Evolutionary Discordance of Grains/Legumes in the Human Diet

Evolutionary Discordance of Grains/Legumes in the Human Diet

e complete re-arrangement of gut morphology or evolution of new enzyme systems capable of handling novel food types is quite unlikely to have occurred in humans in the short time period since the advent of agriculture. Some populations have had 500 generations to adapt to the new staple foods of agriculture (cereals, legumes, and dairy) whereas others have had only 1-3 (i.e., Inuit, Amerindians, etc). Because anatomical and physiological studies among and between various racial groups indicate few differences in the basic structure and function of the gut, it is reasonable to assume that there has been insufficient evolutionary experience (500 generations) since the advent of agriculture to create large genetic differences among human populations in their ability to digest and assimilate various foods.

Of the population differences in gastrointestinal function which have been identified, they generally are associated with an increased ability to digest disaccharides (lactose and sucrose) via varying disaccharidase activity. Although insulin metabolism is not a direct component of the gastrointestinal tract, there is substantial evidence to indicate that recently acculturated populations are more prone to hyperinsulinemia and its various clinical manifestations, including non-insulin-dependent diabetes mellitus (NIDDM), obesity, hypertension, coronary heart disease and hyperlipidemia [Brand-Miller and Colagiuri 1994].

It is thought that these abnormalities, collectively referred to as "syndrome X" [Reaven 1994], are the result of a so-called "thrifty gene" [Neel 1962] which some groups have suggested codes for glycogen synthase [Schalin-Jantti 1996]. Consequently, the ability to consume increasing levels of carbohydrate without developing symptoms of syndrome X is likely genetically based and a function of relative time exposure of populations to the higher carbohydrate contents of agriculture [Brand-Miller and Colagiuri 1994].

There are no generally recognized differences in the enzymes required to digest fats or proteins among human populations. Additionally, all human groups regardless of their genetic background have not been able to overcome the deleterious effects of phytates and other antinutrients in cereal grains and legumes. Iranian populations, Inuit populations, European populations, and Asian populations all suffer from divalent ion (calcium, iron, zinc, etc.) sequestration with excessive (>50% total calories) cereal or legume consumption. All racial groups also have not evolved gut characteristics which allow them to digest the food energy which is potentially available in the major type of fiber contained in cereal grains. Further, most of the antinutrients in cereal grains and legumes (alklyrescorcinols, amylase inhibitors, lectins, protease inhibitors, etc.) wreak their havoc upon human physiologies irrespective of differing genetic backgrounds.

Thus, most of the available evidence supports the notion that except for the evolution of certain disaccharidases and perhaps changes in some genes involving insulin sensitivity, the human gut remains relatively unchanged from paleolithic times.