I remember sitting at my desk, back when I had a desk job, searching fruitlessly on the internet, trying to figure out exactly what makes a belly a belly. Why does that one part of the body protrude? Why can it change so quickly? It seems to be bigger one day, smaller the next. Is it really made of beer? Or fat? Or what? It’s surprisingly difficult to get a satisfactory answer to the question. It’s been in the back of my mind as I’ve studied anatomy and physiology over the years and it’s only within the previous year that I think I can answer the question well.
And so, I am pleased to present to you my first use of the tag “speculative physiology”: My current synthesis from countless sources on this eternal question: “What is a belly, exactly?”
Layer one: visceral fat. This is the answer you’ll get if you do a quick google. It’s the oh-so-dangerous fat that accumulates around your abdominal organs. Ok, sure, that makes sense that it provides some padding and would make the gut bigger, but I just couldn’t believe this was the sole cause of a belly. I mean, why would the size of the belly change so much more than, say, the thighs, if it were just about fat storage? There must be more to this story…
Layer two: the intestines. When things are inflamed, they swell. It’s one of the four signs of inflammation (red, hot, painful, swollen). And intestines are empty tubes when there’s not food in them. So when intestines are full of food and/or gas they take up more space. When inflamed they take up even more space. So, there’s that. Ok.
Layer three: the greater omentum. And then we dissected cats in my Anatomy and Physiology class lab. We slit the belly open and spread the flesh apart and “HOLY CRAP WHAT IS THAT HUGE THING?” The professor looked perplexed. “It’s the greater omentum, I went over it in lecture last week.” Duh. We hear so much about the stomach, the liver, the kidneys, the intestines, the brain, the heart, the lungs. I guess I always thought they were the biggest organs, that their fame would correspond with their size. Cut open a belly, though, and, by far the largest organ you’ll see is the greater omentum. And yet somehow most people haven’t even heard of it. It’s a folded over flap of the peritoneum, which is the sac that envelops all of the abdominal organs. It is rich with lymphatic vessels and so has a creamy sort of look from all that lymph. Now, the lymphatics are one of the main places where your immune system lives and immune cells have many high-energy jobs to do. Nothing provides more energy more efficiently to your body’s cells than fat, so where there are lymphocytes, there is fat. (And where there are fat deposits, there are lymphatics, but that’s a different story.) Your liver can only turn excess dietary fat into long-term fat stores at a certain rate, so it keeps the overflow in the greater omentum, where it can be used by lymphocytes in the meantime. And especially if the liver is so busy turning excess sugar into fat for storage, it needs a place to store the fat in the moment. Once I got all this worked out I felt I understood better why a belly can change size so rapidly. Whew. But why can a belly be so persistent, even after someone changes their diet and loses a great deal of fat?
Layer four: fascia. I took a weekend workshop massage class from a Rolfer, Ritchie Mintz. I already had some experience with fascia-focused bodywork and had had good success helping people with structural problems. Ritchie explained something I had never quite understood before, though. He said to think about the hard tissues of the body – the bones – and the soft tissues – the rest. The soft parts hang from the hard. Over time, the soft parts slip through the bones, pulled by gravity, exacerbated by forward-leaning posture and from a heavy belly due to the three above-listed factors. A situation is created where there is too little tissue on the back, making it feel hard and leaving it without enough slack to be able to move and slide well. Too much tissue gathers in the front, becoming soft and excessively lax. Swimming face-down helps the bones sink down through the soft tissue, giving that nice swimmer’s body with a relatively flat belly. Or a fasically-aware bodyworker can pull the tissue from the front through the spine to the back, flattening the belly in the process.
And so, finally, nine years later and with training in three alternative health care modalities, I have my answer! Phew.
Please, I ask for feedback on all of my posts, but if you, reading this, are also an A&P geek and think I am wrong about anything here or missing some other point, please, please, please write and let me know! This is one of those topics where I feel I have reached a satisfying plateau of understanding, but hope to climb yet higher! Thank you.
Within a couple days of posting this, I was sitting with a group of friends and another theory was mentioned. I love how that happens! It's like when you learn a new word and suddenly hear it all the time. This guy said that he switched to a vegetarian diet and within weeks had a huge belly. He went to a doctor and the doctor told him that was because his intestinal muscles had to work so hard to push all that vegetable fiber through that they had gotten overdeveloped and caused his belly to protrude. The doctor advised that he eat less fruits and vegetables and more meat. Another person at the table said "that's the sort of thing you would never learn unless you talked to a doctor!" Indeed.
Instead of rejecting this theory out of hand, I researched a little about intestinal smooth muscle hypertrophy and megacolon. The consensus in the scientific literature does seem to be (as I thought) exactly the opposite. A high-fiber diet creates chyme and eventually feces that is bulky and soft and therefore fairly easy for the intestines to push through.
Another interesting tidbit – hypertrophy of the smooth muscle surrounding the intestines is closely associated with inflammation, not mechanical demands. That overgrowth disturbs the shape of the surface of the muscle, making diverticula more likely to develop. Huh, ok. So that means that even if the excess bulk that is causing the belly to protrude is partly due to muscle thickening, that might be secondary to inflammation, like I said in the post.
I really enjoyed this post! I've always appreciated how you explain human anatomy in a way that is very easy to digest (pun intended). I've never taken A & P so I've been trying to piece together the body from my own informal reading. Stuff like this is helpful. -Ale