Nightshade vegetables: friend or foe for your health?

Nightshades are a group of plants that belong to the Solanaceae family. They include some very commonly eaten foods such as tomatoes, peppers, eggplants and potatoes. These foods have been eaten for centuries by many cultures around the world and are considered a staple food in many traditional diets. Despite this, if you go digging into ‘health and wellness’ advice on the Internet, you’ll sometimes come across health warnings about nightshades. Digestive issues and inflammation feature prominently. In this podcast, I explore the evidence for any health harms arising from eating nightshades and put this into context for the many health benefits that they also provide.

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Transcript

Nightshades are a group of plants that belong to the Solanaceae family. They include some very commonly eaten foods such as tomatoes, peppers, eggplants and potatoes. These foods have been eaten for centuries by many cultures around the world and are considered a staple food in many traditional diets. Despite this, if you go digging into ‘health and wellness’ advice on the Internet, you’ll sometimes come across health warnings about nightshades. Digestive issues and inflammation feature prominently. In this podcast, I’ll explore the evidence for any health harms arising from eating nightshades and put this into context for the many health benefits that they also provide.

 Nightshades are plants that belong to the Solanaceae family. This is a pretty big family with many of the plants considered inedible – plants like tobacco. But there are a few foods in the family which are staple foods eaten the world over such as tomatoes, white potatoes, eggplant and peppers.

Where the term nightshade came from is unclear. But could be related to their dark and mystical past as some nightshades were rumoured to have been used as narcotics and hallucinogens.

So, the word translates as ‘shade that is active in the night’ where shade here means ghost or spirit.

Nightshades naturally contain potentially harmful compounds called glycoalkaloids which is where they get their fearsome reputation. Glycoalkaloids are there to help the plant defend against insects, disease and some plant-eating animals. And because these compounds can be toxic to predators, then you can see where the health concerns about these foods come in.

But a quick diversion here. There are so many different types of plants that contain compounds that can be harmful to us humans if eaten in high enough amounts. Just because some species of mushrooms are toxic doesn’t mean that all mushrooms are off the menu! So, it does seem interesting that nightshades get singled out here because they can contain a potentially harmful class of chemicals.

But there is truth to potential health harms. One of the main glycoalkaloids in the edible nightshades is a compound called solanine. Solanine is found in the green skin of young potatoes, and you can also sometimes see it under the skin of mature potatoes. It is a good tip that if your potatoes are starting to turn green or sprouting, then don’t eat them. Solanine poisoning can cause digestive issues like an upset stomach, nausea and vomiting. But here, it is quite rare and you’d have to eat a lot of green potatoes. It is also important to note that cooking and processing nightshades can reduce the levels of solanine.

Gut issues aside, probably the most common issue you’ll read about nightshades is that you must cut them out because they’re inflammatory. Firstly, on the topic of inflammation, there are very few foods that are clearly inflammatory or anti-inflammatory foods – the evidence just doesn’t go that deep to make such simplistic statements It is more that dietary patterns and lifestyles trump this and are linked to inflammation. Think of a Mediterranean-style diet as a classic anti-inflammatory diet and a typical Western diet high in added sugar and highly processed food that is linked to inflammation.

But is there any merit in tarnishing the nightshades as inflammatory foods? No. The amount of solanine, which certainly can act as an inflammatory irritant in the gut if you eat enough of it, is incredibly low in the nightshades and it is the dose here that matters. If your diet isn’t rich in green potatoes then you’re good to go.

And to show that it is not as simple as just homing in on one particular component of a food to say if it is healthy or not healthy, when you look at the food as a whole then there is evidence, at least from in vitro studies, that eggplants have anti-inflammatory action. And at least one study, again in vitro, could show that solanine could also demonstrate anti-inflammatory properties with the authors going on to state that it could be a valuable, leading compound in the treatment of inflammatory diseases. And several studies also suggest that solanine may help inhibit the growth of cancer cells.

To counter this, some animal studies suggest that nightshades could have negative effects in people with inflammatory bowel disease suggesting that the alkaloids in nightshades may further aggravate the intestinal lining of people. But more research is needed in humans before recommendations to eliminate nightshades can be made.

Don’t get too excited about this research I’ve profiled though as it is in very early stages and almost all in vitro or in animals, but it serves to show that things are a lot more complex to do with food and health. And it is why foods like potatoes, eggplant, tomatoes and peppers feature the world over in dietary guidelines as healthy foods to eat.

But there is research, and then there is personal experience. And it does seem that certain people, particularly people with autoimmune diseases such as rheumatoid arthritis, fibromyalgia, and lupus, may find that nightshades aggravate their symptoms. While most of the data is anecdotal, some people do report unpleasant digestive symptoms or joint-related pain when they consume nightshades. Whether it is real or imagined, if a person finds they feel better for eating less of these foods then that is a good thing.

If you suspect you have a sensitivity or intolerance to nightshades, it may be helpful to talk with a healthcare provider or a dietitian about eliminating them from your diet in a controlled way and see if that helps with any symptoms you may be experiencing.

But that doesn’t mean that everyone has to stop eating nightshades. I mean, just because some people have severe anaphylactic reactions to peanuts, we don’t tell everyone in the population to avoid them. You can make a case for any food or group of foods as having some level of adverse problems in a subset of people. Nightshades appear to be no different.

So, taking the opposing view, what health benefits are linked to eating nightshades? Nightshades offer several health benefits. For example, tomatoes are a good source of lycopene, an antioxidant that has been shown to lower the risk of heart disease and certain types of cancer. Peppers are also high in vitamin C and other antioxidants. And dietary patterns that include tomatoes, peppers, and eggplants are actually linked to less inflammation in the body.

And here’s another big plus of nightshades: they’re all mostly low in kilojoules and high in nutrients. This makes them an excellent choice for people trying to maintain a healthy weight. And have I mentioned that they’re a good source of dietary fibre, which can help support a healthy gut?

So, let’s wrap all this up. Nightshades are not only safe to eat for almost everyone, but also offer several health benefits. While some people may have a sensitivity or intolerance to nightshades, for the majority of people, they are a healthy and delicious addition to the diet, adding flavour, nutrition, and variety to meals. So, if you haven't already, consider adding more nightshades to your diet and experience the many health benefits they have to offer.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.