Turning Down The Heat When Cooking Meat May Reduce Cancer Risk

Nov 23, 2015
Originally published on January 3, 2016 8:21 pm

Remember the headlines a few weeks back, when the World Health Organization categorized red and processed meats as cancer-causing?

Turns out, the techniques you use to prepare your meat seem to play into this risk.

A new study published in the journal Cancer finds that high-temperature cooking methods may increase the risk of kidney cancer if you consume a lot of meat.

And other studies have found that high consumption of well-done, fried or charred meats is associated with an increased risk of colorectal cancer, pancreatic and prostate cancer.

"The lower-risk methods are baking and broiling," says Stephanie Melkonian, a post-doctoral fellow at the MD Anderson Cancer Center and a co-author of the new study in Cancer.

Other lower-temperature cooking techniques include sous-vide — which is used in some professional kitchens – and preparing meat in a Crock Pot or some other type of slow cooker. Or you can make a traditional pot roast, which skips the high-temperature searing process in favor of lower-temperature browning. This particular recipe cooks at 300 degrees.

If you listen to my story on Morning Edition, you'll hear chemistry professor Matthew Hartings of American University use a steak and a blowtorch to explain the chemical reactions that take place as meat is browned. Remember the Maillard Reaction?

Basically, as the outside of the meat browns up, and the temperature heats up, the chemical reaction creates lots of aroma and flavor compounds, some of which are molecules called cyclic amines. Harting says we evolved to like those flavor compounds. Think of it as an evolutionary nudge from our ancestors, who came to associate these smells as a sign that all nasty bacteria were cooked out.

But here's the potential downside: If you cook the meat too long, at too high a temperature, the chemical reaction keeps going, creating other compounds. Some of them, known as heterocyclic amines (or HCAs), can be carcinogenic when we consume them in high-enough concentrations.

As the National Cancer Institute explains, HCAs "have been found to be mutagenic — that is, they cause changes in DNA that may increase the risk of cancer."

To evaluate the association between cooking techniques and cancer risk, the researchers at MD Anderson documented the eating and cooking habits of people who'd been diagnosed with kidney cancer.

Then, they compared the kidney patients' habits with the habits of a group of healthy, cancer-free people.

"What we found is that the way [people] cooked [their meat] did matter," says Melkonian.

Those with cancer consumed more meat overall. And they were also more likely to pan-fry their meat at high temperatures, cook it over an open flame, or cook it until it was well-done or charred.

The study documented a nearly two-fold increase in the risk of kidney cancer associated with the intake of one particular type of HCA, known as MelQx, which is — according to the paper — "one of the most abundant HCAs commonly created in the grilling, barbecuing, and pan-frying of meats at high temperatures."

As the researchers write in the study, this suggests "that the intake of meat cooked at high temperatures may impact the risk of kidney cancer through mechanisms related to mutagenic cooking compounds."

It's important to point out that other possible mechanisms may explain the link between high consumption of red meat and increased cancer risks.

For instance, as the authors point out, "heme iron and N-nitroso compounds exposures, which were not measured in the current study, also may play a role." In other words: It's complicated.

And as the authors point out, future studies are needed to get a more complete understanding.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.

Transcript

STEVE INSKEEP, HOST:

Today in Your Health, we find out what you can do with a health advisory on red meat. The World Health Organization declared a link between eating red meat and cancer. Turns out the cancer risk depends on how you prepare your meat. Some cooking techniques are known to produce cancer-causing compounds. New research suggests other methods are safer. NPR's Allison Aubrey reports.

ALLISON AUBREY, BYLINE: If you think back to chemistry class, you may remember hearing about a French scientist named Louis Camille Maillard. He documented a chemical reaction in food that came to be known as the Maillard effect. It's basically what happens when you take a piece of meat or other food and you brown it. Chemistry professor Matthew Hartings of American University says the reaction is complicated.

MATTHEW HARTINGS: OK, let's talk about steak real quick, all right?

AUBREY: Hartings has his biochem students in the lab this morning. And he's bringing the Maillard effect alive with a blowtorch.

HARTINGS: So I am torching the steak. I've got a propane torch. And you can see some nice brown color starting to come through, right? We're starting to crisp up the outside.

AUBREY: The steak is sizzling.

HARTINGS: It's a great sound, isn't it?

AUBREY: Now, as the outside browns up and the temperature heats up, just as it would on your grill or a hot pan, the chemical reaction creates lots of aroma and flavor compounds, some of which are molecules called cyclic amines.

HARTINGS: It smells good, doesn't it? You have a natural response to enjoy that smell.

AUBREY: So here's the rub on these flavor compounds - Hartings says we evolved to like them. Think of it as an evolutionary nudge from our ancestors who came to associate these smells as a sign that all the nasty bacteria had been cooked out.

HARTINGS: Now we're starting to smell all of those good cyclic amines that we just talked about, right? Those things that are telling us hey, all the bacteria on the outside of this has been killed. This is now safe to eat.

AUBREY: But here's the potential downside. If you cook too long at too high a temperature, the chemical reaction that creates these compounds keeps going and going and more compounds are created. Some of them, known as heterocyclic amines, can be carcinogenic when we eat them in high concentrations.

HARTINGS: So I've started to get a little bit of black on my steak where it was brown. And that's where we start making these big polycyclics. So that's when I know to stop.

AUBREY: So the longer you cook, the more you have.

HARTINGS: That's right. That's when we start to worry about the types of molecules that we're making in this and what might be dangerous.

AUBREY: So the bottom line - as you go from brown to black at high heat, there are more compounds created that you might want to avoid. Hartings says one workaround - a lower temperature.

HARTINGS: If you like your steaks well-done, turn down your pan and let it cook for longer.

AUBREY: A new study illustrates the value of this advice. Researchers at MD Anderson Cancer Center studied the eating habits of about 1,500 people, half of whom had been diagnosed with kidney cancer. Study co-author Stephanie Melkonian says they asked the participants all kinds of questions about their meat intake.

STEPHANIE MELKONIAN: We were able to gather information about how they cook it, how well-done they cook it, so if they're burning it or charring it or smoking it.

AUBREY: Then they compared the habits of the cancer patients with the healthy people.

MELKONIAN: What we found is that the way that you cooked it did matter.

AUBREY: The people who'd been diagnosed with cancer were more likely to pan-fry their meat at high temperatures...

MELKONIAN: Or cook it over an open flame. It was more likely to be well-done or charred.

AUBREY: Melkonian says it's important to point out that the cancer risk associated with red and processed meat is not fully explained by cooking techniques. But she says there do seem to be safer methods.

MELKONIAN: The lower-risk methods of cooking are going to be things like baking or broiling. These cooking methods really are not associated with the formation of these carcinogens.

AUBREY: Other techniques to cook red meat low and slow include sous-vide, which is usually done in professional kitchens, or in your own home the Crock-Pot. Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.