Chapter 8
Potatoes Should Stay below Ground
Should we be eating potatoes, sweet potatoes, yams, and other tubers, or not? Much new information has come out since I wrote The Paleo Diet There was a time in my life back in the late 1970s and early 1980s when I thought that if I eliminated red meat, eggs, and other animal products and ate a mainly plant-based diet, I would become healthier, decrease my risk for developing heart disease and cancer, and live a longer, fuller life. Part of this conceptual package meant that I should replace meat proteins with whole grains, legumes, potatoes, and other tubers. I faithfully followed the recommendations of such vegetarian gurus of that time as Frances Moore Lappe, Dick Gregory, and others.
Once I started to eat in this manner, I immediately noticed gastrointestinal tract problems—bloating, gas, intermittent diarrhea, joint aches, back problems, increased upper respiratory illnesses, and an inability to train and run at higher intensities. The vegetarian diet books of that era simply told us that it would take time for our bodies to adjust to beans, legumes, whole grains, and tubers. Well, after months and months, my body never did adapt—my symptoms got worse, not better. I should have listened to my body, but no—I simply assumed that the nutritional experts of this era knew better than I, and that my symptoms must be some sort of anomaly.
Being a trusting soul, I continued with these nutritional experiments into my early and mid-thirties. Each and every time I went back to vegan/vegetarian dieting, everything about my health, well-being, and athletic performance declined. It took me a while to get it—diets based on whole grains, legumes, and tubers simply did not work in my body.
Even after all of these on-and-off-again experiments in my life, I tried plant-based diets one last time. Just before I got married and was approaching my fourth decade, I revisited vegetarian dieting. For breakfast, I would eat either brown rice, skimmed milk, and sliced bananas or a big bowl of boiled potatoes with salt and pepper. In those days, I typically got up and did a three- to five-mile run before 7:00 am and then ate breakfast. By 9:00 or 10:00 o’clock, I was famished and agitated, and it was all I could do to make it through until noon to put more high-starch, plant-based foods into my body. By 3:00 o’clock, I was in the same boat and couldn’t wait to get home and eat more plant starch—brown rice, potatoes, chili beans—anything.
I’ll never forget how bad early morning breakfasts of potatoes made me feel. They left me drained of energy and feeling nervous, agitated, and depressed—only a few hours after my morning meal. I lived with it.
In the early 1980s, a brand new concept called the glycemic index, developed by Dr. David Jenkins at the University of Toronto, had just emerged. It showed us that certain foods such as potatoes caused our blood sugar levels to precipitously rise and then dramatically fall. It was this effect that made me feel so bad. Potatoes for breakfast caused my blood sugar levels to spike—only to fall drastically below their original levels shortly thereafter.
Once I figured out how potatoes affected my body, I began to finally question whether vegetarian diets were nourishing or actually caused harmful effects. I now fully understand how potatoes are one of the worst foods we can eat. As with all plant foods, sporadic consumption of potatoes will have little impact on your overall health, but if you eat them regularly as the majority of your daily calories, your health will suffer. Let me explain why.
In the United States we eat a lot of potatoes. The per capita consumption of potato foods for every person in the United States in 2007 was 126 pounds. Out of that total, we ate
Frozen potatoes: 53 percent
Fresh potatoes: 44 percent
Potato chips: 16 percent
Dehydrated potatoes: 13 percent
From this breakdown, you can see that most of the potatoes consumed in the United States 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, and preservatives—that may adversely affect our health in a variety of ways.
If we contrast this total consumption of potatoes with that of all refined sugars (137 pounds per capita) in the following list, you can see that as a country, we eat nearly as many potatoes as we do refined sugars:
Sucrose (table sugar): 62 percent
High fructose corn syrup: 56 percent
Glucose syrup and dextrose: 17 percent
Honey and other sweeteners: 2 percent
Let’s take a look in the following table at the glycemic indices of various potato foods and contrast them with those of refined sugars, and you can clearly see that almost all potato products have glycemic indices that are substantially higher than sucrose—table sugar—or high-fructose corn syrup. Eating potatoes is a lot like eating pure sugars, but it’s even worse for you because of the harm these starchy tubers do to your blood sugar levels.
Comparison of Glycemic Indices among Refined Sugars and Potato Foods
| Item | Glycemic Index |
| Potato Foods | |
| Russet Burbank potatoes, baked without fat | 111 |
| Potato, white without skin, baked | 98 |
| Pontiac potato, peeled and baked | 93 |
| Red potatoes, boiled with skin | 89 |
| Sebago potato, peeled, boiled 35 min | 87 |
| Mashed potatoes | 83 |
| French fries, frozen, reheated in microwave | 75 |
| Potato chips | 60 |
| Refined Sugars | |
| Glucose (dextrose) | 100 |
| Sucrose | 60–65 |
| High-fructose corn syrup | 60–65 |
| Honey | 48 |
It is obvious why those potato breakfasts I ate twenty-five years ago made me feel so awful. I may just as well have been consuming pure sugar or several candy bars for breakfast.
Because potatoes maintain one of the highest glycemic index values of any food, they cause our blood sugar levels to rise rapidly, which in turn immediately makes our blood insulin concentrations increase. When these two metabolic responses occur repeatedly for a week or two, we start to become insulin resistant—a condition that frequently precedes the development of a series of diseases known as the metabolic syndrome.
During the course of months and years, insulin resistance leads to a multitude of devastating health effects. The list of metabolic syndrome diseases is long: obesity, type 2 diabetes, cardiovascular disease, high blood pressure, high blood cholesterol and other abnormal blood chemistries, systemic inflammation, gout, acne, skin tags, and breast, colon, and prostate cancers. The Paleo Diet is your best medicine for the metabolic syndrome because it eliminates not only high-glycemic potatoes from your diet, but also virtually every other food that spikes your blood sugar levels. When you trade in potatoes, grains, dairy, and processed foods for fresh fruits, veggies, meat, and seafood, diseases of insulin resistance and the metabolic syndrome will no longer trouble you. A wonderful success story was sent to me by Dr. Lane Sebring M.D., a general practitioner whose first prescription for his metabolic syndrome patients is The Paleo Diet
Curing Metabolic Syndrome: Dr. Lane Sebring’s Story
About half of the new patients to my clinic know I am a strong proponent of the Paleo Diet before they get here, and about one-third have either read or just purchased The Paleo Diet It truly is the best tool I have to help my patients. One day a forty-three-year-old, 5′8″, 224 pound man—a pack-and-a-half-a-day smoker who had been on blood pressure meds for three years—was brought in by his wife, complaining of blurry vision. I noticed that he had lost 9 pounds since I last saw him, and his blood pressure was 170/100. I also noticed that his neck was smaller since I last saw him—more than you would expect with a 9-pound weight loss, something I’ve seen with new-onset diabetes. I asked him whether he had been getting up a lot in the middle of the night to go to the bathroom. He said, “Yes, how did you know?”
I checked his blood sugar, and it was 611. I increased his blood pressure medication and told him about diabetes. I started him on Avandia for diabetes and told him to read The Paleo Diet Well, he didn’t read it, but his wife did. She took away his lunch money and brought him lunch. At the two-week follow-up visit, he had lost about 3 more pounds and was complaining about no salt and no potatoes, but his blood pressure was fine, and his blood glucose was 254. I gave him some more samples and a script and told him to come back in eight weeks.
At follow-up, he had lost about 4 pounds, his blood glucose was 79, and blood pressure was 112/72, so I praised him and his wife for their good work. The wife then said almost apologetically, “Dr. Sebring, I’m sorry, but we just couldn’t afford the prescription you gave us. He hasn’t taken any pills at all in three weeks.”
He weighs 178 pounds now and is no longer diabetic or hypertensive, and you couldn’t get him off the diet.
Dr. Sebring’s success in curing metabolic syndrome diseases in his patients are not isolated examples, as I have had people from all over the world and from all walks of life contact me.
Approximately ninety-six vegetable crops are grown worldwide that fit under the catch-all phrase “roots and tubers.” Root and tuber vegetables are actually the underground food-storage organs of various plants. These edible below-ground organs are classified into one of five categories:
1. Roots
2. Tubers
3. Rhizomes
4. Corms
5. Bulbs
Some commonly consumed roots are carrots, parsnips, radishes, beets, rutabagas, sweet potatoes, cassava, and celeriac. Frequently eaten tubers include potatoes and yams. Examples of edible rhizomes are arrowroot, ginger, and turmeric. Corms include taro and Chinese water chestnuts; common edible bulbs include onions and garlic. Crops with an enlarged stem, such as leeks and kohlrabi, even when located underground, are generally not classified as roots and tubers.
The table below lists fourteen roots and tubers that can be found in most well-stocked supermarkets or outlets specializing in produce.
Let’s compare how other roots and tubers stack up to potatoes in regard to their glycemic indices and glycemic loads. The glycemic load is determined by multiplying the glycemic index by the carbohydrate content in a standard serving (100g). This calculation is a better overall measure than the glycemic index for how a food affects our blood glucose and insulin levels. Before the glycemic load was developed in 1997, foods with glycemic indices of greater than 70 were classified as high-glycemic foods. From the table, however, you can see that by applying the glycemic load concept, some roots and tubers with high-glycemic indices don’t necessarily maintain high-glycemic loads.
Caloric Content, Carbohydrate Content, Glycemic Index, and Glycemic Load of Common Root Vegetables (100 g [around ¼ lb.] samples)
My recommendation for overweight subjects or for people with diseases of insulin resistance—type 2 diabetes, hypertension, dyslipidemia (elevated triglycerides, low HDL, elevated small dense LDL), coronary heart disease, gout, and acne—is not to exceed a glycemic load of 10 for any given meal and to keep the day’s glycemic load under 40. If you look at the table carefully, you can see that a 100g (around ¼ lb.) serving of baked potato would provide you with half of your daily glycemic-load allotment. Not a good choice, for many reasons. A similar serving of sweet potato would be a better choice, with a glycemic load of 14.8; better choices still would be beets, rutabagas, or carrots, which under normal circumstances you can basically eat until you are full, as it would be quite difficult to consume enough of these foods to exceed a daily glycemic load of 40. Although glycemic index and load values for celeriac have not yet been determined, the amount of carbohydrate per 100g (9.2g) is similar to that for beets, rutabagas, and carrots. It is likely that celeriac has a similar low glycemic load and presents no problems. The same goes for turnips. Enjoy these healthful root and tuber vegetables.
Remember the 85/15 rule—meaning that if one is 85 percent compliant with the diet most of the time, significant improvements in health could occur. I still adhere to this principle, and I believe that minor dietary indiscretions involving potatoes, sweet potatoes, or any other root or tuber on an occasional basis will have few unfavorable effects on your long-term health. In fact, for highly fit athletes or for healthy, normal-weight individuals who do a significant amount of exercise on a daily basis, sweet potatoes and yams represent a good source of carbohydrates, which are necessary to replenish your muscles’ spent glycogen stores. All tubers are net base (alkaline) yielding vegetables; accordingly, they represent superior carbohydrate sources, compared to cereal grains, because they do not leach calcium from our bones or amino acids from our muscles, as do acid-yielding grains. Additionally, when fully cooked and peeled, these vegetables maintain low concentrations of antinutrients known to be harmful to our health. The two exceptions to this general rule are potatoes and cassava, both of which contain a number of antinutrients that, when present in high concentrations, can be either toxic or even lethal.
We rarely consume cassava in the United States except as tapioca, and you can see from the previous table that it has an exceptionally high glycemic load. This characteristic alone should make us shy away from eating this starchy root. Cassava, like lima beans, contains an antinutrient called cyanogenic glycoside, which, unless cooked sufficiently, can be converted into hydrogen cyanide, a deadly poison. Even when fully cooked, cassava root’s cyanogenic glycosides are converted into thiocyanates, which may aggravate iodine deficiencies.
Cereal grains and legumes contain many antinutrients, which I discuss in the chapters devoted to those foods; these compounds may have far-reaching effects on the quality of our diet and health. Unfortunately, most nutritionists have zero knowledge of antinutrients—much less how they may impair body function and promote disease. Even governmental and private agencies that determine and influence national nutritional policy have largely ignored these toxic dietary elements. As was the case with whole grains and legumes, potatoes are laden with antinutrients including saponins, lectins, and protease inhibitors.
I can almost guarantee that if you ask your family physician about dietary saponins and your health, he or she will draw a complete blank. The same can be said for ADA-trained nutritionists at your local hospital or clinic. Even astute complementary health-care practitioners are usually in the dark when it comes to saponins in our daily food supply. Despite a mountain of scientific evidence showing that these compounds can be potent and even lethal toxins, they are rarely considered dietary threats to our health.
Saponins derive their name from their ability to form soaplike foams when mixed with water. Chemically, certain potato saponins are commonly referred to as glycoalkaloids. Their function is to protect the potato plant’s root (tuber) from microbial and insect attack. When consumed by potential predators, glycoalkaloids protect the potato because they act as a toxin. These compounds exert their toxic effects by dissolving cell membranes. When rodents and larger animals, including humans, eat glycoalkaloid-containing tubers such as potatoes, these substances frequently create holes in the gut lining, thereby increasing intestinal permeability. If glycoalkaloids enter our bloodstream in sufficient concentrations, they destroy the cell membranes of our red blood cells.
The following illustration shows how glycoalkaloids and saponins in general disrupt cell membranes, which leads to a leaky gut or red blood cell ruptures. These compounds first bind to cholesterol molecules in cell membranes, and in steps 1 through 4 you can see how saponins cause portions of the cell membrane to buckle and eventually break free, thus forming a pore or a hole in the membrane.
How Saponins Lead to Leaky Gut
Potatoes contain two glycoalkaloid saponins—α-chaconine and α-solanine—that may adversely affect intestinal permeability and aggravate inflammatory bowel diseases, including ulcerative colitis, Crohn’s disease, and irritable bowel syndrome. Even in healthy normal adults, a meal of mashed potatoes results in the rapid appearance of both α-chaconine and α-solanine in the bloodstream. 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 twelve separate cases of human poisoning from potato consumption, involving nearly two thousand people and thirty fatalities, have been recorded in the medical literature. Potato saponins can be lethally toxic once in the bloodstream in sufficient concentrations because these glycoalkaloids inhibit a key enzyme, acetyl cholinesterase, which is required for nerve impulse conduction. The levels of both α-chaconine and α-solanine in a variety of potato foods are listed in the following table. Consumers beware!
Concentrations (mg/kg) of Total Glycoalkaloids (α-chaconine + α-solanine) in a Variety of Potato Foods
| Food Item | α-chaconine + α-solanine (mg/kg) |
| Fried potato skins | 567–1450 |
| Potato chips with skins | 95–720 |
| Potato chips | 23–180 |
| Frozen baked potatoes | 80–123 |
| Frozen potato skins | 65–121 |
| Baked potato with 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 | 1–2 |
Note that the highest concentrations of these toxic glycoalkaloids occur in potato skins. Fried potato skins filled with chili and topped off by sour cream and jalapeno peppers are a real gut bomb with devastating effects on your intestinal permeability. If you ate enough of these hors d’oeuvres, they could literally kill you.
The next logical question arises: should we be eating a food that contains two known toxins that rapidly enter the bloodstream, increase intestinal permeability, and potentially impair the nervous and circulatory systems?
In the opinion of Dr. Patel, “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.”
In a comprehensive review of potato glycoalkaloids, Dr. Smith voiced similar sentiments:
Available information suggest that the susceptibility of humans to glycoalkaloid 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.
The commonly accepted safe limit for total glycoalkaloids in potato foods is 200 mg/kg, a level proposed more than seventy years ago, whereas more recent evidence suggests this level should be lowered to 60–70 mg/kg. In the previous table, you can see that many potato food products exceed this recommendation.
I believe that far more troubling than the toxicity of potato glycoalkaloids is their potential to increase intestinal permeability during the course of a lifetime, most particularly in people with diseases of chronic inflammation—cancer, autoimmune diseases, cardiovascular disease, and diseases of insulin resistance. Many scientists now believe that a leaky gut may represent a nearly universal trigger for autoimmune diseases.
When the gut becomes leaky, it is not a good thing, as the intestinal contents may have access to the immune system, which in turn becomes activated, thereby causing a chronic low-level systemic inflammation known as endotoxemia. In particular, a cell wall component of gut gram negative bacteria called lipopolysaccharide (LPS) is highly inflammatory. Any LPS that gets past the gut barrier is immediately engulfed by two types of immune system cells. Once engulfed by these immune cells, LPS binds to a receptor on these cells, causing a cascade of effects that leads to increases in blood concentrations of pro-inflammatory hormones. Two recent human studies have shown that high-potato diets increase the blood inflammatory marker IL-6. 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 inflict their fatal effects.
A final note on potatoes: This commonly consumed food is also a major source of dietary lectins. On average, potatoes contain 65 mg of potato lectins per kilogram. As is the case with most lectins, they have been poorly studied in humans, so we really don’t have conclusive information on how potato lectins may affect human health. Yet preliminary tissue studies indicate that potato lectins resist degradation by gut enzymes, bypasses the intestinal barrier, and can then bind to various tissues in our bodies. Potato lectins have been found to irritate the immune system and produce symptoms of food hypersensitivity in allergenic and nonallergenic patients.
Root and tuber vegetables such as sweet potatoes, yams, beets, carrots, turnips, and others are nutritious, tasty additions to the Paleo Diet. These foods complement the staples of modern-day Stone Age diets, and I encourage you to regularly include them in your diet.
Paleo Bottom Line
Don’t eat potatoes or cassava; all other root vegetables are generally okay.