Can You Eat Potatoes on a Diet?
Can You Eat Potatoes on a Diet? It has a very bad reputation and is always on the banned food list along with white bread and pasta. It is believed to contain nothing but starch, a high glycemic index, and toxic alkaloids.
More than 10,000 years ago, on Lake Titicaca’s shores, in Peru, people began cultivating a variety of wild potatoes – tuberous nightshade (lat. Solanumtuberosum). Gradually, they developed it into a plant that bears fruit with round, starchy roots and has wide varieties that meet most people’s climatic and gastronomic needs. The first farmers did not know that this plant would one day be eaten by billions of people worldwide.
Wild potatoes, eaten by hunter-gatherers before domestication, contained more toxic glycoalkaloids. These substances protect the plant from insects, infections, and… hungry animals. The first farmers selected varieties containing less bitter glycoalkaloids – they became the ancestors of most modern potato varieties. True, the varieties with a high content have not been completely abandoned. These potatoes are hardier and better tolerate growth at higher elevations, at low temperatures, and under the use of pesticides.
The Andean peoples figured out how to get the most out of this more toxic type of potato: they invented chuños. To do this, potatoes were left in the open air to freeze overnight, then trampled on and dried in the sun for a long time. The result was “chips” with a low content of glycoalkaloids, which could be stored for more than a year.
The nutritional value of potatoes
Potatoes have an undeservedly bad reputation:
- It contains complete proteins with all the essential amino acids.
- Throughout history, potatoes have been the main energy source for entire peoples, and for some people, they have successfully remained so until now.
- Sometimes they eat it raw and with a peel.
Potatoes contain enough important minerals that are highly digestible due to their low phytic acid content ( 1 ). It is high in magnesium and copper, which affect insulin sensitivity and cardiovascular health ( 2, 3 ). It’s also high in potassium, which helps control blood pressure, and vitamin C. Overall, it’s superior in micronutrients to other starchy root vegetables like taro and cassava ( 4, 5, 6 ) and contains more micronutrients than refined carbohydrates— flour, rice, and sugar.
On the other hand, potatoes have a high glycemic index, which means that after eating them, blood sugar levels rise faster than when eating equal portions of other carbohydrate foods. In any case, this is not a problem for healthy people who have normal blood sugar levels ( 7, 8 ).
Potatoes contain fiber but less than other sources of starch. For example, sweet potatoes (yam, a species not related to the common potato) contain more micronutrients and fiber and are a staple food of traditional healthy peoples ( 9 ). However, people in temperate climates all over the world eat potatoes mainly because they are rich in fruit, highly digestible, satisfying, and palatable.
Glycoalkaloids in regular potatoes
Like many plants, potatoes contain substances that protect them from animals and insects. The two main ones that concern us because of their particular toxicity are alpha-solanine and alpha-hakonin. Here is a graph containing information about the concentration of these glycoalkaloids in the main varieties of potatoes ( 1 ):
Based on this graph, we can draw three conclusions:
- Different types of potatoes contain different amounts of glycoalkaloids.
- Typical store-bought varieties such as russet and white potatoes contain low amounts of glycoalkaloids. This is no coincidence: their content is carefully monitored in the US.
- The highest concentration of glycoalkaloids is in the peel (within 1 mm from the surface). Thus, when eating potatoes, the animal eats the poison before it reaches the pulp. Luckily people have potato peelers.
The generally accepted safe level of glycoalkaloids in potatoes is 200 µg/g WW ( 1 ). As you can see, in all varieties, except for one, this level is much lower in its purified form. I have never seen Snowden in a store or farmers’ market. Perhaps it is most commonly used to make chips.
Animal toxicity of glycoalkaloids
The toxicity of large doses of glycoalkaloids is undeniable and has the following negative consequences ( 1, 2 ):
- Death (in humans and animals).
- Weight loss, diarrhea (in humans and animals).
- Anemia (in rabbits).
- Liver damage (in rats).
- Low birth weight (in mice).
- Congenital disabilities (in animals injected with glycoalkaloids)
- Increased intestinal permeability (in mice).
However, it is important to remember the old expression: “The dose determines the poison.” The human body can neutralize a certain dose of plant toxins. Any plant food, as well as some animal products, contains various kinds of toxic substances. We are constantly bombarded by gamma rays, bacterial toxins, free radicals, and other potentially harmful substances. In excess, they can be lethal, but with a small amount, our body can cope, and in some cases, the right dose can even be beneficial.
In almost all studies, the doses of glycoalkaloids exceeded the amount that a person can get from ordinary potatoes. They used green or spoiled potatoes, potato skins, potato sprouts, or isolated glycoalkaloids. What happens when you feed normal potatoes to animals? Nothing special. Many studies have shown that even much larger doses of potatoes did not harm.
Potato Eating Nations: Quechua
The indigenous people of Peru have depended on the potato for thousands of years. At an average of 3170 kcal per day, they received up to 74% of their calories from it, 10% from cereals, 10% from plants of the genus quinoa and canihua, and 4% from animal products ( 1 ).
In 2001, a study of Quechua men living in rural areas found that their average body fat percentage was 16.4% ( 2 ). The average age of the volunteers was 38 years. With age, these people’s representatives increased the fat percentage in the body, and, according to forecasts, by age 65, it should have reached ± 20%. This is far below what can be considered overweight, so most of the men these people are quite slender. A 2004 study of Quechua women living in rural areas found that their average body fat percentage was 31.2% ( 3 ). On average, volunteers are 35 years old. Among the Quechua who immigrated to Lima, the capital of Peru, the fat percentage was higher.
Among women living in rural areas, mean fasting insulin levels were 6.8 µIU/mL, and fasting glucose levels were 68.4 mg/dL, generally indicating good insulin sensitivity and glucose control ( 4 ). The content of insulin and glucose in rural areas was much lower than in urban areas. Blood pressure was low in both groups. This suggests that Quechua women are more likely to be overweight, although to a lesser extent than urban Quechua, who consume fewer potatoes. I don’t think the Quechua diet is optimal, but it does seem to help maintain a certain level of metabolic health.
Potato Eating Nations: Aymara
The Aymara are another Andean people inhabiting Peru, Bolivia, and Chile that depend on the potato. One study showed that the prevalence of diabetes in this population is 1.5%, and prediabetes – is 3.6% ( 5 ). The prevalence of both remained low, even among the elderly. Here is a comparison of these figures with data from the modern US population ( 6 ):
Now let’s discuss a high body mass index (BMI). BMI is determined by the ratio of height to weight and is used to diagnose obesity. The average BMI of these people was 24.9 – this is the borderline value between normal and overweight.
The researchers were surprised at the low prevalence of diabetes in the Aymara, given that they are often overweight. Although, if you look at their photos, you can see that they are undersized, with wide hips and large chests. Can the BMI to body fat ratio be misleading? To answer this question, I found another study that assessed body fat in Aymara by measuring skinfold thickness ( 9 ). This study showed that both men and women remained relatively lean throughout their lives, and only two of the 23 participants were overweight, based on body fat percentage, and were not found to be obese at all.
Going back to the first study, this group of Aymaras had high blood pressure. Serum cholesterol levels were also slightly higher than expected in traditional Aboriginal peoples but still lower than most modern humans (approximately 188 mg/dL). I found it very interesting that Aymara, who does not eat fatty foods, has the same cholesterol levels as Tokelauans. They get almost half of their calories from coconut oil (saturated fat) ( 10, 11 ).
Aymara’s fasting insulin levels are also quite high, which is also curious given their good glucose tolerance and low prevalence of diabetes. This may be due to differences in measurement methodology rather than actual differences, as measurements across studies are often not standardized.
Taken together, these data show that lifetime consumption of high-carbohydrate, high-glycemic foods does not necessarily lead to overweight or metabolic disorders in the context of traditional diet and lifestyle.
Potato Eating Nations: The Irish
Potatoes were introduced to Ireland in the 17th century. It did well in cool temperate climates and produced much better fruit than any other crop. In the early 18th century, potatoes were the main energy source, especially for the poor. In 1839, the average Irish worker got 87% of his calories from potatoes ( 12 ). In 1845, there was a massive infection of potatoes with late blight, which led to the devastation of plantations throughout the country and the Great Famine.
We have no reliable data on the health status of Irish people before the famine, other than reports of vitamin A deficiency ( 13 ). At the same time, the Irish had high fertility rates and were occasionally described as healthy and attractive ( 14 ). The high nutritional value of the potato diet may likely have played a role, but we have too few facts. Adam Smith’s famous dictum that the potato is “particularly suited to a healthy human constitution” can be backed up by many observations by modern researchers with roughly the same result.
Data on the first experiment where people were fed only potatoes was published in 1913. Its goal is to determine the lower limit of human protein needs and the “potato” protein quality. The scientists fed three healthy adult men almost exclusively on potatoes and margarine for 309 days (at the time, margarine was not made from hydrogenated vegetable oils) while subjecting them to increasingly energy-intensive physical labor. They appear to have remained in good physical shape. Here is a description of one of the volunteers:
To see if he could do hard physical work while on a strict potato diet, Mr. Madsen went to work on a farm. His physical condition was excellent. In his book, Dr. Hindhede gives a photograph of Mr. Madsen taken on December 21, 1912, after eating only potatoes for almost a year. This photo shows a strong, robust, athletic figure with well-developed muscles and no excess fat. … Scientists tested it with five doctors, including a general practitioner, a gastroenterologist, a radiologist, and a hematologist. They all concluded that the man was perfectly healthy.
Scientists have concluded that the protein contained in the potato is of high quality, contains all the essential amino acids, and is well absorbed. The protein from the potato alone was enough to keep an athletic man in shape (although that doesn’t make the potato the optimal food).
The next study on the potato diet was published in 1927 and confirmed the findings of the previous one ( 17 ). Two volunteers, a man and a woman ate almost the same potatoes with a little lard and oil for 5.5 months. The man was an athlete, and the woman led a sedentary lifestyle. Body weight and nitrogen balance (reflecting an increase/decrease in the amount of protein in the body) remained unchanged throughout the experiment, indicating that they did not have noticeable muscle atrophy, and the amount of fatty tissue does not appear to have increased. Digestion remained excellent throughout the experiment. Both participants felt good and did not get tired of the monotony of nutrition.
In one of his texts on the paleo diet, titled “Nightshade Consumption (Part 1),” Dr. Loren Cordain cites two studies showing that potato consumption increases serum levels of interleukin-6 (an inflammatory cytokine) ( 22, 23 ). However, two dietary factors changed simultaneously in one study, so it is difficult to say exactly what caused it. And another used potato chips as a source of potatoes. So I don’t think these studies are worth considering.
Chris Voight experiment
Chris Voigt of the Washington State Potato Commission conducted his experiment ( 18 ) to dispel popular myths about the dangers of the potato and prove that it is healthy food.
Before the diet, he consulted doctors to ensure he could survive eating one potato for two months. The diet began on October 1, 2010. Every day, Chris ate 20 potatoes – fried, boiled, mashed, steamed, made chips, and baked without using milk or butter. The diet continued for 60 consecutive days and ended on November 29, 2010.
As a result, Chris has lost a lot of weight, and the levels of glucose, triglycerides, cholesterol, LDL, and LDL / HDL ratio have decreased; that is, the risks of diabetes and cardiovascular disease have become lower. While experts don’t recommend switching to twenty potatoes a day, they agree that potatoes are healthy and nutritious.
Given the recent interest in the impact of the glycemic index on health, several studies have identified a link between potato consumption and health. The results of studies are heterogeneous, some show a positive relationship, some – a negative one ( 19, 20, 21 ), so their value is still doubtful.
Some people feel good when they eat potatoes. Others believe that potatoes and other nightshades lead to digestive problems, increase arthritis, or cause weight gain. I haven’t seen scientific studies that support these potato claims, but that doesn’t necessarily mean there aren’t people with hypersensitivity to it. If potatoes don’t suit you, don’t eat them.
In my opinion, the scientific literature is pretty clear that potatoes can be a healthy dietary component for most people and won’t lead to digestive problems, weight gain, or metabolic problems. Although, it is obvious that eating only potatoes is not worth it.
Follow these simple rules:
- Do not eat green, sprouted, spoiled potatoes.
- Store it in a cool dark place. It does not need refrigeration, but this will extend its shelf life.
- If it’s a staple in your diet, peel it before eating it.