The World Health Organization says processed meat does cause cancer and red meat is probably carcinogenic too.
So what is processed meat?
Processed meat has been modified to either extend its shelf life or change the taste and the main methods are smoking, curing, or adding salt or preservatives.
Simply putting beef through a mincer does not mean the resulting mince is "processed" unless it is modified further.
Processed meat includes bacon, sausages, hot dogs, salami, corned beef, beef jerky and ham as well as canned meat and meat-based sauces.
Red meat is a darker colour than white meat and includes beef, lamb and pork because of higher levels of proteins that bind to oxygen, haemoglobin and myoglobin in blood and muscle.
Why do they cause cancer?
Suspected carcinogenic chemicals can form during meat processing. These include N-nitroso compounds and polycyclic aromatic hydrocarbons.
Cooking the meat at high temperatures, especially on a barbecue, can also produce these dangerous chemicals.
However, the WHO's experts admit that the cancer risk is "not yet fully understood".
How big is the risk?
Each 50g of processed meat per day - fewer than two slices of bacon - increased the risk of cancer by 18%.
Each 100g of red meat per day increased the risk by 17%, although the WHO admits there is limited evidence.
What do the WHO classifications really mean?
The WHO classifies agents into one of five groups:
- Group 1- carcinogenic to humans
- Group 2A - probably carcinogenic to humans
- Group 2B - possibly carcinogenic to humans
- Group 3- not classifiable
- Group 4- probably not carcinogenic
Processed meat has been placed into Group 1 as the scientific evidence says it definitely does cause cancer.
Although this does not mean all Group 1 agents - which include tobacco, plutonium and alcohol - are equally dangerous.
Red meat is in Group 2A, however, because the WHO says there is insufficient evidence to give a definitive ruling.
Is meat as bad as smoking?
Estimates suggest 34,000 deaths from cancer every year could be down to diets high in processed meat.
That is in contrast to one million deaths from cancer caused by smoking and 600,000 attributed to alcohol each year.
How much red meat should you eat?
The WHO says there is insufficient evidence to set safe levels.
The World Cancer Research Fund charity argues for "as little as possible" processed meat and 500g of cooked red meat (or the equivalent of 700g raw) per week.
An eight ounce steak is 225g.
In the UK, official advice is for no more than 70 grams a day of red or processed meat so a couple of slices of bacon.
Should you do veggie?
Meat is still a good source of protein, B vitamins and minerals such as iron and zinc.
Frankie Phillips, spokesperson for the British Dietetic Association, says: "The message is to still include red meat in the diet because it is a good source of key nutrients.
"The general message is it's OK to eat some red meat but perhaps to look at ways of increasing the amount of plant-based foods - in particular, pulses."
How can you cut down?
Frankie Phillips says this can be done in a number of ways, including:
- Boosting meals such as pasta bolognese by using red meat mince plus a handful of pulses such as red lentils
- Making stir fries from strips of lean steak or lamb, combined with plenty of vegetables
- Having some meat-free days during the week.