Cutting back on red and processed meat brings few if any health benefits, according to a review of studies involving millions of people.
The finding contradicts dietary advice of leading international agencies and raised immediate objections from many health experts.
Most people can continue to eat red and processed meat at current average intake, typically three or four times a week for adults in North America and Europe, said the study's authors.
"Based on the research, we cannot say with any certainty that eating red or processed meat causes cancer, diabetes or heart disease," said Bradley Johnson, an associate professor at Dalhousie University in Canada who co-led the review published on Monday in the Annals of Internal Medicine journal.
However, in what amounts to a scientific food fight, a group of doctors from Harvard, Yale, Stanford and elsewhere, including one of the study authors, requested in a letter to the journal that it "pre-emptively retract publication" of the papers pending further review, and said revised guidelines that could lead to increased consumption of red and processed meats would be irresponsible.
A statement scheduled for publication by the Harvard T.H. Chan School of Public Health said, "from a public health point of view, it is irresponsible and unethical to issue dietary guidelines that are tantamount to promoting meat consumption, even if there is still some uncertainty about the strength of the evidence."
The World Health Organisation's International Agency for Research on Cancer (IARC) and the World Cancer Research Fund (WCRF) both say red and processed meat may or can cause cancer.
The WCRF advises eating only "moderate amounts" of red meat, such as beef, pork and lamb - with an upper limit of 500 grams cooked weight per week - and "little, if any" processed meat.
For the latest analysis, researchers from Canada, Spain and Poland conducted a series of reviews of both randomised controlled trials and observational studies looking at the possible health impact of eating red and processed meat.
Among the randomised trials they selected for analysis, which included around 54,000 people, they found no statistically significant link between eating meat and the risk of heart disease, diabetes, or cancer.
Among the observational studies, which covered millions of people, they did find "a very small reduction in risk" in those who ate three fewer servings of red or processed meat a week, but said that this association "was very uncertain."
"Our bottom line recommendation ... is that for the majority of people, but not everyone, continuing their red and processed meat consumption is the best approach," Johnson said.
Ian Johnson, a nutrition expert at Britain's Quadram Institute of bioscience, said people who choose to cut down their meat intake might still improve their health by doing so.
"There are (also) strong environmental and ethical arguments for reducing meat consumption in the modern world."
Australian Associated Press