Welcome to Big Looks at Small Things (BLAST), an in-depth, medically grounded look at the small things, moments, and experiences most of us share in but never think about. Today: We’re looking at the war for your stomach.
Thanksgiving is tomorrow, and by now we’ve all been inundated yet again with the cautionary reports and articles telling us not to overeat during our holiday meals. It’s as traditional as the turkey itself — but overeating, like jaywalking, is one of those things many of us do despite knowing we shouldn’t.
So let’s skip that diatribe. In fact, let’s skip the main course of the meal altogether. Let’s fast forward to a minute or two after you put your dinner fork down, when you’ve eaten way, way too much and the idea of even looking at dessert is almost enough to make you a little dizzy — but just a half hour later, you’re midway through your first slice of pie and giving a hearty glance at a second.
What’s going on in those thirty minutes? What’s happening in the body that takes you from, “There’s absolutely no way I’m eating anything else tonight” all the way to, “Say, that dessert’s looking pretty good” in such short order?
The answer is simple in some ways and complicated in others, so let’s start where the action is: your stomach.
The Bag and the Grinding Machine
Make a fist. That’s a handy — if you’ll pardon the pun — way to estimate the size of your stomach when it’s empty. Doesn’t look very big, right? Especially compared to a full plate of Thanksgiving Day food.
Thankfully, your stomach’s rather pliable.
“The stomach can hold about a liter or eight cups of volume,” said Linda Sartor, RD, MA, CDE, LDN, a Penn Medicine diabetes nutritionist. “Stretch it any further, and there’s literally nowhere for it to go.”
No surprise, there: When you eat things, your stomach will fill up. Simple enough. But there’s far more going on behind the scenes, and a lot of it plays directly into that ability for you, only a short time later, to reach for dessert.
The first step to understanding that process is realizing that your stomach is far more complex than you might think.
“The stomach does lots of different things,” said David Metz, MD, a Penn Medicine gastroenterologist. “It’s kind of a double organ, with two halves — a top half and a bottom half — that have different functions.”
According to Metz, the top half of the stomach is probably close to what you have in mind: It’s more or less a bag. It stretches to accommodate incoming food and holds it there, channeling it into the bottom half of the stomach through a controlled process called receptive relaxation.
That’s where things get messy.
“The bottom half of the stomach is sort of a grinding machine,” Metz said. There, food gets broken down enough to be pushed into the duodenum and begin its journey through your intestines.
Obviously when the stomach doesn’t have any more room to expand, it can let you know in some fairly unpleasant ways — but let’s say you didn’t quite push it that far during dinner. Let’s say you’re just full beyond the point of wanting another bite. Food’s in the bag and making its way into the grinding machine. Room’s eventually going to be made, but you should be satiated for a good, long while. Right?
Maybe. The physical mechanisms are one thing, but the tricky balance between those mechanisms and the body’s chemical response to a massive influx of food is another thing entirely.
The Chemical Component
Something I learned while putting this post together: Discuss the topic of hunger and satiation with medical professionals enough, and you’re going to hear the words leptin and ghrelin with some frequency.
We’ve actually discussed leptin and ghrelin before on this blog (not coincidentally, also right around Thanksgiving Day). They’re the hormones on either side of the battle for your stomach. Leptin’s all about appetite control; it tells you when you’ve put enough away and keeps you from eating more. Ghrelin, on the other hand, is what’s released when your body needs fuel.
According to Metz, the cycle normally goes something like this: You haven’t eaten for a while, and your body notices. It releases ghrelin, which makes you seek out something to eat. Once you eat, your body starts releasing leptin and you feel full for a few hours, until the leptin wears off and the cycle begins anew.
But according to Sartor, when you eat way, way more than you should in one sitting — like, say, around the holidays — things get more complicated.
“High amounts of sugar in its various forms — including carbs, so things like bread, stuffing, mashed potatoes, and yams — kick up your blood sugar, which kicks up insulin production. As the insulin moves the sugar from food into the cells and muscles, the ghrelin drops and the leptin increases — but sometimes these hormones aren’t released adequately or quick enough to stop the eating,” she said.
If leptin and ghrelin are the boxers duking it out in the ring that is your stomach, your huge Thanksgiving Day meal is the guy with a giant fan on his back who parachutes into the middle of the fight and messes everything up.
That’s just a quick overview, of course. There’s more to it than just leptin and ghrelin, including pieces of the puzzle we’re only just now discovering. Metz noted that researchers are still finding new hormones and peptides involved in the process.
Mind Over Matter?
So with your stomach working overtime and your body’s chemicals doing their best to keep things regulated in the face of a massive chemical influx, what is it that ultimately makes you reach for a slice of pie despite being as full as can be?
It may be as simple as mind over matter.
“Human beings were never made to be able to shop at supermarkets,” Metz explained. “We’re opportunistic eaters. Our natural state is to be hungry; we’re supposed to eat to survive.”
Full as you might think you are after you’ve put away that last bite of turkey, it may just be in your nature as a human being to go back for more as soon as it’s made available in the form of, say, pumpkin pie.
“At some point, the feedback just isn’t as strong as the desire for more food,” Metz said.
“When someone goes back for dessert after eating a huge meal, that’s the brain overriding the signals the body’s sending out,” she said. “We can mentally push beyond that.”
In short: Your body certainly isn’t telling you to take some pie. It has enough to keep it busy for a good, long while. Your mind, however, might have other plans — which means it’s mostly about willpower.
And if you need a little extra motivation, it’d be hard to top what Sartor told me to close out our conversation:
“The average person consumes about 3,000 to 4,000 calories during their Thanksgiving Day meal,” she said. “You’d have to walk about 30 miles to burn that off.”