Nutrition is most certainly an evolving science. No one claims to know ALL the answers (and if someone does make such a claim then they shouldn't be trusted). I pride myself on being nonjudgmental of new dietary theories, and I am constantly learning each and every day. I am largely a supporter of raw foods, and I try to keep my diet at about 70-80% raw plant foods. There are, however, some foods I just can't bring myself to eat raw; one of these is my beloved sweet potatoes.
With fall now in full swing, I know they will be showing up more frequently on my plate. I tend to cook more of these grounding root vegetables with the change of season, and I have yet to find a tasty way to prepare them in raw form. That said, I have to admit I was quite pleased to read a recent research study that actually touted cooked sweet potatoes as more nutrient rich than their raw form!
The sweet potato has long been identified as a rich source of beta carotene, which is converted to Vitamin A in the body. One key factor in how much will be converted to vitamin A is the bioaccessibility of the beta carotene. Another factor is the retention of the nutrient, as often vital nutrients are lost, or degraded, in the cooking process. The study, which was published in the journal "Plant Foods for Human Nutrition", compared the bioaccessibility of beta carotene in sweet potatoes in their raw form, and also after preparation through baking, steaming/boiling, and deep frying. It was determined that highest level of bioaccessibility of beta carotene was found in.... drum roll... deep fried sweet potatoes! Yep, that means I don't have to feel guilty about eating favorite "junk food" treat; sweet potato fries.
The next best was steamed/boiled, followed by baked, and coming in last place was raw sweet potatoes. Although the heat processing did result in a decrease in beta carotene retention, this loss was more than compensated by the improved availability of beta carotene due to the change in micro structure of the cell walls.
Since deep frying proved to be the best preparation method, this result can most likely be attributed to the addition of fat in the frying process. Vitamin A is a fat soluble vitamin, which means that it needs fat in its presence to be absorbed and digested optimally. It would make sense then, that it's precursor, beta carotene, fairs better in the presence of fat as well. So what does this all mean? Well I'm certainly not saying that raw isn't an optimal way to ingest MANY plant foods, and I do plan to continue to eat mostly raw, since I feel good eating that way. But this study raises some interesting questions; hopefully ones that will be explored and researched even more thoroughly. But in the meantime, bring on the sweet potato fries please!
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Photo credit: cc: flickr.com/photos/wallyhartshorn