Dietetics

Summary

In ancient and medieval medicine, diaita (the Greek word behind our “diet”) did not mean simply what a person ate. It meant the entire ordered conduct of daily life: food and drink, yes, but also exercise, bathing, sleep, sexual activity, emotional states, and the quality of the surrounding air. Physicians ranked this whole-life management above drugs and surgery as the preferred approach to both preventing and curing disease. The tradition ran from Hippocratic writers through Galen, into Islamic medicine, and into early-modern European practice, where it survived long after the theoretical framework that underpinned it had collapsed. Only in the nineteenth century, when medicine reorganized itself around laboratory science and specific disease entities, did dietetics in the classical sense effectively disappear from learned medicine — though studies suggest its categories never fully left ordinary patients’ thinking.

Diaita: More Than Food

The ancient Greek word diaita is usually translated “diet” or “regimen,” but the translation is misleading. The concept encompassed the whole management of how one lived. The Galenic tradition organized this under six categories of factors external to the body over which a person had some control: surrounding air, food and drink, sleeping and waking, exercise and rest, retention and evacuation (including bathing and coitus), and mental states (anger, sadness, joy, love, and similar passions).(Pormann, 2007) These came to be called the Six Non-Naturals — “non-natural” meaning neither the innate constitution of the body nor outright disease, but the modifiable conditions of life between them.

The scope of the category mattered therapeutically. Because dietetics concerned far more than nutrition, a physician advising on regimen was also giving guidance on how much to walk, when to bathe, how much to sleep, whether to engage in sexual activity on a particular day, and how to manage anger or grief. Al-Razi’s treatise On Spiritual Medicine extended this into moral philosophy, arguing that the avoidance of mental afflictions — greed, lust, fear of death — was both a philosophical imperative and a path to bodily health.(Pormann, 2007) The boundary between medical prescription and ethical counsel was, by design, permeable.

The health benefits of regimen were held to follow from the same humoral logic that governed everything else in the body. Inappropriate food or exercise could create excess or deficiency within the body’s four humours and four primary qualities; appropriate management could correct imbalance before it became frank disease.(Pormann, 2007) Dietetics was therefore, in principle, applicable to the healthy as much as the sick — it was preventive medicine in the literal sense.

The Hippocratic Foundation

Dietetics became central to Greek therapeutics in the mid-fifth century BCE, and ancient sources associated this development with a specific figure: Herodicus of Selymbria, a gymnastic trainer whose expertise in physical conditioning led him to incorporate food and exercise together into a single health regime designed for improvement as well as maintenance.(Nutton, 2023) Whether or not Herodicus was the originator, the development is clear: by the time the Hippocratic Corpus was being written, dietetics was among the fundamental practices of learned medicine.

The Hippocratic text On Ancient Medicine made an even bolder claim — that medicine itself had originated from diet. The argument ran that the raw foods suitable for animals were too harsh for the human constitution, and that cooking and preparation were originally medical interventions before they became culinary conventions. Medicine, on this account, was a refinement of the dietary knowledge that human beings had always needed to survive.(Nutton, 2023) This made dietetics not one branch of medicine but its historical root.

The genealogical argument runs deep in On Ancient Medicine. The author traces both arts back to a common purpose: finding the appropriate chemical process in nutrition that neutralizes potentially harmful effects on specific bodies. He even calls early cooking “medicine,” establishing an identification based on both teleological and methodological similarity. (Hynek Bartoš and Vojtěch Linka, 2024) The two arts aim at securing the good functioning of specific types of body and proceed by the same investigative logic.

Crucially, On Ancient Medicine also insists that the measure for dietetic prescription cannot be found in any number or weight. “You will find no measure,” the author writes, “except the feeling of the body.” (Hynek Bartoš and Vojtěch Linka, 2024) This directs medical knowledge irreducibly toward the particular case and the individual constitution. The cheese example captures the principle well: the same food strengthens some bodies and harms others, proving that disease cannot reduce to a single universal causal factor but depends on the specific interaction between food and the particular humoral balance of each body. (Hynek Bartoš and Vojtěch Linka, 2024) A blanket condemnation of cheese as bad for human nature in general would be wrong, because it does not harm everyone.

Hippocratic physicians were less interested in identifying specific diseases than in understanding “the underlying inner changes within the individual body” that constituted each person’s illness.(Nutton, 2023) This orientation toward the individual made dietetic prescription the natural first response: adjusting a particular patient’s regimen was more precisely fitted to individual variation than any standard pharmacological formula. Diocles of Carystus, writing in the fourth century BCE, carried this further, arguing that experience with foods was a better guide than theory — that the effects of particular foodstuffs could not always be predicted from knowledge of their properties and were better understood through the whole nature of the substance in question.(Nutton, 2023)

Totelin’s survey of Hippocratic therapeutics in the Cambridge Companion underscores both how innovative this tradition was and how porous its boundaries with popular medicine remained. The Corpus introduced systematic dietary regimens alongside drug prescriptions and surgical procedures representing a substantial body of practical knowledge that was genuinely new relative to earlier Greek medicine.(Pormann (ed.), 2018) The governing therapeutic principle across all three domains was allopathic: enantia tois enantiois iatreiai, “opposites cure opposites” — cold diseases treated by warming, dry conditions by moistening, and so forth.(Pormann (ed.), 2018) Drug selection in the Corpus was organized by the drug’s point of entry into the body and its mode of action — purgation upward (emesis), purgation downward, promotion of sweating, or promotion of urination — reflecting a therapeutic logic focused on expelling harmful humors by the most efficient route available.(Pormann (ed.), 2018) Yet this learned framework did not displace popular knowledge so much as incorporate it; many drugs and dietary treatments in the Corpus derive from traditional remedies, and the boundary between folk medicine and learned practice was permeable in both directions.(Pormann (ed.), 2018) The text On Regimen (Diaeta), the most extensive dietetic work in the Corpus, exemplifies the full scope of the ambition: it presents a comprehensive system of health maintenance calibrated to individual constitution, season, climate, and occupation, covering the same range of variables that Galen would later organize under the six non-naturals.(Pormann (ed.), 2018) On Regimen integrates physical and psychological health in a single framework: chapter 35 discusses seven types of fire-water mixture in the soul, and for each type specifies what to do or avoid in each season of the year. (Hynek Bartoš and Vojtěch Linka, 2024) Diet, on this account, shapes not only the body’s constitution but the very quality of sense perception, memory, and intellect.

The Philosophical Dimension: Diocles and the Limits of Causal Explanation

The Hippocratic and early fourth-century tradition of dietetics was not only a practical medical enterprise; it also generated sustained methodological debate about how much causal explanation dietetic reasoning could support. Van der Eijk’s analysis of Diocles of Carystus illuminates how this debate positioned dietetics at the intersection of philosophy and medicine.

Celsus, writing in the first century CE, credited Hippocrates with separating medicine from philosophy.(van der Eijk, Philip J., 2005) He also reports that after Hippocrates, Diocles of Carystus and others proceeded into “diverse modes of treatment.”(van der Eijk, Philip J., 2005) In the same times, medicine was divided into three parts: dietetics, pharmacology, and surgery.(van der Eijk, Philip J., 2005)

Diocles’ contribution to dietetic theory was methodological as much as practical. His fragment 176, preserved by Galen, establishes that similar qualities — flavor, heat, smell — do not guarantee similar powers in foodstuffs, because empirical observation repeatedly reveals dissimilar effects from qualitatively similar substances.(van der Eijk, Philip J., 2005) In that fragment, Diocles attacked a common form of generalization in dietetics: the assumption that substances with similar qualities (flavor, heat, smell) necessarily have similar powers. As van der Eijk reads the fragment, Diocles argues that empirical observation shows many dissimilar effects arising from qualitatively similar substances, and that the right account must refer to the “whole nature” (holē phusis) of the substance — the total configuration of its constituents and the way they are structured and interrelated — rather than any single quality in isolation.(van der Eijk, Philip J., 2005) This is a philosophically precise position: power is not reducible to any isolable quality, but arises from the integral composition of the substance.

Diocles also held that causal explanation, while desirable when available, is not always necessary or even possible in dietetics. Many facts about foodstuffs “resemble starting-points” (archai) and cannot be explained further; in such cases, stating a cause does not add reliability and may not be required for practical use.(van der Eijk, Philip J., 2005) This restricted the scope of causal reasoning without abandoning it: where a causal account is available, Diocles affirms it makes claims more reliable; where it is not, dietetic practice must proceed on empirical observation without theoretical grounding. Van der Eijk argues that Galen misrepresented this position as straightforward empiricism, when Diocles was in fact a Dogmatist who accepted the four primary qualities, innate pneuma, and humours — precisely the theoretical postulates that the Hippocratic On Ancient Medicine had criticized.(van der Eijk, Philip J., 2005) The difference between Diocles and a true empiricist was that Diocles warned against premature generalization, not against causal explanation as such.(van der Eijk, Philip J., 2005)

The Hippocratic text On Regimen 2.39 shares Diocles’ criticism of generalizations about food powers but suffers from the circular and tautologous causal explanations (in chs. 40–56) that Diocles’ methodology implicitly targets.(van der Eijk, Philip J., 2005)

The question of whether dietetics constituted a branch of therapeutics or a more general mode of bodily care was itself a matter of philosophical debate. Van der Eijk argues that dietetics could be defined more broadly as the care of the body in both healthy and unhealthy states, or on the interface between them — rather than as strictly therapeutic, aimed at restoring health from disease. This was the position implicit in the Hippocratic On Regimen, whose scope ran from the preservation of health to the prevention and management of disease.(van der Eijk, Philip J., 2005) Mnesitheus of Athens, Diocles’ contemporary, formalized this by dividing medicine into two branches — the preservation of health for the healthy and the treatment of disease for the sick — rather than placing dietetics within therapeutics as a subdivision. Erasistratus, working a generation later, went further by distinguishing the “healer” (iatros) from the “health specialist” (hugieinon) as different kinds of practitioner.(van der Eijk, Philip J., 2005)

The practical consequence of this expanded scope was a rapid extension of medicine’s claimed territory in the fourth century BCE. As physicians claimed authority over all dimensions of daily life — food, exercise, sleep, sexual activity, emotional states — medicine began to encroach on what had previously been governed by custom, philosophy, or personal discretion. Van der Eijk notes that this “medicalization” of daily life generated resistance, illustrated most vividly by Plato’s attack on dietetics in the Republic: the spectacle of a man who managed every aspect of his life according to medical advice had become, for Plato, a kind of intellectual enslavement.(van der Eijk, Philip J., 2005) The expansion that made dietetics the preeminent branch of medicine was also what made it philosophically controversial.

Sleep as Dietetic Category

The Hippocratic tradition treated sleep not as a passive background condition of life but as an active component of the dietetic system, directly linked to food intake and digestion. This connection rested in part on observable social fact: the ancient standard was one main meal per day, taken in the evening before bed, with an optional smaller lunch at midday. In this food landscape, the soporific effect of eating was a natural and recurring observation. (Hynek Bartoš and Vojtěch Linka, 2024) Diocles confirmed the same pattern, noting that napping after the midday meal was an unremarkable practice. (Hynek Bartoš and Vojtěch Linka, 2024)

The Corpus theorized this observation systematically. On Regimen stated the principle directly: periods of sleep in a person who has eaten “warm and moisten, distributing the nutriment,” while sleep while fasting strengthens and cools, though prolonged fasting-sleep can melt the flesh and weaken the body. The Aphorisms added a seasonal dimension: the bowels are hottest in winter and spring, sleep is longest in those seasons, and therefore more food should be given. (Hynek Bartoš and Vojtěch Linka, 2024) Regimen in Acute Disease observed that a man unaccustomed to eating lunch becomes immediately weak, heavy, and sluggish when he does eat at midday, and must sleep to recover: “it is necessary for him to sleep on it, just as he would sleep through the night after dinner.” (Hynek Bartoš and Vojtěch Linka, 2024) Epidemics 4 put the relationship in aphoristic form, characterizing sleep as “food for the guts” and noting that “wakefulness induces appetite” — suggesting a circular physiological loop between sleep, digestion, and hunger. (Hynek Bartoš and Vojtěch Linka, 2024)

Aristotle incorporated this medical understanding of sleep into his biological framework, making food-digestion the master mechanism of sleep onset in De somno. That text stands out in the doxographic tradition as unique: across all the ancient sleep theories the Aëtian Placita records, Aristotle’s is the only account associated with food rather than with blood, heat, or pneuma. His tacit engagement with the medical rather than the philosophical sleep literature may explain why he departs from his usual practice of opening a treatise by surveying his philosophical predecessors.

Dietetics and the Doctrine of the Mean

One of the less recognized ways in which the dietetic tradition influenced ancient thought is through Aristotle’s ethics. Bartos (in Bartoš and Linka, 2024) shows that the medical background forms an essential part of the inductive basis for Aristotle’s doctrine of the mean in both the Eudemian and Nicomachean Ethics.

In Eth. Eud. 2.1, Aristotle reasons by analogy from bodily good condition (euexia): just as bodily good condition is composed of the virtues of the body’s parts, so complete virtue of the soul is composed of the virtues of its parts. (Hynek Bartoš and Vojtěch Linka, 2024) The analogy works only if the medical facts about euexia are already understood as established by induction. Aristotle makes this explicit: “every disposition is produced and destroyed by the same things being applied one way or another, such as health by food, exercise, and season or climate. This is clear by induction.” (Hynek Bartoš and Vojtěch Linka, 2024) The inductive claim presupposes familiarity with the dietetic framework.

On Ancient Medicine supplies exactly the medical evidence Aristotle invokes but does not spell out. Chapter 9 states that the doctor’s task requires hitting a mean (metrou tinos stochasasthai), but warns that no mean can be found by number or weight, only by the perception of the body. (Hynek Bartoš and Vojtěch Linka, 2024) The language of stochasasthai (hitting a mark by aim rather than formula) appears again in Aristotle’s famous definition: “virtue is a mean state, since it is skilled at hitting the mean (stochastiké ge ousa tou mesou).” (Hynek Bartoš and Vojtěch Linka, 2024) The verbal echo may be deliberate.

On Regimen provides the fullest medical parallel: health requires both food and exercise in the correct proportion to each other and to the individual’s nature, age, season, winds, and local conditions. Food alone does not produce health; the proportion of exercise to food must be calibrated individually. (Hynek Bartoš and Vojtěch Linka, 2024) Aristotle stood on solid inductive ground when he appealed to gymnastic training and medicine as exemplifying the aim at a mean, because this really was a credible medical theory that could be extended from the body’s good condition to a theory of the soul’s habits and moral virtue.

Galenic Elaboration

The fourth-century physicians elevated dietetics to stand alongside surgery and pharmacology; some placed it above the other two, on the grounds that dietetic medicine could prevent disease rather than merely cure it.(Nutton, 2023)

Within this framework, the physician’s duty was not simply to prescribe what to eat. Scribonius Largus, writing in the first century CE, made the point about unity of practice explicit: there can be no proper surgery without dietetics, and vice versa; neither could be practised properly without pharmacology.(Nutton, 2023) The three branches of therapeutics were not alternatives but aspects of a single integrated professio. A physician who neglected dietetics was not practising a trimmed-down version of medicine — he was failing in his professional duty.

Galen’s approach to regimen was individual throughout. Diet had to be calibrated to the patient’s particular temperament, age, season, occupation, and geographic location — the same food that was healthful for one constitution could harm another. This individuation made dietetics demanding to practice, and it also made it impossible to evaluate by anything like a modern clinical trial: the prescription was defined by its specificity to the patient rather than by general efficacy for a disease category. That was not a flaw in the system; it was the system.

Asclepiades of Bithynia, who brought a corpuscular rather than humoral theory to Rome in the late Republic, arrived at a very similar practical emphasis from entirely different theoretical premises. His five basic therapies were regulating food and wine intake, massage, ambulatory exercise, rocking appliances for passive exercise, and bathing — all interventions on the non-natural factors of daily life — under the famous slogan “swiftly, safely, pleasantly.”(Nutton, 2023) That two physicians with opposed theories converged on the same therapeutic priority illustrates how deeply the dietetic emphasis was embedded in ancient medicine, independent of any specific theoretical commitment.

Islamic and Medieval Dietetics

Islamic physicians inherited dietetics wholesale. The six non-naturals remained central to the medical framework, and the Galenic hierarchy — regimen before drugs, drugs before surgery — was preserved and elaborated rather than questioned. Ibn Sina’s Canon of Medicine codified this in a form that European universities would teach for centuries. The tradition also generated a genre of popular health literature, the regimen sanitatis (“regimen of health”), which translated the learned framework into advice for lay readers organized around the six categories: what air to breathe, what foods to eat in each season, how much to sleep, how to regulate exercise and sexual activity, and how to manage emotional states.(Pormann, 2007)

The Almanac of Health by Ibn Butlan (d. 1068) presented this in tabular form — a grid displaying which foods, activities, and environments suited each temperament and season. The work circulated widely, crossed the Mediterranean into Latin, and became one of the most frequently copied medical texts in medieval Europe. The dietetic tradition was not merely transmitted; it was popularized and made accessible across multiple languages and readerships.

Al-Razi’s treatise On Spiritual Medicine argued that the pursuit of pure knowledge and avoidance of mental afflictions such as greed, lust, and fear was both a philosophical imperative and a path to bodily health, linking moral philosophy directly to medicine.(Pormann, 2007) Friedrich Hoffmann’s early 18th-century mechanistic medicine preserved Galenic temperament doctrine by reinterpreting it in corpuscular-mechanical terms, and his work also discussed the six non-naturals, a key Galenic category.(Temkin, 1973)

The Long Decline

Dietetics did not fall when Galenic theory fell. This is among the more striking findings in the history of medicine. Temkin observes that the fall of Galenic science was not identical with the fall of Galenic practice: bleeding, purging, and the prescription of Galenicals continued without interruption, and so did dietetics and regimen. Physicians and patients had used these practices for centuries and had no evidence that they had stopped working.(Temkin, 1973)

The seventeenth-century assault on Galen was, in large part, an assault on his explanatory framework — his use of qualities, humours, and teleological physiology — rather than on his therapeutics. Francis Bacon attacked Galen personally as a “deserter from experience” and held him responsible for medical conservatism,(Temkin, 1973) but this critique was aimed at the theoretical apparatus, not the dietary prescriptions. Nicholas Culpeper’s 1652 English translation and paraphrase of medical texts attacked the College of Physicians for hiding medical knowledge behind Latin, not Galen himself — and Culpeper continued to prescribe Galenicals throughout.(Temkin, 1973) The social complaints and the theoretical complaints were distinct, and neither immediately dislodged dietetic practice.

What gradually displaced the classical model of dietetics was not a single refutation but a shift in the basic framework of what medicine was for. As medicine reorganized itself around specific disease entities, pathological anatomy, laboratory medicine, and eventually the germ theory of disease, the patient’s individual constitution and regimen became less central. A disease caused by a specific bacterium did not require dietary adjustment calibrated to individual temperament; it required an intervention targeting the organism. The six non-naturals were not disproved; they simply ceased to be the organizing category of medical thought.

By 1870, Temkin observes, Galenism as a living tradition was over, and Galen was handed to classicists and historians.(Temkin, 1973) Dietetics, in the classical sense, was carried along in the fall. What replaced it — nutritional science, public health, lifestyle medicine — took different forms, drew on different theories, and did not usually acknowledge the tradition from which they descended.

Nutton notes, however, that the categories were not simply forgotten.(Nutton, 2023) Studies in London in the late twentieth century found that patients continued to hold views about the six non-naturals as the prime determinants of health, and that patients assimilated new biomedical information most readily when it could be placed within a framework of individual balance and environment that descended directly from the Greeks.(Nutton, 2023)

Vitalist Dietetics and the Mineral Theory of Disease

The vitalist tradition of the early twentieth century preserved and extended the ancient link between diet and systemic disease, though on very different theoretical grounds. Henry Lindlahr’s Philosophy of Natural Therapeutics (1918) grounded dietary necessity in a theory of inorganic versus organic mineral salts: every disease arising from internal causes was, in his account, accompanied by a deficiency in blood and tissues of certain organic mineral elements, and this deficiency in turn was caused by unbalanced diet and improper food combinations. Lindlahr held that food combinations could simultaneously create an excess of waste and morbid matter while failing to supply the mineral elements on which elimination of systemic poisons depended — a dual failure that explained why dietary correction was indispensable to any genuine cure.(Lindlahr, Henry, 1918) This argument extended the classical logic of dietetics — that disease reflects an imbalance correctable through regimen — but replaced humoral theory with mineral chemistry and the concept of morbid matter accumulation.

See Also

• Six Non-Naturals
• Preventive Medicine
• Humoral Theory
• Galenism
• Regimen Sanitatis

Sources

• Nutton, Vivian. Ancient Medicine. 3rd ed. Routledge, 2023. Chapters 6, 8, 11, 20.
• Pormann, Peter E., and Emilie Savage-Smith. Medieval Islamic Medicine. Edinburgh University Press, 2007. Chapter 3.
• Temkin, Owsei. Galenism: Rise and Decline of a Medical Philosophy. Cornell University Press, 1973. Chapter 4 (continued).

(Hynek Bartoš and Vojtěch Linka, 2024): On Regimen, the most elaborate account of dietetics, integrates most of these aspects into one single theory, discussing mixtures within the body as well as within the soul and providing practical instructions on how to achieve the best possible conditions for our sense perception, memory and intellect. In ch. 35, the author discusses seven types of fire-water krasis in the soul and for each type suggests what to do or avoid during each season of the year. (Hynek Bartoš and Vojtěch Linka, 2024): the author does not hesitate to give to the art of cooking the name of ‘medicine’, establishing thus an ancient origin for his own art (VM 3.6). This identification is based on a teleological and a methodological consideration … The two arts aim at securing the good functioning of specific types of body, and they use similar means by seeking the appropriate chemical process in nutrition that will neutralise possible harming effects. (Hynek Bartoš and Vojtěch Linka, 2024): For one must aim at a measure; but you will find no measure—nor number nor weight besides—by referring to which you will know with precision, except the feeling of the body (VM 9.1–3, i.588.4–590.1 L.). (Hynek Bartoš and Vojtěch Linka, 2024): Hence the natures of these people differ, and the difference concerns the very thing in the body that is hostile to cheese and is stirred up and set in motion by it. Those in whom such a humour happens to be present in greater quantity and to exert more power in the body will naturally suffer more. But if cheese were bad for human nature in general, it would harm all people (VM 20.6). (Hynek Bartoš and Vojtěch Linka, 2024): If a man accustomed to a single meal decides to eat lunch … it “immediately makes him weak, heavy in his whole body, feeble, and sluggish.” The solution to this stupor is to sleep: “it is necessary for him to sleep on it, just as he would sleep through the night after dinner.” Thus, the body’s proper response to food is to sleep. (Hynek Bartoš and Vojtěch Linka, 2024): He characterizes sleep as “food for the guts,” an enigmatic statement that nevertheless conjures an image of digestion-promoting sleep. … His contention that “wakefulness induces appetite” may further suggest that prolonged vigil creates desire for food and the sleep that it will bring. (Hynek Bartoš and Vojtěch Linka, 2024): It was a standard practice to eat only one meal a day, in the evening before bed, though some people consumed a lunch at mid-day in addition. Various authors attest to this situation in the fifth and fourth centuries. … In this ancient food landscape, then, the idea that sleep and food-intake are directly linked begins to seem a more reasonable proposition. (Hynek Bartoš and Vojtěch Linka, 2024): “the bowels are by nature hottest in the winter and the spring and sleep is longest; in these seasons it is necessary to also give more food.” He then clarifies that heat is the driving factor behind the need for extra sustenance, but he clearly sees increased food and increased sleep as intuitively correlated. (Hynek Bartoš and Vojtěch Linka, 2024): Diocles also confirms this picture of one main meal at the end of the day, with an optional smaller lunch at midday; further, he indicates that napping after the midday meal is an unremarkable practice. (Hynek Bartoš and Vojtěch Linka, 2024): Then, by an analogy to the good physical condition of the body, “complete virtue” will mean the virtue of both of these parts of the soul: “Just as the good physical condition (ἡ εὐεξία) is composed out of the virtues of the parts, so too is the virtue of the soul insofar as it is complete” (1220a2–4). (Hynek Bartoš and Vojtěch Linka, 2024): ⟨1⟩ First of all, let it be established that the best dispositions are produced by means of the best things, and to act best concerning each thing is produced from the virtue of each thing. For example, the best exercises and nourishment are produced from a good physical condition, and out of the good physical condition they exercise best. Further, every disposition is produced and destroyed by the same things being applied one way or another, such as health by food, exercise, and season or climate. This is clear by induction. (Hynek Bartoš and Vojtěch Linka, 2024): ⟨3⟩ For this reason, the doctor’s tasks are much more varied and require more precision. For one should be skilled at hitting a mean (Δεῖ γὰρ μέτρου τινὸς στοχάσασθαι); but you will find no mean—nor number nor weight besides—by referring to which you will know with precision, except the perception of the body (τοῦ σώματος τὴν αἴσθησιν). Hence it is difficult to acquire knowledge so precise that one errs only slightly in one direction or the other. (Hynek Bartoš and Vojtěch Linka, 2024): In section ⟨3⟩, the author makes the essential claim that Aristotle has said is made in the art of medicine: “one should be skilled at hitting a mean” (Δεῖ γὰρ μέτρου τινὸς στοχάσασθαι). In fact, Aristotle may deliberately echo this in the conclusion to the Eth. Nic. 2.6 argument: “therefore virtue is a mean state, since it is skilled at hitting the mean” (μεσότης τις ἄρα ἐστὶν ἡ ἀρετή, στοχαστική γε οὖσα τοῦ μέσου) (1106b27–28). (Hynek Bartoš and Vojtěch Linka, 2024): Eating alone will not make a human being healthy; one must also take exercise. For food and exercise, while possessing opposite qualities, yet work together to produce health. For it is the nature of exercise to use up material, but of food and drink to fill up what has been depleted (ἐκπληρῶσαι τὰ κενωθέντα). And it is necessary, as it appears, to discern the power of the various exercises, both natural exercises and artificial, to know which of them tends to increase flesh and which to lessen it (ἐς αὔξησιν … ἐς ἔλλειψιν); and not only this, but also the proportion (τὰς ξυμμετρίας) of exercise to bulk of food, to the nature of the individual, to the age of the body, to the season of the year, to the changes of the winds, to local conditions, and to the constitution of the year.