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We've all been told that eating vegetables raw is better for you as uncooked veggies contain more nutrients than ones which have been exposed to heat.

But while this might be true of some produce, it's not a one-size fits all rule.

In fact nutritionists are now saying that cooking some vegetables frees up more nutrients for your body to absorb, the Daily Mail reports. 

Tomatoes, spinach, carrots, asparagus and mushrooms are five vegetables and fungi which are much better for you when consumed cooked.

Mel Wakeman, nutrition expert and Senior Lecturer in Applied Physiology at Birmingham City University told FEMAIL: 'Many of the nutrients found in plants are often less readily absorbed in the gut compared to nutrients derived from animal products.

'The fibre found in plants often binds particularly to minerals and makes them less available for the body to use (their bioavailability).

'Heating can help to breakdown the fibre and so release some of the minerals for absorption, and can often increase the phytochemical content of plants which can provide additional non-nutrient benefits to our health.'

According to Ms Wakeman, heating tomatoes increases the levels of lycopene in the fruit, which has been shown to reduce the risk of prostate cancer.

However she advises against only eating cooked tomatoes as heating destroys other vitamins.

'Tomatoes are rich in many nutrients but one is of particular interest to men's health - lycopene has been shown to reduce the risk of prostate cancer,' she said.

'Although inconclusive at the moment there are also suggestions lycopene may also improve heart health. Heating tomatoes increases the levels of lycopene in tomatoes. I would advise against only eating cooked tomatoes as heating does destroy other important vitamins (such as Vit C) so simply have a mixture of cooked and raw tomato products.'

Spinach is rich in oxalates that will bind to valuable minerals in spinach such as iron and calcium.
Both fibre and oxalates can make iron particularly difficult to absorb and we may only get around five per cent of the iron content from many dark green leafy vegetables.

'Heating spinach can help but may not make a significant difference (possibly only reducing oxalate content by up to 15 per cent,' Ms Wakeman explained.

However, it is important not to overcook spinach as other nutrients are lost.

'Light cooking or wilting is certainly better than boiling when the nutrients leach out into the pan and get washed away when we drain the veg,' she added.

Carrots are rich in carotenoids which give them their vivid orange colour. Heating carrots can increase the carotenoid content which can provide many benefits as they have powerful antioxidant properties.

'Again, avoid overcooking,' Ms Wakeman advised.

'Microwaving and steaming often help to retain the nutrient content of veg, rather than boiling. Eat a mixture of raw and cooked carrots too.'

Heating asparagus may help to increase nutrient bioavailability and their polyphenol content.

'Polyphenols - also found in tea, red wine and chocolate - have strong antioxidant properties and provide beneficial effects in terms of risks of heart disease and cancers for example,' she clarified.

Mushrooms contain reasonable amounts of vitamins and minerals.

'Cooking may improve their nutrient value but because they soak up oils like sponges, be wary of the amount of fat you use when cooking,' Ms Wakeman said.

'Common wisdom says cooked food has lower nutritional value compared to fresh produce, but that's not always true,' said Rui Hai Liu, a professor in the department of food science at Cornell University who studied how heat affects food, said to The Washington Post.

'Many nutrients in fruits and vegetables are bound in the cell walls,' he explains. 'Cooking helps release them, so they're more bioavailable and absorbed by the body.'