our our bodies really convert what we eat into power and uncooked supplies? The reply is a neverending sequence of reactions which can be devoted to doing two important, and completely contradictory, issues: One set of chemical reactions destroys the reactants that you just give them, lowering huge, advanced substances into molecular rubble. And the opposite set reassembles that rubble into new and larger merchandise which can be put collectively once more to make you. So our our bodies are continuously reinventing themselves — in a perpetual state of loss, but in addition at all times rebuilding. And though all of that is taking place on the mobile degree, its penalties may hardly be bigger. These two units of reactions are the place every little thing that we’ve realized to date — in regards to the digestive, endocrine, circulatory, and respiratory techniques — actually begins to come back collectively. Collectively, these processes make up your metabolism. Now the sciencey phrase metabolism has come to have a which means in fashionable speech, however metabolism isn’t only one factor. Individuals speak about metabolism as which means, like, how briskly your physique burns the gasoline in your meals, or how excessive your private power degree is. And that’s nice to be used by private trainers and health magazines. However physiologically, metabolism actually describes each single biochemical response that goes on in your physique. And possibly extra importantly, it reconciles two conflicting chemical processes which can be at all times, concurrently underway within you. A kind of chemical forces is anabolism. Anabolic reactions assemble issues and eat power. These are the processes that take the small monomer constructing blocks in your meals — like monosaccharides and fatty and amino acids — and construct them into greater, extra advanced polymers like carbs, and fat, and proteins which can be utilized in your cells. Then, once you want new constructing blocks, or it is advisable to launch some power, these polymers in your physique, or new ones in your meals, get damaged up — by catabolic reactions. The processes of catabolism break down greater molecules, and in breaking their bonds, launch the power it is advisable to keep heat, and transfer round, and supply your cells with gasoline … to construct the polymers again up once more. To be trustworthy, your metabolism is quite a bit like Sisyphus. It really works actually laborious. However it’s by no means completed. And the boulder that your inside Sisyphus is at all times pushing uphill and watching fall again down? That’s vitamins — the molecules that your physique is eternally breaking apart, and then rebuilding, solely to have them break aside once more. And these vitamins — the supplies your physique must construct, keep and restore itself — are available in six main teams. By quantity, nearly all of what we eat — and what makes up our our bodies — is water, in order that’s possibly essentially the most important nutrient. Then there are nutritional vitamins, compounds that are available in both fat-soluble or water soluble kinds. They aren’t used as constructing blocks or for power, however they’re important in serving to the physique make use of different vitamins that do do these issues. Vitamin C, for instance, helps enhance iron absorption, whereas vitamin Ok is essential to blood clotting, and a few B nutritional vitamins are essential within the manufacturing of ATP from glucose. Minerals, like nutritional vitamins, they don’t present gasoline, however they’ve all types of different capabilities. Calcium, magnesium, and phosphorus harden bones and tooth, whereas iron is, in fact, essential in hemoglobin. Plus, potassium, sodium, and chlorine assist keep your physique’s pH steadiness and are utilized in motion potentials. So water, nutritional vitamins, and minerals are all … mandatory. However the three main vitamins that everybody at all times talks about — those you discover on meals labels, from oatmeal to Pop-Tarts — are carbohydrates, lipids, and proteins. A lot of the carbohydrates you’ve ever eaten — except for lactose in milk — initially got here from vegetation. Mono- and disaccharides come from fruits, honey, sugar beets and sugar cane, whereas polysaccharide starches come from veggies and grains. The principle factor it is advisable to know is that the monosaccharide glucose is the be-all-end-all molecular gasoline that your cells have to make ATP. ATP being the molecule that your cells use to drive anabolic reactions, after they want to make new polymers or get anything accomplished — whether or not that’s working a sodium-potassium pump, or detaching the pinnacle of a myosin filament to contract a muscle. However ATP is just too unstable to retailer, so cells typically retailer power within the type of glucose, which they’ll then catabolize and convert to ATP after they want it. Now, a few of your cells can get their power from fat. However lots of an important ones, like your neurons and purple blood cells, feed solely on glucose. So many of the carbs that your intestines take in are transformed to glucose for that motive. However, if it’s not wanted immediately, that power may also get saved as glycogen in your liver and muscle tissue, or transformed to glycerol and fatty acids to make triglyceride fat. And though there appears to be a advertising and marketing warfare occurring in opposition to dietary fat, we most positively want them. The fat in your adipose tissue retailer power, in fact, however additionally they retailer fat-soluble nutritional vitamins, and cushion your organs. Lipids additionally kind the myelin that insulates the neurons in your mind and all through your physique, in addition to the oil in your pores and skin, they usually present the important calorie content material present in breast milk. However there are different essential lipids, like ldl cholesterol, which is the precursor to issues like testosterone and estrogen… …and, in fact, phospholipids, which kind the cell membrane in each single one of many three-dozen-or-so-trillion cells you’ve. Now, should you’re into consuming meat, numerous the fats that you just ingest would possibly come from that. However guess what: Vegetation have fats too. Vegetation use lipids for power storage identical to we do, besides they do it in fruits, and nuts, and seeds. Which, once you consider it, are type of like plant breast milk — it’s meals for his or her rising infants. Both manner, although, once you eat lipids, your physique breaks down triglycerides into glycerol and fatty acids. These molecules can then be processed and used within the making of ATP. Or they is perhaps transformed into other forms of fatty acids, which your cells can then re-assemble into your very personal triglycerides or phospholipids. And your liver occurs to be nice at changing one fatty acid into one other, however there are some it simply can’t synthesize. For instance, omega 6 and three fatty acids are referred to as important fatty acids, as a result of your physique can’t make them, so that they must be ingested. They get became every kind of helpful molecules, like those used for synapse formation in the mind, and for signalling irritation throughout the therapeutic course of. However — if carbohydrates present power, and fat insulate and retailer power, then simply about every little thing else is completed with proteins. They kind the majority of your muscle and connective tissue, however they’re additionally what the ion channels and pumps are made from in your neurons and muscle cells, they usually make up your enzymes, that are accountable for just about each chemical response in your physique. In different phrases, your physique runs on protein, and just about is protein. Nutritionally talking, meats, dairy merchandise, eggs, legumes, nuts, cereals are significantly excessive in protein. However as a result of every little thing we eat was as soon as alive, and each cell of each residing factor incorporates protein, so long as you’re consuming complete meals, you’re at the very least partially re-stocking your protein provides. Now it’d seem to be you’d have eat muscle to make muscle, or eat enzymes to make enzymes, however that’s not the way it works. Since your entire proteins are made up of simply 20 amino acids, the variations between the 1000’s of distinctive proteins are merely within the sequence of these amino acids. And, in fact, you’ve a specialised molecule that is aware of simply which amino acids to place collectively in what order to make a sure protein. It’s referred to as DNA. Whenever you eat some hamburger, for instance, the protein actin within the meat will get catabolized into its element amino acids, which will get combined up with all of the amino acids from the different proteins within the meat — just like the collagen and elastin and titin and myosin — as properly as all of the protein from the bun and the tomato and the mayonnaise. These amino acids then get reassembled utilizing anabolic reactions into your very personal, however considerably completely different, proteins, as outlined by your DNA. Every cell is sort of a choosy little Gordon Ramsay and it has to have each amino acid wanted — each ingredient current — earlier than it should even take into consideration beginning to make a protein. And identical to along with your lipids, your cells can improvise, and convert some amino acids to others in the event that they’re lacking an ingredient. Nevertheless, there are 9 important amino acids that you just can’t make from others, and must eat. Now a number of meals don’t present each important amino acid, however once you mix meals, like beans and rice, or pasta and cheese, you do get all the important amino acids. Which is essential as a result of, keep in mind: after water, you’re principally made from protein. On the order of 16% However what in regards to the one p.c of you? The carbohydrates? How that tiniest fraction of you finally ends up creating all the power, is what we’ll uncover subsequent time. However for now, you’ve realized all in regards to the important vitamins — together with water, nutritional vitamins, minerals, carbs, fat, and proteins — in addition to how anabolic reactions construct constructions and require power, whereas catabolic reactions tear issues aside and launch power. And collectively, these competing forces kind the splendidly conflicted course of often known as metabolism. Thanks to our Headmaster of Studying, Linnea Boyev, and because of all of our Patreon patrons whose month-to-month contributions assist make Crash Course attainable, not just for themselves, however for everybody, all over the place. When you like Crash Course and need to assist us maintain making movies like this, you may go to patreon.com/crashcourse This episode was filmed within the Physician Cheryl C. Kinney Crash Course Studio, it was written by Kathleen Yale, edited by Blake de Pastino, and our marketing consultant is Dr. Brandon Jackson. It was directed by Nicholas Jenkins, edited by Nicole Sweeney; our sound designer is Michael Aranda, and the Graphics staff is Thought Cafe.