Ways in which nightshades may affect health
Alkaloids - The chemistry of nightshades
Most of the health research on nightshades has focused on a special group of substances found in all nightshades called alkaloids. In chemical terms, alkaloids are easy to identify because they all have at least one ring-like structure that contains the element nitrogen. Plants produce alkaloids as a regular part of their biochemical activity, and these alkaloids are primarily designed to help protect the plants from insects that would otherwise eat them.
Four basic types of alkaloids are found in nightshade plants. These types are: (1) the steroid alkaloids, which contain a fairly complicated fused ring structure and are found in most food nightshades including potato and tomato; (to compare the value of one of the most notable steroid alkaloid -solanine-in the foods in which it is most concentrated, please refer to Table 1)(2) the tropane alkaloids, all originating from the simple amino acid ornithine and found in fewer of the overall nightshades, but more extensively researched due to their strong drug-like properties; (3) the pyrrolizidine alkaloid and (4) the indole alkaloids, both important groups from a drug standpoint.
Vegetable Solanine contentmilligrams per 100 gram serving
Common peppers 7.7-9.2
Effect of steroid alkaloids on the nervous system
The steroid alkaloids in potato - primarily solanine and chaonine - have been studied for their health effects in two areas. First is their ability to block activity of an enzyme in nerve cells called cholintesterase. Many of the alkaloids found in nightshades possess this kind of activity, called cholinesterase inhibition. If the activity of cholinesterase is too strongly blocked, the nervous system control of muscle movement becomes disrupted, and muscle twitching, trembling, paralyzed breathing, or convulsions can result. The steroid alkaloids found in potato have clearly been shown to block cholinesterase activity, but this block does not usually appear strong enough to produce nerve-muscle disruptions like twitching or trembling.
Effect of steroid alkaloids on joint health
A second type of problem potentially related to the potato alkaloids involves damage to the joints caused by inflammation and altered mineral status. Whether alkaloids can contribute to joint damage of this kind is not clear from current levels of research. Some researchers have speculated that nightshade alkaloids can contribute to excessive loss of calcium from bone and excessive depositing of calcium in soft tissue. For this reason, these researchers have recommended elimination of nightshade foods from the meal plans of all individuals with osteoarthritis, rheumatoid arthritis, or other joint problems like gout.
Effect of nicotine alkaloid on health
Just as there is no firm research evidence for the impact of the steroid alkaloids in nightshade foods on the nervous system or joints, there is also no solid research evidence for impact of the more drug-like alkaloids in nightshade foods on body systems. But to the surprise of many people, nightshade foods do contain very small amounts of drug-like alkaloids that have long been fascinating to medical and drug researchers.
Consider, for example, the most famous of the one-ring type alkaloids (monocyclic alkaloids) found in the highest concentrations in tobacco (Nicotiana tabacum): nicotine. This alkaloid is found not only in non-food nightshades like tobacco, but also in the food nightshades including eggplant and tomato.
But there is one important difference here: while alkaloids like nicotine are definitely found in nightshade foods, the amount involved is dramatically less. Even in the case of eggplant, which is the food nightshade that appears to have the highest nicotine content after tobacco, the amount of nicotine is far lower than the amount found in tobacco. In the case of green tomatoes, which also contain nicotine, the amount is even less. The levels of nicotine in all nightshade foods are so low that most healthcare practitioners have simply ignored the presence of nicotine in these foods as a potential compromising factor in our health. At the World's Healthiest Foods, we both agree and disagree with this conclusion. While we agree that the amount of nicotine in nightshade foods is very, very small, it still seems possible to us that some individuals might be particularly sensitive to the alkaloids found in nightshades, and that even very small amounts might compromise function in the bodies of these individuals.