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There are many different dietary recommendations for individuals with autoimmune diseases: foods to avoid, foods to make sure you include, different eating patterns, etc. One such suggestion that individuals continue to have questions about is avoiding nightshade vegetables.
Attune Health nutritionist and research associate Natalie Fortune breaks down the relationship between autoimmune conditions and nightshade vegetables:
Nightshades are a botanical family of plants, technically called Solanaceae.
There are more than two thousand plant species in the nightshade family, most of which are highly poisonous. There are several nightshades that most people regularly consume, though. These include:
This is not to say that every single autoimmune patient should avoid nightshades! Rather, there are certain stages in autoimmune conditions when it could be helpful to avoid them. The best way to determine if you have a sensitivity to nightshade vegetables is to avoid them, and then slowly reintroduce them to see how your body reacts. When doing a dietary intervention such as this, however, it is essential to work with a nutrition professional to make sure you are successful.
You are right – they are! There are many compounds found in nightshade vegetables that are very nutritious. Tomatoes, for example, have lycopene, which is a red-colored phytonutrient. It may protect against cancers of the prostate, breast, and skin, and reduce the risk of heart attacks.
In spite of these benefits, however, if any food or type of food is causing you issues and/or inducing flares in your autoimmune condition, you should avoid it to achieve an optimized diet.
Nightshades can be problematic for people with autoimmune diseases due to their lectin, saponin, and capsaicin content. These are all compounds that have a high potency in nightshade vegetables.
All plants and animals contain some lectins. One of lectins’ jobs is to protect the plant, specifically the seeds. Some lectins are associated with an increase in intestinal permeability. These lectins do not break down during digestion or cooking and can strongly interact with proteins in the membrane of the cells that line the intestine. There is a range of effects that different dietary lectins can have on the body – on one end, they could be proinflammatory and promote a leaky gut, and on the other, they could be completely harmless and even therapeutic.
Tomato lectin enters the blood stream relatively quickly in humans, which suggests that tomato lectin may contribute to leaky gut. People with autoimmune disease are more likely to have a leaky gut and have more challenges to healing a leaky gut once it has developed.
Nightshades contain a type of saponin called glycoalkaloids. For those with autoimmune conditions, saponins, such as α-tomatine, can stimulate and exaggerate an immune response. Dietary saponins are believed to increase the immune response to proteins leaking out of the gut.
Another problematic substance is capsaicin, a steroidal stimulant found in chili peppers that produces its spicy flavor. While a variety of health benefits have been attributed to capsaicin, it is also a potent irritant to a variety of tissues, including skin, eyes and mucous membranes. Moreover, there is evidence that capsaicin can increase intestinal permeability.
It can sometimes be tricky to avoid nightshades. There are many products that include nightshade ingredients. Some labels can list ingredients as “spices” instead of what they really are, which is usually paprika. Many spice blends, like curry and steak seasoning, usually contain nightshades. There are many different types of hot sauce, all of which contain nightshades like tabasco or sriracha. Reading/understanding ingredients are a must. Do not be afraid to ask questions when going out to eat.
The good news is that sweet potatoes and black pepper are not in the nightshade family!
A lot of the lectins, saponins, and capsaicin live in the seeds and skin of night shades. Peeling and seeding these vegetables can help them to be more tolerable for our bodies by reducing intake of these compounds.
On a final note, abstaining from nightshade vegetable consumption is not advised for every individual autoimmune disease patient. Instead, there are certain stages of autoimmune conditions, particularly when gut issues are flaring, that these vegetables should be avoided. Additionally, the research underlying this recommendation to avoid nightshades is limited and based primarily on clinical observations. Further scientific studies on this topic would give us more confidence in this recommendation.