From Galens De Sanitate Tuenda to Holistic Health: A Historical Study of the Six Non-Natural Factors

1. Introduction

By the second century CE, the Roman Empire had become a vast arena of cultural exchange and intellectual synthesis. Greek philosophical medicine—rooted in classical medical corpus—had merged with Roman empiricism and Stoic ethics to produce a new medical humanism. Within this context, a prominent physician-philosopher of antiquity emerged as the most influential figure of the era, shaping medical theory for over a millennium. In the treatise De Sanitate Tuenda (On the Preservation of Health), a systematic approach to the maintenance of health was articulated. Unlike therapeutic works of the time, this text addressed the healthy individual and established medicine as an art of living rather than merely an art of healing. As stated in the text, “Health arises not only from the structure of the body, but from the moderation of lifestyle.” (De Sanitate Tuenda, Book I, ch. 2).

The theoretical project extended beyond empirical medicine; it was an attempt to integrate physiology, psychology, and ethics. The six res non naturales (non-natural factors) represented a controllable domain between the natural (innate constitution) and the contra-natural (disease). Within this triadic framework—naturales, non-naturales, and contra-naturales—health was envisioned as a dynamic and moral equilibrium [19]. The physician’s task was thus dual: to restore harmony when disturbed and to instruct patients in how to preserve it through rational living.

2. Theoretical Foundations: Humoral Theory and the Six Non-Naturals

At the heart of the medical philosophy lay the doctrine of the four humors—blood, phlegm, yellow bile, and black bile. Each humor corresponded to specific elemental qualities—hot, cold, dry, and moist—and their balance determined bodily and psychological health. It was maintained that these humors were influenced not only by internal constitution but also by environmental and behavioral conditions.

Six such non-natural factors were identified:

(1). Air (aer): The quality, temperature, and movement of air surrounding the body.

(2). Food and drink (cibus et potus): The nature, quantity, and timing of consumption.

(3). Sleep and wakefulness (somnus et vigilia): The rhythms of rest in accordance with natural cycles.

(4). Motion and rest (motus et quies): The alternation of physical activity and repose.

(5). Excretion and retention (excretio et retentio): The regulation of bodily evacuations and assimilations.

(6). The passions of the mind (accidentia animi): The moral and emotional states affecting bodily humors.

These factors were termed “non-natural” not because they were alien to nature, but because they were between nature and disease—conditions external to the innate constitution yet modifiable through reason and discipline [13]. By maintaining harmony among them, one could ensure the proper balance of the humors and thus sustain health. Philosophically, this framework reflected the Stoic and Aristotelian vision of the cosmos as a system of proportionality and order. The human being, as a microcosm, mirrored the balance of the natural world. “The way of health lies in the harmony of parts, as the cosmos in balance,” as recorded in De Sanitate Tuenda (Book II). This cosmological analogy grounded medical practice in a metaphysics of moderation and proportion.

3. The Six Non-Natural Factors in Practice

De Sanitate Tuenda begins with an analysis of air, calling it “the first condition of health.” Air was described as “the nourishment of the soul” and it was warned that corrupt air breeds disease. Attention to ventilation, climate, and geography prefigured later developments in environmental medicine and epidemiology. For instance, it was observed that “damp and stagnant air weakens the body, while clear and moving air invigorates it.” Practical advice on urban hygiene was also offered, urging that cities be built on elevated ground and well-drained soil—anticipating public health reforms later echoed by Renaissance physicians and 19th-century sanitarian movements [8].

The dietary theory of the time may be regarded as an early form of personalized nutrition. It was emphasized that “the same food does not suit all bodies alike,” and diets were classified according to individual temperament. Sanguine individuals required cooling foods, phlegmatic types needed warming and drying substances, choleric persons benefited from light and moist foods, while melancholic constitutions required sweet and oily nourishment. Prescriptions included not only what but how and when to eat: “One must eat with measure, with season, and with reason.” This triad of moderation reveals the Stoic influence underlying the medical ethics of the era. Dietary discipline was considered a moral act: temperance in consumption mirrored the temperance of the soul. It was famously declared that “sleep is nature’s greatest physician.” In this view, sleep restored humoral equilibrium, allowing the body to “digest and distribute” vital fluids. Sleep patterns were analyzed as diagnostic signs—onset, dreams, and morning sensations indicating internal states.

Advice was given to sleep according to natural rhythms, warning against both excessive wakefulness and gluttonous sleep: “To sleep after a full meal is to swallow poison.” This insight foreshadowed modern findings in circadian biology and metabolic medicine [20]. In Book III of De Sanitate Tuenda, it is written: “Exercise stirs the humors; rest guards the inner heat.” Movement was viewed not as an athletic display but as rhythmic therapy—a means to promote circulation and excretion. The proper measure of exertion was suggested as “until a gentle sweat arises.” Exercise was adapted to age and temperament: the young required vigorous activity, the middle-aged moderate exertion, and the elderly light motion such as walking. The key was proportion and adaptation, principles later adopted in medieval medical regimens and Renaissance health manuals [10].

Balanced evacuation was essential to the hygiene system. It was believed that the retention of waste matter corrupted the humors, while excessive purgation depleted vitality. Recommendations included moderate bathing, controlled sweating, and regular elimination—an approach echoed in modern detoxification and metabolic health practices. Perhaps most innovative was the inclusion of the “passions of the mind.” It was recognized that emotions such as anger, fear, and sorrow directly alter bodily states. “When the mind is agitated, the heart burns, the bile thickens, and the blood surges.” These psychosomatic insights, centuries ahead of their time, anticipated modern psychophysiology and stress research [17].

4. Ethical and Social Dimensions: From Medical Technique to Moral Philosophy

The system of the Six Non-Natural Factors transcended medical practice to become a philosophy of life. Influenced by Stoic ethics, it was maintained that rational self-control was the cornerstone of both virtue and health: “He who moderates his diet and passions needs no physician.” (De Sanitate Tuenda, Book VI). This merging of medicine and morality produced a holistic anthropology: the physician was not merely a healer but a teacher of right living. It was held that maintaining one’s health was a civic duty, since “a healthy citizen contributes to the harmony of the state.” The emphasis on hygiene, diet, and emotional regulation thus had a social and political dimension [15].

Public health, in this ancient sense, was not the responsibility of institutions but of rational individuals guided by medical wisdom. Physicians educated the populace to “live in accordance with nature,” forming what could be called an early model of health promotion. This ideal of shared responsibility between doctor and patient would re-emerge in Enlightenment and modern health education discourses.

5. Transmission and Transformation: Byzantine, Islamic, and Renaissance Medicine

Although the authority of the ancient medical framework waned in the late Roman period with the rise of Christian theology, its conceptual framework endured through Byzantine and Islamic medicine. A Byzantine physician, personal doctor to Emperor Julian, compiled Collectiones Medicae, an extensive synthesis of classical medical writings. It was emphasized that physicians must teach citizens “moderation and cleanliness in all non-natural things,” recognizing hygiene and balance as civic virtues [4]. In the Islamic world, the ancient medical thought was deeply assimilated into a new cosmological and ethical context. In Al-Qanun fi al-Tibb (The Canon of Medicine), the Six Non-Natural Factors (al-ashya’ ghayr tabi‘iyya) were explicitly adopted as the foundation of preventive medicine [1]. “When one regulates life by these six rules,” the text states, “the art of the physician is reduced to observation.” This statement epitomized the Islamic synthesis of Greek rationalism and religious ethics—an integration that transformed the ancient notion of moderation into a moral and spiritual ideal.

During the Renaissance, the revival of classical learning reintroduced the preventive philosophy to Europe. Humanist physicians translated and commented upon De Sanitate Tuenda, blending ancient moderation with Christian moral virtue. Even a prominent figure of the era, despite rejecting humoral pathology, retained the notion that health depended on the harmony between person and environment. By the seventeenth century, mechanical physiology and Cartesian dualism challenged the ancient holism, yet the Six Non-Natural Factors persisted in altered forms. The miasma theory of disease and later public hygiene movements both inherited the conviction that air, diet, and environment govern health [15]. Through this long transmission, the ancient preventive paradigm was never entirely abandoned—it evolved into the ecological and behavioral foundations of modern medicine.

6. Comparison with Modern Holistic Health

Modern holistic health, as defined by the World Health Organization (1948), conceives health as “a state of complete physical, mental, and social well-being” [23]. This tripartite model resonates strongly with the ancient vision of body–mind–environment harmony. The six factors—covering the physical (air, diet, activity), the behavioral (sleep, excretion), and the psychological (passions of the mind)—constitute a complete early articulation of multidimensional health. The ancient metaphor of equilibrium parallels systems theory in modern biology, where health is conceived as homeostasis—a dynamic balance among physiological and psychosocial variables. The emphasis on adaptability (eukrasia, the well-mixed state of humors) prefigures contemporary understandings of resilience and self-regulation in health psychology [13][7].

The twenty-first-century movement of Lifestyle Medicine echoes the ancient principles in striking ways. Defined as the therapeutic use of lifestyle interventions—diet, exercise, sleep, stress management—to prevent and treat chronic disease [3], it reinstates the ancient conviction that “behavior is the primary medicine.” The ancient advice that “motion must alternate with rest, and diet with fasting” corresponds to modern exercise physiology and intermittent fasting research. The insistence that emotions disturb humoral balance finds its analogue in psychoneuroimmunology, which demonstrates how chronic stress and anxiety impair immune function [17]. Thus, the ancient non-naturals reappear today as the scientifically validated determinants of health: environment, nutrition, activity, rest, elimination, and emotion.

Beyond biology, both the ancient framework and modern holistic medicine share an ethical dimension. The WHO’s Ottawa Charter for Health Promotion (1986) defines health promotion as “enabling people to increase control over their health” [24]. The ancient theory expressed the same principle when it declared that “the physician is a guide, but the patient must govern himself.” This participatory model re-emerges in modern patient-centered care and self-management frameworks.

For the ancient theorists, rational self-mastery (enkrateia) was both a moral and medical ideal. Thus, the line between ethics and physiology was blurred: to live temperately was to be well. Modern health education, likewise, rests upon cultivating self-discipline and awareness—values deeply continuous with the ancient Stoic medical humanism [14]. Furthermore, the ancient belief that physicians should educate the populace “to live according to nature” foreshadows the role of public health practitioners in environmental policy and health literacy today. The ancient bios iatrikos—the medical way of life—remains a philosophical ancestor of contemporary wellness culture.

7. Conclusion

The theory of the Six Non-Natural Factors represents one of antiquity’s most profound attempts to conceptualize health as an interactive system. It united physiology, psychology, and ethics under a single paradigm of moderation and adaptability. The synthesis of Hippocratic naturalism and Stoic rationalism offered a model of preventive medicine that survived, in various forms, for nearly two millennia.

Historically, this framework traversed multiple civilizations—Greek, Roman, Byzantine, Islamic, and European—each reinterpreting its principles in light of new cosmologies. In the modern era, as medicine seeks to reintegrate the biological, psychological, and social dimensions of care, the ancient thought regains relevance. Its core conviction that “health lies in self-knowledge, self-restraint, and living according to reason” captures a timeless truth: that medicine is not merely the science of bodies, but the art of harmonizing life with nature. By tracing the conceptual continuity from De Sanitate Tuenda to holistic health, we see that the ancient pursuit of equilibrium endures in contemporary health discourse. From humoral balance to homeostasis, from passions of the mind to psychosocial wellness, the Six Non-Natural Factors continue to inform the ethical and ecological imagination of medicine.

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