Modern Homo Sapiens as a Protein Filter-Feeder (or ‘Miner’ of Low-Grade ‘Ore’)

The low protein content of our modern diet has us by the short hairs and leads us, willy-nilly, around by our mouths and bellies

You can’t always get what you want, but if you try sometime -- you’ll find you can get what you need. 

(Rolling Stones, 1969; from “Let It Bleed”)

Gold mouth sea squirt: a marine chordate ascidian filter-feeder. Photo by Nhobgood. According to Wikipedia, “To obtain enough food, an average ascidian needs to process one body-volume of water per second”. Notice the external morphological similarity of this animal to that of the human stomach.

Because the cells of the human body are incapable of creating all of the 20 amino acids they need to construct and maintain our elaborate protein biochemical machinery, they are reliant on human consumption of protein-containing foods to obtain those protein building blocks.  Indeed, Simpson and Raubenheimer (2012, 2021) have demonstrated that the foremost human nutrient-seeking imperative is to secure sufficient daily dietary protein – everything else eaten is pretty much secondary in nutritional and biochemical importance. 

What this means is that if there is insufficient animal-sourced protein available to provide around 100 or so grams of protein a day to a person, adults will instead eat much increased amounts of protein-poor alternative foods to come as close as possible to that 100 gram daily protein target. 

Unfortunately, eating a protein-poor diet like that currently eaten in the US (12 calorie-percent protein)  inadvertently drags in a lot of high calorie dross that primarily serves only to increase body fat accumulation. Real life examples of this behavior are illustrated in the ternary macronutrient diagram below constructed from Simpson, Batley, and Raubenheimer (2003, 2012) experimental data.  Keep in mind while decoding this diagram that all of the alternative protein food sources available to humans are plant-based and that these are consequently all far, far richer in carbohydrates than they are in proteins. 

Open squares represent average completely free choice macronutrient preferences for five individuals over two days, while filled squares show the forced change in their average eating behavior when provided with only lower protein, higher carbohydrate and fat foods for the following two days.  Numeric labels of each symbol give their average daily caloric intake under the initial free food choice state and then under the experimentally-imposed condition of reduced availability of protein-rich foods.  These before and after labels show that in most (80%) cases, individual daily calorie intake increased about 1000 calories per day when the only available food sources were more protein-diluted with carbohydrates and fats.  Because it requires only about 3,500 calories for the human body to construct a pound of body fat, it is easy to understand from this diagram why eating the protein-poor foods readily available to modern people leads to fat gain.

Conversely, if humans have access – forced or otherwise -- to foods especially rich in proteins, they will automatically and immediately reduce their daily overall calorie intake as soon as their daily protein requirements are met.  The reduced eating effect of this last phenomenon – i.e., the strong appetite satiation effect of protein -- is exactly why high protein diets result in relatively rapid (and relatively painless) weight loss.  Real life individual examples of this consistent human behavior are depicted in the next ternary diagram of Simpson, Batley, and Raubenheimer (ibid.) data from the high protein arm of the same human-feeding experiment.

Open triangles represent average completely free choice food preferences for five individuals over two days, while filled triangles show the average change in their eating behavior when provided with only higher protein and fat, but much lower carbohydrate foods for the next two days.    Numeric labels of each symbol give their average daily caloric intake under the initial free food choice state and the imposed condition of increased availability of protein- and fat-rich foods only.  In most (80%) cases, individual daily calorie intake decreased about 1000 calories or more per day when the only available food sources were intrinsically more protein-rich.  Because about 3,500 calories of energy are available for every pound of human body fat used under calorie-reduced eating conditions, it is easy to understand why protein-rich and therefore calorie- and carbohydrate-lowered diets readily lead to rapid fat loss.

The next ternary diagram maps the dietary shift (along the A to A’ section) from the very high protein/high fat forced diet of Simpson et al. (and the traditional Inuit), then to the mix of proteins-carbohydrates-fats characteristically eaten by modern hunter-gatherers (and our Paleolithic ancestors), and finally to the modern high carbohydrate/moderate protein/moderate fat diet of the average modern citizen living in the US or UK.  The scatter diagram following this graph clearly demonstrates the direct dietary and physical activity causes of the current epidemic of obesity and obesity co-morbidities plaguing many, if not most (e.g., USA), people living in modern industrial economies.

In the Simpson et al. free and forced feeding study, the average participant was a sedentary adult of 25 years of age, a metabolic protein target amount of 93 grams per day, and a basal (resting) metabolic rate of about 1800 calories (Kcal) per day.  The scatter diagram below shows the dietary calorie excess or deficiency the average study subject would experience once they ate and digested enough food to satisfy their ~ 93 grams of protein/day need.