Are Potatoes Bad for Psoriasis Sufferers? The Paleo View
Anecdotal reports suggest that some people with psoriasis feel better when they avoid potatoes. Of course, anecdotal evidence won't stand up to peer review, but if you suffer from psoriasis, it probably won't hurt to give a potato-free diet a try. And, in the best case, you might even notice an improvement in your condition. You see, while there are no peer-reviewed studies proving, or disproving, that potatoes can cause psoriasis flare-ups, we do know that potatoes contain compounds that may be problematic for people with autoimmune diseases and inflammatory conditions (note that we are talking about regular potatoes here, not sweet potatoes). As psoriasis is an inflammatory condition with autoimmune origins, it is easy to see why potatoes may be a trigger food for some psoriasis sufferers.
As far as the potential autoimmunity-promoting and inflammation-causing properties of potatoes go, there are two groups of compounds that are believed to play a major role: glykoalkaloids and lectins. To learn how these "anti-nutrients" might be contributing to your psoriasis, keep reading.
Potato Anti-Nutrients, Leaky Gut and Psoriasis
Alpha-solanine and alpha-chaconine, the primary glykoalkaloids found in potatoes, act as natural pest repellents in potato plants, reducing the risk of the plant being eaten by predators. When consumed in large enough amounts, these compounds are also toxic to humans; however, the amounts you find in properly stored and prepared potatoes are usually so small that most healthy people can eat them without problems, especially if they eat their potatoes peeled (most of the potato glykoalkaloids are in the peels).
That said, some experts believe that in people with autoimmune diseases, such as psoriasis, potato glykoalkoloids might cause problems even when consumed in relatively small amounts. When mixed with water, alpha-solanine and alpha-chaconine create soap-like foams which can create holes in the lining of an already damaged gut. This state is known as "leaky gut", or increased intestinal permeability, and a growing body of evidence suggest that it is particularly common among people with autoimmune conditions such as psoriasis. The problem with a leaky gut is that it allows various undigested proteins and microbes to enter the bloodstream through the holes in the gut lining, which in turn stimulates the immune system and promotes chronic low level inflammation.
To make matters worse for psoriasis sufferers and people susceptible to food sensitivities, potatoes also contain lectins, another class of anti-nutrients that help protect plants against predation. According to Dr. Loren Cordain, author of The Paleo Answer, preliminary tissue studies suggest that potato lectins resist degradation by gut enzymes and are capable of bypassing the gut barrier. They have also been found to irritate the immune system and produce symptoms of food hypersensitivity in allergenic as well as non-allergenic patients.
Should Psoriasis Sufferers Be Wary of (or Avoid) Sweet Potatoes?
For the reasons stated above, some people with psoriasis might reap benefits by avoiding potatoes and other nightshade vegetables including tomatoes and peppers (note that black pepper or peppercorn is not a nightshade). But before you eliminate all potatoes from your diet, know this: sweet potatoes are not a member of the nightshade, or Solanaceae, family of plants. In fact, sweet potatoes, which are part of the Convolvulaceae family, are considered hypoallergenic, meaning that they are relatively unlikely to cause allergic reactions. These nutritious tubers also star in many recipes featured in Sarah Ballantyne's cookbook, The Healing Kitchen.
Now, for those who haven't heard of Ballantyne, she is a scientist turned stay-at-home mom, bestselling author, and one of the most famous advocates of the Paleo Autoimmune Protocol (Paleo AIP), an elimination diet designed to uncover food sensitivities in people with autoimmune diseases such as psoriasis.
Orange-fleshed sweet potatoes are also an excellent source beta-carotene, and research shows that some sweet potatoes contain even more beta-carotene than carrots. An interesting observational study published in the British Journal of Dermatology found an inverse association between the incidence of psoriasis and the intake of beta-carotene from foods. It is important to note, however, that it is impossible to say whether beta-carotene is protective against psoriasis merely based on an observational study as these types of studies are designed to identify associations rather than causal relationships. But while we wait for other studies to come in, it probably won't hurt to start eating more beta-carotene rich foods, such as orange-fleshed sweet potatoes, especially if you have been neglecting them in the past.
References:
T. Kuiper-Goodman and P. Nawrot. Solanine and Chanonine. Bureau of Chemical Safety, Health and Welfare Canada. Link
L. Cordain. Consumption of Nightshade Plants, Human Health and Autoimmune Disease. Link
L. Naldi et al (1997). Dietary factors and the risk of psoriasis. Results of an Italian case-control study. British Journal of Dermatology, 134(1), 101-106.
For More on Diet & Psoriasis
Make it a habit to visit HealWithFood.org's online Guide to Healing Psoriasis on a regular basis. Updated once a week, the sidebar on the home page of the guide contains tons of links to interesting nutrition-related articles hand-picked for psoriasis sufferers. It also contains a weekly smoothie recipe featuring ingredients with psoriasis-fighting potential, as well as a book tip. 
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In her New York Times bestselling book, The Paleo Approach, Sarah Ballantyne draws upon cutting-edge research and her own battle with an autoimmune disease to provide you with a comprehensive Paleo-based diet and lifestyle plan for regulating the immune system and healing damaged tissues. Known as the Paleo Autoimmune Protocol, Ballantyne's groundbreaking plan emphasizes nutrient-dense foods and removes foods that promote inflammation and leaky gut syndrome. Also foods that stimulate the immune system are restricted on the AIP. In addition to explaining how eating certain foods and avoiding others can help put your condition into remission, this 400-plus page tome provides expert tips on how to "go Paleo" easily and economically. To learn more, or to order a copy, click here.
