What do our biological regulatory mechanisms say?
By Travis Weisse
“Nutrition science is today where cancer research was fifty years ago.” These were Richard Mattes’ final words to me after his talk at our Food Choice seminar last week. Forty-nine years ago, the Epstein Barr virus was isolated in the cells of a 9-year old child with Burkitt’s lymphoma and gave hope that cancer had a singular cause, and thus that a singular cure was possible. So, by his offhand remark, Mattes meant that that nutrition science today suffers from a sort of collective delusion. The delusion is that nutritional advice can be narrowed to a small checklist of items that can be given to the entire public without individualized concerns.
Mattes’ talk largely reflected this theme. He started with a simple question: what, in terms of ingestion, does the body regulate? Is it appetite? Hunger? Satiety? The desire to eat? Thirst? Though biological processes can be identified as constituents in each of these ingestive functions (gut peptides, insulin secretion, endocrinal actions etc.), none is deterministic nor accurately predicts ingestive behavior. In fact, Mattes claimed, their variability is what endows them with their functionality. It allows us to gorge before a long winter fast, capitalize on food availability at the height of a harvest, or savor a dessert when we simply can’t have another bite. Alright, so the last one isn’t functional.
If none of these ingestive factors is a sufficient predictor of eating events, what would be? Is it energy intake? Nutrient intake? Nutrient stores? Body weight? Body composition? Mattes shot each of these options down one by one. Each is necessarily dependent on external environmental factors and therefore cannot be internally regulated, or simply lacks a regulatory mechanism as with the protein leveraging hypothesis. But something has to be regulated—right? Or else we would eat until we burst upon first tasting refined sugar. The answer Mattes posed is that either all are regulated or none of them are because many regulate one another.
To make his point, Mattes engaged us with a thought experiment. With a regulatory mechanism in place, as in dogs, we would expect to see a statistical bell curve spread around a constant and average weight. Without a regulatory mechanism, we would expect severe deviations from the mean. It is the latter that we in fact observe. With nearly 1.4 billion people overweight and 1 billion underweight, there are high frequencies at both edges of the curve.
This point raised several interesting questions in the seminar. The first was the extent to which being underweight was a result of food scarcity and the built environment rather than an unregulated biological system. Professor Todd asked if external regulatory mechanisms in the environment could account for the consistency in human behavior. These questions and many like them, must, to some extent, go unanswered, because the research is contradictory. This is the idea to which Mattes turned in the last piece of his presentation.
There are four camps in the nutrition sciences regarding biological homeostasis of human consumption. Eating is either not homeostatic, or it is homeostatic and properly functioning, or the homeostasis is dysfunctional, or eating is somehow both homeostatic and non-homeostatic. Each of these positions is prominent in the nutrition community and each has an entirely unique solution. We can work to match circadian rhythms to minimize weight gain, change the built environment, advocate diet and lifestyle changes on a broader scale, or intervene on eating behavior and appetite. The solution is not as easy as conducting more research. There is physiological and biochemical research in favor of each of these four camps. Instead it may require facing up to the aforementioned truism that everyone is different.