In a separate recommendation, the task force is also advising doctors to counsel certain other at-risk patients who aren't obese about better lifestyle choices.
Both updated recommendations focus on nonsurgical interventions for excess weight, not weight loss surgery.
More than 30% of U.S. adults are obese, the task force notes. It increases their risk of heart disease, diabetes, and other health problems.
The updated recommendations are published online in the Annals of Internal Medicine.
Obesity screening details
Obesity screening can be done by calculating BMI, a measure of weight to height, or by measuring waist circumference, the task force says.
BMIs of 30 or above are termed obese. A BMI of 25 to 29.9 is overweight. Normal BMIs are 18.5 to 24.9.
Waist sizes above 35 inches for women and above 40 inches for men are linked with higher heart disease and diabetes risks.
The task force does not specify how often obesity screening should be done.
Many doctors do not screen for obesity now, Grossman says.
"Just over 40% of adult patients in commercial HMOs had documented BMI measurements in 2009 and 2010," Grossman says, citing a national survey. In commercial PPO plans, only 12% did, he says.
What kind of weight loss program?
If referral to a weight loss program is needed, Grossman says it should be to an intensive program.
Over a year, the program should offer 12 to 26 sessions, Grossman says. "Low-intensity [and] anything less than 12 sessions don't work," he says, citing evidence reviewed by the task force.
Ideally, the programs should help patients become accountable for weight loss and maintenance. To do so, they need to learn such skills as counting calories or fat, he says.
"Really the critical thing is to maintain that weight loss after the program stops," he says.
In 2003, the USPSTF did not find the evidence strong enough to recommend these programs for obese people, he says.
Since then, Grossman tells WebMD, additional studies have been done. The USPSTF found evidence that intensive behavioral intervention for obese adults can help them lose weight and improve their risk factors for heart disease.
The task force found that intensive programs can help obese people lose, on average, about nine to 15 pounds.
The effects for those who are overweight but not obese are not as clear, the experts say.
While some research finds that adding the drugs orlistat (Alli, Xenical) or the diabetes drug metformin (Glucophage, Glumetza, and others) help with weight loss, the task force does not recommend them.
Orlistat has been linked to rare but severe liver disease. Metformin is not FDA-approved to treat obesity.
Counseling non-obese but at-risk
The task force also recommends that doctors consider counseling non-obese but at-risk patients about eating more healthfully and exercising regularly.
The new recommendation combines two previous recommendations that suggested doctors talk about the two separately, Grossman says.
It just makes sense, he says, to counsel patients on nutrition and physical activity at the same time.
Doctors are advised to use their clinical judgment on who to counsel. For instance, Grossman says, a doctor might advise someone with a BMI of 29 and a family history of heart disease to lose weight and exercise more.
"We don't want people to misinterpret this," he says. Physical activity and healthy diet are important for everyone, he says.
The task force is an independent panel of national experts in prevention and evidence-based medicine. It makes recommendations about such services as screenings, medications, and counseling.
Insurers and medical associations look to the recommendations for guidance.
Updated obesity screening: perspective
"I think they got this one exactly right," says Robin Blackstone, MD, president of the American Society for Metabolic & Bariatric Surgery. She reviewed the recommendations for WebMD.
"What really struck me is, they are targeting a BMI of 30," she says. That makes sense, as she and other experts say that BMIs of 30 and higher are linked with higher disease risk.
The recommendation for universal screening may inspire more doctors to do it, she says. "Many doctors are nervous about bringing up weight with their patients," she says, "because patients are so sensitive about it."
"This makes it part of the regular care of their patients."