Nightshades and the Potential Health Concerns They Pose

Recently my wife and I had a brief discussion over nightshade plants and how there are certain health concerns that can accompany diets high in nightshade foods.  Having only a very basic knowledge of nightshade foods, I wanted to research deeper into exactly why there are concerns related to consumption of these otherwise healthy foods.  During my research, I found that there are many articles, blog entries and comment forums online that seem to vilify nightshades and promote not eating them at all, which given the other health benefits of these food, I take considerable issue with.  There has although been research that links nightshade consumption to joint issues, impaired nerve and muscle function and digestive problems. 

Nightshade is a term (classification) that refers to one of 2,800 different species of plants that include potatoes, peppers (all varieties other than black pepper), egg plants, tomatoes, pimentos, paprika and tobacco to name a few.  What sets these plants apart from others is that they contain a particular substance called alkaloids.  Alkaloids contain nitrogen and are produced by plants as a means to help protect themselves from insects.  In that way, alkaloids are a natural defense mechanism that nightshade plants produce to preserve themselves.  There are 5 basic types of alkaloids that are typically researched and associated with potential health issues.  (1) Steroid alkaloids that are found in potatoes and tomatoes (2) Tropane alkaloids (3) Pyrrolizidine alkaloids (4) Indole alkaloids and (5) Nicotine alkaloids which are found in tobacco, egg plants and green tomatoes. 

Most research that I looked into focused on steroid alkaloids and some of the impacts that they can have on health.  One thing that I want to stress here is that the negative health impacts that are noted, appear to only effect those people that have an alkaloid sensitivity or pre-existing joint condition such as arthritis or gout.  While heavy consumption of nightshade foods can cause some negative symptoms in everyone, these symptoms typically cease once consumption is reduced to moderate levels.  That being said, steroid alkaloids have a tendency to block an enzyme (basically a substance that acts as a catalyst for a specific chemical reaction/ function to take place) in the nerve cells called Cholintesterase.  When steroid alkaloids accumulate in the body, symptoms such as muscle-spasms, aches, pains, tenderness, inflammation, and stiff body movements can occur.  Again, this seems to only occur in folks with a known sensitivity or accompanying a diet abnormally high in foods containing this alkaloid type (potatoes and tomatoes).  There is also a link to irritation of the walls of the digestive tract, including more serious conditions such as ulcers, diverticulitis, and polyps in those with sensitivities.  It’s therefore recommended that people with arthritis or digestive issues eliminate nightshade foods from their diet.

A study conducted in 1980 at Rutgers University found that potato alkaloids (steroid alkaloid type) in people eating a diet high in potatoes resulted in decreased bone mineral content, soft tissue mineralization, and a decrease in body weight gain (associated more with the decreased bone content not fat stores, so unfortunately not a good weight loss).  Simply put, this research indicated that these alkaloids can contribute to loss of calcium in the bones and excessive depositing of calcium in soft tissues. 

Foods such as green tomatoes and egg plants, as mentioned earlier, do have nicotine alkaloids present, yet it is generally accepted that the nicotine content is so small in these foods that most health practitioners do not see it as a potential health concern.  I thought this was worth mentioning, as there are so many concerns surrounding nicotine in tobacco use.  Keep in mind that many of the other additives in cigarettes other than tobacco are responsible for many of the health concerns with smoking, not to mention the means of ingestion….meaning inhaling any form of smoke is detrimental to lung functioning.  I just wabted to put that out there so that people do not avoid eating egg plants because they are worried about the trace amount of nicotine present J

So a couple of things to keep in mind with nightshades are potatoes that have green spots or have sprouted should be discarded.  Green spots and sprouts are indicative of a high alkaloid content, which can account for the bitter taste of sprouted potatoes.  Also cooking nightshades can lower the alkaloid content by 40 to 50%, which typically lowers it enough that the risk of alkaloid consumption is insignificant for those that do not have a sensitivity. 

All in all, instead than avoiding nightshades altogether, it is important to simply have an awareness of what they are, what they contain and some of the potential effects that they can have on your body.  Similar to gluten, (see previous blog I posted) just being aware of something can help us to improve our diet and know how to better moderate certain foods.  In my opinion, eliminating nightshades completely from your diet (unless you have a true sensitivity) is unnecessary and you also do not gain the health benefits that these foods can bring to your diet.  Just a few of the benefits that tomatoes provide are they have a high content of vitamins A and C, which are antioxidants (see my previous blog on antioxidants).  They contain chromium which helps to regulate blood sugar levels, and they also contain a high amount of potassium and B vitamins (B vitamins help convert food to energy).  Research has also shown that eating seedless tomatoes can also reduce risk of kidney and gallstones.  Peppers also present considerable health benefits such as being high in antioxidants which in turn helps reduce risk of cancer and supports healthy immune system functioning.  Peppers contain vitamin K and have a decent amount of fiber (1/2 cup of sliced red bell pepper has 1 gram of fiber). 

Sources of research:
Childers, N.F. Ph.D. and Margoles, M.S., M.D. "An Apparent Relation of Nightshades (Solanaceae) to Arthritis". (Published in the Journal of Neurological and Orthopedic Medical Surgery). 1993.

Anonymous. "What are nightshades and which foods are they found?". (www.whfoods.com) . The George Mateljan Foundation. 2012.