We humans, from a purely evolutionary point of view, are rather young. If we consider Lucy (the first known individual of the species Australopithecus afarensis, an early human ancestor) as a link with our primate cousins, we go back only 3.2 million years. This is a relatively short time in evolutionary terms; for example, the bacteria of the microbiota that live within our intestines have an evolutionary history of 5 billion years. The gap is even more evident if we consider our species, Homo sapiens, which is only 200,000 years old.
During our recent history, we have witnessed drastic changes in our lifestyle to which we have not had time to adapt genetically; the process of natural selection is very slow. Unfortunately, our capacity for evolutionary adaptation is not able to occur at the pace with which technological progress has occurred over the last 200 years. In all probability, we are not suited to the modern lifestyle, because our genes have evolved under completely different environmental pressures.
Our closest relative is believed to have appeared on earth just over three million years ago. For most of our history, we have been hunter-gatherers, and our genes have evolved accordingly. Agriculture and the practice of animal husbandry are relatively recent inventions that first appeared around 10,000 years ago. Imagine being able to summarize our evolutionary history over the course of a 24-hour day: we would have been hunter-gatherers for 23 hours and 55 minutes and farmers for just 5 minutes. Many of the most radical changes have happened much more recently. The industrial revolution saw the advent of mechanization and the production of energy from fossil sources. Even more drastic were the changes in the post-war economic boom with the advent of processed foods, chemical dyes and preservatives. Applying the same proportion over the 24-hour period the industrial revolution would have happened during the last seven seconds and the economic boom of the industrialized countries in an infinitesimal fraction of time. From this point of view, it is clear how difficult it is to judge the innovations of the last twenty years in terms of evolutionary adaptation; smartphones and social networking have completely altered our relational dynamics, with inevitable consequences.
Comparing the modern lifestyle with that of our ancestors, it is evident that caloric intake has grown out of proportion. We feed on completely different foods and we also lead a more sedentary life. The abundance of food, responsible today for metabolic diseases such as diabetes and obesity, only became a serious threat after the Second World War. In the past, on the contrary, the norm was food shortage, alternated with very short periods of abundance. With this evolutionary model, it is not surprising that our metabolism has specialized in the accumulation of reserve substances and strongly opposes any attempt at weight loss. Our genes are constantly ready for the possibility of famine. For this reason, it is difficult to lose weight through dieting, and our primordial instinct leads us to feed ourselves to extreme fullness on every occasion. The body aims to accumulate energy reserves to enable it to cope with periods of caloric deficit.
In the past, during a period of food abundance, the excess calories were stored as fats. The adipose tissue is able to mediate the production of hundreds of pro-inflammatory messengers that stimulate the immune system, protecting us from infections and promoting tissue repair. These operations are particularly expensive from the energy point of view, and it makes perfect sense for these activities to occur preferentially in periods of caloric abundance. On the other hand, when food is lacking, the organism enters the caloric restriction mode; this is a sort of energy saving mode, in which the body relies on previously accumulated fat reserves. In this phase, the pro-inflammatory mediators cease to be produced, and the adaptive stress response mechanism is activated. This process, occurring in response to an environmental physical stress, has an extremely positive effect on the organism. It could be defined as a sort of positive stress that triggers an adaptive reaction and forces the body to manage its natural resources. In other words, the adaptive stress response is the response of our genome to environmental stress.
In addition to caloric restriction, other stressors are known that can activate the adaptive response. These include bioactive compounds present in certain foods, physical exercise conducted at a certain intensity, undergoing extreme temperatures (hot or cold), and hormesis, which is the administration of small amounts of toxic substances that at certain doses activate the adaptive stress response (for example, wine).
The adaptive response to stress is a particularly precise survival mechanism, a trace of our ancestral origins, the long period of hunter-gatherer history during which 99.5% of the genes that make us human have taken shape. In other words, our bodies are designed to respond to the kinds of stress that our predecessors would encounter. The diet and the modern lifestyle of rich countries act against the activation of the adaptive stress response. We no longer witness periods of abundance alternating with periods of scarcity, where the inflammatory state was switched on and off depending on the needs. The conditions of the twenty-first century not only deprive the body of adaptive stress, but promote the chronic production of pro-inflammatory mediators as a consequence of the constantly positive energy balance. Rather than promoting the activation of the immune system in a beneficial way, this constant pro-inflammatory state promotes the development of chronic diseases such as diabetes, atherosclerosis, arthritis, asthma, allergies, lung diseases, cancer, and neurodegenerative diseases.
Compounding an already quite complex picture are two factors. First of all, the fact that we have a more sedentary lifestyle than our ancestors. Secondly, the fact that the nutritional value of today's food is poorer than in the past; many of the foods we consume contain empty calories, meaning that they provide a high calorific value but lack health-promoting substances such as phytonutrients, bioactive molecules, antioxidants and dietary fiber. If only we could go back a few generations, our ancestors would not even be able to recognize much of what constitutes our food standard today: processed and cured meats, packaged products, refined flours, canned food, and sugary drinks.
Even in the Blue Zones of the world, the modern lifestyle is gradually replacing the local cultural model. For example, the consumption of simple sugars has grown out of proportion, with obvious consequences for human health.
The arrival of sugar in our tables is a relatively recent fact. Although we know the technique for extracting sugar from sugar cane has existed for thousands of years, the ancient Greeks and Romans virtually did not use it, and even in victorian England it was considered an upper class luxury. In the first twenty years of the last century, numerous U.S. physiological studies on sugar have contributed to rehabilitating its image as a nutritionally positive substance, the perfect fuel for physical and brain activity. In 1986, the United States Food and Drugs Administration positioned carbohydrates at the base of the ideal food pyramid, stating that simple sugars posed no health threat. Consequently, the food industry found a versatile, economical, and highly popular compound, which it began to produce on a massive scale.
As a result, we have gone from an average of 1 kg of sugar consumption per year per capita in the eighteenth century, to 6 kg in the nineteenth, and 70 kg today. The consequence can be clearly seen: a pandemic of diabetes and obesity. In the U.S. alone, 75% of the population is currently overweight.
Our common ancestor (the “cave man") consumed mainly tubers, fruits, vegetables, seeds, and game meat. Although we still have access to foods like this, it would be a gross mistake to think that the characteristics of these products have reached us unaltered. Game meat is nowhere near comparable to the meat currently found in our supermarkets. The quality of the meat of wild animals or left in the wild (free range and grass fed) has a favorable proportion of omega-3 to omega-6 polyunsaturated fatty acids. This is not true for factory-farmed animals (bred and raised on feedlots) that feed on cereal-based feeds, creating an imbalance, with excess omega-6 compared to omega-3. The same imbalance can also be found in fish bred with aquaculture techniques. There are other problems too, such as the contamination by heavy metals like mercury and the bio-accumulation of pesticides in the food chain.
Even the vast majority of the fruits and vegetables we eat today are not found in nature today and were not present in the past. What we find in the stalls is the result of domestication. Certain characteristics have been favored through careful breeding over hundreds and hundreds of years. This preferentially created larger fruits, which are fleshy and sugary but also poorer in polyphenols and antioxidants in general.
Fruits and vegetables produced in greenhouses no longer have the need to defend themselves from the sun and light, from the threat of fungi and microbial contamination, from drought and insects. So, like us, they no longer experience the adaptive response to environmental stress, resulting in the depletion of antioxidant chemicals and the inevitable decay of the food’s beneficial nutritional properties.
Overall, one could say that our genome is unsuitable for modern dietary patterns. Still, this does not mean that we should attempt to return to eating like hunter-gatherers and reject the foods available to us in the modern world. Before food is absorbed, it is broken down into its constituent elements. Once a protein has been disassembled into its constituent amino acids, the body is not able to discriminate whether this molecule comes from a bean or a rib of beef. A given amino acid is the same molecule, regardless of the protein from which it originated.
What matters are the right quantities, proportions, varieties, and possible combinations of the different foods, and the frequency with which they are consumed. To promote longevity, it makes sense to optimize these elements to be as similar as possible to what our metabolism and genes have adapted to process over thousands of years of evolutionary history.