Originally Posted by Joaqu�n P�rez-Guisado

Humanity has existed as a genus for about 2 million years, and our prehuman hominid ancestors, the australopithecines, appeared at least 4 million years ago. This phase of evolutionary history made definitive contributions to our current genetic composition, partly in response to dietary influences at that time. The development of agriculture 10000 years ago has apparently had a minimal influence on our genes and markedly altered human nutritional patterns. In the hunting society of our ancestors protein contributed twice to nearly five times the proportion of total calories that it does for nowadays Americans.Since then, the human diet has changed drastically: protein intake has been reduced to 10-15%; glucid intake has increased to 45-60% through eating more grain and starch products instead of vegetables and fruits available according to the seasonal conditions; polyunsaturated fat has been reduced and saturated fat has increased (lower polyunsaturated-to-saturated fat radio). So we can affirm that healthier fats like monounsaturated and polyunsaturated fats (MUFA and PUFA) have been replaced by more pernicious fat like saturated and, above all, the artificial trans fats. Furthermore, carbohydrates consumed nowadays tend to have a higher glycemic index and glycemic load since they are based on grains, starch and refined sugars instead of vegetables and fruits. In such a short evolutionary period of time, human beings have been unable to adapt to this abrupt change in eating habits, and this has been a significant source of stress for our insulin metabolism.The fact that the nutritional change from a hunter-gatherer diet to a carbohydrate-based diet has affected populations negatively has been revealed by archaeological findings in ancient Egyptian mummies, since tooth decay, cardiovascular disease and obesity were very frequent in those times. More recently, this problem has also been reflected historically by the change in eating habits of Inuit peoples in Alaska. Traditionally, their diet contained 3-5% carbohydrates (since it was based on fish, marine mammals, moose and caribou), obesity was virtually nonexistent and type II diabetes was rare. Since 1961, a growing tendency in type II diabetes and obesity problems has been observed due to a progressive substitution of the traditional protein and fat-based diet by a diet with higher carbohydrate content. This increase has been so dramatic that in 1978, carbohydrates represented 50% of the total calorie contribution in their diet. Another historical fact worth considering when analyzing the nutritional habits of American society is their increased consumption of carbohydrates, either through eating more food in general or by replacing fats with carbohydrates. This leads to an increase in obesity and atherogenic markers such as triglycerides and VLDL].Most hunter–gatherers, for example, are not obese when they live their traditional lifestyle based on a low carbohydrate diet. Many hunter-gatherers consumed a predominantly plant-based diet, which was supplemented with meat when available, and others such as the Inuits consumed a high fat-protein diet. When such people are exposed to high, refined carbohydrate intake, however, they develop truncal obesity and a much higher risk of diabetes, up to 50% in some populations. This high waist-hip ratio and carbohydrate intolerance is shared by all hunter–gatherer populations throughout the world: Canadian Inuits, Native Americans, Mexican Indians, Pima Indians, South American Indians, Middle-Eastern Nomads, African Pygmies, Australian Aborigines, Maoris, South Sea Islanders, etc.Nevertheless, many factors are responsible for the health and metabolic disturbances currently experienced by modern hunter–gatherers like the Inuits. It is important to remember that millions of people worldwide from different countries have predominantly carbohydrate-based diets and the prevalence of obesity is very low in these countries. Hence other risk factor factors, such as sedentarism and high calorie intake, are clearly relevant in addition to the macronutrient composition of the diet.Thus, all these data might suggest that it could be wrong to consider carbohydrates as the basis of the human diet.