I get diarrhea a lot more than I want to. I’ve identified some causes, but I can’t think of anything that might have triggered my current spell.
My ex thought that eating too much would cause it, but he was an idiot, so I am taking that with a grain of salt
IME eating too much greasy stuff and / or too much coffee certainly can cause urgent loose stool in 20-30 minutes. Whether that rises to the level of “diarrhea” is a matter of terminology; lotta folks use that word to mean different things than medics do.
But mere quantity of otherwise innocuous food? Not IME.
As an example, the competitive eaters who overdo it always barf, not shit themselves.
If I’ve been on a relatively strict diet, and then eat a meal that would have been normal for me before, my system doesn’t always respond the way it did before. Diarrhea is sometimes the result.
From WebMD:
If too much salt in your diet makes you dehydrated, your stomach will feel it. You might feel nauseated, or you might have diarrhea.
Just sayin’ 
Seriously though, I hope you resolve your issue soon. In my opinion, too much food alone shouldn’t cause it.
And too much idiot can cause diarrhea. Seriously - although this source of stress is out of your life, stress can certainly exacerbate diarrhea.
So “once”?
Ok. That was funny.
I have noticed that as well.
That seems to happen with me sometimes, but of course I cannot rule out other factors 100 percent. But I feel the correlation is there.
I wonder if what happens in that case is that certain types of ultra processed foods cause people to eat more than intended, past the point of satiety, at which point they get diarrhea and make this correlation when the real culprit is the nature of the food.
I’ve had IBS most of my life. Reducing FODMAPS helped, passing on carbonated beverages at restaurants helped, avoiding certain dairy products helped, changing birth control medications helped. Nothing has ever made it go away completely.
I have heard of carbonation + rich foods causing the dumping reflex so I avoid carbonation when eating rich foods and it really seems to help.
If you haven’t looked into FODMAPS, I would. Doing a FODMAP elimination diet is how I discovered the innocuous foods that worsen my IBS like bananas, blackberries and honey. Stuff you just wouldn’t think about.
I didn’t know if people get loose stool from overeating, but i had a foster cat who did. We over-fed her anyway, because she hated having kittens, and hissed at them and batted them away. And the only time she reliably let them nurse was right after she’d eaten a lot of wet cat food. It’s much easier to clean cat shit off the bathroom floor than to bottle-feed kittens, so we fed her a lot.
And we weaned that litter as early as we could and sent the cat back to the shelter, where she was much happier without all those demanding kittens bothering her.
(We fostered lots of mom-cats, and most enjoyed nursing and grooming their kittens. This one really really didn’t.)
Have you been tested for H-pylori virus?
Certainly eating too much of one thing can affect you. I once had the most perfect cantaloupe. It was heaven. If I didn’t eat the whole thing in one sitting then I was close. Bad idea.
Having had severe constipation once due to a diet I was on, I would have paid many dollars for a sudden bout of diarrhea.
I’ve also learned that sweet drinks can cause the same issue for me; if I eat too quickly, too much of any liquid seems to trigger dumping. So if I know I need to eat a meal (often lunch) in a hurry, I won’t drink anything while eating, and will wait about 30 minutes after my last bite to drink anything. Probably unhealthy, but it reliably keeps that reflex in check.
My body also can’t handle greasy foods, or even oil like you would find in improperly mixed salad dressing or as a garnish for hummus. I’ve also started having issues with dairy. And let’s not get into sugar alcohol-based sweeteners - a known diarrhea culprit - hiding in seemingly random foods. (Wasabi paste??? Really???)
Chronic diarrhea (even if intermittent) should be investigated. Stool samples should be analyzed, food intake and diets reviewed with a professional, and colonoscopy should be considered. Common causes are many, including food sensitivities, true food allergies, malabsorption due to pancreatic dysfunction or other causes), celiac disease (gluten sensitivity), lactose intolerance, GI tract infections/infestations, inflammatory bowel disease, irritable bowel syndrome, and even partial colonic obstruction by masses like tumors. So go ahead and track your diet and symptoms, and maybe adjust some things that may seem possibly causative, but then take that info to a health professional.
Since I started this thread, I figured out why I was having diarrhea so much.
I have a bad habit of buying baked goodies when I shop, then eat them a little bit at a time. For instance, I would get mini cinnamon rolls and eat one or two a day. I also take more than a week to go through a loaf of bread.
So, I decided to toss or freeze baked goods after several days of having them, and stopped having diarrhea.
Basically, I was giving myself food poisoning. 
Sort of like my fondness for Chinese buffet; wherein stopping eating the fried rice at the buffets was also helpful
Yup
Yup. What really pissed me off was an iron supplement my doctor recommended that had both a sugar alcohol sweetener and lactose
I had that done once many years ago and nothing was found. And I really didn’t like the process so I haven’t volunteered for that again
I’ve had an upper GI and a top to bottom GI. I’ve worked with a gastroenterologist because I also have problems with nausea. I do have a hiatal hernia.
Can they test for those, or is it a matter of "we can’t really tell what’s wrong with you so we’ll put it under this umbrella "?
FTR, I have an allergy to Mac nuts, and sensitivity to peanuts and cashews. And a duodenal ulcer* because I have to be different .
*the nexium keeps that at bay
But that is a good checklist
This is what we patients call a multi-faceted disorder that screws you up from many angles, works together to make your life hell and sits in the corner and laughs at you.
Inflammatory bowel disease can generally be diagnosed by colonoscopy with biopsy. Irritable bowel syndrome is more of a ‘we’ve ruled out most other causes, so it’s probably IBS’. I’ve got IBS and went thru a few years of varied studies to get that diagnosis. Treatment with bile acid binders has been successful in reducing symptoms for me.
I’m glad you’ve found what triggers your symptoms and have eliminated them (no pun intended on initial typing of that, but then I decided to not remove the comment, so I guess it is intended. ;-D )
You can certainly mess up your digestive system by overeating. Diarrhea would be one possible result. I think what you overeat is going be a more determinative factor.