In years past, the advice given by doctors to “cut down on the calories” or “go out for a walk more often” was just that: a friendly instruction delivered more or less earnestly depending on the situation. Nowadays, “Thou Shalt Exercise More” and “Thou Shalt Eat Healthy” have become such forceful exhortations that one would think they were newly-issued 11th and 12th commandments.

In response to rising rates of obesity in the population, the matter of diet and exercise has taken a rather grave and pressing tone. Increasingly, local, state, and federal authorities are establishing powerful legal incentives—and sometimes even sanctions—to promote what is perceived as a healthy lifestyle. School districts, city councils, health departments, and even the White House have engaged their full weight in the war on fat.

A couple of years ago, the American Medical Association joined the fray by “declaring” obesity to be a disease, a remarkable development given that there is no established consensus on how to define obesity, let alone how to identify what should be considered a disease. By classifying obesity as a disease, the AMA is supposedly trying to influence government agencies and insurance companies to pay for weight loss therapies, such as counseling, drugs, or surgical interventions. Insurance reimbursement for these treatments may help stem the tide of the obesity epidemic.

But to officially sanction obesity as a disease also opens the door for these same agencies to monitor or modify the behavior of doctors. Increasingly, “pay-for-performance” schemes of financial rewards and penalties are used to compel physicians to respond to certain problems, such as high cholesterol or high blood pressure, in certain ways that are deemed necessary for the health of the population. Conceivably, then, failing to vehemently prescribe a form of exercise or a specific diet may soon be considered negligence or malpractice in the eyes of the regulatory authorities or from the standpoint of insurers.

The rising influence of public health measures into the medical practice of doctors is justified on the basis of serious societal problems that seem to demand forceful responses. The current epidemic of obesity, affecting underprivileged children in particular, could lead to a significant number of strokes, heart attacks, and other severe outcomes in years to come. If nothing is done, a catastrophe may ensue. So goes the reasoning.

Of course, we should not minimize the gravity of the situation. It is incumbent on us all to adopt for ourselves and encourage in others healthy habits of living. But we must also realize that when public health considerations intervene in medical practice, they run the risk of displacing the particular interest of the individual patient in favor of the utilitarian norm (“the most health for the greatest number”). Yet it is the interest of the individual patient that the doctor is first and foremost obligated to serve. The Hippocratic Oath established the sanctity of the doctor-patient relationship 2,500 years ago, an ethical stance that became part of the Christian medical tradition but has been seriously eroded in the West in recent times, primarily on the basis of utilitarian demands.

As Pope St. John Paul II frequently observed, utilitarian goals may have a superficial appeal, but they are not in line with the ultimate good of the person. And health may be a good, but it is only a means to a greater good. While staying healthy and caring for one’s body is often necessary for the journey to holiness, it remains subordinate to the ultimate end of partaking at the divine banquet.

But can exercising sensibly and eating well ever be a wrong prescription? After all it’s natural, cheap, and without side-effects. Who can argue against that advice?

Well, take Thomas Aquinas as a case in point. The historical record does not provide his exact weight or “body mass index,” but that he was very large is an undisputed fact. And the source of his obesity is no great mystery if we recall G.K. Chesterton’s poetic account that, early in life, Thomas “sat down on that sedentary seat of scholarship, that chair of philosophy, that secret throne of contemplation, from which he never rose again.”

So let me ask this question: would you endorse the idea that the Angelic Doctor should have spent more time on his feet and less time on his behind? Would you have wanted him to curtail his caloric input if it risked curtailing his philosophical and theological output? Would you be proud to have prodded the Dumb Ox toward the outdoors, when he felt so near God in the indoors of his contemplative mind?

Woe to the doctor who perturbs the saint!