Sunday, September 19, 2010

Potatoes and Human Health, Part I

Potatoes: an Introduction

Over 10,000 years ago, on the shores of lake Titicaca in what is now Peru, a culture began to cultivate a species of wild potato, Solanum tuberosum. They gradually transformed it into a plant that efficiently produces roundish starchy tubers, in a variety of strains that suited the climactic and gastronomic needs of various populations. These early farmers could not have understood at the time that the plant they were selecting would become the most productive crop in the world*, and eventually feed billions of people around the globe.

Wild potatoes, which were likely consumed by hunter-gatherers before domestication, are higher in toxic glycoalkaloids. These are defensive compounds that protect against insects, infections and... hungry animals. Early farmers selected varieties that are low in bitter glycoalkaloids, which are the ancestors of most modern potatoes, however they didn't abandon the high-glycoalkaloid varieties. These were hardier and more tolerant of high altitudes, cold temperatures and pests. Cultures living high in the Andes developed a method to take advantage of these hardy but toxic potatoes, as well as their own harsh climate: they invented chu├▒os. These are made by leaving potatoes out in the open, where they are frozen at night, stomped underfoot and dried in the sun for many days**. What results is a dried potato with a low glycoalkaloid content that can be stored for a year or more.

Nutritional Qualities

From a nutritional standpoint, potatoes have a bad reputation, but this is undeserved in my opinion. If I had to pick a single food to eat exclusively for an extended period of time, potatoes would be high on the list. One reason is that they contain an adequate amount of complete protein, meaning they don't have to be mixed with another protein source as with grains and legumes. Another reason is that a number of cultures throughout history have successfully relied on the potato as their principal source of calories, and several continue to do so. A third reason is that they're eaten in an unrefined, fresh state.

Potatoes contain an adequate amount of many essential minerals, and due to their low phytic acid content (1), the minerals they contain are well absorbed. They're rich in magnesium and copper, two minerals that are important for insulin sensitivity and cardiovascular health (2, 3). They're also high in potassium, which helps control blood pressure, and vitamin C. Overall, they have a micronutrient content that compares favorably with other starchy root vegetables such as taro and cassava (4, 5, 6), and they offer considerably more micronutrients than refined carbohydrates such as white flour, white rice and white sugar.

On the other hand, I don't have to eat potatoes exclusively, so what do they have to offer a mixed diet? They have a high glycemic index, which means they raise blood sugar more than an equivalent serving of most carbohydrate foods, although I'm not convinced that's a problem in people with good blood sugar control (7, 8). They contain adequate fiber, but less than some other sources of starch. For example, sweet potatoes, an unrelated species, contain more micronutrients and fiber, and have been a central food source for healthy cultures (9). However, the main reasons temperate-climate cultures throughout the world eat potatoes is they yield well, they're easily digested, they fill you up and they taste good.

In the next post, I'll delve into the biology and toxicology of potato glycoalkaloids, and review some animal data. In further posts, I'll address the most important question of all: what happens when a person eats mostly potatoes... for months, years, and generations?


* In terms of calories produced per acre.

** A simplified description. The process can actually be rather involved, with several different drying, stomping and leaching steps.

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