Earlier this year, the disputatious Dallas billionaire Mark Cuban stirred controversy when he called for universal quarterly blood testing “for everything available…so you have a baseline of your own personal health”. Around the same time, the US state of Arizona passed a law allowing consumers to obtain any laboratory test directly from licensed laboratories—without a physician's order. Theranos, a California company pioneering cheap, complete blood analysis with just a fingerstick, has advocated for such laws. The founder of Theranos, Elizabeth Holmes, has stated: “Our purpose is to give people access to the basic right of being tested when they need to or want to.”

Meanwhile, from the east coast of the USA at the Geisel School of Medicine at Dartmouth, H Gilbert Welch offers a different perspective, with characteristic candour. Responding to Cuban's comments, he said, “This is potentially a recipe for making all of us sick.” Welch's new book, Less Medicine, More Health, is fundamentally an elaboration of this argument—that the modern health-care system has run amok with testing, diagnosing, and treating. All of this activity yields more data, yes, but often little useful knowledge. While doing more in medicine may seem intuitively appealing, it can lead to large-scale iatrogenesis, Welch asserts.

Welch, a practising primary care doctor, has dedicated a distinguished research career to studying the unintended consequences of medicine, with a particular focus on overdiagnosis in cancer screening. His research findings have informed his earlier books Overdiagnosed and Should I Be Tested for Cancer? This new book aims more squarely at the layperson by organising around seven assumptions that, according to Welch, drive too much medical care. Welch's conversational tone, anecdotes, and witty parenthetical asides will speak to a broad audience, but he doesn't shy away from statistical subtleties or epidemiological concepts like prevention bias.

Welch is at his best when marrying patients' stories with otherwise abstract ideas. For example, he illustrates the “cascade effect” in medicine—how one test can often lead to another—in describing the incidental discovery of renal cancer after a workup initiated by the symptom of hoarseness in one of his patients. In a clever analogy, he invokes a barnyard pen of animals to describe cancer screening. The goal is to keep the animals in the pen—to keep cancer from spreading and becoming deadly. Turtles are the languid, usually non-lethal cancers. The rabbits are more dangerous, but might be stopped by early treatment. And the birds are the most aggressive cancers. The pen itself represents screening, which can only help with the rabbits; turtles, like most prostate cancer, aren't going anywhere, and the birds are already gone. We learn that Welch's patient with renal cancer had a turtle, based on an autopsy after a fatal pneumonia. Yet he was subjected to more than 20 abdominal CT scans and more than 10 years of worry.

Welch documents the different types of harm from overdiagnosis: anxiety from false alarms, the complications of unneeded procedures, and risks associated with excessive treatment. He tries to cast narrative light on these hazards, too. For instance, he tells of an older patient whom he started on diabetes medication after routine blood work. Soon after, the patient had a hypoglycaemic event while driving, causing a traumatic accident. A chastened Welch successfully managed his patient's diabetes without medication from that point onwards.

But Welch is a physician, and the public does not regard these harms in the same way. As cardiologist and writer Lisa Rosenbaum has pointed out, people do not experience the ills of overdiagnosis viscerally. Instead, they usually feel gratitude about catching a disease early or relief when a false positive turns into a true negative. Clinicians will recognise this as a challenge in communicating about medicine.

The seven assumptions that Welch confronts, which include “sooner is always better”, “it never hurts to get more information”, and “action is always better than inaction”, could be equally termed intuitions. It remains to be seen whether Welch's approach—marshalling the evidence around myth-busting, sometimes counterintuitive explanations—is effective as mass communication. But physicians can enlist in the cause by absorbing Welch's messages and making them our own. A burgeoning movement around high-value health care, emphasising judicious intervention and de-escalation of care, has already begun to take root.

If Less Medicine, More Health falls short in one area, it's that it skews far more to the former half of the title than the latter. Although Welch addresses the social determinants of health, his prescriptions for how to tackle key health-promoting behaviours, such as nutrition and physical activity, only scratch the surface. Such factors as poor diet, sedentary lifestyles, risky substance use, and psychosocial stress underlie the major non-communicable diseases of the modern era. We should not overmedicalise our approach to these factors, particularly in healthier people, as Welch points out. At the same time, we should not relinquish our profession's responsibility to influence public health.