Are White Potatoes Paleo or Not?

White potatoes are classed as a neolithic food because they have not been around for more than 10,000 years.

They are nutritionally similar to sweet potatoes.

Donn Wiss's strict definition of the Paleo Diet classes white potatoes as non-Paleo.
Loren Cordain and Staffan Lindeberg have condemned white potatoes for containing too many lectins.

White potatoes are a "nightshade".

Q: Is a "nightshade" a kind of food that makes you feel sleepy?
A: No, but nightshades have lots of other bad affects on the body. White pow-tay-­toes are part of the night­shade fam­ily and con­tain small amounts of neuro-​​toxin, sola­nine, that build up in your sys­tem over time. Many peo­ple are very sen­si­tive to this toxin. The tox­ins found in Night­shades (scopo­lamine , atropine, sola­nine, nico­tine and more) may be the lead­ing cause of Arthritic inflam­ma­tion, can­cer, Alzheimer’s, Migraine headaches, birth defects, mis­car­riages, inflam­ma­tory bowel dis­or­der, and Crohn’s Disease.
Q: Is a sweet potato a "nightshade" too then?
A: No, this very scary web-page answers that question. (warning: don't read if you want to carry on eating white potatoes)
Q: Is pumpkin a nightshade?
A: No, pumpkin is in the gourd family along with the squashes, cucumbers and melons.
Q: If sweet potato is not a nightshade, then what is it?
A: The potato's scientific name, Solanum tuberosum reflects that it belongs to the Solanaceae family whose other members include tomatoes, eggplants, peppers, and tomatillos.
The sweet potato, on the other hand, belongs to the Convolvulaceae plant family and is known by the scientific name of Ipomoea batatas. The well-known flower called "Morning Glory" belongs to the same botanical family as the sweet potato.
Q: List of Nightshades
A:

Culinary Vegetables

Bell pepper (sweet pepper)
Italian pepper
Chile pepper
Aubergine
Potato
Tomato
Tomatillo

Spices
Cayenne
Chili powder (some ingredients of)
Curry (some ingredients of)
Paprika

Sauces
Ketchup
Tabasco

Culinary Fruit
Cape gooseberry
Goji berry
Pepino
Tamarillo

Other
Tobacco


From healthcorrelator by Ned Kock

Look at the third column from the right, which shows the insulin responses per gram of each food, compared with the response to white bread, always shown at the top for each group of related foods (e.g., protein-rich foods). The gram-adjusted response for whole-meal bread is rather high, and so is the glucose response. The gram-adjusted insulin response to potatoes is less than one-third of the response to white bread, even though the non-gram-adjusted glucose response is higher. The insulin response to beef is also less than one-third of the response to white bread, gram-for-gram. Even cheese leads to a gram-adjusted response that is about half the one for white bread, and I don’t think many people will eat the same amount of cheese in one sitting as they would do with white bread.

In summary, insulin responses to protein-rich foods are often 50 to 70 percent lower than responses to equivalent amounts of refined carbohydrate-rich foods. Also, insulin responses to unrefined carbohydrate-rich foods (e.g., potato, fruits) are often 70 to 90 percent lower than responses to equivalent amounts of refined carbohydrate-rich foods.

Tables from From Holt, S.H., Miller, J.C., & Petocz, P. (1997). An insulin index of foods: The insulin demand generated by 1000-kJ portions of common foods. American Journal of Clinical Nutrition, 66, 1264-1276.


The insulin response to white potato (in terms of area under the curve) is about 23 percent higher than for white bread; the glucose response is about the same:

These numbers may not look very good, but they assume portions of potato and white bread with the same number of calories.
On a gram-for-gram basis, the insulin response to white potato is less than one third of the response to white bread (big difference; data also from the post above).
The reason for this discrepancy? The huge gap between glycemic loads of refined and unrefined carbohydrate-rich foods:


Conclusion

I think people should worry more about cutting out processed foods and worry less about the toxins in single ingredient foods like vegetables. I mainly eat sweet potatoes but won't shy away from white potatoes.