Muscle. Almost always muscle. Muscle and fat. Let me repeat again, muscle.

But if you're eating liver, you're literally eating the liver organ. If you're using giblet gravy, the giblets typically include the heart and gizzard (both specialized muscles) as well as the liver. Stock will contain the collagen from bones. Other organ meats are no longer common in the US but can be found in specialty markets.

Meat Equals Muscle Tissue

Almost everything we think of as "meat" is primarily muscle tissue. Sometimes skin is involved. There is also fat involved as well, but for most meat the fat and skin are a very small fraction of what you're eating.

There is also organ meat, which are organs. Liver (Italian Style Beef Liver is the perfect example), heart and intestines (tripe) are the most common organs, but others are eaten as well.

"Meat" can also include bone marrow, but this is usually its own thing. When I was a little girl, I had bone marrow many times and it was incredible. Like pure deliciousness you could spread on toast.

When I Am Eating Meat, What Am I Actually Eating?

Let's be honest - when you're cutting into a steak, you're probably not thinking "ah yes, dead muscle tissue, mostly water." But that's exactly what's on your fork, and once you know it, cooking meat well makes a lot more sense.

Plot Twist: It's Mostly Water

I know, I know - you paid $30/lb for water. But it's true: meat is 56-75% water depending on the cut and animal. Beef hovers around 60%, chicken closer to 65%, fish up to 70%. That water is the juice pooling on your board, the steam hissing off your pan, and the entire reason overcooked chicken turns into a sad, dry hockey puck - you basically cooked all the water out of it.

The Protein Squad

Behind the water is protein, sitting at a modest 17-20% of the meat. This isn't one boring blob - it's a whole team with different jobs:

• Myosin and actin - the duo that made the muscle actually move, and now make up most of the protein you're chewing
• Myoglobin - the pigment responsible for that red-to-brown color shift, basically meat's built-in "doneness" indicator
• Collagen and elastin - the connective tissue that holds everything together, and the reason low-and-slow cooking turns tough cuts into fall-apart, saucy magic (collagen melts into gelatin)

Fat: The Supporting Actor

Fat swings wildly from 5% to 28% depending on the cut. A skinless chicken breast is basically fat's ghost town, while a well-marbled pork shoulder is throwing a fat party. Either way, fat's job is to keep things juicy once the water starts evaporating in the pan. Here's interesting take on Why Fat Doesn't Make for a Flavorful Steak.

Working Muscles Taste Different

Not all muscle is created equal, and how much work a muscle did while the animal was alive changes what ends up on your plate. Hard-working muscles like chuck, skirt, or shank are loaded with connective tissue and myoglobin because they're built for constant motion and endurance, which is exactly why they carry deeper, beefier flavor and need slow cooking to break that collagen down into gelatin.

Tenderloin, by contrast, is a muscle that barely does anything-it just hangs out along the spine, protected and underused. That's why it's famously tender but comparatively bland; it never had to build up the connective tissue or myoglobin density that gives working muscles their character.

• Chuck, skirt, brisket: high collagen, high myoglobin, big flavor, needs low-and-slow heat or a hot fast sear to work
• Tenderloin, ribeye cap's neighbor (the eye): low collagen, low connective tissue, tender out of the gate but milder tasting
• Oxtail, shank: extreme end of "worked hard," almost all connective tissue, built for braising

This is really the same water-protein-fat-collagen framework as before, just applied unevenly across the animal-muscles doing constant work accumulate more of the flavor-and-texture-building components, while the "lazy" muscles stay soft and mild.

The Amino Acid Plot Twist

One more nerdy detail worth knowing: because most of what we eat today is muscle meat - steaks, breasts, fillets - rather than whole-animal cuts with skin, bone, and connective tissue, our diets lean heavy on an amino acid called methionine and comparatively light on glycine, which mostly comes from collagen-rich parts like bone broth and skin. Not something to panic over, but it's a big part of why grandma's bone broth obsession wasn't just a "waste not" thing - it was actually balancing the amino acid math.

So next time you're eating a steak, you're really just eating water, held together by a protein scaffolding, seasoned with fat, and colored by a pigment.

Quick Overview

Muscle, fat, veins and arteries, maybe skin. Offal is "meat" too, organ meat. Some organ meat might be muscle, as with heart, for example. Some offal isn't muscle; it's glands like liver, sweetbreads, etc. Then there's tongue, which is definitely meat, but is muscle and glands.

Put The Meat Science To Work

Put the Science to Work

Now that you know why hardworking muscles need low, slow heat to break down all that collagen, it's the perfect excuse to try a Red Wine Braised Beef Chuck Roast (Fork-Tender, Dutch Oven) or an Apple Cider Pot Roast - Tender, Fall-Apart Beef - both let time and moisture do the collagen-to-gelatin conversion for you.

If you'd rather lean into that deep, worked-muscle flavor without the long braise, an Instant Pot Irish Beef & Guinness Stew gets you there faster, or go the other direction entirely with quick-cooking cuts in Sizzle & Flavor: Perfectly Marinated Beef Kebabs.

Curious how breed and marbling change the fat-to-protein ratio we talked about? What Is Black Angus Beef? A Cook's Guide to Better Steak breaks that down. And if you want to see the water-loss principle in action during smoking, How to Wrap Meat in Pink Butcher Paper (With Beef Tallow) shows you how to manage moisture during long cooks.

For quicker weeknight ways to use ground beef - where muscle structure has already been broken down for you - try the Mexican Ground Beef and Rice Skillet (Easy One-Pan Dinner), Ancho-Chipotle Pulled Beef Street Tacos, or see how it stacks up against chicken in Ground Beef Ramen Stir Fry vs. Chicken: Which Is Better?