To what extent does lifestyle cause or contribute to disease and disability? And what exactly is a healthy lifestyle anyway? There is much confusion about what type of diet or exercise is best, not to mention how much sleep, stress or sex is ideal. Nor is it clear how best to motivate people to change their habits.

This lack of clarity has inspired a growing movement to inform health professionals and patients about the importance of lifestyle in preventing and treating disease. Its aims are to disseminate scientific research about what it means to live well and to encourage doctors and other providers to incorporate this knowledge into their practices.

Two years ago, a group of doctors founded an organization with the goal of making lifestyle medicine a credentialed clinical specialty and a part of basic medical training. Symptomatically treating disease without assessing patients’ lifestyles or offering them guidance on how to change is “irresponsible and bordering on neglect,” said Dr. John H. Kelly Jr., president of the fledgling organization, the American College of Lifestyle Medicine.

A professor of preventive medicine at the Loma Linda University School of Medicine in California, Dr. Kelly said the group was formed because of people like his uncle.

Given a diagnosis of heart disease, the uncle had a stent surgically implanted to open a clogged artery but received no advice on how he might change his lifestyle, even though research shows that diet, exercise and stress management could greatly improve his condition.

Dr. Kelly says lifestyle medicine is essential in fighting the national epidemics of obesity, diabetes and cardiovascular disease. “We cannot solve the health problems of society unless we change our focus from acute, episodic care to health promotion and wellness — lifestyle medicine,” he said.

The Centers for Disease Control and Prevention reports that 1.7 million Americans die and 25 million are disabled each year by chronic diseases caused or made worse by unhealthy lifestyles. And a 2005 study in The New England Journal of Medicine predicted that average life expectancy in the United States would decline in the next 20 years as a result of unhealthy lifestyles, reversing a trend dating to the 1850s. The American College of Lifestyle Medicine has 150 members in a wide array of specialties — nutritionists, ophthalmologists, gastroenterologists and oncologists, among others. Helping their cause is a new publication, The American Journal of Lifestyle Medicine, which appears every other month with peer-reviewed research on the way daily habits affect health.

“Bottom line is we want to promote the science, education and practice of lifestyle medicine,” Dr. Kelly said.

Lifestyle medicine proponents include researchers and clinicians from the fields of medicine and public health. While they agree on the importance of questioning patients about their lifestyles and giving tailored advice on how to make improvements, there remains disagreement about who should provide such counseling and with what sort of training. Nor is there a widely accepted prescriptive approach for encouraging patient compliance.

“We know lifestyle interventions can be very powerful,” often more effective than drugs or surgery, said Dr. JoAnn Manson, a professor of epidemiology at Harvard’s School of Public Health and a member of the editorial board of the new journal. “But we need to provide the scientific evidence on how to incorporate that knowledge into practice.”

Doctors may vaguely recommend that patients lose weight or get more sleep, for example, but they do not necessarily know how to help them do it.

Moreover, many physicians themselves have unhealthy habits that may prevent them from offering advice.

Sleep-deprived doctors who scarf candy bars for lunch “tend to feel inhibited in counseling others when they aren’t exactly setting an example,” said Dr. Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health and a member of the lifestyle medicine college’s board of advisers.

“Primary caregivers at least should have extensive training in lifestyle medicine,” Dr. Willett said. “And it’s reasonable for there to be a medical specialty” so patients can consult a trained practitioner who is certified as an expert in the field.

Others say lifestyle medicine should be incorporated into every facet of health care.

“I don’t think it’s appropriate to segment it off,” said Dr. Thomas W. Rowland, chief of pediatric cardiology at Baystate Medical Center in Springfield, Mass., who routinely counsels children and parents on how to adopt healthy lifestyles. “It needs to be a fundamental part of every doctor’s practice” and therefore a part of every medical school’s core curriculum.

Still, he acknowledges that there are significant obstacles, because lifestyle counseling is time-consuming and is seldom compensated by Medicare or health insurers.

Reimbursement is a chief concern of the American College of Lifestyle Medicine. The group plans to lobby Congress to that end. And it wants Congress to require that patients be informed about the relative effectiveness of lifestyle changes before receiving certain medications — including blood pressure, acid reflux and cholesterol drugs — and before undergoing procedures like back surgery, bypass surgery and stent placement.

But first, Dr. Kelly said, patients and insurers need to be assured of the professionalism of lifestyle medicine providers.

Some doctors say the movement suffers from fringe elements that advocate unproven strategies like strict vegan diets and daily saunas.

“Lifestyle medicine has to be scientifically based to distinguish it from all the quackery out there,” said David R. Brown, senior behavioral scientist in the division of nutrition and physical activity at the disease control center.

Dr. Kelly agreed. “We need to have a certification process in place with rigorous, evidence-based standards,” he said.

Proponents of lifestyle medicine are quick to distinguish it from alternative medicine. “This is mainstream medicine supported by mainstream medical research,” said Dr. James M. Rippe, associate professor of cardiology at Tufts University School of Medicine and the editor of The American Journal of Lifestyle Medicine. “The lifestyle medicine movement is not an anti-procedure, anti-medication movement.”

Rather, he said, it advocates that lifestyle interventions become part of the doctor’s arsenal in fighting disease: “For too long we’ve ignored our most powerful weapon when it should be our first line of defense.”