Digging Up the Truth About Potatoes
Ireland is a beautiful country known for shamrocks, leprechauns, the color green, and a historic over-reliance on potatoes. In honor of the past and present Irish love of potatoes, let’s explore the humble tuber and any possible health benefits. Potatoes are one of the big staple foods on the planet, being a major source of calories for 1.3 billion people [1]. Potatoes provide the fourth largest amount of calories from any crop, surpassed only by corn (maize), wheat, and rice [1]. Environmentally, potatoes require less water to grow than rice, and you can grow more pounds of potato per acre than either wheat or rice [2]. Though originally from Peru, potatoes are now grown worldwide, with China as the largest producer by far [2].
Nutritionally, foods contain three major macronutrients, just like the Irish flag is made of three colors. Potatoes contain barely any fat, are a low source of protein, and are mostly made of carbohydrates [2]. The carbohydrate-heavy composition of potatoes leads many to write them off as unhealthy, especially considering that they have a higher glycemic index (GI) than almost any other food [3]. The glycemic index is a measure of how quickly carbohydrates enter the bloodstream. Low GI foods have an index under 55, and high are above 70 [3]. Potatoes range from 38 to 103 on the GI scale, which is a crazy range [3]. The numbers vary somewhat by potato variety but much more by the cooking and serving method. Baked potatoes have a lower glycemic index than boiled and when potatoes are served chilled, the GI numbers decrease drastically [3].
Understanding how cooking methods alter the glycemic index (GI) of potatoes requires examining the role of resistant starches (also called ‘digging where the potatoes grow’). Resistant starches are carbohydrates that “resist” being digested in the small intestine, similar to dietary fiber [2]. Resistant starches pass into the large intestine where they are fermented by gut bacteria and act like prebiotics, feeding beneficial bacteria [4]. This process can create a healthier gut microbiome, which is associated with improved digestion and overall health [4]. Resistant starch amounts vary slightly by potato variety and are heavily affected by the preparation method [2]. Heating the potatoes in water degrades the starches (making them easier to digest) and chilling the potatoes helps the starches recrystallize into a resistant form [1, 2, 5]. Cooking “low and slow” increases resistant starch, and baking is better than microwaving, which is better still than boiling [5]. Boiling potatoes also leeches out vitamins and nutrients like vitamin C and potassium, which are quite high in potatoes [2].
Because resistant starches are not digested in the small intestine, they have minimal impact on blood sugar levels, which can improve insulin sensitivity for Type 1 diabetics [4]. If you think of normal carbs as venomous snakes, resistant starches are like St. Patrick, banishing other carbs from your small intestine. Besides cooked and cooled potatoes, other foods that contain resistant starches include green bananas, beans and lentils, whole grains like barley, and cooked and cooled rice [4].
Water surrounds the island of Ireland, just like water surrounds carbohydrates in a raw potato. Around 80% of a potato’s weight is water, which helps potatoes make you feel full [2]. Satiety is how full you feel after eating a food, and a food with high satiety makes you feel fuller with fewer calories [2]. Potatoes, especially boiled and mashed potatoes, have the highest satiety score of any food in multiple studies [2]! Because of effects like this, some replace the glycemic index with a different measure, Glycemic Load (GL). Glycemic load links the glycemic index to the serving size, so potatoes tend to do much better. The “middle” range for glycemic load is between 10 and 20, and potatoes range from 8-21 [3]. When chilled, potatoes are almost all in the “low” glycemic load range, ranging from 8-11 [3].
So, are potatoes healthy? Long-term clinical trials are needed to find this out for sure [2, 6, 7]. The best data we have for health comes from non-experimental, epidemiological studies where researchers can’t control extra variables. These studies find no definitive data on potatoes being unhealthy [2, 6]. The data we do have show no evidence for increased rates of obesity, type 2 diabetes, or cardiovascular disease for potato-eaters [2, 6]. These data don’t hold up for people whose source of potato is “french fries,” however [6]. So this St. Patrick’s day, let’s wear some green, dance a jig, and appreciate the potato!
Creative Director Benton Lowey-Ball, BS, BFA
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References:
[1] Sagili, V. S., Chakrabarti, P., Jayanty, S., Kardile, H., & Sathuvalli, V. (2022). The glycemic index and human health with an emphasis on potatoes. Foods, 11(15), 2302. https://pmc.ncbi.nlm.nih.gov/articles/PMC9368276/
[2] Robertson, T. M., Alzaabi, A. Z., Robertson, M. D., & Fielding, B. A. (2018). Starchy carbohydrates in a healthy diet: the role of the humble potato. Nutrients, 10(11), 1764. https://www.mdpi.com/2072-6643/10/11/1764?gsid=ba4def2d-71eb-4462-a8ac-9fda238e474b
[3] Atkinson, F. S., Brand-Miller, J. C., Foster-Powell, K., Buyken, A. E., & Goletzke, J. (2021). International tables of glycemic index and glycemic load values 2021: a systematic review. The American journal of clinical nutrition, 114(5), 1625-1632. https://www.sciencedirect.com/science/article/pii/S0002916522004944
[4] Fuentes-Zaragoza, E., Riquelme-Navarrete, M. J., Sánchez-Zapata, E., & Pérez-Álvarez, J. A. (2010). Resistant starch as functional ingredient: A review. Food Research International, 43(4), 931-942. https://www.sciencedirect.com/science/article/abs/pii/S0963996910000621
[5] Raatz, S. K., Idso, L., Johnson, L. K., Jackson, M. I., & Combs Jr, G. F. (2016). Resistant starch analysis of commonly consumed potatoes: Content varies by cooking method and service temperature but not by variety. Food Chemistry, 208, 297-300. https://pubmed.ncbi.nlm.nih.gov/27132853/
[6] Borch, D., Juul-Hindsgaul, N., Veller, M., Astrup, A., Jaskolowski, J., & Raben, A. (2016). Potatoes and risk of obesity, type 2 diabetes, and cardiovascular disease in apparently healthy adults: a systematic review of clinical intervention and observational studies12. The American journal of clinical nutrition, 104(2), 489-498. https://ajcn.nutrition.org/article/S0002-9165(22)04562-2/fulltext
[7] McGill, C. R., Kurilich, A. C., & Davignon, J. (2013). The role of potatoes and potato components in cardiometabolic health: A review. Annals of medicine, 45(7), 467-473. https://www.tandfonline.com/doi/full/10.3109/07853890.2013.813633
