“Hungry or Undernourished?” is what I would call a BIG question. It is way out of my league to propose a scientific answer or even describe the parameters of a proper study. I will venture, however, to tackle the matter as an opinion piece: I think it can be parsed into at least two different lines of reasoning, and I will attempt to posit and briefly explore them. I welcome informed comments from my erudite readers.
Proposition #1: We will eat until our STOMACH IS FULL. This is the “common sense” hypothesis; we have all experienced it. When we are “full,” we stop eating. Of course, there are lots of exceptions. We sometimes eat for other reasons, e.g., “nervous” or compulsive eating. There’s also taste and palatability. See this link to carbohydrate-induced overeating (in rats). Lay’s potato chips captured this with the memorable meme, “Bet you can’t eat just one!”
There is a large body of new evidence that the “until full” hypothesis is hormonal. Hunger is regulated by a small organ in the brain, the hypothalamus, which gets signals to induce eating from ghrelin, a hormone produced in the lining of the stomach. and shuts down when another hormone, leptin, signals that hunger has been satisfied. Ghrelin was only discovered in 1999 and appears to have other functions as well. And “leptin resistance,” as a cause of obesity, is still a mystery. So, this is why the hormonal hypothesis of “eating until full” is also just a hypothesis.
Proposition #2: We are “driven” to eat until the body has met its requirements for ESSENTIAL NUTRIENTS. If this sounds like a tautology, let me explain. It is, of course, more nuanced, and at this point in the state of nutrition science, little is known. The theory is that it is what we eat, not how much, that determines when the body is satisfied and hunger stops. Ergo, if your diet consists primarily of nutrient-poor components, aka processed carbs, you will need to continue to eat until your body gets everything it needs.
These essential nutrients include the both macronutrients and micronutrients. The macros are fats, broken down to fatty acids: saturated and unsaturated (monounsaturated and polyunsaturated), proteins (broken down to their 22 amino acids), and carbohydrates, including simple sugars and longer chains of glucose (starches). The micronutrients are vitamins, minerals and phytochemicals, many or which are as yet unknown.
A few of the amino acids from protein are essential, meaning the body cannot make them, and we therefore must get them from food. A few of the fatty acids from polyunsaturated fat, specifically Omega 3’s and Omega 6’s, are also essential. We must “eat” them or take a supplement. No carbohydrate – repeat, NO CARBOHYDRATE IS ESSENTIAL.
My recollection is that this second line of reasoning is suggested in such very good books as “The Perfect Health Diet,” by Paul and Shou-Ching Jaminet, and Catherine Shanahan’s “Deep Nutrition.” It is a rational hypothesis, and I am biased in favor of it in part because the science re: essential fats and essential amino acids is pretty well established, particularly how their absence is detrimental to human health. As such, the body takes care of itself until we get them
It also appeals to me because it supports the idea that all dietary carbohydrates, while a good source of quick energy, are not essential nutrients in the human diet. When carbs are not available to eat, our bodies are designed to make all the glucose it needs from protein and fat, through gluconeogenesis. The body also produces ketone bodies (brain food) from fat, and it uses stored glucose (glycogen in the liver) and gets additional glucose from the animal products we eat (intramuscular glycogen and from organ meats like liver some of us eat). Admittedly there still isn’t a lot of evidence to support this hypothesis. Philosophically, though, it appeals to me. I believe the body takes care of itself.If I had to guess, I’d hedge my bet by speculating that the ultimate answer will involve or combine these two hypotheses. In the meantime, we can be guided by what we “know” and eat with the knowledge that our bodies will determine how much we need to eat and what a healthy diet is. I find my body likes it best when I eat mostly “healthy” fats (saturated and monounsaturated), and moderate amounts of protein from eggs and pastured meats and poultry and wild-caught fish. I try my best to avoid polyunsaturated fats (all “vegetable” oils) altogether and since I am Insulin Resistant (34 years a diagnosed type 2 diabetic), I try to eat as few carbohydrates as possible.