A controversial study says cutting sausages, ground beef, steak and all other forms of red or processed meat is a waste of time for most people.
The report – which disagrees with most major organizations on the planet – says the evidence is weak and any risk is small.
Some experts praised the "rigorous" assessment.
But others say "the public can be put at risk" by such "dangerously misguided" research.
What counts as red or processed meat?
Red meat includes beef, lamb, pork, veal and venison – chicken, duck and game birds do not count.
Processed meat has been modified to extend its shelf life or change its taste – and the main methods are smoking, curing or adding salt or preservatives.
Pure ground beef doesn't count as processed, but bacon, sausage, hot dogs, salami, canned meat, pates and ham all count.
Are they bad for your health?
One of the main concerns has been around bowel cancer.
The World Health Organization's International Cancer Research Agency made headlines around the world when it said processed meats cause cancer.
He also said red meat is "probably carcinogenic," but the evidence is limited.
- Processed Meats Cause Cancer – WHO
In the UK alone, processed meat is believed to lead to about 5,400 cases of bowel cancer each year.
Links to heart health and type 2 diabetes were also suggested.
The scientific consensus is that overeating is bad for your health.
What does the study say?
The researchers – led by Dalhousie University and McMaster University in Canada – reviewed the same evidence that others have seen before.
The evidence, published on Annals of Internal Medicine, suggest that 1,000 people cut three portions of red or processed meat per week to:
- one life there would be seven fewer cancer deaths
- 11 years there would be four fewer deaths from heart disease
And if every week for 11 years, 1,000 people cut three portions of:
- red meat there would be at least six cases of type 2 diabetes
- processed meat there would be 12 fewer cases of type 2 diabetes
The risks reported are broadly similar to those previously suggested – but the interpretation of what they mean is radically different.
The researchers say:
- the risks are not that great
- the evidence is so weak that they could not be sure that the risks were real
"The right choice for most people, but not everyone, is to continue eating meat," one of the researchers, associate professor Bradley Johnston, told BBC News.
"We are not saying there is no risk, we are saying that there is only low certainty evidence of a very small reduction in cancer and other adverse health consequences of reduced red meat consumption."
How was the study received?
Statisticians largely supported the way the study was conducted.
Kevin McConway, an emeritus professor of applied statistics at Open University, called it "an extremely comprehensive job."
And Professor David Spiegelhalter of Cambridge University said: "This rigorous, even relentless, review does not find good evidence of important health benefits from reduced meat consumption.
"In fact, he finds no good evidence."
And the conclusions?
This study frankly fell like a lead balloon, with many in the field disagreeing with how the findings were interpreted.
England's public health officials told BBC News they had no intention of revising their advice on limiting meat intake.
Oxford Spring's Marco Springmann said the "dangerously misguided" recommendations "underestimate the scientific evidence," which in any case comes from "a small number of meat-eating individuals from high-income countries."
Giota Mitrou of the World Cancer Research Fund said that "the public may be put at risk" if they conclude that they can eat meat according to the content of the heart, because "this is not the case."
Professor Nita Forouhi of Cambridge University said, "They said the link's magnitude is small, right?"
The study suggests that there would be 12 fewer cases of type 2 diabetes as a result of 1,000 people cutting three portions of processed meat per week for just over a decade.
And she said, "For a common condition, such as type 2 diabetes, at the population and country level, this is not trivial."
Why is the quality of the evidence so bad?
Welcome to the challenging and challenging world of nutrition research.
Because you can't arrest people for life and force them to determine the health impact of different foods, you need to rely on imperfect research.
There are two main types of scientific study in this field:
- Observational Studies
- randomized controlled trials
In observational studies, you can track a large number of people for decades, record how they behave, and see what happens to their health. But separating the role of a food from all the things they eat and all the other things they do is a challenge.
In a randomized trial, you set different diets for people. But they don't cling to them forever and you have to follow them for years before diseases like cancer or heart attack come along.
"The scientific community needs to recognize that conducting clinical trials of specific dietary interventions, unlike pharmaceuticals, and following people for long periods until disease or death occurs is simply not feasible," said Professor Forouhi.
We live in a world of imperfect data and it is not about to change.
How does anyone understand this?
The weight of scientific opinion is on the side of reducing consumption of red and processed meat.
This analysis and those previously done highlighted similar risks and it is worth noting the report's authors: "We are not saying there is no risk."
But the question of whether reducing red meat will make a difference for any individual is very difficult.
For example, about six out of every 100 people in the UK develop bowel cancer at some point in their lives.
If they all eat an extra 50g of bacon a day, the number is estimated to rise to seven in 100.
But what no one can tell you is if you will be that extra case.
How much red meat should people eat?
The NHS advises anyone who eats more than 90g of red or processed meat per day to reduce to 70g per day on average.
"Globally, the evidence indicates that people who eat red and processed meat should limit their intake," said Professor Louis Levy.
"While it may be part of a healthy diet, overeating can increase the risk of developing bowel cancer,"
Is this the full picture?
Meat is just one aspect of diet – previous studies have suggested that vegetables can have a major impact on health.
- Fruits and Vegetables: For a Longer Life, Eat 10 a Day
- The Planetary Health Diet: The Flexing Diet to Feed 10 Billion
And health is just one reason to gauge the amount of meat to eat.
Diets that reduce meat or eliminate it all together – from flexor to vegan – are becoming more popular.
But the reasons involve health benefits, environmental concerns and animal welfare issues.
- What is the carbon footprint of your diet?
Beef and lamb tend to have relatively high greenhouse gas emissions, although farming practices around the world make a big difference.
Attempts have been made to reconcile all these things and create a "planetary health diet."
And it recommends that most proteins come from nuts and vegetables (such as beans and lentils) rather than meat.
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