Questioning the safety of a favourite kitchen appliance.
North America's obsession with the oh-so-quick and convenient microwave may be pushing us from the frying pan into the fire. An estimated one out of every two households has a microwave oven. Modern cookbooks abound with recipes for cooking with this handy device. Yet an increasing body of evidence is calling into question the safety of one of our favourite kitchen appliances.
History of the Microwave
Microwave ovens were introduced into the market for domestic use in the early 1970s. At that time, they were considered relatively safe if properly cleaned and with door seals well maintained to prevent leakage. There was but a hint that their safety and the nutritional values of microwaved foods weren't what the public believed. However, in 1989, Dr. Hans-Urich Hertel, a Swiss food scientist, and professor Bernard Blanc of the Swiss Federal Institute of Technology began conducting extensive research on the effects of microwaved food on humans. Using a carefully controlled protocol, nine people, including Dr. Hertel, were alternately exposed to microwaved and conventionally cooked foods from organic sources. Samples of participants' blood were taken right before eating and at certain intervals after eating.
Researchers found that after microwaved food consumption, there was significant reduction of all blood hemoglobin and cholesterol values (both good HDL cholesterol and bad LDL cholesterol), and that bad cholesterol levels were elevated relative to good cholesterol levels.
Lymphocyte (white blood cell) activity decreased notably after ingestion of microwaved foods compared to that of non-treated foods. When exposed to blood from those who had eaten microwaved foods, bacteria that glow when examined under a special light glowed much brighter than when exposed to blood samples from those who had eaten non-treated food. This established an association that energy from microwaved foods may be passed on to those who consume the food.
Free Radical Effects
There were non-thermal effects that altered cell membrane permeability, making cells susceptible to invasion by bacteria, fungi and viruses. Other adverse effects included the change of cells from a healthy aerobic (oxidation) status to an unhealthy anaerobic (fermentation) condition. Anaerobic cells produce damaging free radicals such as hydrogen peroxide and carbon mono-xide, which increase the need for neutralizing antioxidants in the body such as vitamins A, C, E and selenium.
Dr. Hertel holds that when food is microwaved, the oven exerts a massive power input that destroys and deforms food molecules and produces new "radiolytic" compounds unknown in nature. Exposing food to ionizing rays such as gamma or X-rays (irradiation) creates URPs (unique radiolytic products) in the food. URPs have free-rad-ical capabilities that destroy healthy cells and contribute to abnormal growth, a cause of cancer. Conventional wisdom has contended that microwaves are non-ionizing. Dr. Hertel's evidence would appear to contradict that notion.
Decreased Nutritional Value
Other problems reported with microwaved foods include the destruction of nutritional value of meat proteins, lowered metabolic activity of important plant substances such as alkaloids, glucosides, galctosides and nitrilosides, and reduced bioavailability of certain vitamins and minerals, which affects the body's ability to absorb these nutrients.
Pediatrics (1992; 89: 667-9) reported heating or thawing human milk at low temperatures of 20 to 53 degrees Celsius reduces the level of infection-fighting factors in milk. Another study found microwaving milk at temperatures in excess of 72 C caused a significant decrease in all of its infection-fighting factors. The authors strongly objected to the use of microwaved human milk in hospitals.
The Journal of Natural Science (1998; 1: 2-7) reported a Tulsa, Oklahoma, patient who died of anaphylactic shock as a result of a transfusion of blood warmed in a microwave. Microwaves appeared to have altered the blood sufficiently to cause the death of the patient.
A study published in Lancet (1989; 913: 92-3) demonstrated high rates of change in microwaved food proteins not seen with conventional cooking. The authors warned that such effects on amino acids could be hazardous and "can lead to structural, functional and immunological changes."
The Journal of the American College of Nutrition (1994; 13: 209-10) reported that although the quantity of proteins changed were small, microwaving infant formula can produce molecular changes in the amino acid components in milk proteins that cause toxicity and compromise the nutritional value of the formula.
Another problem with microwaving food is the migration of chemicals from packaging materials into food.
Dr. Hans-Urich Hertel was not the first to investigate the health effects of microwaved food. Scientists in the former Soviet Union had been doing so 30 years earlier. According to William Kopp in the Journal of Natural Science (1998; 1: 42-43), from 1957 to 1999, researchers experimenting with microwaves at the Institute of Radio Technology at Klinsk in Byelorussia found that prepared meats, cereal grains, root vegetables and milk heated in a microwave created cancer-causing agents in these foods. Ingestion of microwaved foods caused a higher percentage of cancerous cells in blood. Disorders of the digestive system were associated with chemical changes in the ingested microwaved foods. These chemical alterations were also associated with a statistically higher incidence of stomach and intestinal cancers with degeneration of peripheral cellular tissues and a breakdown of digestive, urinary and bowel excretion among those who consumed such foods. Microwaved foods caused malfunctions in the lymphatic system's capacity to protect itself against growing tumours. Such findings caused microwaves to be banned in Russia in 1976. After the collapse of the Soviet Union, the ban was lifted.
While microwave cooking has been demonstrated to cause significant decreases in nutritional value of all foods studied, what about reheating previously microwaved food? The practice of reheating leftover food further compromises nutrient quality and content. Microwaved foods also offer no better protection from food-borne illnesses than conventional cooking. Reheating food in a microwave is potentially dangerous, according to researchers in the American Journal of Epidemiology (1994; 139: 903-9) investigating a salmonella outbreak among 30 picnickers who took home leftover meat. All 10 who used a microwave to reheat the meat became ill. None who used a skillet or regular oven to reheat the meat became ill.
Pass on the Plastic
Another problem with microwaving food is the migration of chemicals from packaging materials into food. The PVC (polyvinylchloride) plastic film that covers foods during microwaving has been shown to release plasticizers to such an extent that it has been recommended that PVC not be in direct contact with the food.
In microwaving breakfast cereals sold in convenient waxed packaging for heating, 60 per cent of the wax was transferred to the food in spite of strict adherence to instructions (Food Additives and Contaminants, 1994; 11: 79-89).
To enhance the appearance and flavour of prepared foods for microwaving, the food industry has developed specialized synthetic food additives. According to Australian researchers Ashton and Laura (The Perils of Progress, Zed Books, 1999): "An example of one new type of flavour-producing technology designed for use in microwave ovens is 'susceptors.' These devices are usually glued to the packaging of microwavable foods and are used to achieve local areas of high temperature. This has the effect of browning the food during microwave cooking. A subtle side-effect of some of the pre-1992 susceptor devices involved the release of small amounts of a toxic chemical, bisphenol-a-diglycidyl ether (BADGE), into the food during microwaving. BADGE was a component of the adhesive used to fix susceptors to packaging." The authors then cited a 1992 study that showed the chemical was found to migrate in the food when cooked according to instructions (Food Additives and Contaminants, 1995; 17: 79-87).
To the shame of Switzerland as a democracy, Dr. Hertel was essentially gagged by Swiss microwave oven manufacturers through the use of trade laws and the courts. In 1994, the Swiss Federal Court confirmed an earlier conviction against Dr. Hertel with the levy of a fine of 8,000 Swiss francs and the threat of imprisonment. In August 1998, the European Court of Human Rights ruled that the Swiss Court's verdict was in contravention of the Human Rights Code and ordered Switzerland to pay Dr. Hertel 40,000 Swiss francs in compensation. However, in spite of government and industry efforts to gag Dr. Hertel, other evidence concerning the hazards of microwaved foods has surfaced around the globe in peer-reviewed journals. Whether it's concerning the chemical or nutritional changes in the food itself, or the apparent effects of microwaved foods on humans, there are yet more questions to ask about this popular technology.