Myth
What the research says
Raw vegetables are healthier than cooked.
While some vegetables are more nutritious eaten raw , there is also evidence that we absorb certain important antioxidants (such as the beta-carotene in carrots and the lycopene in tomatoes) better when these foods are cooked particularly along with some healthy fat, such as olive oil.
Cooking destroys all the nutrition in vegetables.
The way you cook your foods can certainly have a significant effect on the final nutrient content of your meal. Overcooking can lead to a loss of many vitamins but there are also some nutrients which are improved by cooking. For example, cooking carrots has been found to increase the availability of beta-carotene.
All vegetables should be eaten raw.
It depends on the vegetable in question. Some vegetables really need to be cooked to be edible (think potato and sweet potato) while some are better raw (such as most salad vegetables) and others are a nutritious choice raw or cooked. The best option is to include a variety of raw (such as salads) and lightly cooked (such as steamed or stir-fried) vegetables. Choose a variety of different vegetables and salads each week, aiming to make your plate as colourful as possible.
References:
https://www.ncbi.nlm.nih.gov/pubmed/14673607
https://www.sciencedirect.com/science/article/pii/S146685640700046X
https://pubs.acs.org/doi/abs/10.1021/jf0115589
https://www.ncbi.nlm.nih.gov/pubmed/15927929
