To be clear, I’m asking what property is in food that, upon accumulating in the stomach, causes me to go from hungry to full?
The two top contenders in my mind are mass and volume. Although for all I know it could be something obscure like fiber content or the color green.
I’m fairly sure it isn’t calories, or else obesity wouldn’t be a problem.
On a related note, when we talk about ‘calorie-dense’ foods how are we measuring density? Is it calories per mass, calories per volume, or something else entirely?
I don’t know the full answer but I once worked closely with a professor that did research on this. The thing that stuck with me was how big and complex this seemingly simple topic seems to be. The scientific term is called “satiation” and involves several neural pathways within the brain, especially the hypothalamus, and complex chain of events to trigger it. The stomach actually doesn’t have all that much to do with it from a behavioral perspective although it is a key basic component to kick of the real events. Actually, I am fairly certain that no one has the full answer to your question and a summary of where the research stands today would require a full college level class.
That said, you can look up satiation and satiety on the web to get some current research.
In 2005 my stomach perforated and when the doc operated he took my esophagus and attached it directly to the small intestine. In other words, no food goes into the stomach any more.
Why do I feel full or hungry? (or maybe why do I not always feel hungry?)
Related question: I never feel full after soup (apart from soup with chunks of meat or veg in it). Should I? If I eat, say, half a lobster, I feel full. If I eat the same amount of lobster puréed into a bisque, it doesn’t seem to fill me up. Yet if I eat a soup as an appetizer, I can rarely finish my entrée. That doesn’t seem to make sense to me. Is this just psychosomatic?
A quick search turned up this metaanalysis which suggests that the glycemic index of food (i.e., how much of a blood sugar spike it causes) is a factor.
Control of satiety (or appetite) is extremely complex. There are physical factors (eg. stomach distention), neurologic factors, psychologic factors, behavioural and social factors and, of course, hormonal factors.
With respect to hormone control alone, look here for a sense of the sheer number of hormones involved (let alone their interplay with one and other). VERY impressive.
Given the critical evolutionary need to eat, it’s not too surprising that the system is filled with redundant mechanisms. “Curing” (or preventing) obesity won’t be a quick fix.
The latest issue of *New Scientist * had a report of an ingenious study.
One group was given essentially a fasting drip of saline solution. The other a drop of PYY, “a powerful appetite-suppressing hormone that is naturally secreted in the gut after eating.” They were then offered an all-you-can-eat buffet. fMRI scans were taken before and after to see changes in brain activity.