Purple Sweet Potatoes, More Great News; Exemplifying the possibilities offered by deeply colored vegetables

The term superfood gets thrown around too much.  Many of the foods are great for one reason or another but they seldom provide enough bulk to our diet (such as starch, other macronutrients, and/or fiber) to go along with their exceptional antioxidant content.  We would be hard-pressed to acquire a significant amount of our daily energy from many of the most popular foods featured on the Dr. Oz show.  Mangosteen, cacao, green coffee beans, blueberries, acai, and green tea are all amazing in one way or another, but they should never constitute a significant percentage of what we eat daily.  True superfoods would be those that offer much more than a unique antioxidant or polyphenol content, but that also provide an additional foundation of nutrients, and that are compatible with human physiology on multiple levels.  The lack of difficult-to-digest anti- nutrients, and possessing low levels of sugar and polyunsaturated fats are critical characteristics.  The superfood should also be highly supportive of our micro biome and foster the growth of beneficial organisms while inhibiting the growth of potentially pathogenic ones.

These are all characteristics shared by a handful of foods, many of which have supported populations and entire cultures for thousands of years.  The purple sweet potato is maybe the best example I can think of.  After 20 years of research, teaching, and clinical experience, I would struggle to come up with a better staple to our diet.  New research strengthens the potential of this root vegetable in offering us daily nourishment on so many levels.  Purple sweet potatoes, and all sweet potatoes to a significant extent, are incredibly diverse in the array of macro and micronutrients they carry. Vitamin E, selenium, carotenoids, anthocyannins, magnesium, high levels of potassium, and fermentable fiber are just the highlights.  Their contributions are so great that when offered to animals as a modest percentage of total energy intake, they reverse disease processes (1).

At least part of their effect is due to how selective they are at shaping intestinal flora populations.  Bifidobacterium populations are essential for good health. Many of us need considerable help in sustaining bifidobacter levels that are protective against inflammation, diabetes, and numerous chronic diseases.  The resistant starch and fiber qualities, coupled with the polyphenolics, in purple sweet potatoes not only help grow bifidobacterium but also inhibit the growth of specific microbes that can cause GI distress and inflammation.  Purple sweet potatoes have demonstrated significant antimicrobial effects towards Clostridium and Prevotella species known to cause GI issues.

There are places where the nutritional value of sweet potatoes is not lost and where their daily consumption is emphasized. The Okinawans for to instance, noted for their longevity and low risk for chronic disease, eat several sweet potatoes weekly, many of which are purple. Areas of Korea, also high in centenarians, are equally fond of the tuber.

As an aside, every year, the Environmental Working Group (http://www.ewg.org) puts out two lists called “The Dirty Dozen” and “The Clean Fifteen,” which ranks conventionally-grown foods based upon the level of pesticides they contain. Sweet potatoes are members of the “Clean Fifteen” group which is good news for all of us!

~ John Bagnulo MPH, PhD.

Reference:
1. Ju R and Zheng S. Purple Sweet Potato Attenuate Weight Gain in High Fat Diet Induced Obese Mice. J Food Science 2017 March;82(3):787-793.

2. Zhang X et al. The Modulatory Effect of Anthocyanins from Purple Sweet Potato on Human Intestinal Microbiota in Vitro. Journal of Agriculture and Food Chemistry 2016 March 30;64(12):2582-90.