Image copyright BBC HORIZON Image caption Dr Michael Mosley ate around 130g of meat a day to research the effects on his body

There have been a lot of news reports about the health risks of meat eating, but are they justified? Dr Michael Mosley has been investigating the truth behind the headlines for BBC Horizon.

I like eating meat, but what was once an innocent pleasure is now a guilty one.

If you believe the headlines, regularly indulging in a steak or a bacon sandwich raises your risk of heart disease and cancer.

The threat to health comes not from eating white meat, like chicken, but from red and processed meat.

Despite the negative headlines, on average Brits still eat about 70g of red and processed meat a day, with a quarter of men eating almost twice as much.

I decided to go on a high-meat diet to see what effects doubling my intake to around 130g a day would have

My wife, Clare, who is a GP, has for many years been trying to cut our family's consumption of red and processed meat. I, however, was resistant.

So we were both delighted when Horizon asked me to investigate what, if any, the risks really are.

I visited numerous experts, finding out what they themselves eat.

I also decided to go on a high-meat diet to see what effects doubling my intake to around 130g a day would have.

High fat content

There are lots of good things in red meat. Beef, whole or minced, is a great source of protein and essential nutrients, like iron and vitamin B12, which are vital for health.

On the downside, however, red and processed meat tend to be high in saturated fat.

Bacon and sausages have around 16 times more saturated fat per gram than tofu.

Image copyright Science Photo Library Image caption There are lots of good things in this steak, but there is also a lot of saturated fat

If you are a cheese-eating vegetarian you should not feel too smug. Cheese is, gram for gram, an even richer source of saturated fat than burgers.

Red and processed meat

Red meat includes steak, lamb, pork and mince.

Red meat looks darker than white meat like poultry because of higher levels of haemoglobin and myoglobin, the iron and oxygen-binding proteins you find in blood and muscle.

Processed meat includes bacon, sausages, salami and ham.

But how much does this matter?

One of the best ways to try to assess the impact of particular foods on our health is by doing cohort studies. You take a large group of people with varied diets, find out what they eat, then follow them for many years to see what diseases they develop.

Eating lots more processed meat certainly had a bad effect on my body. After a month of bacon sandwiches and burgers I had piled on the weight...

Mortality risk debate

Professor Walter Willett, of the Harvard School of Public Health, heads a team that have been tracking the diets of tens of thousands of people for many years.

"We found that those who consumed higher amounts of red meat had a higher risk of total mortality, cardiovascular mortality and cancer mortality," he told me in the Harvard cafeteria, while I nonchalantly ate a large steak.

On the basis of one of the studies he co-authored - Red Meat Consumption and Mortality, published in Archives of Internal Medicine - he estimates regularly eating a small amount of unprocessed red meat (85g, around 3oz) is associated with a 13% increased risk of mortality, while eating a similar amount of processed red meat (a hot dog or two slices of bacon) is associated with a 20% increased risk.

Not surprisingly, he almost never eats meat.

He makes an extremely convincing case, yet as I discovered his results do not match those of a more recent European study published in BMC Medicine in 2013, Meat Consumption and Mortality.

Researchers from the European Prospective Investigation into Cancer and Nutrition (Epic) followed half a million people in 10 countries for more than 12 years.

The researchers found that eating moderate amounts of red meat had no effect on mortality. The lowest overall mortality rates were in those eating up to 80g a day.

Image copyright Patrick Llewelyn-Davies Image caption Scientists agree that too much processed meat, such as bacon, ham and salami, is not good for health

Although there was a small increase in overall risk for those eating more than 160g, there was also a higher all-cause death rate amongst the non-meat eaters.

The researchers concluded that "a low - but not a zero - consumption of meat might be beneficial for health. This is understandable as meat is an important source of nutrients, such as protein, iron, zinc, several B-vitamins as well as vitamin A and essential fatty acids."

Dangers of processed meat

Before meat eaters go off rejoicing, there is a significant sting in the tail.

The Epic study, like almost every other study that has been done, found that eating processed meat, such as bacon, ham or salami, had a negative effect on health. Anything over 40g a day and deaths from heart disease and cancer began to climb.

The science is far from settled. The experts I met have strongly held but different opinions, reflected in what they themselves eat. In this Horizon we try to present the facts; where the truth lies is something only you can decide.

Eating lots more processed meat certainly had a bad effect on my body. After a month of bacon sandwiches and burgers I had piled on the weight and my blood pressure and cholesterol levels both soared.

I have gone back to my old diet, eating the occasional steak and pork chop. But there will be fewer burgers and sausages on the BBQ this year.

Making sense of the statistics

An increased mortality risk of 20% means your risk of dying over the next year is 20% higher than if you did not eat the processed meat.

Professor Sir David Speigelhalter of Cambridge University says another way of looking at this is, if the studies are right, that you would expect someone who eats a bacon sandwich every day to live, on average, two years less than someone who does not.

Pro rata, this is like losing an hour of your life for every bacon sandwich you eat. To put this into context, every time you smoke 20 cigarettes, this will take about five hours off your life.

Horizon - Should I Eat Meat? The Big Health Dilemma is broadcast on BBC Two at 9pm on Monday, 18 August.