Nightshade vegetables: Hazard or health food?

Nightshade vegetables — even the name is ominous. Some people believe that they worsen arthritis and cause inflammation. So, should we avoid them?

In today’s short episode of ZOE Science & Nutrition, Jonathan and Will ask: What are nightshade vegetables, and how can they benefit our bodies?

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Episode transcripts are available here.

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[00:00:00] Jonathan Wolf: Hello and welcome to ZOE Shorts, the bite-sized podcast where we discuss one topic around science and nutrition. I'm Jonathan Wolf, and today I'm joined by Dr. Will Bulsiewicz. And today's subject is nightshade vegetables.  

[00:00:17] Dr. Will Bulsiewicz: These veggies have gotten a really bad rap. Some celebrities avoid them. Others claim that they make their arthritis worse or they cause inflammation. 

[00:00:26] Jonathan Wolf: So Will, I don't even know what a nightshade vegetable is. Is this something else I've got to start worrying about or is it just a load of nonsense? 

[00:00:36] Dr. Will Bulsiewicz: That's exactly what we're going to look at. And spoiler alert, our investigation involves green potatoes. 

[00:00:43] Jonathan Wolf: Green potatoes do go on. So Will, what are these mysterious-sounding nightshade vegetables? 

[00:00:51] Dr. Will Bulsiewicz: So, Jonathan nightshades are plants from a large family of plants called Solanaceae, and the group includes more than [00:01:00] 2000 varieties. The group also includes many common vegetables like tomatoes, peppers, potatoes, and eggplant, which of course you would refer to as an aubergine. Nightshades are found in plenty of our usual sauces and spices as well, Jonathan. So classic condiments, like ketchup or hot sauce or some of the spices that we often reach for garam masala and paprika, and then tobacco. Many people don't realize is also a nightshade.  

[00:01:24] Jonathan Wolf: So I think no one listening to this podcast is gonna be surprised they should give up tobacco. But what's the big deal about the rest of this? I mean, I can't even imagine giving up tomatoes. So why do people have this fear around nightshade vegetables? 

[00:01:38] Dr. Will Bulsiewicz: Well, the concern comes from some of the specific phytochemicals or plant-based chemicals that you will find in nightshades, specifically alkaloids or glycoalkaloids that include solanine, capsaicin, or like with tobacco, nicotine. These alkaloids are, um, nitrogen-based organic substances that are produced by plants, and they have [00:02:00] a rather intense impact on both human and animal physiology. I mean, even at low doses, they can affect, um, our physiology. So for humans, that impact in some cases is extremely desirable. But in other cases, it could be toxic or it depends on the dose. It could be both.  

[00:02:20] Jonathan Wolf: So this I do know, so some nightshades are dangerous. So belladonna, uh, is also known as deadly nightshade. And uh, Will was explaining to me earlier that that's because it contains these alkaloids, and I'm sure, uh, many of our listeners remember that scene in Romeo and Juliet, where Juliet fakes her death. So apparently it's thought that this poison would've been Belladonna. And this was sort of well understood at this, uh, time when Shakespeare was writing it, Will. I have my own brush-with-death story about the deadly nightshade, however, and apparently, my mother had driven to like the library in this little car park. I had a little brother who was just a couple of years younger, really little.

[00:03:00] So I got out, my mother was trying to, you know, get this baby out of the car seat and I'd gone over to like the side of the road and there was this, um, deadly nightshade with these beautiful looking berries, and my mother saw it and she's immediately like, Jonathan, you absolutely mustn't eat that. That's poisonous. It's really dangerous. Uh, apparently I looked at her straight in the face, grabbed a whole bunch of these berries, looked directly at her, stuffed them in my mouth, and swallowed them. My mother freaked, grabbed me, put me back in the car, and drove straight to the hospital, they pumped my stomach, I was fine because, you know, it was all dealt with rapidly, but it wasn't a lot of fun.

What I am sure about though, is I'm now very careful about eating berries that I find in the woods. So I, I think that clearly, uh, I understand that deadly nightshade is not a vegetable that we should miss surround with what was going on there, Will? 

[00:03:50] Dr. Will Bulsiewicz: Well, if we talk about poisoning with nightshades, so belladonna being the example, uh, going back to Romeo and Juliet, a person's pupils will become [00:04:00] very dilated. Their heart rate will start to pick up, which we call tachycardia. In some cases, they become very confused or even have hallucinations.

The sort of package of symptoms that I've just described, we have a medical term that we use for this. We call them anticholinergic. So these anticholinergic symptoms actually can be beneficial. So belladonna has been used to ultimately lead to new drug developments. An example of a drug that's been developed and used in this is atropine. I've personally given atropine to patients when they need it. And you give this medicine in that emergency and it gently brings their heart rate back up.  

[00:04:34] Jonathan Wolf: It's amazing. And I guess is a brilliant example of something we talk a lot about on the show, right? Which is sort of food as medicine, but I think it is a sort of example, isn't it, of just thinking about our food as a sort of inert substance, which has just got calories and fat. It's just so far away from the reality of what, you know, we evolve to eat, which is this immensely complex set of different foods with I think we now believe, you know, a hundred thousand chemicals and, [00:05:00] and growing as we're able to, to better measure them. 

[00:05:02] Dr. Will Bulsiewicz: Yeah, who knows how many, to be completely honest with you. I think the other comment on this real quick, Jonathan, is that the dose is important. So, I think again, let's not be fearful of these things where, taken at the right dose, can be extremely healthy and beneficial to us.  

[00:05:16] Jonathan Wolf: Now, all of that said, I think we agree that the appropriate dose of belladonna is probably none, but what about my tomatoes and my peppers, you know, my aubergine? Is it because of this that people are concerned that eating nightshade, and these other nightshade vegetables could lead to health issues?  

[00:05:32] Dr. Will Bulsiewicz: There's no evidence, Jonathan, that consuming these normal nightshade foods that you will find in your supermarket or your farmer's market or you grow in your garden in normal amounts is toxic. There's no evidence for that. And you know, I will say like if there's something that we could have a concern about is green potatoes. When potatoes are exposed to sunlight, the light will turn them green. And that's because this chemical that I referenced earlier, solanine is developing. But um, even in research where they [00:06:00] start feeding people, these glycoalkaloids from potatoes in a controlled way. Even then, there weren't any issues. I mean, you would need to eat a massive amount of effective potatoes to become seriously ill.  

[00:06:12] Jonathan Wolf: Either way, it's funny, this is another one of the things that my mom always told me, you can't eat the green bits on potatoes. I remember. You know, you gotta cut them out. The other thing I read, and we had a lot of questions from listeners about was, what about gut damage from the nightshade chemicals. Is there any risk there?  

[00:06:28] Dr. Will Bulsiewicz: Well, rodent studies have suggested that the glycoalkaloids from potatoes could injure the gut microbiome. Rodent studies are not the same as human studies in these rodent studies. The mouse or the rat may be getting pumped up with concentrated chemical extracts or a completely unnatural diet, and it's not the same as a person who is cooking with a tomato or a pepper.  

[00:06:51] Jonathan Wolf: And I think that's something that. You know, I've heard a lot of scientists talk about on, on this show will it just because there's a study on, you know, [00:07:00] mice or rats that show something happens, you know, very often when you then apply it either to humans and even more so sort of to humans in, in the real world with their normal behavior. You don't see any of the, uh, results that you saw in these, um, these animals. 

[00:07:14] Dr. Will Bulsiewicz: These animal-based studies, Jonathan, are good for building theories or hypotheses. They're good for helping us to understand mechanisms, but they are not proof in and of themselves. We should always move to verify them in human-based studies to ensure that the way that it works in humans is the same as what we see in these, you know, sort of animal models. So people can be sensitive to these types of foods. It may not be because they're nightshades. I mean, let's not necessarily assume that it's the fact that it's a nightshade that's causing the trouble. So in many cases, it's instead a food intolerance that's causing the problem. 

[00:07:52] Jonathan Wolf: Good. So I don't need to give up my tomatoes. I'm very happy about that. Um, could any of these sort of alkaloids and other [00:08:00] chemicals in these, um, plants we're talking about actually be helpful for our guts?  

[00:08:04] Dr. Will Bulsiewicz: A hundred percent. I mentioned earlier that one of the alkaloids is capsaicin, which is a part of the pepper that makes it have heat or spice, and there's a significant amount of research, in my space as a gastroenterologist, Jonathan, with irritable bowel syndrome, where people with irritable bowel syndrome, who took a capsaicin supplement saw significant improvements in their abdominal pain and bloating when compared to a placebo. So, uh, capsaicin, by the way, is also commonly used to treat joint pain. You can find capsaicin at your local drugstore, and it's intended for people to have arthritis.

And if we go back to potatoes for a moment, there are some redeeming qualities for potatoes. There are ways in which potatoes are really good for our gut microbiome, and that's because potatoes are very high in what's called resistant starch. It's able to escape digestion, passing through the intestine. And it gets broken down by our gut microbiome in our colon, and it releases in a powerful [00:09:00] way, short-chain fatty acids like butyrate. And we know from our research that these short-chain fatty acids are beneficial to our health. 

[00:09:05] Jonathan Wolf: So will, having seen what happens to my blood sugar when eating a potato, you're going to have to be very convincing here.  

[00:09:12] Dr. Will Bulsiewicz: Okay. So let me sort of give a pro tip something that's worked for me in healthily bringing potatoes into my diet. You can get more resistant starch by heating and then cooling your potatoes, Jonathan. And so each time that we heat and cool a potato, Jonathan, we're producing more of this resistance starch, which provides benefits to our gut biome.  

[00:09:32] Jonathan Wolf: Well, I think that's a great tip. Uh, and I'm afraid I'm still going to be swapping out potatoes for foods that score better for me. Um, you know, for someone like me with poor blood sugar control, really any of these starchy foods with sort of low levels of fiber like potatoes tend to lead to these huge blood sugar spikes. And, then very often these big dips sort of two or three hours later make you feel tired and hungry. Um, so I think I'm gonna be [00:10:00] sticking to the peppers and the aubergines and the tomatoes out of the nightshade family and, and leaving the potatoes, uh, with you.  

[00:10:08] Dr. Will Bulsiewicz: Well, I think that's all very fair, Jonathan, but I think that what you're speaking to is your personalized approach to how you attack your diet using ZOE scores, using the information that you have learned from ZOE, such as your blood sugar control and seeing how your blood sugar control is correlated to the way that you feel. So I think this is very important, but also being the CEO of a personalized nutrition company, you know, there's no one size fits all. That what works for you may not be what works for other people that  

[00:10:35] Jonathan Wolf: Absolutely. And I don't want all the potato farmers across the world chasing after me and saying, I'm, I'm all anti-potato. So, let's just say, I agree. I think we, nothing should be off the table. Um, and the last thing I'd leave you with though, which is interesting is, I went to Peru once a long time ago. Um, and this is where the potato comes from. And what's interesting is when you go to Peru, there are like 50 different varieties of potato. They're mainly really small. [00:11:00] They're colorful.

We are now eating this incredibly managed food that's been optimized to like, create this enormous potato that's all starch and no fiber and like, you know, really easy to grow and, and all the rest of it. And, and so sort of wildly different from, uh, the sort of big variety of, um, plants that we had. And, and so my guess would be, you know, if I was eating those Peruvian potatoes, that I would see a very different set of responses than I do with, uh, you know, the white potato that I would buy, um, from my grocery store.  

[00:11:32] Dr. Will Bulsiewicz: I, I am wholeheartedly on board with that. And also the fact that you mentioned the colors of the potatoes, which those colors, uh, imply that there are specific phytochemicals, many times, polyphenols, that are beneficial to our health. So for you, it may be a blood sugar focus, but for some people it's about improving their digestive health, improving their gut health.

Part of the proposition here from my perspective is that when you heat and cool the potato, you are producing a resistant starch, which is beneficial to your [00:12:00] gut microbes, and yet very easy to tolerate for people that have digestive health problems. And so this an opportunity to start to add some heating and cool potatoes into your diet to get those resistant starch benefits without having to, um, suffer through a digestive problem.  

[00:12:14] Jonathan Wolf: Um, before we fall off the important topic, of the nightshade vegetables, we also had a lot of questions from listeners saying, is it true that nightshades can lead to autoimmune disease? Is there any truth to that?  

[00:12:26] Dr. Will Bulsiewicz: There's no credible evidence that would implicate nightshade vegetables in autoimmune diseases, to be honest with you, Jonathan. If anything, if we take a step back and look at the bigger picture. Here we see a lower incidence of autoimmune disease in people who are consuming a nightshade-heavy Mediterranean diet.

You know, you think about these tomatoes and these peppers and the eggplant, and it's like we're describing a Mediterranean diet. And yet the Mediterranean diet is widely accepted as a healthful diet and has been researched to suggest more likelihood of developing autoimmune disease, and that's because of the [00:13:00] polyphenols and the fiber and the phytochemicals that all support our microbiome, that balance our immune system and in essence, is the opposite of inflammatory. 

[00:13:08] Jonathan Wolf: So Will, what's the verdict then? Should we be wary of the nightshade? 

[00:13:17] Dr. Will Bulsiewicz: I think we should be wary of the green potato. I don't think that we should be, uh, consuming berries on the side of the street in Washington, D.C., that we're not getting from our market. But these nightshades, you know, specifically the tomatoes, the peppers, the eggplant or aubergine, these foods when consumed, um, as part of a balanced healthful diverse diet are anti-inflammatory, beneficial to our gut microbiome.

What we're missing here is that we should be adding more of these foods and crowding out the things like fried foods, unhealthy fats, and sugary beverages, like we need more of these types of foods and less of these other ones.  

[00:13:56] Jonathan Wolf: If after the show you'd like to try ZOE's personalized nutrition program to learn how to [00:14:00] eat for your body and improve. 

You can get 10% off by going to I'm Jonathan Wolf.  

[00:14:08] Dr. Will Bulsiewicz: And I'm Dr. Will B.  

[00:14:09] Jonathan Wolf: Join us next week for another ZOE Podcast.

This podcast was produced by Fascinate Productions.