1. The Trouble With Nightshades. Maybe.
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A Field Guide to the Curious Clues of Nightshade Sensitivity

My family has been cooking without potatoes, tomatoes, and peppers for 10 years now. I wanted to share these no nightshade cooking experiences earlier, but some confusticating science slowed me down.

TL;DR Can nightshades harm human health? Skepticism is justified, yet many nightshade plants produce bioactive substances. These may affect the gut, the nervous system, and the immune system. This document collates that information in the hope that medical science will connect the dots.

If you care at all for the opinions of doctors or scientists, having a nightshade sensitivity puts you in an awkward place between modern medicine and personal experience. In short, nightshade sensitivity is considered quackery. I write about science and medicine for a living, so credibility in this arena matters a great deal. But sometimes science lets us down, in classic where’s-my-jetpack fashion.

The argument is quite simple: We know that nightshades—including potatoes, tomatoes, peppers, and eggplants—all contain many bioactive compounds, some of them poisonous. That cannot be disputed. We also have very good reason to believe that most people are not significantly affected by these compounds at their usual levels. But there is evidence that they bother some biological systems, and some people. We don’t really understand how it happens. That doesn’t mean it’s not happening.

One Family’s Nightshade Puzzle

When I first discovered my son’s apparent nightshade problem, I was certain I’d find a paper trail blazed across 50 years of digestive disease research. After all, I’d used basic scientific thinking to figure it out. I closely observed his diet and subsequent symptoms. That led to the hypothesis that nightshades were causing the pain and bleeding. We removed nightshades and the worst symptoms quickly faded away.

We accidentally replicated the experiment several times in the following months when he was exposed on vacation and at school to foods containing nightshades. Agony returned. In a perfect world, we would have tested him against every nightshade, at different amounts, and at different time intervals. Unfortunately his autoimmune conditions are serious enough not to risk such provocation. It was more important to let him heal. Then, over the next few years, other family members discovered they also had problems with nightshades.

That sealed it for us. We didn’t expect a Nobel Prize or anything, but it felt like a very logical conclusion.

I assumed that medical science, with its more sophisticated toolkit, must know more. But when I tackled the literature there were few breadcrumbs. Not only was there no clear and obvious trail, there was a lot of professional static in the literature. This matched the overall disinterest from the specialists we encountered. Only later did I learn that the literature of food sensitivity included a not completely unjustified tendency to wonder if that sensitivity might just be in our heads.

Medicine is always evolving—for example we know a lot more about gluten and health than we did 10 years ago. But when I started looking for nightshade information online most of what I found that supported our experience seemed to come from the DIY, self-help, infomercial school of medicine. That’s changing, but reputable medical information sites still extol, without reservation, the virtue of spicy foods. They suggest potatoes as part of a bland diet for intestinal distress. A WebMD slide-show casually labels links between nightshades and rheumatoid arthritis as mythical. (Evidence is tenuous and limited, but does actually exist.)

Still, skepticism around diet and health claims is a good scientific and business practice. Dietary delusions have been the foundation of quackery for centuries. Even among the most credentialed scientists there is continuous and shifting debate about the precise role of of fat, protein, and carbohydrates in diet and health. You may know the joke: If you don’t like the dietary advice in today’s paper, just wait three months.

So, what’s a science writer to do when an evolutionary plant biologist immediately grasps how nightshades could have negative health impacts but your medical doctors mostly shrug? Keep reading. Be thorough. Be patient.

And over the last ten years the needle has moved. The medical literature now fully acknowledges how significant a role diet can play in GI maladies. We understand more about how particular foods are good, and how some foods aren’t so good, and how different people can respond differently to the same foods. Research validating elimination diets as a diagnostic tool is gaining traction. Research exploring connections between GI disorders, autoimmunity, and the microbiome is rapidly advancing and opening new vistas—some of which might help explain nightshade sensitivity.

Still, a definitive, causal explanation for nightshade sensitivity does not, in my opinion, exist.

Where does that leave you if you’ve figured out that you’re nightshade sensitive?

Maybe that discovery is all you need. But maybe you’re like me, and really want to know why. I’ve assembled this reference essay for those interested in finding a clear scientific explanation of the role of nightshades in health. What follows is a brief chronicle of the scientific ideas and literature, along with some speculation about how nightshades might cause health problems. Critiques and additions are welcome. This is a live document, subject to change. I’ve tried to footnote all sources, but if something is missing that you want to follow up on, please ask.

NEXT: Nightshades—Just Side Effects?

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