“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.
The first line of reasoning in the “hungry or undernourished?’” debate is that we will eat until our stomach is full. This is the “common sense” hypothesis; we have all experienced it. When we are “full,” hormones signal us to stop eating. Of course, there are exceptions. We sometimes continue to eat for other reasons. I’m a compulsive peanut eater. 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 the hypothalamus in the brain 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.
The other line suggests that hunger drives eating until the body has met its requirements for essential nutrients. I know this sounds like a tautology and needs more explanation. It is, of course, more nuanced but at this point in the state of nutrition knowledge, the science is unknown. The theory is that what we eat, not how much, determines when the body is satisfied and hunger stops. Ergo, if your diet consists of nutrient-poor components, aka processed carbs, you will need to continue to eat until your body gets everything it needs.
These essential nutrients or components include the macronutrients and micronutrients. The macros are fats (fatty acids, SFAs, MONOs and PUFAs), proteins (and their 22 amino acids, into which protein breaks down), and carbohydrates, (none of which – repeat, none, are essential). The micronutrients are vitamins, minerals and phytochemicals, many as yet unknown.
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 known science about the different fats and the amino acids has pretty well established how important they, or their absence, are to human health.
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 gets glycogen, to make glucose, from storage and from the animal products we eat (intramuscular, subcutaneous, and from organ meats like liver). Admittedly there still isn’t a lot of hard evidence to support this hypothesis. Philosophically, though, it appeals to me.If I had to guess, I’d hedge my bet by speculating that the answer ultimately will involve or combine these hypotheses. In the meantime, we can be guided by what we “know” and eat with the knowledge that 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 pastured meats and poultry and wild-caught fish. I try my best to avoid polyunsaturated fat (vegetable oil) altogether and since I am Insulin Resistant (32 years a diagnosed type 2 diabetic), I eat as few carbohydrates as possible.