Is bacon back on the menu?

Recent reports have linked eating red meat with the same cancer risks as smoking, but does the science behind the scare stories stack up? We asked the experts at examine.com for the health facts behind the headlines

Over the past couple of years you’ve probably read headlines claiming that eating red meat is as carcinogenic as smoking and that eating too much red meat too often can significantly increase your risk of getting cancer.

The headlines are based on a short summary paper that referred to a massive analysis of more than 800 studies. Back in October 2015, experienced researchers met at the International Agency for Research on Cancer (IARC), an arm of the World Health Organisation (WHO), and came up with some strong conclusions on red meat.

Specifically, with regards to colorectal cancer, they classified processed red meat as a ‘Group 1’ carcinogen – which means it causes cancer in humans – while non-processed regular red meat was classified as a ‘Group 2A’ carcinogen (suggesting it could probably cause cancer in humans).

Red meat is red because of haemoglobin, the red pigment in blood. When we eat red meat, part of this pigment is processed in the gut into N-nitroso compounds (NOCs), which can damage the gut lining. When cells in the gut lining are damaged, the gut repairs itself by cell replication, and DNA damage can occur over time.

Unprocessed red meat, such as steak or ground beef, doesn’t have as direct an impact on gut damage as processed red meat, such as bacon, ham or hot dogs, because chemicals in these products lead to NOCs being formed at a faster rate.

So were all those articles telling you to give up eating bacon, steaks, sausages and all the other meaty foods you love accurate? And why is red meat apparently so bad, when white meat from chicken and fish is still a fantastic source of protein, healthy fats and other essential nutrients?

Devil in the detail
As with most click-bait headlines, the devil is in the detail, and the connection between red meat and cancer is more complex than most of the articles suggested.

First, the findings were mostly referring to cancer of the colon or rectum. While colorectal cancer is a very serious problem – it’s the third-leading cause of cancer death in the US – we can’t generalise the researchers’ findings to all other types of cancer.

Second, this isn’t really new information. It’s based on studies that have been conducted for the past ten to twenty years. Processed red meat has been strongly linked to colorectal cancer for many years. Unprocessed red meat is more of a mixed bag in terms of evidence, but still has several mechanisms by which it may increase cancer incidence. So this is more of a new framing of evidence than a presentation of new evidence.

Third, just because the WHO is a very big deal doesn’t mean they can’t sometimes be a little wide of the mark. For example, its guidelines on salt intake call for less than 2,000mg of salt per day, despite other organisations, such as the US Center for Disease Control and Prevention (CDC), having updated its position based on new research. A large amount of research shows that keeping salt intake under than 2,000 mg per day not only lacks evidence of health benefits, but might actually be harmful.

Fourth, much of the evidence that was reviewed was epidemiological evidence, observing people over time to uncover whether disease develops. Some people mistakenly ignore this type of study, thinking that the ‘gold standard’ randomised trial is the only acceptable type of scientific evidence. But you can’t really do randomised trials on cancer because it takes so long to develop and there are so many potential causative factors involved. Because much of the evidence reviewed was observational and/or epidemiological in nature, rather than from randomised trials, it means that causation is very hard to pin down.

Finally, and we can’t stress this enough, but the dose makes the poison. Red meat is not inherently unhealthy, but if you make a habit of eating bacon for breakfast, ham for lunch, and sausages for dinner, then your total daily intake of processed red meat is going to be very high. However, if you have an organic, grass-fed beef burger once or twice a week, that intake of red meat isn’t enough to be a sure-fire route to cancer.

Eat your greens
One mechanism for red meat increasing the risk of colorectal cancer is gut damage from chemicals such as NOCs. This comes about directly from the red pigment in these meats. But red meat as part of a plant-rich diet might be less dangerous.

Luckily, most people don’t eat an all-red-meat diet. And it turns out that if you eat green veggies with your meat, evidence (from animal studies mostly) suggests that the colon cancer risk can be substantially reduced. The reason is that the green chlorophyll molecule is basically a heme molecule, but with a magnesium atom instead of an iron atom in the middle. Having some of that in your gut to compete with the meat pigment might reduce or potentially eliminate them from being turned into dangerous chemicals.

High heat problems
So what are the other potential problem compounds found in red meat that have been linked to increased risk of cancer? Char, that delicious burnt crust that forms on grilled foods from high-heat cooking,creates chemicals that can damage the gut, such as heterocyclic amines (HCAs).

Red meat produces higher levels of these chemicals than white meat. As a side note, this is an excellent example of literal caveman/paleo eating not being inherently healthy: cooking meat over an open fire on a regular basis would subject you to high levels of harmful chemicals.

Yet again, you have to consider the entirety of a meal. Certain compounds in cruciferous veggies, such as broccoli or Brussel sprouts, may substantially reduce the impact of HCAs in cooked meat. And marinades with certain spices can reduce HCAs, and Caribbean spices seem to perform the best. Those black char lines might be a flavouring benefit but a health disaster, depending on how frequently you eat them, plus whether you eat certain veggies with them, or marinate the meat before cooking.

Too much iron

Red meat is rich in iron, which is the Goldilocks of all minerals. Many people are low in iron, so anaemia is a public health concern. But iron is very easily oxidised (it’s what causes rust). The iron in meat can easily build up in intestinal cells because it isn’t tightly bound to other compounds as it is in many plants. When this iron oxidises it eventually causes cell damage, which makes its link to colorectal cancer quite easy to understand. There’s a reason why iron supplements aren’t recommended to the general population: in the body, even moderately high levels of iron can be dangerous, especially to colon cells, according to the recent IARC paper.

Another possible culprit is TMAO, which stands for Trimethylamine N-oxide, a controversial compound that some research has linked to colon cancer. Different meats have different amino acid profiles, and red meat happens to be high in L-carnitine, which gets metabolised by some of the bacteria in your gut, and eventually turns into TMAO.

While many studies link TMAO to disease, there’s more to this than meets the eye. If you’re a gut microbiome junkie, you probably know that two individuals can have extremely different gut bacterial profiles. In fact, vegans and vegetarians produce less TMAO from a given dose of L-carnitine than meat eaters. It turns out that certain types of bacteria can increase your TMAO production, while other types can decrease it.

It’s possible that a gut full of friendly flora could make TMAO much less of an issue. TMAO got a lot of press around 2012-2013 for being ‘the reason’ why red meat is unhealthy. But that’s simplistic: your gut bacteria are the factories that produce TMAO, so gut health and bacterial profile is key in determining the impact of red meat.

Everything in moderation
I’s pretty clear from the evidence that eating red meat every day has a decent chance of increasing cancer risk, specifically colorectal cancer. Consuming high amounts of processed red meat in particular is really playing with fire. And cooking with fire – in the form of grilling meat over a high heat – can also increase the number of carcinogenic compounds in the meat that ends up on your plate.

That said, the evidence is mostly observational or mechanistic. Because of the practical impossibility of running multi-decade controlled trials, the increased risk from eating different amounts of red meat is not really known. In this case, as in many others, moderation may be key.

It’s important to remember that just because something is shown to have carcinogenic effects, doesn’t mean it will cause cancer. An increased risk can be small or big, and while the increase seen with processed meat is relevant because it’s avoidable, the risks are still nowhere near as high as with something such as smoking cigarettes.

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