Those longing for a study that concludes it’s healthy to eat bacon will have to put that dream to rest.
The news came in no uncertain terms on Monday: Bacon can cause colorectal cancer. So can bologna, ham, beef jerky, sausage, and all manner of salted, cured, fermented, and smoked meats. And hot dogs, too.
That’s the verdict from the World Health Organization, which added its voice to the many groups that for years have urged people to eat less red meat, especially processed meat.
The WHO’s cancer research arm, the International Agency for Research on Cancer, reviewed hundreds of studies and concluded there is sufficient evidence to classify processed meats — such as Americans’ beloved bacon and hot dogs — as “carcinogenic to humans” for colorectal cancer. Processed meats typically contain pork or beef, but may also include other red meats, poultry, or meat byproducts.
The agency classified unprocessed red meat as “probably carcinogenic’’ because of limited evidence of an association between eating red meat and developing colorectal cancer. Red meat includes beef, veal, pork, lamb, and mutton.
Warnings about the health effects of a meat-heavy diet are nothing new. The World Cancer Research Fund concluded in 2011 that convincing evidence showed red meat and processed meats increased the risk of colorectal cancer. The American Cancer Society has been advising people to limit red and processed meats since 2002.
But the WHO report cast a sharp spotlight, by labeling processed meat a carcinogen and specifying that 50 grams a day (1.7 ounces) can increase the risk of colorectal cancer by 18 percent. The data also show that the less one eats, the lower the risk.
The Global Burden of Diseases Project, an independent academic research organization, estimated that 34,000 cancer deaths a year worldwide can be blamed on diets high in processed meat. (To put that in perspective, tobacco smoking is responsible for some 1 million deaths a year.)
“This shouldn’t be a big surprise to anyone who’s been following the field,” said Dr. Walter Willett, a nutrition professor at the Harvard T.H. Chan School of Public Health.
Nutrition specialists welcomed the attention the declaration brought, especially because the US Department of Agriculture is in the process of revising its dietary guidelines.
For the first time, a USDA scientific review committee plainly recommended that those guidelines call for reduced red meat consumption, Willett said, but the department is getting “huge pushback from the meat industry.” The WHO declaration may give the USDA a reason to resist that pushback, he said.
Dr. Dariush Mozaffarian, dean of the Tufts University Friedman School of Nutrition Science & Policy, said he hopes the WHO’s pronouncement will prompt the US government “to specifically focus on processed meat.”
And Joan Salge Blake, nutrition professor at Boston University’s College of Health & Rehabilitation Sciences: Sargent College, said the WHO report might influence people, at long last, to reconsider their diets.
“Maybe we can expand our horizons this year, start looking at a more varied diet,” she said, suggesting one loaded with fruits and vegetables. “This may be a good time to start thinking about incorporating fish, or go meatless for a day. . . . Mix this all up so we’re not eating a large percentage of processed meats.”
Most of the studies implicating processed meats in causing cancer looked at beef, pork, or lamb, Willett said. But the chemicals used in preparing the meats are thought to be responsible for the harmful effects. So it is possible that deli meats made from turkey or chicken may also be unhealthy.
The North American Meat Institute, which represents meat and poultry companies, noted that many studies found no association between meat consumption and cancer. Janet M. Riley, senior vice president, called the WHO report “a huge overreach.”
The global health agency, she said, looked only at the harms, not the benefits. “Their job is to find cancer hazards,” she said. “They’re not tasked with looking at the nutrition benefits that meat offers. . . . What kind of nutritional deficiencies might we cause because people aren’t getting their best source of iron, of zinc, and of vitamin B-12?”
It remains to be seen whether consumers are willing to cut back.
At Bova’s Bakery in the North End, Nick Bova, 21, whose father owns the business, said a customer favorite is a sandwich made with prosciutto, fresh mozzarella, basil, tomatoes, and dressing.
“If I put a sign up that said this causes cancer,” said Bova, pointing toward the bakery’s menu, “people wouldn’t believe it. I think they’d buy two sandwiches.”
Frank Mendoza, owner of Monica’s Mercato & Salumeria nearby, where raw sausage links hang high on the walls and salami, prosciutto, ham, and more are on display, also doubted the report would affect his business, or his customers’ diets. “People are going to eat what they want to eat,” Mendoza said.
Eileen Kerkeslager, 32, who was touring Boston from Washington, D.C., had this assessment of the WHO conclusion: “I take it all with a grain of salt.”
Peg MacDonald, 66, who was visiting the North End from Connecticut with her daughter, said they still planned to indulge in the neighborhood’s renowned Italian sandwiches.
“We don’t have [red or processed meat] every night, and when we do, it’s always a treat,” MacDonald said.
She may have the right idea. “It’s not an all-or-nothing situation,” Harvard’s Willett said.
Nutrition specialists say it’s not essential to totally give up salami or bacon — just keep it to a minimum. “Have red meat the way we think of lobster, a special event, a few times a year,” Willett advised. And replace red meat with vegetable sources of protein, such as nuts and legumes, as well as a moderate amount of poultry.
That’s what Willett does, and he forgoes processed meats altogether.
Mozaffarian, of Tufts, said he eats red meat about once a week and processed meat about once a month.
BU’s Salge Blake said she sometimes eats deli meats and Italian sausages. “I’m Italian,” she said. “We’re talking about my grandmother here. My grandmother made it right in front of us.” But she also eats plenty of fruits and vegetables.
“If I want [processed meat], I’m going to have it as part of my diet,” she said. “It’s not going to be the focus of my diet.”
Globe correspondent Sarah Roberts contributed to this report. Felice J. Freyer can be reached at email@example.com. Follow her on Twitter @felicejfreyer.