You might often hear 'cooking destroys all nutrients, it is best to consume raw', but this might not be the case for all types of veggies.
Certainly, many cooking methods alter the nutritional composition of vegetables, where essential nutrients such as vitamin C, vitamin B1, and polyphenols can be reduced or lost completely.
Marjorie Green, qualified dietitian and founder of Finally Slim Forever, and Marita Moore, dietitian and founder of Lotus Fitness Academy, give some tips about the best way to cook your vegetables to retain the most nutrients.
Keep it raw
Many vegetables of the Brassica family – such as broccoli, cauliflower, cabbage, brussels sprouts and kale – are known for their powerful anti-cancer chemicals called ‘glucosinolates’. The Brassicas also contain an enzyme called ‘myrosinase’ which provides protection against bacteria and other fungi and harmful organisms.
Green explains: ‘These health-giving compounds are released when the plant is chewed, or crushed. Cooking destroys enzymes and your body will struggle to use the glucosinolates from cooked Brassicas.’
Of all the vegetables, the one that produces really important nutrients when eaten raw, is onion, believes Green. ‘Chopping a raw onion releases anti-inflammatory, and anti-cancer substances called ‘organosulfides’: the compounds that make you cry when you are chopping a raw onion. Heat can deactivate these substances’.
Onion also contains an important nutrient which is great for curbing hunger, says Moore. ‘When eating raw onion, you get the most of this phytonutrient allicin’.
Mix cooked and raw
There is no single formula or preparation method that works for all vegetables. And certainly ‘eat all raw’ is not necessarily a golden rule. In general, experts recommend having a mix diet of both raw and cooked vegetables because research has shown that while cooking can degrade some nutrients, it can enhance the availability of others.
This applies in the case of peppers, spinach, carrots and other vegetables high in vitamin C. When cooked or heated, these vegetables can lose some vitamin C content. This is especially true when the vegetables are boiled because vitamin C and other nutrients such as vitamin B1 and folate are leaked into the water.
However, a 2008 report in the Journal of Agriculture and Food Chemistry found that cooking preserves antioxidant compounds, particularly carotenoids, in carrots, courgette and broccoli. Carotenoids are important because they decrease the risk of disease, particularly certain cancers and eye disease.
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Basically, these vegetables have benefits both cooked and raw.
Green recommends following a tip she learned while living in France. ‘The French seem to have an innate understanding of how to get the best from food,’ she says.
In France, it is common to begin a meal with a plate of raw cruditées: broccoli and cauliflower florets, carrot sticks, mixed strips of pepper, tomatoes, olives. In the middle of the plate, there is usually a dip of aioli (a garlic and olive-oil paste). This is then followed by a meal including cooked veggies.
‘This is a very healthy way of providing your body with nutrients and enzymes, which will help you digest the cooked food in your next meal’, she says.
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Heat it up
Raw vegetables are not always healthier, according to our experts. Green recommends eating tomatoes and mushrooms cooked, instead of raw.
‘Cooking tomatoes breaks down their thick cell wall and releases the cancer finding property ‘lycopene’’, she explains.
Lycopene is a red pigment found in tomatoes and fruits such as watermelon, ping guava and papaya. Studies have shown that a high consumption of lycopene is associated with a lower risk of cancer and heart attacks.
One 2002 study published in the Journal of Agriculture and Food Chemistry found that actually cooking boosts the amount of lycopene in tomatoes. Rui Hai Liu, author of the study and associate professor of food science at Cornell University told ScientificAmerican.com that the level of one type of lycopene, cis-lycopene, in tomatoes rose 35 percent after he cooked them for 30 minutes.
In the case of mushrooms, when cooked they release powerful polysaccharides thought to inhibit tumour growth, says Green.
Moore adds to the list: asparagus. ‘When heated asparagus increases in cancer fighting antioxidants”.
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Boil, steam, saute or pressure-cooking
When we are facing this difficult decision, experts recommend to follow this simple rule: Try to keep cooking time, temperature and the amount of water to a minimum.
That is why steaming and pressure-cooking may be better than boiling.
As said before, boiling vegetables may cause important nutrients to leach into the water. ‘However, a way to preserve these nutrients is to use the water for sauces, soups or shakes’, says Moore.
Steaming vegetables has been found to be one of the best ways to cook. A 2009 study prepared broccoli using five popular methods - boiling, microwaving, steaming, stir-frying and stir-frying/boiling. The study found that steaming kept the highest level of nutrients.
Sauteing can also be healthy because many of the vitamins and nutrients in vegetables are fat soluble, meaning the body absorbs them better in the presence of fat. ‘The best oils for cooking are avocado and coconut oil’ according to Green/
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Another method for cooking that appears to be back in fashion is pressure-cooking, says Green. ‘Many people were wary of using a pressure cooker to cook food as they believed the high temperature would destroy more nutrients. However, pressure cookers actually cook at a lower temperature than most other methods. They do it more efficiently’, she explains.
‘A study found that pressure-cooking preserved nutrients in food more than other cooking methods. Since pressure-cooking doesn’t require a much higher temperature and shortens the cooking time, there is less time for nutrient loss,’ she adds.
(Images: Getty)
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