Microwave ovens have risen to a place of special prominence in U.S. households. A 2013 study showed 97% of all households now include a microwave oven, and in one survey of life satisfaction in the U.S., ownership of a refrigerator and a microwave were found to play an important and measurable role—right alongside of televisions and washing machines. Without question, microwave cooking has become a fundamental part of kitchen practices in the U.S., and use of a microwave oven has become part of normal, everyday life for many people.
Overall, studies on the impact of microwave cooking on food nutrients have been favorable. In other words, when microwave cooking has been compared to other cooking methods—including steaming, boiling, baking, and frying—it has usually been shown to be superior to at least several other methods in preserving a particular nutrient in a particular food. Microwaving does not come out on top for every nutrient in every food—but then again, neither does steaming or boiling or baking. If one thing has been made clear by decades of research on cooking methods, it is the absence of any single cooking method that will hold up best as a way of preserving all nutrients in all foods.
With respect to vegetables, microwave cooking has been shown to be generally comparable to steaming. This very rough and generalized conclusion definitely has some exceptions. But we have also seen numerous studies where it holds true. With the cooking of broccoli, for example, microwaving has been found to do a better job of preserving both chlorophyll a and chlorophyll b than steaming. Yet, the microwaving of broccoli has been found to do a poorer job in preserving quercetin and kaempferol (two flavonoids). With cauliflower, more quercetin has been shown to be retained with microwaving compared to steaming; yet steaming scored ahead of microwaving in kaempferol retention. With red cabbage, total anthocyanin content has been found to be better preserved by microwaving than by steaming. In fact, total phenol retention in red cabbage has been shown to be improved by microwaving versus steaming. Yet, at the same time, the steaming of red cabbage has been shown to do a slightly better job in preserving vitamin C than microwaving. In the case of watercress (a green leafy cruciferous vegetable), microwaving and steaming have been shown to be comparable in retention of overall phytonutrients. These examples appear to show that neither steaming nor microwaving is superior when it comes to overall nutrient retention, with microwaving showing some unique benefits and steaming showing others.
Interestingly, the microwaving of potatoes has been linked to a lower glycemic index (GI) value than boiling. For boiling, the GI range for potatoes is typically 85-95. For microwaving, this GI range is typically 65-80.
Another interesting and potential health benefit of microwaving involves green tea. With bagged green tea previously steeped in boiled water, the addition of one minute in the microwave has been shown in one study to increase extraction of catechins from the tea leaves into the hot liquid tea.
Most plastics, including film food wraps (often made from LDPE, or low density polyethylene, displaying a Number 4 recycling symbol) and styrofoam containers (typically made from PS, or polystyrene, and displaying a Number 6 recycling symbol) have been shown to migrate in small amounts from plastic packaging into microwaved foods. While this contamination of food with plastic particles has been well-documented in the science research, the degree to which this migration represents a health risk is strongly controversial (due to the small amounts that can migrate) and remains an issue of ongoing science debate. Researchers who look at "invisible" changes occurring inside human cells (including metabolic patterns and nutrient ratios) often find reasons for broad-based concern about the use of plastic packaging in microwave ovens. Researchers who focus more on clinical problems and documented health concerns find no reason for broad-based concern. From our perspective, if you do decide to use a microwave oven as a part of your ongoing food preparation, it makes sense to minimize risks that still fall into this "potential risk" category and microwave your food in non-plastic food containers, including glass, Pyrex (TM), CorningWare (TM), and all microwave-safe ceramics.
The above studies on microwaving and nutrition have typically involved fresh or frozen vegetables microwaved "from scratch." However, the majority of U.S. adults do not report use of their microwave ovens in this way. In fact, a 2010 food and health survey of U.S. adults showed that only 15% of all participants used their microwave to prepare a meal from scratch with 58% using their microwave to thaw frozen foods or frozen beverages. By far, the most common use of microwaves was to reheat leftovers (92%) or prepare prepackaged products (84%) such as frozen meals, frozen soups, or popcorn. In other words, use of microwave ovens has been most closely tied to reheating of leftovers or preparation of prepackaged frozen foods—not to the cooking of fresh vegetables (or other fresh foods). With increasing purchase of microwave "supercookers" that combine microwave cooking with traditional convection heating, it is possible that this trend may change. But at present, convenience in preparing frozen prepackaged foods and heating leftovers remains the key uses of microwave ovens in U.S. households.
Two broad categories of environment-related issues are most often mentioned in discussions of microwave cooking: (1) the energy efficiency of microwave ovens, and (2) the predicted lifespan and disposal of these appliances.
in question and the overall cooking goal. Because the construction and operating frequency of a traditional microwave oven allows for a direct energy impact on water molecules, some foods (for example, a single whole potato) can be microwaved quite quickly in comparison to the cooking time that would required for oven baking. In this particular case, the electricity cost to cook a single baked potato in the oven would be greater than the electricity cost for a single baked potato in an electric oven because the time involved would be much shorter. Yet, if you compared the per-minute use of electricity in kilowatt hours (kWh) of a microwave to an electric oven, you might not find much of a difference in the per minute electricity use.
Many consumer websites describe the expected lifespan of a microwave oven as falling into the range of 5-10 years; in other words, they generally expect a microwave oven to need replacement after this period of time. Since six to eight million microwave ovens have been sold each year in the U.S. over the past decade, future disposal of these appliances raises important environmental concerns. Even if repair of a particular non-working microwave oven might be possible, the cost of this repair for the consumer might be considerably more than purchase of a brand new microwave that features new technological features (for example, the combination microwave/convection oven spoken of previously). Since most waste management programs do not accept microwave ovens for disposal, there is typically more effort required on the part of consumers to properly dispose of a non-working microwave. Even the services of an appliance recycler may go unused by consumers due to lack of convenience or lack of readily available information. These disposal challenges seem greater than the comparable challenges posed by electric or gas stoves. These cooking appliances have a longer lifespan that commonly extends for 15 years, and due to their sheer size and weight, they may more often get disposed of through established recycling channels.
At WHFoods, we discourage use of microwave ovens for any type of cooking. While we recommend avoidance of microwave cooking in all circumstances and regardless of the food or nutrient in question, our reasons are not based on nutritional studies or environmental concerns. We discourage use of microwave ovens for an entirely different set of reasons, which we would summarize with the phrase "relationship with food."
Put most simply, we believe that there is a unique joy to be had from healthy eating! Nutrient-rich cooking is great for our health, and it can definitely lower our risk of many health problems. But nutrient-rich cooking is not just something that we need to do. It is something we can take delight in doing. Watching the color in a fresh vegetable become more vibrant in the first minute of steaming; savoring the subtle shifts in aroma between minute one and minute two of steaming; having a food right there on the stovetop, right at your fingertips: these are pleasures of food and cooking that seem critical to the experience of healthy eating. Even with the best available viewing window in the door of a microwave oven, the food being microwaved is still locked in a box and our cooking experience is physically changed in a very undesirable way.
Equally undesirable is the potential change that might occur in our thinking about food. At WHFoods, we know for a fact that the pleasures of healthy eating and nutrient-rich cooking are available to everyone. It is never too difficult to prepare and enjoy great tasting food! And yet if 84% of U.S. adults use their microwave to prepare prepackaged food products and only 15% who use their microwave to prepare food from scratch, it may become all too easy for us to start thinking about "cooking from scratch" as being not only inconvenient for us but perhaps even impossible on an everyday basis. Along with the widespread adoption of microwave ovens has come the production of so many non-fresh, prepackaged processed foods that are not only custom-tailored for convenience but also custom-tailored for the microwave oven itself. In fact, there are processed food products that are only meant to be prepared in the microwave! For us, it is so important for everyone to experience how fun, easy, and enjoyable healthy eating can be, and how much pleasure can come into our lives through our relationship with the World's Healthiest Foods.