Cooking for your Health

Dinner Most cookbooks address cooking techniques: How to boil, fry, sauté, steam, bake, microwave, and so on. Cookbooks don't usually mention, however, that these different cooking methods can add to, or detract from, the nutrient value of foods, and that they may cause additional harm!

Fry Me to the Moon

Although most North Americans probably fry a lot of their foods, this is not necessarily the best way to cook. To many people, frying is putting food in a pan, along with butter or oil, and then, well, frying it, usually for a prolonged period of time. Prolonged heating can destroy nutrients, and the butter or oil used to fry is absorbed in varying degrees by the food, so you get a bit more fat than you may think.

Often touted as the healthy way to fry, and to cook in general, is stir-frying. This technique, used extensively throughout Asia, means cutting food into small pieces, putting them in a pan with very little oil (or using a sauce as oil), and cooking them very quickly at a very high heat. Because it is one of the fastest ways to cook, vitamin-rich veggies, such as broccoli and carrots, retain more nutrients, as well as their texture and color (although the high heat probably zaps the enzymes). More importantly, stir-frying does not require a ton of fat to bring out the flavor of foods. A typical "French-style" recipe for sautéed chicken breasts calls for an entire stick of butter, plus whatever the sauce calls for. A stir-fry recipe, however, requires only two to three tablespoons of oil. This relatively small amount of oil not only cooks the chicken, but any veggies you may want to throw in!

There are ways to control the amount of fat you get through oil absorption in cooking. The veggies and meat you fry will absorb oil. How much depends on the food. In a study published in the Journal of the American Dietetic Association, the authors show that vegetables drink up the oil used in cooking. More specifically, coarsely chopped eggplant cubes absorb most of the oil because eggplant contains numerous air cells, which soak up oil like a sponge during frying. (Flattening the eggplant with a heavy weight squeezes the air out of the cells and reduces the amount of oil the vegetable can absorb.) Leafy vegetables with small stems absorb slightly more oil than those with large stems. Nonleafy vegetables such as broccoli, cauliflower, and finely shredded carrots absorb about as much oil as leafy vegetables. Gourds, peas, and green peppers absorb about half of the oil used in cooking. The amount of oil absorbed by various cuts of meat depends on their fat content; the higher the fat content, the less oil is absorbed. It seems obvious that you should consider the type of oil used when stir-frying. Unsaturated fats, such as those found in many vegetable oils,would be healthier than saturated fats, such as those from animal sources.

Oil temperature should also be considered. When oil burns it becomes toxic and free radicals are produced. When oil smokes, you should throw it away.

In another article published in The Journal of the American Dietetic Association, nutrient retention was compared when beef strips were stir-fried, broiled, and microwaved. The report notes that the true retention of vitamin B6, iron, zinc, and magnesium were significantly higher in strips that were cooked by stir-frying than in those cooked by microwaving or by broiling. Although many people today are not necessarily big beef-eaters, this tells us something about the relationship between food preparation and nutrients.

Boil me Over

Boiling has a bad rap in the cooking community. This stems not only from the fact that boiling does leech out nutrients—the water in which you boil food may be better for you in the end than the cooked food—but also because many people grew up with boiled-to-death foods that were a tasteless mush of green mystery.

However, some foods are best boiled. Mustard greens, turnip tops, collards, and similar vegetables have too strong of a taste for other methods of cooking. Annemarie Colbin, in Food and Healing, notes that boiling kale and bitter greens results in a pleasant meal, while if you steam them (the preferred choice today), they may not be taste sensations. Boiling food does not necessarily mean that you "waste" nutrients; the water in which the food is boiled can be used for other purposes.

Full Steam Ahead

Steaming preserves the vitamins and minerals in foods. It is also healthy because you do not have to add any oils or fats. Steam can actually help melt some of the excess fats in foods, which end up in the water that was heated to make the steam. When you steam rather than charbroil foods, you also avoid the danger of consuming carcinogens that are present in blackened foods.

Steaming also concentrates the intrinsic flavor and juiciness of foods. This not only makes foods taste better, but also brings an indirect health benefit: When we taste what foods really are like, we may not be as tempted to use rich sauces or unhealthy condiments to spice them up.

Nuke It

Although most homes now have microwave ovens, these appliances remain controversial. Many people say they are safe, while others contend that they can cause health problems.

Microwave ovens heat foods by alternating the magnetic polarity of their atoms; that is, the positive pole is made negative and then positive, and vice versa, thousands of times a second. On the other hand, "fire"—that is electric or gas heat—heats foods by friction, where molecules move around and rub against one another to generate heat.

As far as nutrition goes, stir-frying results in foods with more of certain nutrients. However, many reports argue that foods cooked in microwaves retain more nutrients than foods cooked by other means. Still, many people believe that nutrient loss is not the major problem with microwaving. They say that the real danger is that microwaving may affect immunity and blood cells.

A study in the April 1992 issue of the medical journal Pediatrics reports that warming breast milk in a microwave oven at high heat (72 C to 98 C ) destroys 98 percent of its immunoglobulin-A antibodies (necessary for the passive immunity that breast milk gives to infants) and 96 percent of its lysozyme activity (which inhibits bacterial growth). Even when microwaving breast milk at lower temperatures of 20 C to 25 C , E coli growth was five times as great as that of control breast milk. The researchers concluded that "This preliminary study suggests that microwaving human milk could be detrimental," and "… our data indicate that microwave radiation is not a suitable heat treatment modality, as there is a significant loss of immunologic properties."

A 1992 German study with eight subjects also found problems with microwaving. In this two-month study, the researchers found that the microwave heating of milk or the microwave cooking of vegetables is associated with a decline in various hemoglobin levels (which carries iron in red blood cells). They also found that microwave cooking of vegetables is associated with a drop in lymphocytes (a type of white blood cell that produces antibodies important to our immune system) and the highest rise of overall white blood cell counts. The same study also revealed that high-density and low-density lipoprotein levels—measures of cholesterol—rose in the subjects after they consumed vegetables prepared in a microwave.

The Best Way to Go?

Steaming and stir-frying do the best for capturing nutrients, and also give you the option, at least for stir-frying, to try healthy and great-tasting sauces. These cooking methods also take little or no oil, so you miss out on some of the fat.

However, the best thing to do isn't cooking at all. Instead, eat as many raw fruits and vegetables as possible. When you do this, no vitamins, minerals, or enzymes are lost, and you gain optimum benefits. Juicing fruits and vegetables is also a great nutrient-catcher.

Suggested Reading

Quan, Richard, M.D., et al. "Effects of microwave radiation on anti-infective factors in human milk."
Pediatrics. Vol. 89, No. 4. April 1992.

Valentine, Tom. "Microwave cooking." Search for Health. (813) 263-4101.

Wen-harn Pan, et al. "Cooking oil absorption by foods during Chinese stir-frying: implications for estimating dietary fat intake."
Journal of the American Dietetic Association. Vol. 93, No. 12, December 1993.

Yang, Jing, et al. "Sensory qualities and nutrient retention of beef strips prepared by different household cooking techniques."
Journal of the American Dietetic Association. Vol. 94, No. 2, February 1994.

The article "Cooking for your Health" is reproduced with the permission of AIM International
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