Why the wrong kitchen equipment or cooking method can reduce the amount of nutrients you glean from even the healthiest meals.
Who doesn’t love the aroma of food cooking on the grill on a warm summer night? Or how about that little boost you get when you reach for your favorite, well-seasoned cast-iron skillet? But did you know that certain cooking methods and pots and pans can actually diminish the nutrients you get from those meals you so painstakingly prepare?
In today’s busy world, those of us who take the time to shop for fresh ingredients and then cook well-balanced healthy meals want to ensure we’re getting the biggest nutrient bang for our efforts. With a little bit of knowledge about the cooking methods and utensils that maximize nutrient retention, you and your clients can do just that!
“Preparing food at home provides control over what we—and our family—are eating,” says Pat Baird, MA, RD, a nutrition consultant and author in Greenwich, Connecticut. Experienced cooks use certain techniques to greatly influence the taste, texture, aroma, color, safety and nutrient value of food. This process starts with knowing the best food preparation and storage methods.
When foods are cut, the area scored is similar to a wound: This is where the most nutrients leach out or bleed from! That’s why it is advisable to leave foods whole or in the largest pieces possible. It is also why you should always turn food—especially meats and poultry—with tongs or a spatula rather than a fork during cooking. This way you avoid piercing the food and releasing its nutritious juices. Whenever possible, cook fruits and vegetables with their skins intact; these skins act as a protective coating, which helps retain nutrients.
Time is also a nutrient killer. The longer foods are stored, the more the nutrients break down. Cook foods as soon after purchase as possible and eat any leftovers within a few days. Safety is also an issue here; to prevent bacterial growth, food should always be kept at below 40 degrees Fahrenheit (˚F) and cooked at above 140˚F.
As a rule, rapid cooking techniques are better for retaining nutrients than slower methods. In fact, spending the least amount of time cooking is the way to go! Any type of cooking changes food in some ways. In general, nutrients are lost when food is exposed to heat, light, moisture and air (Robertson 1986). The longer food is exposed to these factors, the greater the nutrient loss. To retain the most nutrients possible, most experts recommend that you cook food thoroughly but rapidly.
The methods that typically preserve nutrients best can be ordered from quickest to slowest, as follows:
The nutrient retention achieved through these methods may vary according to the food type, size and shape and your own cooking technique. Note that boiling is not a preferred cooking method because it does the most nutrient damage (Robertson 1986). This is especially true when foods are boiled in too much water, which is then poured down the drain (along with the nutrients themselves!). A practical way to recoup the nutrients that are released into boiling water is to retain the liquid after cooking and use it as stock for soups.
A pressure cooker is a pot outfitted with a locking lid. This device cooks food quickly and healthfully by creating steam under pressure, thereby increasing the cooking temperature. Foods that are the best candidates for this cooking method are beans, grains and vegetables.
When using a pressure cooker, timing is essential since vegetables can become overcooked in seconds! It is also important to use precisely the amount of liquid called for in the recipe. When you are cooking grains or beans, allow enough room for them to expand; do not fill the cooker more than half full. To prevent beans and grains from foaming over, add a few teaspoons of oil (Margen et al. 1992). (Cooking in high altitudes will require more liquid and a longer cooking time.) For best results, be sure to follow the instructions that come with the pressure cooker.
Can anyone imagine life without the microwave now that we have become accustomed to its speed and convenience? Microwaving uses electromagnetic radiation to heat foods (McGee 1984). Water in the food is the predominant molecule affected in this process; the water moves back and forth rapidly, creating energy that causes the temperature of the food to rise quickly.
Microwaving is undeniably fast and uses a minimum amount of liquid, producing great-tasting vegetables and fish. However, this method is less successful for cooking meat and poultry. Quick heating can cause greater fluid loss and result in a drier texture. Also, meats and poultry can’t be browned as they can with other methods, since the food’s surface never gets any warmer than the interior; this affects both the flavor and the appearance of foods (McGee 1984).
Little is known about the long-term safety of microwaving food. Concerns have been expressed about microwaves altering the protein chemistry of foods in ways that may be harmful (Weil 1997). For this reason, some health experts recommend using the microwave only for rapid heating and defrosting, not for longer cooking.
One major health concern that has recently surfaced about microwaving involves the use of plastic containers or plastic wrap—even those types labeled “microwave safe.” It appears that chemicals from the plastics (known as “plasticizers”) can migrate into food and may eventually interfere with the body’s hormonal balance, contributing to birth defects, reproductive abnormalities, early puberty in girls and some hormone-dependent cancers (Walsh 1998; Welland 2000). Heat and light accelerate this potentially detrimental process (Welland 2000). The hotter the food is, the greater the risk of these plastic particles melting into the food. To avoid this danger, use glass or ceramic containers like Pyrex™ or Corningware™, which do not react with food. To keep food moist, cover it with a glass or ceramic lid, paper towel or wax paper.
This healthful cooking method retains most nutrients, since the food is not immersed in water. Almost any food that can be boiled can be steamed, especially any type of vegetable. Invest in a metal steaming basket or bamboo steamer or improvise using a metal colander in a pot topped with a tight-fitting lid. A large steamer pot is ideal since it provides ample space for the steam to circulate, cooking the food most efficiently. Water will boil away as the food is cooking, so be sure to start off with enough liquid in the pot.
Traditionally an Asian cooking technique, stir-frying rapidly cooks small, uniform-sized pieces of foods, most commonly mixed vegetables. Thinly sliced pieces of beef, chicken or shrimp can also be stir-fried in a wok or large, nonstick frying pan. Stir-fried meals are healthful because foods cook rapidly at relatively high temperatures. Very little oil is needed with this cooking method, just enough to form a thin film on the pan (Hensrud et al. 1998). If desired, broth, wine or nonstick cooking spray can be used instead of oil. (Just be sure to add more liquid to the pan as it evaporates.) Gradually add the oil or broth to the pan, heating until hot but not smoking. Then toss in the food and stir constantly until meats are thoroughly cooked and vegetables are just tender and crisp (Margen et al. 1992).
BROILING & GRILLING
Both of these cooking methods expose food to direct heat, leaving food crispy on the outside and juicy on the inside with a characteristically intense flavor. These methods work well with meat, seafood, poultry, vegetables and even fruit! For best results, meat should be cut in chunks 1 to 2 inches thick; however, leaner meats, such as chicken or fish fillets, can toughen and overcook under such high heat. Depending on the food’s thickness and the heat intensity radiated by the broiler or grill, position meat about 4 inches from the heat source; place chicken and fish about 6 to 8 inches away (McGee 1984; Margen et al. 1992). For a great marinade that can be used on most grilled or broiled foods, see “Marvelous Marinade” above.
Sturdy vegetables can also be broiled or grilled. However, this works best if the veggies are in fairly large pieces (like whole baby carrots or mushrooms), thickly sliced (like red potato wedges) or cut in half (like eggplant). You can either marinate the veggies and cover them with aluminum foil or brush them lightly with oil and put them in a wire basket, which can be easily turned during cooking. Place the vegetables about 4 inches from the heat source and, as the veggies cook, baste them once or twice with broth, marinade or juice. When they begin to brown, turn them over to lightly brown the other side (Margen et al. 1992).
When broiling, use a pan with a rack to allow the fat drippings to slip through; this will lower the fat content of meat and prevent flare-ups caused by dripping fat. Although grilling causes fat to drip away, flare-ups when barbequing can result in harmful substances forming on meat. The smoke coats the barbequed food with polycyclic aromatic hydrocarbons (PAHs), which may promote cancer (Golub 2001). The high temperatures of grilling (and broiling) can also cause carcinogenic substances called heterocyclic amines (HCAs) to form on the surface of well-done and charred meat (Golub 2001). For tips on how to grill more safely, see “Healthy Barbequing Tips” on page 27.
Sometimes called pan-frying, sautéing rapidly cooks small, uniform-sized pieces of food in little or no oil. The best candidates for this method are vegetables and thin cuts of meats or seafood, such as pork medallions, boneless chicken breasts and scallops. Traditionally, most cooks have used butter or oil to sauté, but very little fat is needed if a nonstick pan is used (Margen et al. 1992). Depending on the recipe, broth, wine or water can replace all or some of the oil. (Keep in mind, however, that these liquids do not heat as quickly as oil and may slightly alter the cooking process and flavor.) I personally prefer to sauté garlic lightly in olive oil, then add a cut-up vegetable like broccoli (either raw or blanched) for a quick side dish; for an entrée, I add some broth and pasta.
The key to sautéing is to use a hot skillet, heating the liquid until hot—but not smoking—so that the food cooks quickly. Once the liquid is hot enough, add the food immediately and stir. To avoid releasing juices (and nutrients), turn meats with tongs or a spatula instead of a fork. If using broth or water in place of oil, replenish the liquid as it evaporates. The pan should be large enough to avoid crowding, or the food will actually steam rather than sauté!
This stove-top cooking technique gently simmers foods in water (or other liquids, such as broth, vinegar, wine, fruit juice or vegetable juice, to add more flavor). ‰ Meats, poultry, fish, seafood, vegetables and fruit can be poached. The nutritional advantage to poaching is that the liquid becomes part of the dish itself but contains little or no added fat. The liquid can be thickened by adding flour or cornstarch. To poach food most efficiently, choose a pan that best suits the size and shape of the food, so a minimum amount of liquid is used; this also minimizes cooking time (Hensrud et al. 1998).
Braising involves slow cooking in a small amount of liquid inside an open or covered pan. Suitable for meat, poultry or vegetables, braising can be done either on the stove top or in the oven (Hensrud et al. 1998). The braising liquid can be water, broth, juice or wine. This is one of the best methods to tenderize a tough piece of meat, since slow cooking in liquid softens the connective tissue. (Pot roast is a familiar example of a braised meat.) Be aware that fatty, tender cuts of meat will become tough with this cooking method (Margen et al. 1992).
Like baking, roasting uses the dry heat of an oven to slowly cook food such as meat roasts, whole chicken or turkey. However, roasting is typically done at higher temperatures than baking. Almost any kind of fatty or lean meat can be roasted, although the method works best for larger cuts. Sturdy vegetables can also be roasted to intensify their flavors.
While vegetables can be roasted on a baking sheet, it is best to roast meats in a broiler or in a roasting pan with a rack so that fat can drip away from the meat during the cooking process. For easy cleaning, coat the rack with cooking spray and line the pan bottom with foil. Cooking time will vary with this method, depending on the size, shape and cut of meat. A good meat thermometer inserted into the thickest portion is essential to judge when the meat is cooked thoroughly (Margen et al. 1992).
When we think about this method, the first foods that usually come to mind are baked goods, such as breads, cookies and cakes. But this dry-heat technique, which cooks food by surrounding it with heated air in an oven, can be used to cook uniform-sized pieces of veggies, fruit, seafood, poultry or lean meat. Baking works well when little or no fat is added to a dish (Margen et al. 1992). Use a shallow baking dish, and cover it with foil or a lid to keep foods moist.
Rattling Those Pots & Pans
Like the food you prepare, a quality set of pots and pans is an essential ingredient in any successful recipe. There are two basic qualities to look for in cookware. First, it should be made from a material that conducts heat evenly and efficiently to prevent “hot spots” from developing and food from burning. Second, the pot’s surface should not be chemically reactive, which would allow atoms from the metal to leach into the food, potentially affecting the food’s flavor or color; examples of cookware with this drawback include cast-iron and aluminum pans (Garrison & Somer 1995). Unfortunately, while there are many good products on the market, no one material currently meets both the criteria listed here. For example, metal pots and pans are good heat conductors but they are usually chemically reactive.
The advantages of aluminum are that it is inexpensive, a very good heat conductor (second only to copper) and lightweight, making it easy to handle (McGee 1984). Unfortunately, food molecules can easily penetrate its surface, particularly acidic ones like tomatoes, alkaline ones like milk and sulfur-rich foods like eggs. These molecules can cause light-colored foods to become noticeably discolored. The sulfur odor that is emitted when cooking foods such as cruciferous vegetables (e.g., cauliflower and broccoli) is also intensified in aluminum pots and pans.
In the 1970s, aluminum cookware was linked to an increased risk for Alzheimer’s disease when Canadian scientists observed a higher than normal level of aluminum in the brain of patients with this disease (Schepers 2000). However, other researchers have been unable to duplicate these results (Schepers 2000). Aluminum cookware and utensils contribute about 2.5 milligrams (mg) of aluminum to the average American’s daily diet. This is small in comparison to food additives and leavening agents, which add 25 to 50 mg of aluminum daily; buffered aspirin, which adds 125 to 725 mg; or common antacids, which add 850 to 5,000 mg. If concerned, avoid aluminum cookware, but be aware that far greater sources of aluminum are regularly consumed without much fanfare (Schepers 2000).
Considered the best heat conductor, copper cooks food quickly and evenly. Unfortunately, it is highly reactive with anything it encounters, including food. To prevent copper from leaching into food, the copper must be coated with stainless steel (Schepers 2000). (Older cookware was often lined with tin, which wore off easily, revealing the copper below.) While copper is an essential mineral, too high an intake can be toxic. Never serve or cook food in unlined copper pots or pans or in utensils whose lining is worn even minimally. Pure copper pots and pans are truly for decorative use only!
Don’t tell Grandma that her old cast-iron skillet is a relatively poor conductor of heat. Chances are, her prized pan is so thick and heavy it will absorb and hold heat well, regardless of its poor conductivity! Iron cookware needs to be regularly oiled and gently cleaned to avoid corrosion. This cookware can also leach iron into food, which can be a good or bad thing. Increased iron intake can benefit children, adolescents and menstruating women, who typically need to boost their levels of this nutrient. But older people and those at risk for hemochromatosis (iron overload disorder) should avoid additional dietary iron intake (Schepers 2000).
This cookware is created by placing a nonstick coating (like Teflon®) over metal. The obvious advantage is that this minimizes the amount of fat needed to prevent food from sticking to the pan. However, the coating itself can chip. Although the material is nontoxic and will pass through the body without being absorbed (Schepers 2000), chipping is obviously undesirable and can cause food to be unevenly cooked. To protect the coating, avoid using metal utensils with nonstick cookware. If you have a pot or pan with a significant amount of chipping or peeling, throw the piece away since the damage affects cooking performance.
Although stainless steel is a poor conductor of heat, it is chemically the least reactive of the metals. Stainless steel cookware tends to be expensive, so some manufacturers skimp on the thickness of the metal. A pan that is too thin will create hot spots, causing uneven cooking. The transfer of heat is vastly improved if the pan has a copper or aluminum inner core or if the bottom of the pan is coated with copper (McGee 1984). Despite their inferior heat conduction, stainless steel pots and pans—particularly the hybrids that are “clad” or combined with other metals—are probably the best forms of cookware available today.
Ceramic pots and pans are poor conductors of heat, especially when used on a stove top, so they don’t distribute heat evenly over a surface. Ceramic material is a better choice when used as an oven casserole dish or a Crockpot™, because the heating process is slower and more diffuse. Ceramic pots and pans do retain heat well, making them good candidates for keeping food hot at your next dinner party! However, a word of caution is in order: Do not cook or store food in that beautiful ceramic pottery you purchased on your last trip to Mexico, South America or the Mediterranean! Many of the ceramic items produced in other countries are not fired at high enough temperatures and, as a result, can leach lead from the ceramic glaze into food. Even in small amounts, lead is extremely toxic and can cause brain or nerve damage and impair the immune system (Schepers 2000).
Marinades can not only add great flavor to food but also tenderize tougher cuts of meat. From a safety perspective, marinades may help reduce some of the carcinogens that can form on food when it is grilled or broiled (American Institute for Cancer Research 2001).
The following marinade works well when grilling or broiling vegetables, tofu or meats. Slice veggies—such as eggplant, zucchini, summer squash, bell peppers, mushrooms, cherry tomatoes and/or red onion—into thick rounds or, if small, leave whole. Cut lean meat, skinless chicken, seafood or firm tofu into 2-inch cubes.
1/2 cup rice or white-wine vinegar
1 tablespoon canola oil
1/4 cup finely chopped onion
1 small bay leaf
2 sprigs fresh (or 1/2 teaspoon [tsp] dried) rosemary, thyme or oregano
2 cloves garlic, finely minced
1/2 tsp freshly ground pepper
In bowl, combine marinade ingredients until well blended. (Use a nonmetal container to prevent off flavors from forming.) You’ll need about a 1/2 cup of marinade for each pound of food. Add the food and turn several times until all sides are coated. Cover and refrigerate for at least 30 minutes, occasionally turning food so that marinade is distributed evenly. Drain and discard marinade. Thread skewers for meat and vegetables separately or place in aluminum foil or wire baskets (cooking times will vary, depending on the food). Place on grill and turn often with tongs or spatula to prevent charring. If you want marinade for basting, make a second bowl, to prevent spreading bacteria.