The emphasis placed in recent years on the concept of sustainability—particularly in relation to food supply chains and dietary models—is scientifically driven by an extensive body of data. This data, with remarkable consistency, highlights the growing exploitation of natural resources beyond certain safety thresholds. It is precisely on the basis of this evidence that the push to reduce human pressure on ecosystems has emerged.

However, partly due to the pervasive use of the term "sustainability" in public discourse, there is a common tendency to take for granted the synergies that are assumed to exist among the various factors encompassed by the concept itself. Sustainability is often perceived not as a "magnitude"—something to be evaluated and measured in relation to different parameters and processes—but rather as an inherently positive value, almost by definition associated with beneficial outcomes for health, the environment, the economy, and more.

Yet, precisely because sustainability is a complex concept, it must be acknowledged that the scenarios in which it is applied are equally complex. This complexity can lead to potential paradoxes and challenge intuitive assumptions that common sense often accepts as true.

Nutrition and food security provide a useful framework to demonstrate that finding a virtuous balance among the various factors in the "grand game" of sustainability is far from straightforward.

Consider, for example, one of the major environmental challenges tied to the concept of sustainability, which also features prominently in public discourse: global warming. This term refers to the rise in average global temperatures caused by the high release of specific gases into the atmosphere (particularly carbon dioxide, methane, and nitrous oxide) due to human activities. These gases intensify the greenhouse effect, leading to negative consequences such as rising sea levels and an increased frequency of extreme weather events.

As is now widely recognized, a significant share of these emissions is linked to food supply chains. This sector is responsible for approximately one-third of total emissions (with estimates ranging from 21% to 37%), primarily originating from agricultural and livestock production phases [1].

On this topic, the available data is abundant and, despite inevitable variations and discrepancies, consistently indicates that animal-based foods—particularly meat from ruminant animals raised on feed—are among the most significant contributors to greenhouse gas emissions [2]. In summary, these findings suggest that a plant-based diet, characterized by the predominant consumption of plant-derived foods (grains, fruits, vegetables, legumes, and nuts) and a reduced intake of animal-based foods (especially beef), tends to have a lower environmental impact in terms of greenhouse gas emissions compared to a diet with opposite characteristics [3, 4].

To provide some figures: a 2,000 kcal diet rich in meat might realistically be associated with approximately 5 kg of CO2 equivalents per day, whereas an isocaloric vegetarian diet would more likely result in around 2.5 kg of CO2 equivalents per day—about half (of course, the magnitude of this difference depends on the overall characteristics of the diets being compared) [4].

It is often assumed that promoting a predominantly plant-based diet would not only help reduce emissions but also significantly improve the general population's health.

Taking a closer look at this point and considering data on the nutritional risks associated with different diets, it becomes clear that the situation is more nuanced. While many Western and economically developed countries face health issues linked to hypercaloric diets—often excessively rich in animal-based foods compared to recommended intake levels—emerging and developing countries (including those experiencing demographic growth) grapple with opposite challenges. These include insufficient consumption to maintain proper health or diets that are quantitatively adequate but fail to meet nutritional requirements effectively [5].

In such contexts, reducing the consumption of animal-based foods could lead to deficiencies in essential nutrients such as calcium, iron, zinc, vitamin B12, and others. Consequently, the adoption of nutritionally adequate diets in these regions could paradoxically increase greenhouse gas emissions from food production rather than reduce them [6, 7].

A nutritionally adequate diet inevitably involves a certain level of greenhouse gas production, even when minimized.

Considering this, population growth—particularly concentrated in regions where dietary patterns tend to increase emissions as nutritional levels improve—poses a significant challenge in limiting overall emissions from food production. This straightforward deduction is supported by data showing that countries with very low per capita greenhouse gas emissions from diets (such as China, India, and sub-Saharan Africa) contribute far more to global totals than countries with much higher per capita emissions but smaller populations (such as the USA, Australia, and Western Europe) [8].