I have to confess to being a Michael Moseley fan. Not as accomplished a communicator as Alice Roberts or some of the other current female science/arts/history documentary presenters but eminently watchable nevertheless.
His most recent offering – in two parts – aims to assess the impact of meat eating firstly on human health and then on the global environment.
The health promotion messages about meat eating and health are almost as confusing and changing as those about saturated fats and health.
One thing that seems to be a fixed point in the meat and health debate is that white meat, eg poultry, is not associated with any documented health problems. So Moseley’s focus was entirely on so called red meat – beef, lamb and pork – and on processed foods such as bacon, ham, sausages and salami type products.
On the positive side red meat is a good source of protein providing all the essential amino acids, and of micronutrients like iron and zinc, and of vitamin B12 and other B vitamins.
On the alleged cardiovascular impact of red meat consumption the evidence is unclear and often contradictory. A large study in Southern California looking at the impact of lifestyle on longevity, involving a population of Seventh Day Adventists, among whom vegetarianism is common, shows a lower risk of heart attacks among vegetarians and a 5 year positive difference in life expectancy compared to red meat eaters. But evidence from the EPIC (European Prospective Investigation into Cancer) study suggests that a low but not zero amount of meat may be positively protective.
So what is it in red meat that is the cause of the problem? At one time it was thought that it was the saturated fat content. Now the evidence is that the harmful effects of saturated fats have been overstated. A low saturated fat diet can seemingly make the lipid profile worse and a high saturated fat diet can lower the risk of stroke.
The harmful agent in red meat seems to be l-carnitine which is changed by gut flora into trimethylamine-N-oxide (TMAO) which reduces cholesterol excretion resulting in a clogging of the arteries.
Turning to processed meats the evidence is much clearer – they increase the incidence of cardiovascular disease and of certain forms of cancer, notably intestinal cancer. The main culprit for cancer seems to be the sodium nitrite they contain. This reacts with aminoacids in the gut to produce nitrosamines which are carcinogenic.
So, what is the level of risk associated with eating processed meats? 20% seems to be the currently accepted figure. Undoubtedly a very significant risk.
A piece of good news, not unexpected, is that a high fibre diet is partially protective against the harmful effects of red and processed meats.
Michael Moseley majors in personal participation in his programmes and though he baulked at having an endoscopy performed to see whether he has developed any of the intestinal polyps that are the precursors of bowel cancer, he did submit himself to a high red and processed meat diet for a month to see what effect it had on his health indices. The result was significant increases in blood cholesterol, low density lipoprotein, body fat (mainly abdominal) and blood pressure.
Moseley’s interpretation of this evidence is that a healthy diet is predominantly plant based supplemented with meat, preferably white meat, or better still fish. Clearly meat must no longer be the centrepiece of a meal but at most an accompanying garnish. And, probably, one should remove all processed meats from one’s dietary until further notice.
Paul Walker, August 2014.