The mantra goes something like this. Eat your vegetables – they’re good for you! But is that universally true? You may have read on some online sites that nightshade vegetables are unhealthy and you should limit how many you consume or eliminate these veggies entirely from your diet. There’s no shortage of dietary advice online and some of it lacks scientific support. Is the nightshade issue one of them? Let’s dig a little deeper and see whether they’re a good or bad addition to your diet.
What are Nightshade Vegetables?
Why is there concern about nightshade vegetables? Nightshades are veggies that contain solanine, a bitter chemical that plants use to protect themselves against predators. Solanine belongs to a class of chemicals called alkaloids, a class of plant-based compounds that have both toxic and therapeutic properties. For example, morphine and codeine are alkaloids as are some anesthetic agents. Yet, alkaloids, like strychnine, are poisonous.
Vegetables that contain solanine include tomatoes, white potatoes, eggplant, okra, tomatillos, and goji berries. Some foods that aren’t classified as nightshades also contain solanines. These include apples, blueberries, huckleberries, cherries, artichokes, and okra. Certain spices are also a source of this bitter plant chemical, including paprika, cayenne, and red pepper flakes. As you know some of these foods, particularly goji berries and tomatoes are quite nutrient dense.
Here’s a sobering fact. Solanine in high doses is poisonous. In fact, taking in large quantities of this compound can cause abdominal cramping, nausea, vomiting, hallucinations, and even death. However, nightshade vegetables contain only small amounts of this toxic chemical, far below the amount that is toxic to the human body. For example, you’d have to eat over 60 potatoes to develop even mild solanine toxicity. Most of us don’t eat that many!
So, why the concern about solanine? The driving force behind solanine avoidance is that this chemical may incite inflammation, especially in people who have inflammatory conditions, like arthritis. Since nightshade vegetables contain small quantities of solanine, eating these veggies exposes us to minute amounts, enough in the minds of some people, to cause inflammation.
Some alternative practitioners also believe that components of nightshade vegetables can damage the lining of the gut and cause it to leak. That’s because nightshade vegetables contain lectins, carbohydrates that bind to proteins. The theory is that these carbohydrates bind to the tiny, projections on the lining of the gut, called microvilli, and damage them. If the gut is damaged or leaky, proteins from food can enter the bloodstream and activate the immune system. Therefore, proponents of lectin avoidance believe that nightshade vegetables may aggravate autoimmune diseases, like some forms of arthritis. Based on this, they recommend avoiding nightshade vegetables of any kind. However, lectins are in a variety of foods. In fact, up to 30% of plant-based foods contain lectins, including may that we eat for their health benefits. Beans, peanuts, and whole grains are a significant source of lectins, for example.
Can Nightshades or Their Lectins Cause Health Problems?
There’s no evidence that nightshade vegetables or the solanine and lectins they contain cause health problems in healthy people. What’s less clear is whether people with inflammatory or autoimmune diseases should avoid them.
There is some evidence that a percentage of the population may be sensitive to the lectins in nightshade vegetables. On the side of avoiding lectins, a 2017 study found that lectins stimulate the release of inflammatory cytokines in mice. However, mice are a different species and it’s not clear whether they fuel inflammation in humans. If you have an inflammatory or autoimmune disease, try eliminating nightshade vegetables from your diet for a few weeks and see if your symptoms improve. Keep a food journal and record what you eat and your symptoms when you eat a nightshade-free diet.
It’s true that you can’t digest lectins and if you eat them in large quantities or have a sensitivity to them, they could cause issues. In fact, there is one lectin that is definitely harmful. Raw beans contain a lectin called phytohemagglutinin that can cause digestive symptoms. That’s why it’s important to cook beans thoroughly before eating them. Don’t munch on raw kidney beans!
Can You Reduce the Solanine Content of Nightshades?
Potatoes are a vegetable many people eat on a daily basis. Although you’d have to eat a lot of potatoes to get a major dose of solanine, there are ways to lower the solanine content of potatoes. One is to peel a potato before cooking and eating it. Between 30 and 80% of the solanine in potatoes is just under the skin. So, peeling lowers the reduces of solanine in potatoes. On the downside, much of the fiber in a potato is in the outer skin. Also, avoid potatoes that are damaged or have green areas. Green potatoes and those with areas of damage have higher levels of solanine.
What about lectins? Cooking lectin-rich foods reduces the lectin content. So, it’s best to cook foods that contain lectins thoroughly, particularly beans. Fermenting foods also reduces their lectin content.
Should You Limit Nightshade Vegetables or Avoid Them Entirely?
Nightshade vegetables are nutritious. In fact, some of these foods form the very basis of healthy diets like the Mediterranean diet, an eating style linked with lower mortality. Don’t forget that many lectin-rich foods also contain antioxidants with anti-inflammatory activity. What would the Mediterranean diet be without tomatoes? Tomatoes are a rich source of lycopene, an anti-inflammatory that may offer protection against certain chronic health problems, including cardiovascular disease and certain forms of cancer. But, until we know more about how lectins impact the intestinal tract in humans, don’t eat raw nightshade vegetables or raw foods that are high in lectins. Cook them first. Always cook potatoes, legumes, and whole grain foods well too.
If you have any type of inflammatory or autoimmune disease, talk to your physician about whether nightshades should be part of your diet. If you reduce or eliminate nightshades from your diet, be sure to eat plenty of other fruits and vegetables that are low in lectins. There’s no doubt that plant-based foods have health benefits and most of us don’t eat enough of them.
References:
Medical News Today. “Do nightshade vegetables make arthritis worse?”
Food-Info.com. “What is Solanine and Is It Toxic?
Am J Clin Nutr 2004, 79:47-53.
J Immunol published online 13 January 2017.
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