OVERVIEW
· A high intake of plant foods is a healthy way to go, but is eating meat actually bad for us?
· Get the lowdown on recently published evidence that helps us better understand the link between meat eating and cancer risk.
· Understand how the type of meat you eat, and how you cook it, are decisive factors in determining just how good or bad meat is for your health.
· Dispense with the urban myths and understand how to reap the nourishment meat offers, while slashing its health risks.
‘If animals were not meant to be eaten, they would not be made out of meat’. So goes an antediluvian adage for those with little tolerance for the vegetarian way of life. But vegetarian diets are now an increasingly popular choice. Obviously there are well-principled moral and ethical motivations for eating plants over animals, and we have total respect for that. One thing’s for sure: we’re not here to preach on moral issues – you can make up your own mind whether eating meat is right or wrong. We won’t be going there. We’ll be sticking to what we know, and getting to the bottom of whether eating meat is bad for us, and, if so, whether we should all be joining the ranks of the vegetarians for the sake of our health.
As early as 500 years ago, the Italian physician Gabriele Falloppio cited beef and salty and bitter foods as the cause of cancer. Fast-forward five centuries, and the debate rages on. Remember the prolific-selling The China Study in the last chapter, and its assertion that dairy products were fanning the flames of chronic diseases such as cancer? Well, meat doesn’t fare any better. Which leads us to ask the simple question: is this beef with meat justified?
Meat and bowel cancer
There’s a classic urban myth that’s been knocking around for years that says something along the lines of ‘We can’t digest meat properly, so it just sits and rots in our guts’. Nice. In fact, the story gets more and more exaggerated and the last we heard was that red meat sits in the intestines for at least seven years! Now that’s a lot of meat. It was after the death of John Wayne that the rumour mill really shot into overdrive. Supposedly, during his autopsy, two kilos, then later 9kg, 18kg and up to 36kg, of red meat faecal matter was found impacted in his colon. How about that for an image to put you off your steak dinner?
Do we even need to say it’s a load of crazy nonsense? Can you possibly envisage that just one steak a week would mean that you have 350 steaks sitting in your intestines? Or that you can have kilos of red meat building up inside you and never notice it? It’s blatantly ridiculous. Of course we can digest meat; after all, we’ve had enough practice over countless millennia. All this prattling absurdity detracts from the real issue, which is that, folklore aside, there is legitimate concern that meat consumption is linked with increased bowel cancer risk.
Red meat refers to beef, lamb, pork and goat. Processed meat refers to meat that has been preserved by smoking, curing, salting, or the addition of chemical preservatives, and includes ham, bacon, salami, sausages and hot dogs1.
Let’s take a novel approach, and see what the science has to say. A meta-analysis published in 2009 looked at the intake of animal fat in relation to bowel cancer2. It found no increased risk for each 10, 20, 30 and 40g increase in intake of animal fat. It also showed no increased risk for animal protein intake. If you take that at face value, you could happily conclude that meat is off the hook. But a closer look tells us that it’s far from a done deal. As is so often the case with research into diet, the devil is in the detail, and in this case, it’s red and processed meats that perform the role of the devil. The meta-analysis we’ve just mentioned didn’t differentiate between different types of animal protein, rather it lumped them all together. On closer inspection of the broader evidence, we see a different story. Poultry has a neutral effect, while fish is seemingly protective. In stark contrast, red and processed meat consumption dramatically increases bowel cancer risk.
Bowel cancer is the third most common type of cancer in men and women, with around 390 new cases diagnosed each day in the USA alone3. If you want to tip the odds in your favour, it’s time to wise up to the type of animal protein you eat. In short, you’d do well to watch your intake of red, and especially processed, meats.
In 2007, the World Cancer Research Fund, in collaboration with the American Institute for Cancer Research, determined that red meat is a ‘convincing’ cause of bowel cancer. After an exhaustive review of all the evidence available, they determined that eating 100g of red meat a day increases your risk by 29%1. That is the equivalent of eating just three 8oz steaks a week (or the equivalent in chops, roasts, burgers or mince). Put it like that and this sizeable increased risk starts to look a bit scary. For processed meat, it’s a grimmer picture still. Eating just 50g per day increases your risk by 21%.
So what’s the score? What is it about red meat that so clearly links it to the risk of bowel cancer? First, cooking meat at high temperatures leads to the formation of some noxious cancer-causing chemicals called hetrocyclic amines, aka HCAs. It’s the browning and charring of meat that generates these nasties. The EPIC study found that the risk of colorectal adenomas was increased by 47% in those with the highest HCA intake compared to those with the lowest4. Adenomas are benign tumours that frequently become malignant. The authors of the study found that the high HCA intake corresponded to those whose cooking methods produced excessively browned meat (sorry BBQ enthusiasts, but you’re the worst offenders).
Cooking meat at high temperatures by frying, grilling or barbecuing ramps up the formation of HCAs. Cooking at lower temperatures, such as stewing, boiling or poaching, minimizes the amount of HCAs formed1.
As well as HCAs, there are also polycyclic aromatic hydrocarbons (or PAHs). These are also thought to be carcinogenic and are formed during grilling or barbecuing. They are created when fat drops onto a direct flame, which leads to PAHs sticking to the surface of the food1.
Red meat contains a particularly potent form of iron called heme iron, which is also a contender for the increased bowel cancer risk seen in high red meat consumers5. This could also help to explain why an increase in bowel cancer occurrence is not observed in poultry eaters. Heme iron causes fat oxidation, which produces nasty peroxyl free radicals that can be toxic to our genetic material. The heme iron in red meat also induces production in the body of nitroso compounds, which are carcinogenic. It is the formation of harmful nitroso compounds from the nitrite preservatives in processed meats that explains the particularly marked association between intake of these products and increased risk of bowel cancer.
Meat and breast cancer
While our take on the whole red meat and bowel cancer issue is pretty clear, when it comes to breast cancer, the waters are distinctly muddy. In fact, the only conclusion we draw is that there is no conclusion. As soon as one study is published saying one thing, another is published saying the opposite. Put simply, we have no definite answers on this one.
Take 2009, which looked like it would be the year the puzzle finally got solved. This was when the results of some of the largest trials investigating meat and breast cancer were published. It started in May, when the International Journal of Cancer reported the results of the ‘NIH-AARP Diet and Health Study’ cohort of 120,755 postmenopausal women who were followed for eight years6. The findings were pretty clear: a high intake of meat, including red meat, was not associated with increased risk of breast cancer. They looked at cooking methods too, and cooking at high temperatures, which as we now know produces a large amount of HCAs. Again the results showed no association with cancer incidence.
Just one month later, the British Journal of Cancer reported the results of the ‘Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial’, which looked at the diets of 52,158 people7. Red meat was found to be associated with a 23% increased risk of invasive breast cancer, which appeared to be linked to its iron and HCA content.
Fast-forward three months to the September issue of the American Journal of Clinical Nutrition, and results from the ‘EPIC’ study were reported8. After following 319,826 women for eight years, the researchers were ‘unable to consistently identify intake of meat, eggs, or dairy products as significant risk factors for breast cancer’. But there was an interesting side story. While there was no overall association of red meat with breast cancer, there was a lot of variation between different countries. Further investigation found that those countries that predominantly used high-temperature cooking methods showed red meat consumption to be associated with a 16% increased risk of breast cancer for each 150g per day, but this link was not evident for low-temperature cooking.
Just as a link was beginning to emerge, the ‘Swedish Mammography Cohort’ results were published in November9. Here, following 36,664 women for 17 years, no association between red meat or processed meat intake and risk of breast cancer was found. Back to square one. At the end of 2009, we were left more confused than ever.
When it comes to red meat and breast cancer, on the whole the evidence doesn’t stack up in any convincing way. There may be no smoke without fire, but in the courts of science, innocent until proven guilty stands and the jury needs to be 95% confident to find the defendant guilty. Especially when we consider that meat eaters are more likely to be overweight10and on hormonal contraceptives11 – factors known to increase the risk of breast cancer anyway. It’s all very ambiguous. For now, the onus rests with the scientific community to collect more evidence and see if a conviction is warranted.
Meat and prostate cancer
Despite what you might have heard, the evidence for a causative role for meat in prostate cancer has always been pretty thin on the ground, with evidence pointing to a possible role for processed meat alone. In the 2007 report on diet and cancer, the World Cancer Research Fund/ American Institute for Cancer Research concluded that there was ‘limited evidence from sparse and inconsistent studies suggesting that processed meat is a cause of prostate cancer’.
Since then, more studies have been conducted. A 2010 meta-analysis of prospective studies found no association at all between red meat intake and prostate cancer12. While processed meat was associated with a 5% increase in risk, this was only a weak correlation and ‘non-significant’, which means it could easily have been down to chance and not a real effect.
Making meat safer
OK, so the prostate cancer link holds no water, the breast cancer association is distinctly murky, but the bowel (or colorectal) cancer link stands up and conveys worry. So how much meat is safe to eat, if any?
Well, those clever boffins at the World Cancer Research Fund put their heads together and came up with the recommendation that people who eat red meat should consume less than 500g per week (cooked weight) and consume very little, if any, processed meat. We should point out, however, that this is a bit of an arbitrary guideline, based on practicality more than science. It will only mitigate, not quench, the bowel cancer risk. It is one thing to advise against processed meat, a pretty noxious product made by human interference, but strike red meat off the menu altogether, and likely the only people who will listen are those who renounced the red stuff long ago. So a happy medium of 500g was chosen to limit damage, while still allowing you to consume your weekly 16oz tenderloin. Yet it has been calculated that once you go above 70g a week (a measly 2.5oz), you start elevating your bowel cancer risk13.
When observing the guidelines it is worth noting that 500g of cooked red meat is roughly equivalent to 700– 750g of raw meat1.
We have to say, we’re not too keen on this compromise. Don’t get us wrong, we enjoy a good steak, but to pass off an arbitrary amount as a safe limit, with no further guidance, is quite lacking. For many, this may be incentive enough to reduce red meat intake, but we also know there are a lot of meat fiends out there who won’t be stopping any time soon. So we’re going to take up where the World Cancer Research Fund left off and describe some simple tips for how you can make that 500g limit a whole lot better for you.
Step one: reduce the amount of HCAs produced and you will reduce the cancer-causing potential of red meat. Marinating meat before cooking will dramatically reduce HCA formation, especially if the marinade is packed full of herbs and spices. Indeed, one study showed a whopping 88% reduction in HCA formation with a Caribbean-style marinade14. Then, how you cook it is key. Avoid cooking at high temperatures, which burn or excessively brown the meat (particularly barbecuing). It’s better to cook meat at lower temperatures for longer – for example, a slow-cooked casserole would be spot on.
The simple trick of marinating will confer protection, but to really reduce those HCAs include some proven effective quenchers. Choose virgin olive oil instead of refined oils15. Add lemon juice, garlic, onions16, and herbs and spices such as rosemary and turmeric17,18. And when it comes to beer or wine, it’s beer over wine every time19.
Make your marinade from scratch. Researchers have noted that some commercial sauces (e.g. barbecue sauce) can increase HCA formation, possibly due to high fructose corn syrup or honey in the mixture18.
Step two: stop iron activity. In the last chapter, we saw that just a 200g serving of milk per day is associated with a 9% reduction in bowel cancer, likely due to the beneficial effects of calcium on the cells in the gut. As well as this, calcium inhibits heme iron absorption20, so by taking a dairy food such as a yoghurt or milk (preferably low-fat) with or after meals, or using a yoghurt-based marinade, you can help stop the deleterious effects of iron.
Step three: incorporate flavonoids into your dish of red meat. So get busy with all the trimmings. Go full on with the onions, big it up with a citrus-based marinade, have a nice cup of green tea, or indulge in some after-dinner dark chocolate – all foods that pack a flavonoid punch.
Flavonoids not only appear to prevent iron absorption21, they also prevent activation of HCA compounds. In the EPIC study, where HCA and high red meat intake was associated with a 47% increased risk of adenoma development, this association was rescinded in those with a high dietary flavonol intake4.
THE PARTING SHOT
A lot of folk are pretty quick to ‘diss’ red meat, and we have to admit that, of all the anti-animal-product fervour that exists, this is the one that actually stands up to scrutiny. But at the same time, let’s not forget that red meat is actually a highly nourishing food. It chalks up points for its plentiful supply of protein, well-absorbed iron (notably important for young women, among whom iron-deficiency anaemia is rife), zinc and vitamin B12. Clearly we’re not giving you carte blanche to scoff as much as you want. Red meat comes with its caveats, especially with regard to the risk of bowel cancer, but used wisely it can definitely form part of a balanced diet. Keep your intake moderate, follow the advice set out above, and there’s no reason why you can’t have your steak and eat it.
SUMMARY AND RECOMMENDATIONS
· Fish and poultry show no adverse effects on cancer risk and are nutritious inclusions in the diet, especially fish, which may even reduce your cancer risk.
· Red meat and particularly processed meat are more suspect, and have been strongly linked to elevated incidence of bowel cancer.
· For this reason, processed meats such as ham, bacon, salami, hot dogs and sausages should be kept to an absolute minimum.
· If you do eat red meat, keep your intake below 500g per week (cooked weight), following the advice of low-temperature cooking, marinating and incorporating dairy products to reduce HCAs and iron activity.
· Red meat is best consumed as part of a diet rich in plant foods, especially flavonoid-rich foods such as vegetables (especially onions), fruit (especially berries, apples and citrus fruits), green tea, red wine and dark chocolate, which further neutralize any harmful effects.
· Let’s not forget that red meat is an excellent source of vitamins and minerals such as iron, zinc and vitamin B12, and can make a valuable contribution to your intake of these essential nutrients.