Heavy legacy
Diabetes mellitus as an evolutionary trap
Today, every eleventh adult in the world suffers from this disease, despite the fact that half of the cases are not even diagnosed. The number of patients has tripled over the past 20 years and may reach 700 million people by 2025. The reasons why this previously rare non-communicable disease is spreading around the world like a pandemic, according to Professor of the Russian Academy of Sciences, Doctor of Medical Sciences V.V. Klimontov, should be sought in the distant history of mankind.
When we talk about diabetes, the key word here is insulin, a hormone produced after eating by beta cells of the pancreas. His task is to "stock up" in the cells what came with food to use in the "hungry" time. In this sense, insulin is a universal anabolic, enhancing the synthesis of fat, protein and glycogen (animal "starch"). But the reverse catabolic functions, including the formation of glucose, it slows down.
In diabetes mellitus, the concentration of "sugar" (glucose) in the blood increases, and the reason lies in a decrease in the level of secretion and / or the effectiveness of insulin. Type 1 diabetes is an autoimmune disease in which beta cells are attacked by the body's own antibodies, making it impossible to produce insulin. But in the case of type 2 diabetes mellitus, which makes the main contribution to the modern "epidemic", everything is much more complicated: in addition to the dysfunction of beta cells, we meet here with another pathology - a violation of the sensitivity of cells to insulin. And there are much more people with insulin resistance, which at first is accompanied by increased synthesis of this hormone, than there are official patients with diabetes mellitus.
The concept of insulin resistance is the basis of the popular concept of "metabolic syndrome", which refers to a whole cluster of risk factors for the development of diseases that determine the structure of mortality in modern people. By the way, abdominal obesity, in which fat accumulates in the abdominal cavity, can serve as an external expression of a decrease in insulin sensitivity. By: (Mendrick et al., 2017).
So where does type 2 diabetes come from? Genome-wide studies revealed the presence of many genes associated with the development of this disease, but the contribution of each such gene was very small. So, to predict the development of diabetes mellitus in a particular patient, it is much cheaper and easier to measure the waist circumference instead of genetic analysis and find out what his parents were ill with. But with the help of a bioinformatic approach and the study of "gene networks" underlying the pathogenesis of type 2 diabetes mellitus, it was possible to find out that it is based on groups of very "ancient" genes that arose at the early stages of evolution.
The stages of progression of type 2 diabetes mellitus are accompanied by hyperglycemia, a decrease in insulin production and an increase in cell resistance to this hormone. By: (DeFronzo, 2004).
The latter fact forces us to pay close attention to the situation with energy exchange in the history of the hominin subfamily, which includes modern man and all his distant and close "relatives". Having "run through" our family tree, from Australopithecines to Neanderthals and Sapiens, we will notice that in the course of evolution, serious changes took place in the lifestyle and diet of these primitive people. The food became more caloric, the proportion of animal protein and fat increased in it, which was reflected, first of all, in the increase in the size of the brain.
It is believed that this main human organ is able to consume up to 40-45% of all energy produced in the body on an empty stomach! There is a hypothesis that such an energetically imperfect structure could develop and increase in volume precisely due to the very insulin resistance. For our ancestors, a decrease in insulin sensitivity in muscle cells, liver, adipose tissue and other peripheral organs could become a protective mechanism for survival in extreme situations, for example, during prolonged fasting.
Indirectly, this assumption is supported by the results of a study of Jamaicans who, before birth and in early childhood, suffered from insanity – a state of deep energy deficiency (Francis-Emmanuel et al., 2014). These people turned out to be less sensitive to insulin, they were found to have more disorders of carbohydrate metabolism and cases of diabetes mellitus. Usually, such changes are explained by the fact that with a lack of energy substrates, the "bookmark" of beta cells is disrupted. But you can look at it in another way: perhaps these people survived because they were initially less sensitive to insulin, which gave their brains the opportunity to develop. And not so long ago, a new genetic locus associated with the development of diabetes was discovered in modern humans, which we inherited from Neanderthals.
Radical changes in the lifestyle and nutrition of a person, which could serve as a prerequisite for the modern epidemic of diabetes mellitus, began to occur about 15-10 thousand. years ago, when hunters, nomads and gatherers began to move to a settled life. The most striking difference was a sharp increase in the consumption of carbohydrates, including fast ones, and an equally sharp reduction in the consumption of fiber. Subsequently, foods that were completely unthinkable for our ancestors began to play an increasingly important role in nutrition: refined carbohydrates, vegetable oils, processed cereals and dairy products. Nowadays, their share in the diet reaches 70%, and they all require a rapid and significant release of insulin, which means a heavy load on the beta cells of the pancreas.
Nevertheless , until the middle of the XX century . rapid spread of diabetes mellitus was not observed. Most people continued to engage in intensive physical labor, and such activity is associated with increased sensitivity to insulin. In addition, for most of the world's population, the problem remained rather a lack, rather than an excess of food.
The Industrial Revolution brought new changes to the structure of human nutrition, which we know firsthand – from fast food to an increase in the total caloric content of the diet, and motor activity began to decline, including due to the development of transport, the advent of the computer and the Internet. All this immediately affected the spread of obesity, primarily among the population of industrially developed countries in America and Europe. This is where the epidemic of diabetes mellitus began.
One of the striking consequences of the industrial revolution is the widespread prevalence of obesity among adults and children. The graph shows the proportions of men (blue bars) and women (pink bars) over the age of 18 with overweight or obesity in different regions of the world, according to WHO. By: Global Report on Diabetes, WHO, 2016.
By the way, life itself has put an experiment on Native Americans – Indians of the Pima tribe, whose traditional diet was based on beans, corn, zucchini and other crops. When Pima from the US state of Arizona was pushed back to the territory where farming became impossible, they actually began to starve. Later, the US government began to supply food aid to the Indians in the form of flour, sugar, lard and canned foods, which, in conditions of low physical activity, led to the rapid spread of obesity and diabetes. By the end of the last century, every second adult Indian was already ill! However, this in no way applies to representatives of another pima population living in a remote area of Mexico and preserving a traditional way of life and nutrition (Schulz et al., 2015).
How to prevent a negative scenario? The recommendations are banal: a healthy diet (which does not necessarily mean a return to the "stone Age diet") and high physical activity. After all, even in people genetically predisposed to the development of type 2 diabetes, intensive fitness classes for three years reduced this risk by 60% (Florez et al., 2017). And although the human genetic program has recently come into conflict with the changed lifestyle, it depends only on us whether we will fall into this "evolutionary trap".
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