Watch out for moldy sweet potatoes?!?

By Susannah F. Locke | Posted December 15, 2007
Posted in: Life Science Blog

At Thanksgiving, a family friend used to warn us to never eat sweet potato skins. This November, when I found myself in the yearly ritual of warning friends of the dangers of sweet potatoes, I decided it was time to track down this factoid once and for all.

According to Toxicants Occurring Naturally in Foods (National Academy of Sciences, 1973), sweet potatoes can churn out a bunch of nasty chemicals in response to fungi and other foes. I haven’t found any reference to skins, although it makes sense that this would be the front of the fungus versus sweet potato war.

These chemicals include ipomeamorone, which has caused serious liver damage in animal studies, and other toxins that have caused lung problems among herds of animals that have eaten moldy sweet potatoes. But I didn’t find any mention of people having sweet potato problems (maybe we’re less likely to binge on moldy tubers?).

Looking at ipomeamarone levels in sweet potatoes from the supermarket and toxicity data, it looks like one good-lookin’ potato could kill . . . about a seven-pound weakling. (But could liver damage perhaps accumulate over a lifetime of consistent skin-eating? I don’t know.) People are still studying ipomeamarone today.

Apparently baking your sweet potatoes won’t completely rid them of creepy chemicals, so I guess I’ll make sure that any I ingest are free from signs of disease. And I’ll probably skip the skins.

For more info, you can check out the Handbook of Natural Toxins (1983), which is on Google Books.

Posted in: Life Science Blog
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  1. Wow great article. I’d always wondered if eating potato skins were safe. Thanks for the amusing blog.

    Marti, December 16, 2007 at 1:34 am

  2. Does this hold true for yams too?

    Karina, December 16, 2007 at 3:03 pm

  3. Fascinating! I have noticed a bluish substance — like bread mold? — on broken ends of uncooked sweet potatoes. This confirms my instinct to trim it off.

    Ralph, December 16, 2007 at 6:45 pm

  4. As far as I can tell, it doesn’t hold true for yams, which are an entirely different species altogether. Everything I’ve read has been “sweet potato, sweet potato, sweet potato.”

    “Toxicants Occuring Naturally in Foods” mentions that yams don’t make these chemicals when moldy, but they didn’t include a citation for it.

    I don’t even think I’ve ever eaten a true yam, though.

    Susannah F. Locke, December 16, 2007 at 7:50 pm

  5. Interesting, especially since the skins are often served.

    Clara, December 17, 2007 at 12:31 pm

  6. I’ve always peeled my sweet potatoes, for reasons unknown to man (primal instinct? mom said to one day and I filed it away?). Strange, as I tend to enjoy normal potato skins in my food, and it would follow that potato skins that are delicious in one way would be good in another way, too…but thanks for saving my LIFE in case I ever was going to binge on sweet potatoes. Bagfuls.

    Ali, December 19, 2007 at 3:08 pm

  7. In response to Ralph, the Japanese noted that the potato needed to be damaged in order to find the toxin:

    “Ipomeamarone 15-hydroxylase activity was not found in fresh tissue of sweet potato roots. However, the activity appeared and increased markedly in response to cut-injury.” This comes from a paper titled “Properties of a Mixed Function Oxygenase Catalyzing Ipomeamarone 15-Hydroxylation in Microsomes from Cut-Injured and Ceratocystis fimbriata-Infected Sweet Potato Root Tissues” written by Masayuki Fujita, Kazuko Ôba, and Ikuzo Uritani from the Laboratory of Biochemistry, Faculty of Agriculture, Nagoya University, Chikusa, Nagoya 464, Japan, and published in the journal Plant Physiology.

    Great observation, Ralph.

    Victor, December 23, 2007 at 7:26 am

  8. Great article! I was always told as a child to eat the skins, but (rebellious me, I guess!) I didn’t like them. And since I’ve done my own shopping, I have noticed discoloration, and have continued not eating the skins. Fascinating (and a bit frightening) to know what that discoloration can indicate. Many thanks!!

    Louise, December 23, 2007 at 9:25 am

  9. I suggest you check out the link here that tells exactly why you SHOULD eat sweet potatoes skins.
    http://www.whfoods.com/genpage.php?tname=foodspice&dbid=64.
    “three times the antioxidant quantities found in the skin than in the flash of the sweet potatoe”.

    Mike, October 8, 2008 at 2:32 am
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