Nutrition and changes in our habits

Throughout the long span of the Paleolithic era, which lasted for over two million years until approximately 10,000 B.C., the diet of our hunter-gatherer ancestors was a direct reflection of what the surrounding nature could provide. Lean meat from small animals or young specimens of larger species, fish, eggs, wild fruits and vegetables, nuts, seeds, and roots formed the basis of a rich and varied nutritional regimen, yet one free from excess. Over time, cooperative organization in hunting allowed for the acquisition of larger prey, expanding the availability of animal-based proteins and fats (Konner et al., 2010) [4].

Daily life did not include the sedentary behavior typical of the modern world: our ancestors traveled long distances on foot, modulating the intensity of their effort based on necessity. Running was reserved for dangerous situations or hunting, while constant movement occurred primarily at an intensity that favored aerobic metabolism, using fats as the main fuel source. Glucose, on the other hand, was reserved for the brain and emergencies, acting as a “reserve tank” to be used only when essential (Zucoloto, 2008) [5].

From a nutritional standpoint, carbohydrate sources were scarce and strictly linked to seasonality: fruits, vegetables, and honey were available only at certain times of the year, while tubers and roots required specific gathering and preparation techniques. This natural limitation meant that overall carbohydrate intake was low, especially regarding starch, while dietary fiber was present in much higher quantities than current recommendations (Brand-Miller et al., 1998) [6].

Anthropological studies (research that analyzes human beings in their cultural, social, and biological dimensions) and nutritional studies on traditional populations confirm that ancestral diets had well-defined characteristics: very few refined carbohydrates, a fiber and protein content significantly higher than that of modern diets, and a fat intake similar in quantity but qualitatively better, with a prevalence of unsaturated fats (fats considered “good” for health, found in foods such as olive oil, nuts, and fish) (Konner et al., 2010) [4]. Among Australian Aboriginal hunter-gatherers, for example, even the plant-based portion, which could account for up to 40% of daily energy, provided low-glycemic index carbohydrates rich in fiber, antioxidants, and micronutrients. This minimized insulin demand, thereby protecting against insulin resistance and other metabolic dysfunctions (Brand-Miller et al., 1998) [6].

In essence, the Paleolithic diet was an “ante litteram” low-glycemic impact food system, perfectly calibrated to the level of physical activity and the physiological needs of an organism constantly in motion. Today, by comparison, the abundance of refined carbohydrates and high-calorie density foods represents a condition completely opposite to the one for which our metabolism evolved.

The Paleolithic era ended around 10,000 B.C., when agriculture emerged in Southwest Asia. This transition marked an epochal turning point: it not only led to a reduction in protein consumption but also introduced cereals such as oats, barley, rye, and wheat into the diet—foods entirely new to our genome, which until that moment had had very little evolutionary experience with them (Cordain et al., 2005) [7]. Humans no longer needed to move constantly in search of food: cultivation and animal husbandry allowed them to settle in fixed locations, ensuring a more predictable food supply less subject to the uncertainties of hunting and gathering (Zucoloto, 2011) [8].

However, this dietary revolution came at a price. Systematic cultivation reduced biodiversity and depleted the overall nutritional value of the diet, while the increase in agricultural productivity fostered population growth and, consequently, a sedentary lifestyle (Prentice, 2005) [9]. Archaeological evidence, drawn from the study of human remains in various regions of the world, shows a clear deterioration in health status during this period: more frequent dental caries, occlusal anomalies, iron-deficiency anemia, bone infections, and loss of mineral density (Larsen, 2003) [10].

Anthropological and historical comparisons reveal that hunter-gatherer societies enjoyed an overall better state of health compared to early farmers. A plausible explanation is that the primitive agricultural diet was based primarily on cereals, foods poor in phytochemicals and micronutrients compared to the variety of wild plants and animal-based foods of the previous diet (Cordain et al., 2005) [7]. Some scholars point out that the reduction in meat and the increase in cereals created a metabolic context for which we were not prepared, facilitating the emergence of new chronic diseases.

From an evolutionary perspective, these changes occurred in too short a time for our genome to adapt effectively. This created a true "evolutionary collision" between an ancient genome and the nutritional properties of recently introduced foods, a factor that many researchers consider to be at the root of most chronic diseases typical of Western civilization (Cordain et al., 2005) [7].

A frequent objection to the Paleolithic diet theory is that hunter-gatherers did not develop age-related degenerative diseases simply because they died young. However, comparative studies on young adults from industrialized societies and contemporary hunter-gatherer populations have highlighted marked differences: the former show high rates of obesity, hypertension, insulin dysfunction, and signs of atherosclerosis, while in the latter such conditions are rare, and instead, greater muscle strength and higher aerobic capacity are observed (Cordain, 2002) [11].

With the advancement of industrialization and technological expansion, our diet has undergone a radical transformation, far removed from what our metabolism had known during millions of years of evolution. The need to feed a constantly growing population has favored the massive introduction of processed foods, characterized by a high presence of refined carbohydrates, added sugars, and saturated fats. With the Industrial Revolution, new processing techniques made possible combinations of nutrients and calories never before encountered in the history of Homo sapiens, creating a dietary context completely foreign to our ancestral biology (Cordain et al., 2005) [7].

Today, in the United States, dairy products, grains, refined sugars, refined vegetable oils, and alcohol provide over 70% of daily energy, whereas in the pre-agricultural era these foods would have played almost no role (Cordain et al., 2005) [7]. The constant availability of such products has coincided with increasing urbanization and a drastic reduction in physical activity: while in the Paleolithic era humans walked an average of 12 km per day, today about a third of the world's population is physically inactive, a condition that represents a serious public health problem (Rodulfo, 2019) [12].

Added to this is a qualitative deterioration of food: fruits and vegetables are grown using chemicals, while meat from intensive farming has a lipid content and fatty acid profile very different from that of the game that nourished our ancestors. Our genome, shaped for a diet rich in dietary fiber, low in simple sugars and concentrated fats, now finds itself managing meals that overstimulate the reward system and interfere with satiety signals. In other words, modern food "tricks" the brain mechanisms that have regulated appetite for millennia, leading to excessive and disordered eating.

Experts identify six fundamental steps that, from the agricultural revolution onwards, have shaped food production: domestication of species, intensive agricultural practices, industrial food processing, technological development and industrialization, selective breeding, and urbanization. While these innovations have allowed for population growth, they have also led to significant losses in terms of dietary diversity, nutritional quality, and ecological balance.

In summary, the contemporary lifestyle—industrial diet, widespread sedentary behavior, and high caloric density of foods—has created an abysmal distance from what we are "biologically programmed" for. This distance is not only cultural but deeply metabolic: it represents one of the main factors underlying the chronic diseases that afflict industrialized societies today.

In the pre-Neolithic period, all food of animal origin came exclusively from wild animals and fish, and its consumption varied based on geographic area, season, and hunting conditions. In cold areas with little vegetation, meat was the primary source of energy. Hunting, in addition to ensuring survival, played a fundamental role in the social development of the human species, fostering cooperation and the development of language (Cordain et al., 2005) [7].

An often overlooked aspect concerns the diet of the wild animals themselves: they fed on wild plants rich in phytochemicals, which helped make their meat naturally more nutritious and beneficial. While rich in protein, the hunter-gatherer diet also included monounsaturated and polyunsaturated fatty acids, omega-3, fruits, and vegetables. Wild animals were lean by nature, as their subcutaneous and abdominal fat reserves were depleted for much of the year. Body fat content was proportional to the animal's mass, but in most cases, unsaturated fatty acids prevailed, making it unlikely that saturated fat intake would reach harmful levels on an annual basis.

Today, however, the meat we consume almost always comes from animals raised in intensive conditions, fed with concentrated grain-based diets. This practice, which spread from the mid-19th century thanks to innovations such as the steam engine, the mechanical reaper, and the railway network, has profoundly transformed the composition of meat. The shift from pasture-based feeding to corn and wheat-based feeding has drastically increased the amount of fat in meat, taking it from the 4% typical of game to the 25–30% of modern domestic animals. Furthermore, the lipid profile has changed: more saturated fatty acids, fewer omega-3s, and an excess of omega-6s (essential fatty acids that, if in excess, can promote inflammation), with the n-6/n-3 ratio shifting from the 2:1–3:1 typical of Paleolithic diets to about 10:1 in current US diets (Cordain et al., 2005) [7].

In the United States, before 1850, almost all cattle grazed outdoors and were slaughtered at 4–5 years of age. By 1885, thanks to rapid fattening techniques, a 545 kg beef steer was ready in 24 months, characterized by the typical "marbling" (distribution of white fat streaks within the muscle tissue), due to the accumulation of triacylglycerols (fat molecules composed of glycerol and three fatty acids) in the muscle adipocytes. In the 1950s, intensive farms began managing up to 100,000 head of cattle, with animals reaching 30% body fat in just 14 months. Today, 99% of the beef consumed in the United States comes from grain-fed cattle, a condition that, from an evolutionary perspective, is extremely recent. This change has contributed to a diet richer in saturated fats and omega-6s, drastically reducing the intake of beneficial unsaturated fats and altering a nutritional balance that had characterized the human diet for millennia.

During the Paleolithic era, humans fished and consumed wild marine animals that were lean, protein-rich, and naturally provided a favorable lipid profile, with high levels of omega-3 fatty acids and a low content of saturated fats. This food source, along with other wild resources, contributed to an optimal nutritional balance shaped by millennia of evolution.

With population growth and technological progress, fishing has become progressively more intensive, leading to a decline in the populations of certain species and increasing pressure on marine ecosystems. In recent decades, aquaculture has taken on a central role in supplying fish for human consumption. However, the nutritional quality of farmed fish varies widely depending on management practices, feed, and environmental conditions.

To reduce production costs, the share of plant-based ingredients in fish feed has increased from 10% to 70% over the last thirty years, a choice that profoundly alters the nutritional composition of the final product. Furthermore, intensive sea farming results in the production of over 500,000 tons of waste per year, enriching the surrounding environment with excess nutrients and promoting algal blooms and ecological imbalances. To control parasites, algae, and infections, large quantities of antibiotics, disinfectants, herbicides, insecticides, and even antidepressant drugs, such as amitriptyline, are used to prevent stressed or "depressed" fish from reducing their food intake (Ziarrusta et al., 2019) [13]. Experimental studies have shown that even low environmental concentrations of these drugs can alter the brain and liver metabolism of fish, with significant eco-toxicological implications.

Added to these factors is contamination from marine pollutants, particularly heavy metals such as methylmercury (MeHg), a neurotoxic substance that bioaccumulates along the food chain. According to an analysis published in Nature, in 66 countries, fish consumption exposes the population to mercury levels higher than those considered safe for fetal development (Schartup et al., 2019) [14]. In the United States, 82% of MeHg exposure comes from seafood, and nearly 40% from fresh or canned tuna alone. In the Atlantic, MeHg concentrations in cod increased by up to 23% between the 1970s and the 2000s, partly due to overfishing, which has altered trophic chains, and ocean warming, which amplifies its accumulation in the tissues of predatory fish.

The overall result is that modern fish, while remaining a valuable source of protein and nutrients, now presents a qualitative profile and safety level very different from those that characterized marine resources in the Paleolithic. This transformation raises questions about the long-term sustainability of current fishing and aquaculture practices, and the need for production models that are more consistent with human health and the protection of marine ecosystems.

For much of our evolutionary history, wild plants were an essential component of the hunter-gatherer diet, as they utilized whatever nature provided in their habitat. Wild grains, which were small, difficult to harvest, and hard to digest without grinding and cooking processes, were not a regular food source. It is with the appearance of stone tools for processing that we can begin to glimpse, in the fossil record, the moment when grains started to become a stable part of the human diet.

Until the Industrial Revolution, milling was done with stones, and the flour retained all parts of the grain—germ, bran, and endosperm—thereby preserving dietary fiber, vitamins, and minerals. The turning point occurred in the second half of the 19th century with the introduction of steel roller mills and automated sifting systems: the germ and bran were removed, leaving a refined product consisting almost entirely of endosperm, which is rich in starch but poor in dietary fiber and micronutrients. This change, relatively recent on an evolutionary scale, marked the beginning of massive consumption of refined flours in the population (Foster-Powell et al., 2002) [15].

In parallel, starting from 1850, the increase in atmospheric CO₂ concentration, from about 280 ppm to over 400 ppm in 2017, has altered the composition of grains, increasing carbohydrate synthesis at the expense of proteins and minerals. Long-term studies have detected a 26% reduction in the protein content of wheat between 1850 and 2016, a phenomenon accentuated since the 1960s with the introduction of short-straw varieties, selected for higher yields but resulting in further protein and mineral dilution (Ben Mariem et al., 2020) [16].

Excluding soy, all major agricultural crops were grown and consumed primarily for their starch content (Campbell et al., 2016) [17]. The selection of plants that could accumulate more starch played a crucial role in providing plants with the amount of energy needed to ensure more abundant harvests, unfortunately at the expense of protein and mineral content.

Agricultural selection has therefore favored plants with greater starch accumulation, such as sweet corn, which today contains up to four times the sugar of its wild ancestor, teosinte (a herbaceous plant native to Mexico and Central America, considered the wild ancestor of modern corn) (Szymanek et al., 2015) [18]. This process has led to a progressive nutritional imbalance: more sugars and easily digestible carbohydrates, fewer dietary fiber and micronutrients. It is not surprising, therefore, that unrefined wild plant foods have very low glycemic loads (values indicating how much a carbohydrate-containing food affects glycemia after being consumed) (average GL: 5.7 for vegetables, 7 for fruit), while grains and derived products, even whole grains, have significantly higher values (average GL: 48.6), contributing to chronic increases in glycemia and hyperinsulinemia (Foster-Powell et al., 2002) [15].

Today, in the US diet, 85% of the grains consumed consist of highly processed refined products. High-glycemic-load sugars provide nearly 19% of total energy, while high-GL refined grains contribute over 20%. In other words, more than 39% of daily energy comes from foods that, from an evolutionary perspective, were absent or extremely rare in the human diet until about two centuries ago. This transition has helped create the metabolic conditions favorable to the development of insulin resistance, obesity, and chronic diseases.

In the Paleolithic era, wild fruits and vegetables were a primary source of nutrients and phytochemicals, with concentrations significantly higher than those found in varieties cultivated today. Over the last 12,000 years, with the beginning of plant domestication, agronomic selection has favored high yields and disease resistance, often at the expense of nutritional value. Plants that grow faster and reach larger sizes have less time to absorb from the soil and synthesize vitamins, minerals, and bioactive compounds (substances present in foods, especially of plant origin, which are not essential nutrients but can have positive health effects) internally. Furthermore, higher yields lead to a "dilution" of nutrients: the same soil must nourish a much larger production volume, resulting in a decline in proteins, minerals, and vitamins in modern fruits, vegetables, and grains (Davis et al., 2004) [19].

The problem is amplified by industrial agricultural practices that, while increasing harvests, damage soil health. Intensive irrigation, chemical fertilization, and early harvesting disrupt the symbiosis between roots and mycorrhizal fungi (fungi that live in symbiosis with plant roots, helping them absorb water and nutrients from the soil), reducing the plants' ability to absorb nutrients such as phosphorus and nitrogen. Fruits and vegetables are often harvested before full ripening to improve their transport resistance, then ripened artificially in chambers with ethylene (a natural gas produced by plants, which acts as a plant hormone regulating various processes) and other agents. This further reduces the content of protective phytochemicals (natural compounds present in plants, not as essential as vitamins or minerals, but capable of providing beneficial health effects), such as the powerful antioxidants found in ripe fruit (Müller et al., 2007) [20] or the anti-inflammatory anthocyanins in berries.

Native varieties, such as certain types of figs (Ficus carica L.), still show higher levels of phenols (chemical compounds found mainly in plants, known for their antioxidant, anti-inflammatory, and protective properties) compared to their commercial counterparts (Hssaini et al., 2020) [21], and the same applies to Andean tomatoes, which are richer in phenolic compounds than market tomatoes. However, many of these bitter and astringent principles, which are also linked to taste perception, have been intentionally eliminated through varietal selection and industrial "de-bittering" processes to make them sweeter and more palatable (Komarnytsky et al., 2022) [22].

Comparative analyses conducted by the United States Department of Agriculture (USDA) confirm significant nutrient declines between 1950 and 1999: -6% protein, -16% calcium, -15% iron, -38% riboflavin, and -15% vitamin C (Davis et al., 2004) [19]. Added to these data is the decline in antioxidant vitamins and essential minerals that support the immune system and counteract chronic diseases.

A further aspect concerns the accumulation of nitrates (chemical compounds naturally present in fruits, vegetables, and water, but also used as additives in cured meats and sausages) in vegetables grown under conditions of low sun exposure or in heavily fertilized greenhouses. Nitrates themselves are not toxic, but in the gastrointestinal tract, they can be converted into nitrites and subsequently into nitrosamines, compounds associated with an increased risk of gastrointestinal cancers (Karwowska et al., 2020) [23].

Finally, as also observed for grains, the increase in atmospheric CO₂ has altered the composition of fruit and vegetable crops, increasing carbohydrates (especially sugars) and reducing protein and mineral density. Domestic watermelon, for example, now stores up to 15% more water and three times more sugar than its wild African ancestor (Ren et al., 2018) [24]. This phenomenon contributes to a diet that is globally more caloric but less nutrient-dense, moving the modern diet even further away from the model for which our organism evolved.