A StomperNet friend tweeted a link on differences cooking makes in available nutrients in carrots. Here's the link itself: http://news.bbc.co.uk/1/hi/health/7998801.stm . What the researchers found was that cooking carrots increased the beta-carotene absorbed over that available in raw carrots.
This has been known in 'standard' nutritional circles here in the US for a while - I have to assume that the British study brought something new to the party that the news report didn't cover. That fat-soluble vitamins held in hard cellulose structures (raw veggies and fruits cells) are more available after cooking is so well known that it's even cited on Whole Foods website, with scientific references to 2002 and before.
Of course, while cooking breaks down those cellular cellulose walls, cooking and any water the veggies are cooked with tend to destroy and/or wash out the water soluble vitamins such as C and B complex.
What does this mean for your home kitchen?
I'll tell you.
Well, at least I'm going to make some SWAGs - Scientific Wild-Ass Guesses.
Winter Cooking SWAGs
My guess is that especially over winter, eat your sources of Vitamin C raw - it is not widely spread in most winter season foods. Especially if you're eating stored local food, since vitamin C oxidizes away over time. In fact, if you're eating locally over winter your main sources of fresh vitamin C foods are likely to be bean/seed sprouts that you've exposed to the sun so they develop some green and vitamin C and any green onions you grow.
Your B vitamins don't oxidize away as quickly as the C does, for the most part. Some will be in your stored fruits and veggies, even dried/frozen/canned, lots of some of them in whole grains.
And cook most of your high-carotene veggies - sweet potatoes, hard squash, etc.
Summer Cooking SWAGs
Who wants to cook in summer? It's hot and humid here. Eat stuff raw if that's good for your taste/body. Do minimal cooking, early in the day when it's cool, and serve things chilled. Just because that's how *I* like to eat during the summer [grin]. And with all the fresh produce around, you'll get enough beta carotine from strawberries, then cherries, then muskmelons and peaches, etc. Not to mention the lovely spring greens, followed by fresh peas and pea pods, then beans, then peppers, then tomatoes, etc.
I'm fond of taking a multipurpose vitamin supplement daily in winter when the range of foods isn't as large or has a lot of food-miles and age on it. Since I buy cheap generics, it's sort of cheap insurance here. OTOH, humans have survived for 15,000 or more years dealing with cold winters, lousy food storage, etc without them. Without chocolate too, I might add, and that I REALLY don't understand.
Catch you later!