I n the gym that I frequent too infrequently, there hangs a New Yorker–style cartoon depicting a doctor speaking to an overweight, middle-aged man sitting on the examination table. The caption reads: “What fits your busy schedule better — exercising one hour a day, or being dead 24 hours a day?”

Michael Kaufman makes a similar point at the outset of his potentially lifesaving new work, Am I My Body’s Keeper? Torah, Science, Diet and Fitness — for Life. “Since a prerequisite for living a Torah life is obviously ‘living,’ the Jew must be keenly aware of the very first duty to be healthy, for otherwise no mitzvos can be observed and no Torah learned.”

In his haskamah to Kaufman’s work, Rabbi Yosef Fleischman, rosh kollel of one of the largest Choshen Mishpat kollels in the world, notes a striking paradox. No religion puts such an emphasis on the sanctity of life and the preciousness of every moment as Judaism. “One would think therefore that religious Jews would live a life-promoting lifestyle. However, many religious Jews engage in practices that are harmful to their health. It would seem that… many are sadly unaware of the facts, and they are paying for their ignorance.”

Anyone who has ever stood in the checkout line on an Erev Shabbos in a religious neighborhood can readily confirm Rabbi Fleischman’s observation. Entire shopping carts are filled with the most caloric, least nutritious nosh and sugary soft drinks. And we will not even discuss the preservative-laden cold cuts that are staples at so many Shabbos tables and kiddushim.

Judy Siegel-Itzkovich, the Jerusalem Post’s excellent health columnist, writes in a review of Am I My Body’s Keeper that “chareidi Jews and to a lesser extent modern Orthodox are at higher risk of heart attacks, stroke, cancer, diabetes, and other chronic maladies than the secular population.” (Happily, that does not mean we live less long. Chareidim in Israel live, on average, three years longer. Other factors such as social networks, a sense of meaning in our lives, and a large familial support system compensate for the dietary deficits.)

Kaufman is hardly the first Jew to advocate strongly for a healthy lifestyle. The Rambam was the great champion of preventive medicine. “A physician’s ability to prevent illness is greater proof of his skill than his ability to cure a sick person,” he writes. The Rambam had few of the modern physician’s diagnostic or curative tools at his disposal. But the basics of preventive medicine have remained largely unchanged: a healthy diet and regular vigorous exercise remain the keys.

If one follows his rules of diet, exercise and sufficient sleep, the Rambam assures us, we will enjoy good health and freedom from disease until we become old and die. And he warns those who learn diligently the entire day that they too must not neglect the necessity of physical exercise involving the entire body and all the limbs.

In our times, the Chofetz Chaim was careful to prevent bochurim in Radin from overexertion in learning. “The entire Torah,” he writes, “is dependent upon the mitzvah of taking care of your body.”

Historically, Jewish and Christian attitudes to the necessity of preserving the health of the body differed radically, as Kaufman details in one of the book’s most fascinating chapters. Torah places a high value on personal hygiene, as well as on the cleanliness of the surrounding environment. Bathhouses were central public facilities in every Jewish community. The stench of garbage or human refuse constituted halachic bars to davening.

Paul, the organizational founder of the Church, ridiculed Jews for their punctilious concern with personal cleanliness. “The Pharisees and all the Jews do not eat unless they wash their hands properly… and when they come from the marketplace, they do not eat unless they wash. And there are many other traditions [of cleanliness] that they observe, such as the washing of cups and pots and copper vessels and dining couches.”

Meanwhile medieval European cities were running cesspools of garbage and refuse, human and animal, everywhere. Moreover, a disdain for the body was taken as a sign of saintliness. Kaufman writes of many Christian “saints” whose saintliness consisted primarily in never bathing and giving off a stench such that no one could approach them. During the Spanish Inquisition one of the signs used to ferret out insincere converts to Christianity was their continued affinity for personal hygiene.

Jews remained far less susceptible to the recurrent plagues that affected the medieval Christian world because of their efforts to keep their surroundings clean and the frequent washing of their hands. That Jewish communities were relatively less hard-hit by the bubonic plague was one of the key pieces of evidence cited by Christians that Jews were poisoning the wells.

BESIDES THE FASCINATING halachic and historical material he brings, Kaufman does a superb job of summarizing the current state of scientific evidence concerning diet and exercise in a concise and compelling fashion. (He avoids taking sides where the evidence is conflicting, such as the ongoing debate over the pros and cons of coffee.)

Some of his information will be familiar to those who attempt to keep abreast of the relevant literature, such as his list of the ten healthiest foods: apples, almonds, broccoli, blueberries, oily fish (salmon, sardines), leafy green vegetables, sweet potatoes, wheat germ, avocadoes and oatmeal. Even that list, however, may be news to many readers.

But Am I My Body’s Keeper is laced with many genuine surprises. An entire chapter is devoted to the dangers of a sedentary lifestyle. As the current saying goes, “Sitting is the new smoking.” And most of us spend many hours of our day sitting, whether it is learning in kollel or in front of a computer screen.

Some of the first hints of the dangers of lack of regular movement came from NASA studies of the first astronauts. NASA scientists found that just three orbits around the earth at zero gravity left John Glenn considerably aged. Even regular exercise is not sufficient to overcome the effects of too much sitting, as proved by the study of astronauts, who were in superb physical condition.

Let me just give some hint as to how compelling the chapter on sedentary lifestyles is. When I first read the chapter in the manuscript over two years ago, I immediately undertook to follow Kaufman’s example of standing for all of davening, except where there is a strong halachic preference for sitting. And when I reread the published book, I did so standing up the entire time. Now, all I have left to do is create the same shtender/work desk, at which Kaufman stands and does all his learning and writing.

(Incidentally, Am I My Body’s Keeper is Kaufman’s ninth book, including a seminal work on Feminism and Judaism, and his memoir In One Era and Out the Other which discusses the American Jewish community and the yeshivah world in the immediate postwar period.)

Ultimately, Am I My Body’s Keeper is an extremely optimistic book. True, none of us gets to pick our genes. But twin studies show that lifestyle choices can be far more powerful than genetics in determining both the length and the quality of our lives. There is now evidence, for instance, that not only can exercise delay various aging processes, but that it can even reverse them. In 2007, a team at Columbia University observed something long thought impossible: The creation of new brain cells in an already mature brain among those who exercised regularly. And this process was taking place in the prefrontal cortex and temporal cortex, parts of the brain connected to thinking and memory, and which are particularly vulnerable to aging. And we are not talking about Olympic athletes. Researchers found that healthy but sedentary adults in their sixties who started walking 40 minutes three times a week experienced a two percent annual growth in the hippocampus, which controls memory.

There is nothing, according to Kaufman’s studies, that is not improved by exercise and a proper diet — health, mobility, cognition, and mood. With respect to the latter, exercise has been shown to be as effective as the leading medications for conditions related to depression.

But in addition to all the good things mentioned above, it must be noted that discipline is required to follow Kaufman’s dietary and exercise prescriptions. And that discipline, in turn, has implications in all aspects of our lives, including our avodas Hashem.

Those working with struggling teenagers have long known that the gym is one of the best places to start. There teens learn discipline and gain self-esteem. Every time one lifts a weight one more time, despite the yetzer’s call to stop, or surpasses a previous personal milestone, one experiences the feeling of having overcome oneself, which is at the root of self-esteem.

When Jordan Peterson, who went on to become a Harvard professor and today one of the most influential public intellectuals in the world, speaks about turning his life around at 25, he always refers to steps right out of Am I My Body’s Keeper: He stopped smoking two packs a day, gave up his heavy drinking, and started lifting weights, more than doubling the amount that he could bench press in a short period of time.

Certainly, Kaufman is his own best advertisement for his advice. Now in his 86th year, though he has finally given up running, he still stands ramrod straight. He rises at 5 a.m. each morning for the neitz minyan at the nearby Ger beis medrash. A vigorous cardio workout on the elliptical machine is followed by learning an amud yomi, and then on to the gym to workout with weights. A brisk walk comes next, and three times a week swimming laps. Only then is he ready for breakfast, and the ten-hour workday at his shtenders/desk. On Shabbos he walks from the end of Geula to the neitz minyan at the Kosel.

For having taken it upon himself to show us all the way to a longer, healthier, and more fulfilling life, I wish Kaufman, “l’chayim.”

Originally featured in Mishpacha, Issue 699. Yonoson Rosenblum may be contacted directly at rosenblum@mishpacha.com