Yes, its true, potatoes are not primal - paleo. This post provides an overview about why this is the case.
The potato (solanum tuberosum) plant is a nightshade that originated from South America. Genetic testing of cultivars and wild species indicate a single origin for potatoes in the Peru - Bolivia area about 7,000–10,000 years ago. The plant was introduced into the outside world including throughout Europe only 400 years ago!
The average (non-paleo) Western person is said to eat 30+ kg of potato each year!
Potatos contain a high glycemic load and high glycemic index. The glycemic index is comparable to refined sugars. This is not a good thing and just as refined sugars are associated with various diseases so to are potatos for similar reasons.
Potatoes contain toxic compounds known as glycoalkaloids including the saponins: solanine and chaconine. These antinutrients (ie poisons) protect potatos from microbes and insects that consume these "seeds" by dissolving cell membranes. Saponins will exert similar effects in humans consuming them. In humans, consumption of glycoalkaloids, or substances containing them, will cause headaches, diarrhoea, cramps, and in severe cases coma and death. Poisoning from potatoes has occurred and is probably underestimated. The symptoms of glycoalkaloid poisoning eg cramps, diarrhea with some headache is similar to microbial food poisoning symptoms and could be confused with that. Sometimes, it might not be the take away chicken (eg chicken and chips) or the seafood (eg seafood and chips) that was off. It might be the potatos contained higher amounts of saponins.
Glycoalkaloid content in potatos is increased by exposure to light, physical damage and age. The green colour is not a reliable guide to saponin content ie if it ain't green it can still contain significant amounts of saponin.
Cooking at high temperatures, over 170 °C reduces gylcoalkaloid content but, depending on the original concentration prior to cooking, substantial quantities may remain. So, fire is also needed before significant consumption of potato can occur that will mostly avoid acute toxicity ie temporary or permanent adverse effects shortly after eating (including death). No one should ever eat raw potato. But through avoiding light and through cooking may not be sufficient.
While cooked potato flesh has 20-200 mg/kg of glycoalkaloid, a cooked green tuber contains ~250+ mg/kg, and cooked skins ~1500 mg/kg. 200mg/kg was used as a safety standard by the industry for many years but, many scientists believe that the figure should be substantially reduced perhaps to around ~50mg/kg. You can see that many potato foods will exceed these numbers.
Google around if you want more data around this theme.
Potato glycoalkaloids increase intestinal permeability, which allows foreign compounds to gain access to the blood and body tissues, and if consumed over a long time this will contribute to chronic inflammation and associated diseases such as cancer, autoimmune disease, cardiovascular disease and diseases arising from insulin resistance.
Potatoes also contain significant amounts of lectin. This lectin almost certainly resists degradation by gut enzymes, passes thru the gut barrier and bind tissues inside our bodies. It is believed that lectins such as potato lectin play a role in autoimmune and allergic processes.
It is to be noted that from the bodies perspective it is always the total dose that is important. So, in relation to intestinal permeability it is the total dose of substances that increase intestinal permeability (eg saponins, gluten (wheat etc) etc)
and those factors that tend to reduce intestinal permeability (eg vitamin D via zonulin tightens up junctions between intestinal lining "barrier" cells). Similarly, in relation to lectin load it is the total body load that is important and lections are found various other foods eg gluten is also a lectin.
- humans only domesticated the potato 7,000 to 10,000 years ago, in a smallish part of the South American continent and consumption would have been limited to a few months of the year due seasonal nature of crop and hazards of storage (ie increased saponins). Widespread distribution and consumption of the potato by European humans has only occurred for <400 years.
- potato's have a glycemic index as high as refined sugar.
- potato's contain saponins and lectins in sufficient amounts to exert chronic effects over a period of time including reduced intestinal permeability, chronic inflammation etc
Potato's are not paleo. Optimists can reserve them as a treat ie the 10-15percent of "fun" foods that some versions of the paleo - primal diet permit........ If you have any susceptibility to active disease processes, particularly if increased intestinal permeability, chronic inflammation, allergy\ immune response, hyperinsulemic response etc are component then potatos are likely to exert an additive or synergistic effect in relation to other risk factors.
Why not find a substitute for potatos? For example, sweet potatos, pumpkin, carrots etc do not contain significant quantities of lections or glycoalkaloids and have lower glycemic index values.