Eating
red meat introduces a potentially dangerous molecule into
the body tissues, according to researchers.
Scientists
from the University of California in San Diego believe it
could cause heart disease and cancer by triggering a harmful
immune response.
Humans cannot produce the molecule - a type of sugar - but
it occurs at high levels in lamb, pork and beef.
The research is published in the Proceedings of the National
Academy of Sciences.
Human volunteers
Several studies have associated red meat diets with cancer
and heart disease.
But these have focused on saturated fats and chemicals produced
during the cooking process.
The new research focuses on a sugar called N-glycolylneuraminic
acid (Neu5Gc).
"It
could be that the damage only builds up over years"
--- Professor Ajit Varki
Tests on three human volunteers - all members of the research
team - confirmed that if the sugar is present in the diet, it
is absorbed into body tissues such as the blood vessels.
The tests also suggested that because the molecule is not naturally
present in the body, it is viewed as an invader by the immune
system, which is sparked into action.
Lead researcher Professor Ajit Varki said the molecule was almost
certainly not immediately toxic, and it was possible that humans
had built up a tolerance after hundreds of thousands of years
of eating meat.
"It could be that the damage only builds up over years," he
said.
"However, we are now living longer and the question arises whether
the gradual accumulation of Neu5Gc and the simultaneous presence
of antibodies against could be involved in some diseases of
later life."
Animal
transplants
Professor Varki said the molecule may be one of the main obstacles
in the path of developing animal-to-human organ transplants.
Scientists are trying to find ways to stop the powerful immune
response that occurs when a pig organ is put into a human.
The three scientists who were involved in the study drank a
solution of Neu5Gc purified from pork.
Tests showed that most of the molecule was eliminated by the
body, but small amounts were absorbed into the body.
About two days after ingestion, Neu5Gc levels were raised two
or three-fold.
By four to eight days, levels had dropped almost to their original
level.
Good evidence'
Dr Julie Sharp, from Cancer Research UK, said a third of all
cancers were linked to diet.
"There is good evidence that a diet rich in fruit, vegetables
and fibre and low in fat and red meat can reduce the risk of
the disease.
"However these results are preliminary and were obtained from
analysis of only three individuals.
"Large-scale population studies would be needed to prove if
this molecule has any role in human disease including cancer."
A spokesman for the British Dietetic Association told BBC News
Online: "We would encourage people to eat a balanced diet based
mainly on starchy carbohydrates, fruit and vegetables with small
amounts of protein from a variety of sources, including diary,
vegetables, meat, fish and poultry."
Scientists
from the University of California in San Diego believe it
could cause heart disease and cancer by triggering a harmful
immune response. 
