Let’s face it. Some of us grew up in houses where our fathers habitually burned the toast and set off the smoke alarm on a daily basis. Perhaps our mothers roasted the Thanksgiving turkey until you could weave an absorbent bath towel with its fibers. Or maybe grandpa’s grilling style charred every piece of meat beyond visual recognition. Yes, comparative tales of over-cooking are the stuff of familial nostalgia and domestic comedies. We knew it tasted bad (O.K., wrenchingly bad), but was it that bad for us?
Let’s first say that MDA is not about to go raw foodie. We love our veggies and meats, and we say this first and foremost: eat ‘em any way you can. Nonetheless, the bulk of research seems to suggest that cooking, specifically with certain temperatures and methods, can do a real number on the food we eat.
First let’s get the arguments on the table. There’s Grandma Mabel in her house dress sitting in one corner spouting off on how all her relatives lived to 90+ and had two sides of cooked vegetables and well done meat (of course!) at every meal, thank you very much. On the other side is the raw foodie in slouchy jeans saying carcinogenic compounds are waiting to attack your every cell if you dare put that spoonful of cooked carrots in your mouth. O.K., that’s not exactly how it is on either side of the food fence, but we love the visual
Much of the argument for “raw” boils (teehee) down to this. When food is cooked, the natural enzymes and micro-organisms are eliminated, nutrient levels plummet, and harmful compounds such as heterocyclic amines are formed.
Hmmm. Grandma? “Ha! Then what about my homemade cooked tomato sauce and the increase in lycopene and overall antioxidant activity?” (Never underestimate Grandma.)
Well, we’ll leave you two to duke it out in the corner with that basket of raw beets. As for the rest of us, why don’t we just take a closer look. When it comes to cooking, what’s lost? What’s gained? If we tend to side with Grandma, are there things we can do to maintain or enhance the healthfulness of the foods we cook?
Before we move onto the specifics, one overall principle seems to be this: low temperatures are generally better for retaining the highest nutrient content of food and for reducing oxidation and its associated toxic by-products. High heat, prolonged cooking? Not so good. But we’ll get to that.
First, the nutrient question. As we reported in January, Italian scientists had found that different cooking methods had varying impact on the vegetables tested. Sometimes cooking depleted nutrients (as in frying) and sometimes it enhanced them (boiling and especially steaming). But that doesn’t tell the whole story. Other researchers at the University of Warwick found that steaming, microwaving and brief stir frying of Brassica vegetables (e.g. broccoli, cauliflower, Brussel sprouts) maintained the veggies’ anti-cancer properties otherwise known as glucosinolates.
Boiling, however, resulted in significant loss of glucosinolates: “broccoli 77%, Brussel sprouts 58%, cauliflower 75% and green cabbage 65%.” The researchers in the Warwick study boiled the vegetables for 30 minutes, which was a much longer duration than that used with the other cooking methods. High, direct heat and long duration both contribute to the leeching of nutrients into the water. Other cooking methods such as frying and broiling use very high heat as well and are not recommended. Another tip: hold off on adding lemon juice and other acids for flavoring. Acids can break down vegetables, particularly more delicate varieties, encouraging additional nutrient loss.
To maintain nutrient levels (PDF), let your senses be a guide. Remember those dull, anemic, limp little mushy cylinders that passed for green beans in school lunch? There’s a reason they looked gross to you then (and now). It turns out the more appealing a bean looks, the healthier it probably is. Green beans, for example, that are briefly steamed or “poached” in a few tablespoons of water will be even more vibrantly colorful than they were before that quick dip in the pot. The texture will be tender but still a bit crisp. This is what you’re looking for when cooking produce: when they look like they belong on the cover of Bon Appetit, they’re done. (Hint: you may even want to briefly blanch them in some ice water to completely halt the cooking process.) And, as a general rule, keep the lid on while you’re cooking/steaming. The food will cook faster, and less time subjected to the heat is good). Low and enclosed does it.
Cooking, as in the example of Grandma’s lycopene-rich tomato sauce, can “activate” nutrients, and can even make them more bioavailable. Certain foods are to some degree poisonous or unhealthy to humans in their raw state. Many tubers, for example, must be cooked to be a healthy and digestible nutrient source for humans.
The question of cooking involves not just retaining the good but avoiding formation of the bad. One of the foremost toxins associated with cooking are heterocyclic amines (HCAs), a variety of carcinogenic compounds formed during the cooking of muscle meats through a reaction involving creatine and amino acids. (HCAs form with the “carmelization” and charring we see most prominently when grilling.) Studies have linked the intake of HCAs with cancer of the stomach.
High heat cooking such as frying, broiling and grilling produces higher levels of HCA. In fact, HCA levels can triple when temperatures are raised from 392 degrees to 482 degrees Fahrenheit.
A better cooking option for meat is oven roasting. Even better yet are stewing or braising, which keeps temps at or below boiling (212 degrees). With these slower, lower cooking methods, it’s still advisable to cook meats to “medium” doneness. Check the meat rather than let the crock pot decide when it’s ready.
Other harmful substances associated with high heat cooking are AGEs (a.k.a. glycotoxins), which have been associated with inflammation, oxidative stress and aging. A diet that contains meats cooked with high heat methods such as grilling, broiling and frying has been associated with higher levels of AGEs.
Another word on oxidation and cooking. While stir frying at low to medium temperatures offers a good option for veggies and meat strips, it’s important to not undo the good by using oils that will be cooked rancid in the process. Use broth, coconut oil, clarified butter or refined oils that are appropriate for higher temperatures.
Some of us love our grills and cooked foods of all varieties. And, as we mentioned earlier, we’re all about meat and vegetables in a pot, on a house, with a spork, etc., etc. So, are there “measures” we can take to minimize the damage our cooking methods and their accompanying temperatures may cause?
Using the microwave to partially cook meats before grilling or broiling can cut HCAs by as much as 90%. Likewise, using marinades with herbs such as rosemary, thyme, oregano, garlic, basil or parsley can lower HCAs by up to 87% (and adds some antioxidant action to boot).
Our final word: Eating a diet rich in vegetables and meats is what we’re all about. But we’re always looking for ways to make a good thing even healthier. We think there’s enough reason to eat raw when it makes sense to and when you prefer it that way. Yet, cooking figures into the picture for most of us, and we think a little information can make a healthy (and tasty) difference.
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