Scientific Zapping

Is microwave cooking bad for your Health?
Most Australian homes use microwave ovens for cooking their meals. These are so convenient, energy efficient and easy to operate, that even professional chefs prefer microwave over conventional ovens. Microwave cooking is known as a healthy way of preparing just about any food. From scalloped potatoes and steamed veggies, to ‘poached’ eggs and baked desserts, not a single day goes by without a microwave. Because we are so used to having microwave around, we don’t question it’s safety, and certainly not the health effects. However, many scientists started revealing some awakening facts and changing our outlook on modern technology.

Various sources state that eating micro-waved food causes immune system deficiencies, cancerous tumors, loss of memory and concentration, emotional instability and "impaired intelligence". Additionally, "exposure to microwave radiation leads to long term brain damage due to the change of body’s electrical impulses which de-polarize or de-magnetize the brain tissue." The question remains: Are Microwave Ovens safe or not? Find the answers to your burning questions about cooking, food, radiation and everything else there is to know about Microwave Ovens.

What are the microwaves?
Like visible light, microwaves are a part of the electromagnetic radiation spectrum. Also used for signal transmission in telephone calls, television, radio, X-rays and ultraviolet and infrared light in medicine, microwaves have high frequency. The higher the frequency of radiation, the shorter its wavelength The waves used for cooking in the Microwave Ovens are extremely short and fast (with a frequency of 2450 megahertz travelling at the speed of light of 300,000 km or 186,000 miles per second), hence the name microwaves. (FM radio waves are generated at 100 MHz and cell phones transmit 800 MHz).

How do Microwave Ovens work?
Microwave ovens contain a magnetron tube which converts electricity from the power outlet into electromagnetic waves. Radiation is a way in which energy travels invisibly between two things without direct contact. That energy can be transformed into heat. You know the pleasant feeling of warming sun rays, but how do you get hot when the sun is so far away? The hot waves take their journey through space onto your body’s surface by invisible radiation. This is the same way your food is heated in the Microwave Oven, only faster.

The waves penetrate the food or liquid by agitating all polar molecules with negative and positive charges. Water has the strongest polarity, that is why microwaves love water the most. Everything that contains moisture absorbs microwave energy, including fat, protein and sugars in food.

This causes intermolecular friction and produces heat. Cooking time is usually much shorter than in a conventional oven. The rate of heating depends on the moisture content, shape, volume and mass of food present. Molecules of water in the food change polarity from positive to negative with each cycle of the wave, the power of your kitchen helper creates movement within the food molecules millions of times every second.

Which is better – raw or cooked food?
Our ancestors used fire for centuries, so we know that heating food is a good way to kill dangerous bacteria making many foods easier to digest. Besides improving taste of food, cooking vegetables breaks down starches, so humans can absorb the nutritional benefits of these. Additionally, vital nutrients and anti-oxidants, such as beta-carotene from carrots and lycopene in tomatoes, increase their bio-availability when subjected to heat.

But overcooking food at high temperatures, such as in barbecuing, is not recommended. The delicious slightly burnt crispiness from barbecued meat contains aromatic hydrocarbons which has been shown to cause cancer.

What is the difference between conventional and microwave cooking?
Radiation is relatively new with a number of suspected differences in food preparation. Microwaves cook the food unevenly – or from "Inside Out", as some say. The conventional oven distributes the heat by conduction from the outside of the food toward the middle But microwave heating excites the food molecules everywhere all at once changing their polarity rather than transferring or conducting heat from the outside. Some parts of food have more water in them than others, so they attract microwaves and are heated first. Due to this uneven distribution of polar molecules thick pieces take longer to be cooked.

The heating air in the ovens is also dry, but Microwave Ovens are tightly sealed when closed, thus the moisture of the content is kept inside and the food is not dried (cannot form ‘crust’).

Do microwaves make food radioactive?
Just like switching off the light cuts the electric current, waves generated in Microwave Ovens stop their action once the power is off, and they do not remain in the food afterwards. Neither can they make the food or the oven radioactive. Therefore, there is no way the food cooked in a microwave oven can be radioactive.

Can Microwave-cooked food damage the body’s health?
There are claims that microwaved food is depleted in nutrients and/or is full of carcinogenic chemicals. In one study ("Aminoacid Isomerisation and Microwave Exposure", Lancet, 1990 February 24;335(8687):470) the authors microwaved milk, and found that one of the proteins changed shape from L-proline to D-proline, which in large concentrations is toxic to the kidney and liver.

Scientists (Hertel and Blanc, Journal Franz Weber 1992 January-March 19) have also found that when the eight volunteers ate microwaved food, they showed disturbing changes of blood chemistry - levels of red and white blood cells (or erythrocytes and hemoglobin, leukocytes and lymphocytes) had decreased while Cholesterol values had jumped up reflecting low-grade anaemia.

Does microwave cooking destroy the nutritional goodness of the food?
Researchers from the Spanish scientific research council CEBAS-CSIC (Journal of the Science of Food and Agriculture, 2003) found that cooking by microwave is the worst way to preserve antioxidant compounds (flavonoids, sinapics and caffeoyl-quinic derivatives) in vegetables. By comparison, the loss of these nutrients is minimal when the produce is steamed. The produce loses 11 percent, 0 percent and 8 percent of the very same antioxidants.

A different research from Stanford University (Pediatrics, 1992) found that re-heating of human breast milk in a microwave oven at a low setting destroyed bacteria- fighting lysozyme. Microwaving baby formula converts certain trans-amino acids into trans-fatty acids known to be poisonous to the nervous system and to the kidneys (Lancet, 1989).

The follow-up tests by others commented that this change was only possible if milk is exposed to much greater levels of microwaves than are used in the home environment.

Are vitamins and minerals preserved or lost during microwaving?
We do know that water-soluble vitamins (such as C and the B-group) are susceptible to both heat, and to dissolving in the water. These vitamins are retained in microwaved vegetables as well as if they had been steamed, and much better than if they had been boiled.

Microwaved vitamins that are insoluble in water (such as A and D) are exposed to less heat and for a shorter time than when foods containing these are cooked in the oven or on the stove top for many minutes. So, it may turn out that all these micronutrients survive better in microwaved foods.

So, quick microwave cooking and reheating, just like steaming, keeps minerals and vitamins, particularly vitamins A, E, C and Thiamin, within the foods when these are microwaved in minimal amounts of water for a brief time. This is better than boiling which leaches micro-nutrients into the cooking water and the high heat that destroys the beneficial healthy properties of your nourishing essentials. However, conflicting evidence exists about Vitamin B-12 found in dairy and meat. Some say it can be destroyed by microwaving (Science News,1998) much more than by other cooking techniques.

All minerals are inorganic and are not destroyed by heat. However, being soluble in water, these can leach out when cooked in water – be it boiling, baking, steaming or microwaving. The less water you use, the more minerals you will keep.

What about proteins, sugars and fats?
Fats and carbohydrates are broken down by both regular heating and microwaving. Proteins suffer less oxidation in a microwave oven than in conventional cooking, but Microwaves break down proteins differently to conventional heating. Cooking meat or fish in the oven or on the stove top takes a long time at a relatively low temperature. Elecromagnetic energy heats up the food all the way through without browning or overcooking, which theoretically keeps the quality of protein at the topmost level.

Claims that microwave cooking can "mutate and change cellular structures into carcinogenic substances", "accelerate structural disintegration of food", "destroy the value of nucleoproteins in meats", decrease the "bioavailability of nutrients", etc. may just be too loud. When food is subjected to heat, it doesn’t have a choice and simply has to undergo certain changes in its structure.

Can Microwave Ovens leak radiation?
Leakage of microwaves can only occur if your kitchen appliance has holes in its metal walls, over the front window and the seals around the door. All operating machines approved for sale are tightly sealed when closed, however some leakage may occur around certain microwave ovens. The amount of "the microwave leakage at any point 50 millimetres or more from the external surface of the appliance shall not exceed 50 watts per square metre" as regulated by The Australian/New Zealand Standard AS/NZS60335.2.25:2002 Household and similar electrical appliances – Safety Part 2.25: Particular requirements - Microwave ovens. This minimal amount has shown no effects on human health, just like radiation from your oven, television set, telephone or the sun. Even modern pacemakers do not suffer interference with the emission of waves from Microwave Ovens when placed in the near space.

Is it safe to thaw food in the Microwave?
The best way to thaw any food is in the refrigerator. But it is a slow process, so microwave ovens come in handy. In a matter of minutes the food is ready to be served. Thawing food between 4°C and 60°C for a long time creates a fertile ground for the dangerous microorganisms in foods, which is dangerous.

Can I burn myself by Microwave cooking?
Microwave ovens are less likely to cause burns than are conventional ovens, but the steam emitted from closed packages, plates covered with plastic and unevenly heated foods can be dangerous. Using oven gloves, letting the steam escape by careful removal of the lid or plastic while keeping the face away are good safety techniques.