Question:
A naturopathic doctor told me to avoid microwave ovens because studies show they alter vital nutrients in food and may cause systemic harm. I’ve microwaved vegetables for years with good results. Could the retained nutrients still be harmfully altered?
Answer:
If we could zap a nutritious dinner into existence in three seconds flat, most of us would. Sadly, Star Trek food replicators haven’t arrived, but the humble microwave oven is here, and for the time-poor among us, it can be a great help in getting dinner on the table faster.
But look hard enough on the internet and you will find stories about nutrients obliterated, toxins unleashed, your vegetables somehow rendered dangerous by radiation.
Are the worries justified? All food changes when heated, whether it’s in a standard oven, a microwave or over an open flame. Research from the 1980s and 90s suggests microwave heating of food produces much the same types of changes in macronutrients such as protein, fat and carbohydrates that you see with other cooking methods.
Microwaves may better preserve vitamins, minerals and phytochemicals, because they cook quickly with little or no added water. For example, one study found microwave drying of kiwifruit and pepino (a South American fruit) retained more antioxidants and bioactive compounds than conventional oven drying.
A 2003 study often cited to claim microwaving destroys nutrients used small broccoli pieces cooked in a large amount of water for five minutes. This preparation matters because nutrient loss, particularly of water-soluble vitamins, is mainly influenced by water quantity and how much vegetables are cut, rather than the cooking method itself. Smaller pieces increase surface area, and, along with excessive water, promote leaching of nutrients.
Subsequent research confirms microwaving with proper food preparation techniques causes lower antioxidant losses compared with boiling. Indeed, both steaming and microwaving preserve more nutrients than boiling. However, factors such as cutting technique, peeling, water levels, temperature and duration all affect nutrient loss – the appliance itself is only part of the story.
To maximise nutrient retention from vegetables:
• Keep veges as intact as possible (less chopping means fewer vitamins escape).
• Use minimal water – just a splash is fine.
• Avoid overcooking – shorter times mean more nutrients survive.
Still, some foods don’t appreciate microwave cooking. For example, garlic’s superpowers come from allicin, a compound formed when the enzyme alliinase meets its substrate, alliin, after you crush or chop the cloves. However, just 60 seconds in the microwave (or 45 minutes in a conventional oven) can destroy alliinase, meaning no allicin formation. To prevent this, let your crushed garlic “stand” for about 10 minutes before heating – then the enzyme alliinase has time to work its magic before the heating process shuts it down.
Human breast milk, too, is more than a food; it contains important immunoprotective factors to boost baby’s immune system. Although microwaving doesn’t harm breast milk’s macronutrient content, it does reduce these delicate immune properties, as does boiling. That’s why health authorities recommend warming breast milk gently by placing the bottle in warm water instead.
To get the best results and preserve nutrients when cooking with a microwave, keep these simple tips in mind:
• Stir and stand – microwaves heat unevenly, so stir partway through or let food stand after cooking to allow heat to distribute (important for food safety).
• Choose shallow, round dishes – these heat more evenly and help prevent overcooking at the edges.
• Use the right plastics – only microwave-safe containers should be used; replace them if they show signs of wear.
• Avoid plastic wrap touching the food – use a sheet of kitchen paper to stop splatter or leave a gap for steam to escape.
• Minimal water for veges – to retain colour, crunch and vitamins.
Microwave ovens aren’t the nutrient-destroying villains of internet legend. When used properly with minimal water, short cooking times and appropriate containers, they can be a quick, safe and nutrient-friendly way to cook.
