Solanine, Green Potatoes, Nightshades, and Arthritis
What Is Solanine?
Solanine is a toxic chemical found in members of the nightshade family, also known as the Solanaceae family. The chemical acts as a natural pesticide. Plants produce solanine to protect themselves from insects and fungi that attack them. Solanine and related chemicals have been found in potatoes, tomatoes, eggplants, peppers, and other nightshade plants (but not in black pepper, which belongs to a different plant group).
In sufficient concentration, solanine produces unpleasant and even deadly effects in humans. Luckily, foods generally don't contain enough solanine to hurt us. The solanine concentration is often increased in green potatoes, though, so they should be avoided.
Some people report that nightshade plants make their arthritis worse and have attributed this effect to chemicals in the solanine family. Scientists say that there is no experimental evidence that potatoes, tomatoes, and other nightshades have an effect on arthritis. It's possible that a specific nightshade may be problematic for some people, however, although the problem may not be due to solanine.
Green Potatoes and Their Potential Dangers
Solanine is classified as a glycoalkaloid. All parts of the potato plant contain solanine, but the largest amounts are in the sprouts and in green potatoes. If a potato has sprouted, all the sprouts should be removed before the potato is cooked.
Green patches in potatoes represent areas where chlorophyll has been produced. Chlorophyll is the green pigment that plants use to absorb light energy and produce their food. The pigment is safe to eat. However, the presence of chlorophyll indicates that the potato, which normally grows underground, has reacted to the presence of light. The green colour is often accompanied by the production of solanine, which the exposed potato produces to protect itself from attack by pests.
To complicate matters, not all green potatoes contain a high level of solanine, although the risk is greatly increased, and potatoes don't have to be green to develop a lot of solanine.
A high concentration of solanine can make potatoes taste bitter. Even without this bitter taste we shouldn’t eat green potatoes because they may still contain enough solanine to cause harmful effects.
Symptoms of Solanine Poisoning
Solanine poisoning affects the digestive tract and the nervous system. Symptoms of mild solanine poisoning include headache, dizziness, a burning sensation in the mouth, stomach cramps, nausea, vomiting, and diarrhea.
Severe solanine poisoning can cause drowsiness, weakness, confusion, vision problems, hallucinations, weak pulse, low blood pressure, and rapid breathing. Solanine ingestion may be fatal if a large amount of the chemical is eaten. The symptoms of poisoning may appear within minutes after ingesting the solanine or may not appear until hours later.
Scientists agree that solanine is poisonous, but there is uncertainty about how much green potato must be eaten to obtain a harmful dose of the poison. This may depend on body mass and individual sensitivity as well as the solanine concentration in particular potatoes and the number of potatoes that are eaten.
The poison is found throughout the plant, but especially in green potatoes and new sprouts. Never eat potatoes that are spoiled or green below the skin. Always throw away the sprouts.— NIH National Library of Medicine
Dealing With Green Potatoes
The Extension Department of Michigan State University has a web page describing how to deal with green potatoes. The department gives the following recommendations.
- Completely remove sprouts and eyes from potatoes.
- Completely remove any small green areas.
- If there are more than a few small green areas, discard the potato.
- If the potatoes are going to be given to children, discard ones with any sprouts or green areas. Children have a lower body mass than adults and are therefore more susceptible to experiencing problems from solanine.
- If potatoes taste bitter, don't eat them.
In addition, the NIH (National Institutes of Health) says that potatoes that are green below the skin should be thrown away.
How to Reduce the Solanine Level in Potatoes
Always check for green spots on potatoes before you buy them. It’s better to buy loose potatoes instead of bagged ones, since it’s easier to check loose potatoes for green areas. It’s also easier to check whether brown or yellow potatoes have turned green than to check red or purple varieties. If you grow potatoes, check that they stay covered by soil as they develop. When you're storing potatoes in your home, keep them in a cool and dark place to reduce solanine formation.
Once potatoes are cooked, solanine can no longer form because essential enzymes needed for its production are destroyed. However, any solanine made before the potatoes were cooked will remain. Solanine isn't destroyed by boiling, steaming, baking, microwaving, or frying potatoes. Deep frying at very high temperatures partially destroys the chemical.
Dietary Recommendations From Arthritis Research UK
Diet and Arthritis
Scientists say that there is no connection between arthritis and eating specific foods, or at least that there is no evidence for this connection. Research suggests that a healthy diet filled with vegetables, fruits, fibre, and essential fatty acids may dampen inflammation and reduce arthritis pain. The idea that some foods such as nightshades or the solanine within them can trigger arthritis pain is controversial.
Some people say that their joint pain is worsened when they ingest nightshade plants or a specific member of the nightshade group. At the moment the evidence for this link is anecdotal, not experimental. The effect seems to be strongest for people who suffer from rheumatoid arthritis. Even if nightshades affect some people with arthritis they may not affect everyone with the disorder, however. In addition, although solanine is often assumed to be the culprit by people who support the nightshade and arthritis theory, there is no proof that this is true. If a nightshade plant does cause pain, this may be due to a reason other than the presence of solanine.
Some health agencies and dieticians say there is no link between nightshades and arthritis pain, others say that there may be a link for some people, and some say that there is a link. These different viewpoints are shared in the last three references below. Individuals will need to explore the possibility that nightshades increase their own pain for themselves (if they want to do this).
My Experience With Tomatoes and Joint Pain
I have osteoarthritis in my neck, but as far as I know I have no osteoarthritis in my elbows and no rheumatoid arthritis. A few years ago I went through a period when I developed elbow pain whenever I ate tomatoes, however. The effect was obvious and consistent, so I avoided tomatoes for a while. The pain disappeared. Many months later I tried eating tomatoes again. This time there were no problems.
Scientists say that the solanine-like chemical in tomatoes is not really solanine but instead is a related chemical called tomatine. The problem that I experienced after eating tomatoes may have had nothing to do with tomatine, though. In addition, the fact that the problem was only temporary suggests that it may have been controlled by variable factors such as the type of tomatoes that I ate or the state of my intestinal lining at the time. It did show me that tomatoes can influence joint pain under some conditions, though, at least in my body.
An Elimination or Exclusion and Challenge Diet
If you have arthritis, an elimination diet could be used to discover whether foods in the nightshade family affect your condition. If you decide to go on this diet, you must ensure that you eat nutritious food. Foods from nightshade plants contain some valuable nutrients. It's important to obtain as many as these nutrients as possible from other foods if a nightshade is eliminated from the diet.
An elimination diet is sometimes known as an exclusion and challenge diet. When the diet is followed, a food is temporarily excluded from the diet and observations are made about the body’s response to the elimination. After the elimination period, the food is eaten again (the "challenge" part of the diet) to see if symptoms return.
If you have to eliminate a nutritious food from your diet and are unable to find a suitable replacement, or if you have to eliminate multiple foods from your diet, it's time to visit a health professional. A doctor, nutritionist, or dietitian should be consulted for advice.
How to Follow an Elimination Diet
Choose only one food to temporarily eliminate from your diet. A different trial is needed to test another food. While you are on the diet, keep a daily record of what you eat and how your arthritis responds.
After a three to four weeks on the diet, you should assess the results. The eliminated food should be reintroduced for several days to see if symptoms reappear or worsen. If they do, then you’ve probably found a food that you’re sensitive to. By eliminating that food from your diet your symptoms should improve.
If your pain doesn't improve on the elimination diet and reintroducing the food makes no difference to the intensity of your pain, then you know that the food that you eliminated doesn’t need to be removed from your diet.
A Registered Dietitian Discusses Diet and Arthritis
In the video above, the dietitian explains why people with arthritis should eat certain foods and avoid others. It's interesting that nightshades are on her avoid list, yet unlike the case for the other foods she doesn't discuss them. Perhaps this reflects the controversy about nightshades and their effects.
Rheumatoid Arthritis and Nightshades Poll
If you have rheumatoid arthritis, do nightshades increase your pain?
Potential Problems With Elimination Diets
Elimination diets can be time consuming to carry out. A food must be removed from the diet for several weeks so that all traces of the food and its metabolites can be removed from the body. In the case of a nightshade exclusion diet, it also takes time to discover if only one nightshade or if all nightshades need to be eliminated from the diet. A person may discover that some nightshades need to be restricted to occasional ingestion instead of being completely eliminated from the diet.
Nightshade vegetables have great nutritional and health benefits. It's important that you don't eliminate any of them from your diet (except during a short-term exclusion diet) unless this is necessary to reduce pain.
Despite the potential problems, an elimination diet could be very helpful. The time and effort required to determine whether foods affect your arthritis and to identify the specific foods that cause problems could be well worthwhile if the result is pain reduction or relief.
Is it safe to eat a green potato? from Michigan State University Extension
Potato plant poisoning - green tubers and sprouts from the National Institutes of Health
Glycoalkaloids in Foods from Health Canada
Should I Avoid Certain Foods? from Arthritis Research UK
The Truth About Nightshades and Arthritis from the Arthritis Foundation
How to Ease Your Arthritis Pain With Simple Food Swaps from the Cleveland Clinic
Questions & Answers
© 2010 Linda Crampton