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The message that we should all include more vegetables in our diet – five serves a day – is well known, but is the way we prepare and eat them also important?
Have you ever wondered, when chopping that colourful array of vegetables, how much of their nutrient content survives the storing, prepping and cooking process? Alternatively, do some cooking methods actually promote the health benefits of some vegetables?
“Depending on the cooking method and what things are cooked in, the levels of some nutrients can be affected, both positively and negatively,” says Clare Evangelista, accredited practising dietitian and spokesperson for the Dietitians Association of Australia.
Heating can destroy some nutrients, while others are leached out in the water that the vegetables are cooked in.
Vitamin C, for example, is heat-labile, which means it starts to deteriorate as soon as the vegetable is heated. A fragile vitamin, C also dissolves in water.
“When boiling, nutrients can actually leach out of the vegetable into the water; particularly water-soluble nutrients like vitamin C and B,” explains Evangelista.
Fat-soluble nutrients – vitamins A, D, E and K – are more stable than water-soluble vitamins and are better retained during cooking.
The cooking methods that are the healthiest for us and that retain the most nutrients are steaming, boiling in just a small amount of water or very quick blanching. The key is to only cook the vegetables for a short amount of time so that less of the vitamin content dissolves.
But that doesn’t mean we have to steam our vegies every time. In fact, the experts tell us not to limit ourselves to just one or two cooking methods because variety, taste and texture are what motivate us to fill our plates with more vegetables in the first place.
“Use a variety of cooking methods and presentation forms. For example, incorporate salads as well as cooked vegetables into your day,” says Evangelista.
No matter what cooking methods you use, follow these tips to get the best out of your vegetables:
Foods containing carotenoids are actually better for us when they have been lightly cooked.
Carotenoids, a type of antioxidant, are stored inside the cells of the vegetable so when they are cooked the cells break down and the nutrients are more easily absorbed by our bodies, explains Associate Professor Catherine Itsiopolous, head of dietetics at La Trobe University and a practising dietitian.
Examples of these carotenoids are lycopene, found in tomatoes, and lutein, found in broccoli and dark-green leafy vegetables such as spinach.
Chopping these vegetables and blanching, steaming or simmering them in soups and casseroles increases the concentration of the antioxidants that are absorbed by the body.
While chargrilled and deep-fried vegetables (i.e. chips and tempura) often whet our appetites, they should be limited – and not just to benefit our waistlines.
Browning and caramelising foods creates chemical compounds called Advanced Glycation End Products (AGEs), which have been linked to an increased risk of developing age-related diseases such as cataracts, Alzheimer’s Disease, heart disease and stroke.
In particular, people with conditions such as diabetes or chronic renal disease should limit their intake of heavily browned or caramelised foods, says Itsiopolous.
“We know from studies that people with diabetes have significantly higher levels of AGEs than anyone else,” she says.
Also, because AGEs are cleared from the body through the kidneys, they can start to build up in people who have poor kidney function or chronic renal disease.
The good news is that because vegetables are low in sugar and fat they don’t produce as many AGEs as other foods, such as meat. (Hot potato chips are the exception as their high carbohydrate and fat content make them high in AGEs.)
Itsiopolous also stresses that people shouldn’t feel they can’t enjoy caramelised or grilled vegetables occasionally.
“The research on AGEs is relatively new and we don’t want to put the message out that any browning is dangerous because we don’t know the long-term effects,” she explains.
So while it’s best not to have browned vegetables or hot chips every day, enjoying them once a week is fine.
And finally, don’t forget that the battle to get the most out of your veg starts before you’ve even begun to make dinner.
While the nutrition content is highest 24 to 48 hours after a vegetable is picked, eating this fresh all the time is just not practical – or possible – for most of us.
Fortunately, storing vegetables correctly can help retain most of the nutritional content.
The NSW government has some great storage tips on its Love Food Hate Waste website.
But a simple rule of thumb is that most vegetables last longest in an airtight bag or container in the fridge.
Here are some other storage tips to consider.
When choosing how to prepare vegetables, it’s all about balance, explains Evangelista.
“You would be very bored if you only cooked vegetables a certain way each time to retain nutrition,” says Evangelista.
And it’s worth remembering, the key to good health still lies with getting enough variety and volume of vegetables into our diet.
“The old adage of eating a variety of fruit and vegetables every day and using them in a variety of ways really is the easiest and best message.”