Red and processed meats that have been linked with heart disease and cancer may be a major factor with another disease that's epidemic - type 2 diabetes.
Science has already identified red meats - beef, lamb and pork - and processed meats as contributors to cardiovascular disease, including heart attacks and strokes, as well as colon cancer. But a recent study by the Harvard School of Public Health says a new look at the 123,000 people involved in a 20-year study ending in 2006 found elevated red-meat consumption to be linked with an increase in diabetes.
In type 2 diabetes, either the body does not produce enough insulin or cells resist the effects of insulin, which is necessary for the body to be able to use glucose for energy.
According to the study, increased red meat intake in a four-year period resulted in increased diabetes in the following four years. When compared with a group with no change in red meat intake, the study showed increasing red meat intake of more than a half-serving a day - equivalent to half the size of a deck of cards - for four years was associated with a 48 per cent elevated risk of diabetes in the subsequent four years.
The opposite was also true. When meat consumption was reduced by more than a half serving per day, risk dropped, states the study published in the Journal of the American Medical Association, Internal Medicine in June.
"The association of red meat and cardiovascular disease are quite clear," said Walter Willett, Harvard School of Public Health's chairman of the department of nutrition. "It does look as though replacing red meats with other major sources of quality protein - nuts, legumes, chicken and fish - is a good thing to be doing."
Iron, long heralded as a key nutritional attribute of red meat, might represent the hazardous link between red meat and type 2 diabetes.
Haem iron from red meat is absorbed even if the person already has sufficient stores of the mineral. Non-haem iron from plants is expelled from the body once the person has a sufficient supply. "Our bodies don't regulate haem iron well, and it can damage cells that secrete insulin," Willett said.
Processed meats often involving beef and pork contain more sodium, preservatives and sometimes nitrates that, he said, "cause chemical reactions that may create compounds that are toxic".
But the American Meat Institute disagrees with the study's results and countered "that meat is a nutritious part of a healthy balanced diet".
"While some recent studies have generated headlines linking meat to different ailments, it is important to remember that conditions like heart disease, cancer and diabetes are complex conditions that cannot simply be caused by any one food," institute spokesman Eric Mittenthal said.
A deeper look at the diabetes study, he said, shows data was gathered through questionnaires about eating habits every four years. "This imprecise approach is like relying on (consumers') personal characterisation of their driving habits in prior years to determine their likelihood of having an accident that kills them in the future," he said. "It has a high likelihood of giving erroneous conclusions."
Evidence and common sense, he said, suggest "a balanced diet and a healthy body weight are the keys to good health".
T. Colin Campbell, Cornell University professor emeritus of nutritional biochemistry, says the healthiest diet excludes animal-based foods including dairy. His research was the basis of the 2011 documentary, Forks over Knives.
"Meat is a member of a class of foods that doesn't do much good for anything," he said.
"Animal products, if they have any effect at all, tend to be not good. When animal products go up, these diseases go up, and it might not just be because people are consuming more animal food. They also are decreasing plant foods."
However, Beef + Lamb New Zealand said there's no need for Kiwis to change their meat eating habits.
"International and national dietary guidelines are based on a large body of scientific evidence and these recommend red meat is an important part of a healthy, balanced diet," they said in a statement.
"New Zealanders currently eat red meat in amounts well within these guidelines."