To Heat or Not to Heat?
…that is the question. Well, the question I’m askin’, anyway; not so sure if you care. Think about it, though; haven’t you ever wondered if the sickly green water you pour out after boiling cabbage or broccoli or spinach (assuming you eat these guys; you should) contains all the vitamins that used to be in the now-softened plant provisions? Is what’s left over meaningless slop that you salt to oblivion to give it that taste like “mother used to make?” Welp, I’m here to answer this, and other questions (read: WHAT ABOUT MEAT?), regarding food heatery!
A vegetative state, vitamin-wise?
The overwhelming concern I had learning about this stuff was the common conception that heating vegetables too much causes vitamin and mineral degradation. Most recently, the past year or so, I’ve mostly been eating vegetables like broccoli and carrots raw because of this. In the case of broccoli and other cruciferous vegetables (those would be ones like cabbage, spinach, and kale), it seems that heating does have some vitamin-draining effects; said effects might not be “bad,” however. In fact, cooking the cruciferous critters results in a 200% increase in iron dialyzability- this means the amount that comes out of the vegetable, and in this case opposed to room temperature chewing. I suppose this could mean that the weakened cell walls of cooked versions of these vegetables could have them offering more iron during ingestion or that the water in which they’re cooked (if water is used) would contain iron that might not otherwise be accessible. As for broccoli itself: When heated, elements within broccoli bring out sulforaphane, a potent anti-carcinogen. This isothiocyanate (big word, but trust me; they’re great for health!) would not be bioavailable at room temperature. The good news for heated broccoli seems to continue when it’s considered that the softening of vegetables like it and carrots through pan-frying seems to create an increase in antioxidant capacity, parameter, and power.
Still, and this was noted in the last cited study, heat does seem to degrade the originally readily-available phenol, antioxidant, and vitamin/mineral content of some vegetable foods, but I suppose one could argue that it is a moot point considering the effects cooking has on bringing out “hidden” or inert antioxidants and the like (as in sulforaphane, mentioned above); beneficial items that we wouldn’t otherwise receive without heat. Take this study, for example, which found that heating fruits and vegetables (tomatoes, bananas, and melons) increased flavonoid content, sometimes at the order of 37 times higher (in oriental melon heated at 150C), polyphenol content, and ascorbic acid content (highest in watermelon heated at 170C for 2 hours). Now, I don’t know anyone who’s going to heat watermelon (much less for two hours), but the point should be well-taken: For what is lost through heating vegetables, it seems a lot more could be gained…and nobody’s telling you to never eat raw veggies again; but if you’re like I used to be, afraid to cook vegetables lest you’ll lose all the great stuff inside and be left with meaningless mush, you can now rest easy as you steam-up some fresh ‘uns.
The last thing I want to talk about, while on the subject of vegetables, is legumes: i.e. our pals, beans. They have their own properties which become altered through cooking. If you recall my article on the dangers of soy, you’ll remember little baddies called “trypsin inhibitors.” These are found in many plants and specifically legumes, and are natural defenses designed to stop the plant’s nutrients from being utilized by those who might eat said plant. Well, good news!: cooking inactivates these! At the same time, however, cooking has the “bad” effect on beans of degrading lysine and lectin content. Since lysine is an essential amino acid, this may spell trouble for vegetarians/vegans who are attempting to match foods based on amino acid content so that they might get complete protein throughout the day. Get out those thermometers if you wanna steam-treat: the study authors found exposing the beans to a steam temperature of 119C for 5-10 minutes was a good compromise between trypsin inhibitor inactivation and lysine degradation.
Still, overall protein digestability of legumes is improved through cooking methods, and both that issue and the issue of trypsin inhibitors are best-handled through pressure cooking, which also brings out the highest amount of ash and phosphorus when compared to other methods (microwaving and boiling).
Now, onward to another pressing issue: MEAT COOKERY.
Where’s the beef……………in all of this? hurhur
We all know you can’t go around not cooking (most) raw meat, unless of course you have some manner of super-sanitary lab and the meat is ultra-fresh. Since most of us get our red, white, and blue stuff (all right, just red and white. It’s nearing the 4th of July so I thought I’d…) from our local grocery store, it’s obvious that a little heat-treatment is in order.
As I named this section “Where’s the beef,” et cetera, we’re going to start with that crimson-hued protein. There’s a lot to say, really, and some of it is pretty scary. Lots of people are already on the “red meat is BAD” bandwagon, and I’m afraid I’m not set to derail it with this info.
What should be understood about all meat, regardless of its color (and even its character), is that cooking it in almost any way produces carcinogens called heterocyclic amines (or, HCAs) and, in some cases, polycyclic aromatic hydrocarbons (or, PAHs). These substances have some degree of cancer proliferation in rat models. HCAs are mutagenic (DNA-changin’) to microbes and their precursors are creatine or creatinine, sugars, and amino acids in meat and fish. The unfortunate news that I have to report is not just about HCAs or PAHs, but the fact that almost every study done on them, specifically on their role in colorectal cancer (little portmanteau of colon cancer and rectal cancer) is a case-control population study. What does this mean? Two annoying things:
1. First and foremost, it means that the studies are based on questionnaires and not testing done in a controlled laboratory setting. Obviously, people can (and do) lie on questionnaires, whether on purpose due to trying to fit within social norms or inadvertently from having poor memories or by a bad questionnaire design. On this topic, the next problem is “confounders,” or anything in a study that its authors find need to be adjusted for; this is usually done by complex mathematics and may perhaps improve accuracy, but it is still not very scientific or acceptable as proof in my view.
2. Secondly is case bias. Many of these studies were commissioned as cause-effect studies in meat’s supposed role in colorectal and other cancers. I’m not saying they absolutely have no role, but to 1) attempt a study based on an assumed or correlated fact and 2) recruit volunteers who have/have had colorectal cancer and giving them a questionnaire with pictures of food, asking them “is this how you cook it?” is well…
Sorry for the long aside, just irritates me how virtually every study I found on this is a population study; all the correlation-causation and speculative junk makes it really hard to figure out what’s fact, so I’m mostly going to stick with the subject of HCA/PAH creation in meats through cooking; their presence in cooked meat, as I’ve found by more responsibly-done studies, is irrefutable. Their status as cancer-causers is much-less irrefutable, but is probable in my mind and I’m gonna expatiate on that. BACK TO THE BIZ:
So, what should your beef be with beef and is red meat really worse than other meats because of this HCA/PAH content? Well, the quick answer to that last question is “yes.” The long answer to both questions is that it all depends on cooking temperature, time, and heme content of the meat in question. HCAs appear in differing quantity in different meats depending on doneness: In steak and hamburger, an HCA called 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (or MeIQx for short) was produced under almost all cooking methods, while another, pyrodine (PhIP), was found in higher content depending on the higher level of doneness of hamburger and steak (and in the case of hamburger, only in very well-done hamburger). Roast beef contained no HCAs, but the gravy of roast beef did contain both MeIQx and PHiPs. Great day for some acronyms!
Anyway, how about some specifics for times and temps? Meats fried at 150 degrees celsius have very low HCA amounts that go up as temperature rises. Sharp increases in HCAs were seen in pork chops, pork belly and bacon when temperature was increased from 200C to 225C. For sirloin steak and ground beef patties, the amount of HCAs increased greater than 10-fold between 175 and 200C. More processed meats like sausage and meatballs had HCAs at all cooking levels (150, 175, 200, 225). The specific HCA 2-amino-3-methylimidazo[4,5-/]quinoline (shortened to IQ) was only found in sirloin steak fried at 150C. Citing other studies, it says mutagenic activity (i.e. HCAs) is mostly found only in the browned crust of meats, though about 20 to 30% can be found in the inner meats depending on cooking temperature; to that end, a higher cooking temperature was found to contribute to a higher amount of HCAs in inner meats.
Now, I know I said I hate population control studies; but there was an interesting one done by physicians on physicians that took a lot of the biases (not all) out and since it was done by physicians it’s at least a little more trustworthy than questionnaires given to random dopes of society. Anyway, it found that the enzymes that activate HCAs (called N-acetyltransferases or NAT-1s and NAT-2s) seem to have no association to colon or rectal cancer risk, except in men who were rapid acetylators for both types of NATs (this is dependent on genetic make-up; in other words, alleles of these men are more predisposed to accelerate NATs), where those 60 and older were at higher risk for colon or rectal cancers. The NATs cause the HCAs to have the ability to bind to DNA in colon cells, which is the cause for potential cancers. Mostly, this study talks about colon and rectal cancers being more prevalent for those of older ages with foods across-the-board, also mentioning a small positive correlation in older populations and cruciferous vegetable and protein intake, and also men with the aformentioned rapid acetylator genes.
You might be confused on the cruciferous vegetables angle, above. Basically, cruciferous vegetables like broccoli (and its anti-carcinogenic sulforaphane) activate those aforementioned NAT-2 enzymes, which actually activate potent antioxidants in the body like glutathione which assist in detoxifying HCAs. Again, I’m sure you’re confused at all this; just know that whatever adult told you to eat your broccoli as a kid was right, especially if you’re going to be eating overcooked meats.
Switching gears, I wanted to get into why red meat is significantly higher in HCAs than its white counterparts, pork, fish, and chicken. It’s because of heme, a cofactor found in blood and muscle fiber of red meat and not white meat (which is also partially responsible for the high iron content of red meat). If you read/remember my post about food additives (off-site here), you might recall baddies from the additive nitrite called n-nitrosos; aside from their oxygen-depriving qualities, n-nitrosos are involved in helping HCAs do their damage; and wouldn’t you know it, they’re present as-can-be in the heme of red meat, ready to do their mutagenic worst. Again though, cruciferous vegetables and indeed all green vegetables can assist in detoxifying; the chlorophyll present in green vegetables inhibit the ill effects of the heme found only in red meat. Having steak or burgers? Side-up the broccoli!
So, I’ve given a lot of attention thus far to HCAs, and left ol’ PAHs in the dust. This is partially because HCAs are formed in all cooked meats, whereas PAHs are formed only in meats subjected to certain cooking methods and partially because I didn’t want to confuse you with studies that simultaneously mention both of the two carcinogen types. PAHs are mostly garnered through smoking methods of cooking.
Though usually harmless through ingestion and inhalation, as they are found in minute amounts, PAHs can become dangerous in higher amounts; wood-smoked and smoked foods can contain one carcinogenic form of PAH, benzo[a]pyrene, with sausages cooked over burning logs having about 200 times the amount of this PAH than in normal meats (Also remember that sausages, as processed meats, are worse than fresh meats for HCAs as well). Beef steak cooked over charcoal also has high concentrations, possibly due to a chemical reaction caused by the beef’s fat dripping onto the charcoal; these benzo[a]pyrene concentrations are lower in chicken and pork cooked over coals. This study recommends oven-cooking or cooking with a heat source above meat. Like HCAs, PAHs (notably benzo[a]pyrene) are mostly found in overcooked meat products, primarily beef and chicken with skin. Surprisingly, PAHs are also found in a significantly disturbing amount in some overcooked greens like collards and kale, as well as cereals.
Methods to reduce cooking-induced carcinogens
The love of flavor might be an evolutionary design to make us live longer; apparently, marinating our meats is a sure-fire way to reduce HCAs in the cooked product. We’re talking a reduction of 90+%, so long as the cooking time stays under 40 minutes. One HCA, MeIQx, actually increased its presence through marination, but only when the meat in question was cooked for over 30 minutes. MeIQX was found to increase due to the use of sugar, so perhaps axing it from your rubs would deter its proliferation.
Again, here’s an area where my conceptions proved to be misconceptions; I’ve always been under the impression that microwave cooking is somehow inferior to normal cooking methods. I guess a lot of stuff tastes funky or has a relatively bad texture when cooked in the microwave in comparison to things cooked on the stove or in the oven. However, it seems that microwaving has its place in the world of HCA reduction; thawing one’s meats in the microwave can result in up to a 30% reduction in HCAs, along with up to a 95% reduction in all other mutagenic activity (n-nitrosos, for example). Still, microwave heating also causes a significant drop in the vitamin B-12 content of meats (one of the exclusive vitamins in meat; not easily found elsewhere!), so it is perhaps best to thaw in the microwave, and do the “real” cooking on the stove or oven.
The medium which you use to prepare a meat is important, too. Heating meats on ceramic or enamel surfaces reduces the amount of mutagenic compounds like HCAs in comparison to Teflon (eck) or even metal surfaces like cast-iron. In hamburger meat, the study cited above found no difference in mutagen value between fatty meat and lean meat, so just remember: moderation with the red!
Preconclusions and asides
Well, that’s about it for now. I did want to add a few other things that didn’t really fit anywhere above before I get to the conclusions/bullet point list of things you should remember.
I was under the impression that heating honey destroys most of the nutrients (and keep in mind we’re talking about the real stuff, raw or unprocessed honey- not that stuff in the bear which already has most nutrients sapped.). However; apparently heating, and in particular prolonged heating, increases antioxidant activity in honey.
I’ve already covered the safety of cooking oils in another post, but I’ll reiterate here that heating any polyunsaturated oil (soy, safflower, et cetera) is a HUGE no-no; besides the fact that any inherent antioxidants (like vitamin E) are destroyed, there’s this, using that study’s own words: heated oil “was similar to the bulk oil in polymer content.” Mmm, polymer! Not to mention that polyunsaturates become rancid through heating. If you have to use an oil to cook (which I don’t recommend because of the extra calories and unnaturally-added fats), definitely look to monounsaturated or saturated oils.
Okay, now we’re at the point you’ve all been waiting for (or scrolled down to to avoid reading so much): The bullet points!:
• Despite popular belief, the heating of vegetables does not necessarily degrade their vitamin/mineral/antioxidant content. In fact and in most cases, it allows us to utilize such compounds that we wouldn’t be able to utilize in the raw product through chemical processes that “snake-charm out” inert beneficial compounds and cut down on adverse compounds like trypsin inhibitors in beans. Basically, there are pros to both raw and cooked veggies; so, go tell all the staunch, hippie-ish raw food diet advocates to stick that in their homemade corn cob pipe and smoke it! Don’t really, it might hurt their feelings.
• Heating meats creates carcinogens within the meats, which multiply exponentially with increased heating times and meat temperatures. Though these carcinogens, primarily heterocyclic amines (HCAs), polycyclic aromatic hydrocarbons (PAHs) and n-nitrosos, undoubtedly exist in cooked meat, most studies on the matter just seem to find such a weak association between carcinogen content and colorectal cancers, so I guess moderation is the key? That, or don’t cook your meats; hope you like sushi!
• On the subject of moderation, perhaps the very common and popular conception “red meat and cancer are pals” compared to other meats is true; while HCAs and PAHs do occur in long-cooked fish, chicken, pork, and others, the heme in red meat increases its HCAs relative to these other meats. N-nitrosos are higher in red meats, as well, and processed meats like sausages and meatballs are prone to heightened levels of all three of the mentioned carcinogens/mutagens. So, for sure, moderation in red and processed is key; and don’t overcook any type of meat!
• Christmas is a good influence on your diet. Well, its colors are, anyway. What I mean is to team-up red with green; if you’re eating red meat, have some nice green vegetables along with- the chlorophyll and antioxidants within the green guys help negate the effects of HCAs/PAHs.
• Finally, remember the two Ms of preparation: Marinade and microwaves. Marinades with ingredients like olive oil, cider vinegar, garlic, mustard, lemon juice and salt dramatically reduce the amount of HCAs in a final cooked product, and microwave thawing of meats does the same for mutagens in general. Also, cooking on ceramic or enamel surfaces vs. traditional metals or Teflon is a way to reduce mutagens even further, after preparation.
Glad I got this out in time for 4th of July shopping- now get out there and buy some broccoli to serve with your medium-done (hopefully grass-fed) burgs; maybe even some cabbage, carrots, et al to make a nice slaw. Mmm mmm! Happy and healthy 4th! ♦