Many people with diabetes have already stopped eating potatoes for several reasons. Now we have one more.
Some varieties of potatoes raise our blood glucose level faster and higher than just about anything. The glycemic index of a baked russet potato is 111 on the scale where glucose equals 100.
About 80 percent of a potato's carbohydrate comes from starch, a white, tasteless, and odorless powder. But starch is cheap, and adding salt and fat can make it palatable.
Since hashed brown potatoes and french fries count as a vegetable, the potato is America's most important vegetable crop. More than 30 percent of the vegetables that we eat are potatoes, and we eat 142 pounds of them each year.
Maybe people with diabetes eat fewer potatoes than other Americans. I hope so. But everyone who eats lots of potatoes not only indulges in a very high glycemic and very high carb food but also is at risk of potato poisoning.
Potatoes are a member of the deadly nightshade family. This family includes Jimson weed, mandrake, belladonna, tobacco, as well as potatoes and tomatoes. While potatoes, tomatoes, and other members of the nightshade family are important food sources, they are often rich in alkaloids, which are toxic to humans and animals and can range from being mildly irritating or fatal, depending in part on how much we eat. By affecting the nervous system, this poison causes weakness and confusion. Some people are especially sensitive to foods in the nightshade family and experience allergy-like symptoms from the alkaloids. These alkaloids protect the plant from attacks by microbes and insects by dissolving their cell membranes.
But this poison hasn't discouraged us from eating lots and lots of potatoes. Cooking them long enough and avoiding the green parts and sprouts reduces their toxicity. But when people eat foods in the nightshade family, the alkaloids can create pores in the lining of the gut. This increases intestinal permeability, and if enough of the alkaloids gets into our bloodstream, this destroys the cell membranes of our red blood cells.
The large amount of potatoes that we eat is what makes them a concern to Loren Cordain, who has been has been a professor in the Department of Health and Exercise Science at Colorado State University since 1982. His new paper, "Consumption of Nightshade Plants, Human Health and Autoimmune Disease Implications," interested me so much that I bought a copy for $21.29. It was worth the money.
We eat somewhat less tomato products, and relatively few bell peppers, chili peppers, and eggplants, some of the other food crops in the nightshade family.
"When the gut becomes 'leaky,' it is not a good thing," Dr. Cordain writes, "as the intestinal contents may then have access to the immune system, which in turn becomes activated, thereby causing a chronic low level system inflammation." The increased intestinal permeability, particularly in people with diseases of chronic inflammation -- like type 1 diabetes -- and diseases of insulin resistance -- like type 2 diabetes -- particularly troubles Dr. Cordain.
His conclusion is "to eliminate or drastically reduce potato consumption, and for autoimmune and allergy patients to be cautious with the consumption of tomatoes, chili peppers, and eggplants."
Until recently, I had a weakness for hashed brown potatoes, as I have written here. Even though I knew that potatoes are both high glycemic and high carb, that wasn't enough to stop me. But knowing that they are poisonous did.