Paleo Diet Newsletter: Potatoes and Autoimmune Disease
Dr. Loren Cordain released this information about potatoes being part of the nightshade family and causing autoimmune diseases. Do you have an autoimmune disease? Maybe it is time you stopped eating potatoes.
This is not new info for me, we stopped eating potatoes some 4 years ago. The full text is posted at Raw Paleo Forum
Nightshade is the common name for flowering plants belonging to the botanical family Solanaceae, which contain more than 75 genera and 2,000 species. Some notorious non-edible nightshades include tobacco, petunias, jimson weed, mandrake, and deadly nightshade. The family comprises well known food plants such as potatoes, tomatoes, green peppers, chili peppers, eggplants and tomatillos. Note that chili peppers include all varieties of peppers from the genus Capsicum, including bell peppers, jalapeno, wax, cayenne, habanero, Anaheim, Thai, Tabasco, cherry, pepperoncini and Serrano among others. Chili peppers are commonly consumed as dried powders such as paprika, chili powder and cayenne, and are near universal ingredients in hot sauces, Tabasco sauces, and salsas.
Now on to potatoes:
Let’s first examine potatoes. Potatoes generally maintain one of the highest glycemic index and load values of any food3-6. Regular consumption of high glycemic index carbohydrates may promote obesity and diseases of insulin resistance, including type 2 diabetes, cardiovascular disease, abnormal blood lipids, gout, acne, polycystic ovary syndrome, epithelial cell cancers (breast, colon and prostate), acanthosis nigricans (a skin disease), and male vertex balding7. Consequently in both of my books I do not recommend that potatoes be included as a regular component of Paleo Diets. Additionally, as you can see from Table 1, most of the potatoes consumed in the U.S. are highly processed in the form of french fries, mashed potatoes, dehydrated potato products, and potato chips. Processed potato foods typically are made with multiple additives (salt, vegetable oils, trans fats, refined sugars, dairy products, cereal grains, preservatives, and other food additives) that may adversely affect health in a variety of ways.
An additional nutritional property of potatoes that is rarely considered in regard to human health is their saponin content. Saponins derive their name from their ability to form “soap” like foams when mixed with water. Chemically, saponins are classified as either steroid glycosides or triterpenoid glycosides. A glycoside is any of a group of organic compounds occurring abundantly in plants that yield a sugar and one or more non-sugar substances upon hydrolysis (chemical decomposition in which a compound is split into other compounds by reacting with water). Steroid glycosides are commonly called glycoalkaloids.
Both categories of saponins are widely distributed throughout the plant kingdom including many cultivated crops. The primary function of saponins is to protect the plant from microbial and insect attack by dissolving cell membranes of these potential predators8. In mammals, including humans who consume saponin containing plants, these substances frequently create pores in the gut lining, thereby increasing intestinal permeability8-10. If they enter the bloodstream in sufficient concentrations, they cause hemolysis (destruction of the cell membrane) of red blood cells8-10.
Figure 1 shows how saponins disrupt cell membranes which may lead to a leaky gut. Saponins first bind cholesterol molecules in intestinal cell membranes due to the affinity of a saponin component (the aglycone moiety) for the membrane sterol (cholesterol)9. In the series of steps that follows, you can see how saponins cause portions of the cell membrane to buckle and eventually break free, forming a pore or a hole in the membrane.
Figure 1. The proposed mechanism by which dietary saponins may elicit pores in intestinal cells leading to a “leaky gut” (adapted from 9).
Potatoes contain two glycoalkaloid saponins: ?-chaconine and ?-solanine which may adversely affect intestinal permeability and aggravate inflammatory bowel disease11, 12. Even in normal healthy adults, a meal of mashed potatoes results in the rapid appearance of both ?-chaconine and ?-solanine in the bloodstream13. The toxicity of these two glycoalkaloids is dose dependent – meaning that the greater the concentration in the bloodstream, the greater is their toxic effect. At least 12 separate cases of human poisoning from potato consumption, involving nearly 2000 people and 30 fatalities have been recorded10. Potato saponins can be lethally toxic once in the bloodstream in sufficient concentrations because these glycoalkaloids inhibit a key enzyme (acetyl cholinesterase) required for the synthesis of acetylcholine, a neurotransmitter required for nerve impulse conduction10. The concentration of both ?-chaconine and ?-solanine in a variety of potato foods are listed in Table 3. Note that the highest concentrations of these toxic glycoalkaloids appear in potato foods containing the skins.
Table 3. Concentrations (mg/kg) of total glycoalkaloids (?-chaconine + ?-solanine) in a variety of potato foods (adapted from 10).
Food Item ?-chaconine + ?-solanine (mg/kg)
Fried skins 567-1450
Chips with skins 95 – 720
Chips (US potatoes) 23 – 180
Frozen baked potatoes 80 – 123
Frozen skins 65 – 121
Baked potato w/jacket 99 – 113
Dehydrated potato flour 65 – 75
Boiled peeled potato 27 – 42
Canned whole new potatoes 24 – 34
Frozen fried potato 4 – 31
Frozen French fries 2 – 29
Dehydrated potato flakes 15 – 23
French fries 0.4 – 8
Frozen mashed potatoes 2 – 5
Canned peeled potato 1 – 2So the next logical question arises: Should we be eating a food that contains two known toxins which rapidly enter the bloodstream, increase intestinal permeability and potentially impair the nervous system?
In the opinion of these authors: “. . . if the potato were to be introduced today as a novel food it is likely that its use would not be approved because of the presence of these toxic compounds.” 11
Other researchers state: “Available information suggest that the susceptibility of humans to glycoalkaloids poisoning is both high and very variable: oral doses in the range 1 – 5 mg/kg body weight are marginally to severely toxic to humans whereas 3 – 6 mg/kg body weight can be lethal. The narrow margin between toxicity and lethality is obviously of concern. Although serious glycoalkaloid poisoning of humans is rare, there is a widely held suspicion that mild poisoning is more prevalent than supposed.” 10
The commonly accepted safe limit for total (?-chaconine + ?-solanine) in potato foods is 200 mg/kg, a level proposed more than 70 years ago, whereas more recent evidence suggests this level should be lowered to 60 – 70 mg/kg10. If you take a look at Table 2 you can see that many potato food products exceed this recommendation.
I believe that far more troubling than the potential toxicity of potato glycoalkaloids is their potential to increase intestinal permeability over the course of a lifetime, most particularly in people with diseases of chronic inflammation (cancer, autoimmune disease, cardiovascular disease and diseases of insulin resistance). A leaky gut has been recently proposed to be a universal initiating trigger for autoimmune diseases14 – a conclusion that I agree with15, as well as promoting cardiovascular disease16, 17 and diseases of insulin resistance18. When the gut becomes “leaky” it is not a good thing, as the intestinal contents may then have access to the immune system which in turn becomes activated thereby causing a chronic low level systemic inflammation known as endotoxemia16 – 18. In particular a component of the cell walls of gut gram negative bacteria called lipopolysaccharide (LPS) is highly inflammatory. Any LPS which gets past the gut barrier is immediately engulfed by two types of immune system cells (macrophages and dendritic cells). Once engulfed by these immune cells, LPS binds to a receptor (toll-like receptor-4) on these cells causing a cascade of effects leading to increases in blood concentrations of pro-inflammatory cytokines (localized hormones) including interferon gamma (INF-?),interleukin 1 (IL-1), IL-6, IL-8 and tumor necrosis factor alpha (TNF-?)16, 19. Two recent human studies have shown that high potato diets increase the blood inflammatory marker IL-620, 21. Without chronic low level systemic inflammation, it is unlikely that few of the classic diseases of civilization (cancer, cardiovascular disease, autoimmune diseases and diseases of insulin resistance) would have an opportunity to take hold and wreak their fatal effects.
A final note on potatoes – to add insult to injury, this commonly consumed food is a major source of dietary lectins. On average potatoes contain 65 mg of potato lectin per kilogram. As is the case with most lectins, they have been poorly studied in humans, so we really don’t have conclusive information how potato lectin may impact human health. However, preliminary tissue studies indicate that potato lectin resists degradation by gut enzymes, bypasses the cell wall barriers and can then bind various tissues22, 23. Potato lectins have been found to irritate the immune system and produce symptoms of food hypersensitivity in allergenic and non-allergenic patients24. Just say “no” to potatoes!!
I would like to thank Dr. Cordain for his work and encourage you to subscribe to his newsletter at http://www.thepaleodiet.com/newsletter/