Plant Alkaloids: Dangers to your Health?

Plants in the nightshade family include many of our most common foods. They developed bitter-tasting alkaloids as protection from being eaten. Alkaloids can be poisonous at high concentrations and alter animal metabolism at low concentrations. Alkaloids can harm nerve-muscle, joint, and digestive functions.


Nightshades belong to the scientific order called Polemoniales, the scientific family called Solanaceae and include 

• potatoes (Solanum tuberosum), 
• tomatoes (Lycopersicon esculentum), 
• many species of sweet and hot peppers (all species of Capsicum, including Capsicum annum),  
• eggplant (Solanum melongena), 
• tomatillos (Physallis ixocapra), 
• garden huckleberry (Solanum melanocerasum), 
• tamarillos (Cyphomandra betacea), 
• pepinos (Solanum muricatum), 
• naranjillas (Solanum quitoense), 
• Pimentos (also called pimientos) (Capsicum annum)
• paprika, cayenne, and Tabasco sauce.

Green parts of potato plants such as the stems, leaves, and eye sprouts contain alkaloids. It is a good idea to peel potatoes to remove green a possible green layer below the skin. New potato species cannot be sold as food if they have alkaloid concentrations greater than 20 mg per 100 grams of potato. 


To keep alkaloid levels low, store potatoes in dark areas and do not eat any green parts of the potatoes. If the potatoes taste bitter, they probably contain large alkaloid concentrations. For more information go to
http://www.ansci.cornell.edu/plants/toxicagents/steroid.html,

In a New York Times article, Harold McGee discussed the toxicity of tomatoes. Europeans initially considered tomato plants and fruits toxic when they were first introduced from the Americas, however the ripe fruits are now highly admired. 


The alkaloid in tomatoes that could be harmful is called tomatin, however there is very little confirmed evidence to support the popular belief that it is harmful. Even tomato leaves, which are widely considered harmful, would only harm a person if ingested in large quantities. Green tomatoes contain large quantities of tomatin, but when they are pickled or fried, they may actually help reduce buildup of cholesterol. For more information you can find the article at http://www.nytimes.com/2009/07/29/dining/29curi.html.


Cooking only lowers alkaloid content of nightshade foods by about 40-50%, so highly sensitive individuals may want to avoid them altogether, while non-sensitive individuals may be able to eat these foods, especially in cooked form, without problem. 

"Nightshade" is actually the common name used to describe over 2,800 species of plants, many with very different properties and constituents. To give you an idea of the diversity associated with this group of plants, consider the fact that tobacco, morning glory, potato, and tomato are all classified as nightshades.

Nightshades are also famous as drugs. The best-known of these nightshades include mandrake (Mandragora officinum), tobacco (Nicotiana tabacum) and belladonna, also called deadly nightshade (Atropa belladonna).


More information about the health effects of food alkaloids can be found at

• http://www.whfoods.com/genpage.php?tname=george&dbid=62 and
• http://www.embracinghealthblog.com/k-is-for-kale/.

Practical tips for avoiding excessive intake of potato alkaloids

• Store potatoes no longer than 1-3 weeks in a cool, dry, dark place. Light increases alkaloid formation. 
• Wash all potatoes before cooking so you can see the green areas, if any.
• Thoroughly cut out all green areas, especially green areas on the peel, before cooking. After cooking, discard the potato if it tastes bitter.
• Do not buy potatoes that have been waxed, or apply wax to potatoes yourself. Waxes do not help reduce greening and can increase potato decay by cutting down on gas exchange in and out of the potato.

9 Plant Substances That Can be Dangerous to Eat

Some plants that we eat contain harmful substances if the wrong parts are eaten, or the right parts are eaten at the wrong time in their life cycle. This post will contain an overview of these substances and future posts will contain more details.

1. Alkaloids
 Alkaloids are bitter tasting substances that evolved in plants about the same time that mammals emerged. For this reason, alkaloids are thought to be part of a plant's protective mechanism against being eaten by a mammal.Commonly eaten plants of the nightshade family, such as potatoes and tomatoes, contain alkaloids. Green potatoes and potato sprouts contain dangerously high levels of alkaloids and should not be eaten. Alkaloids in large doses are poisonous

and in small doses alter the metabolism of mammals.The metabolism alteration may be the reason that nicotine and caffeine are so compelling for people.

2. Cyanogens 

These molecules also warn animals of their dangers through a bitter taste. However, they produce hydrogen cyanide which damages the enzymes that animals use to generate energy. Foods containing cyanogens can be made safe by open boiling, leaching in water, and fermentation. These foods include manioc, bamboo shoots, and some kinds of lima beans. The seeds of citrus, pome fruits, and stone fruits also generate cyanide.

3. Oxalates

These are salts of oxalic acid and waste products of plant metabolism. Soluble oxalates can combine with calcium to form painful kidney stones. In very large amounts, oxalic acid is corrosive and can be fatal. Oxalates are found in small amounts in spinach, chard, beets, amaranth, and rhubarb. 

4. Hydrazines 

These are compounds found in fairly large quantities in white mushrooms that we eat. They have been found to cause liver problems and cancer in mice, but not rats, and it is still unknown whether they cause problems in humans. It is probably wise to avoid eating large amounts of mushrooms.

5. Psoralens

These compounds can damage DNA and cause skin inflammations. They occur in some vegetables that have been handled poorly. They are found in celery, celery root, parsley, and parsnips that have become stressed by near-freezing temperatures, intense lights, or mold infections. The best precaution to take against these compounds is to buy these vegetables only when they appear to be very fresh.

6. Protease Inhibitors and Lectins

These compounds interfere with digestion. Protease inhibitors block the actions of protein digesting enzymes. Lectins bind to intestinal cells so that the cells cannot absorb nutrients. Lectins can also enter the bloodstream and bind red blood cells together. These compounds are found mostly in soy, kidney, and lima beans, however they can be inactivated by boiling for a long time. To avoid these compounds, do not eat raw or undercooked beans. Symptoms of exposure are similar to food poisoning symptoms.

7. Flavor Chemicals

These are generally eaten in small quantities, but can cause problems when eaten in large quantities. They include Safrole, an ingredient that was used in traditional root beers, but is no longer used. It causes DNA damage and was banned in 1960. Ingestion of large amounts of Mtyristicin, the major flavor compound in nutmeg, can cause intoxication and hallucinations when ingested in large amounts. Glycyrrhizin, a component of true licorice root can induce high blood pressure. Licorice candy today is made from artificial flavoring, not true licorice root. Coumarin is found in sweet clover, lavendar and tonka beans (a vanilla-like flavoring), and interferes with blood clotting.

8. Bracken-Fern Toxins

Bracken ferns contain toxins that can cause blood disorders and cancer in animals that graze on them. It is best to eat fiddleheads of other types of ferns such as ostrich ferns (Matteuccia species). Safety of eating ferns has not been the subject of extensive research, so it is not known for sure whether it is harmful in humans. The best approach may be to eat fiddleheads of bracken ferns in small quantities.

9. Toxic Amino Acids

Alfalfa sprouts and jack beans contain large amounts of Canavanine, a protein that interferes with some cell functions and has been associated with Lupus. Fava beans contain vicine and convicine which cause an blood cell destroying anemia in susceptible people.