Potatoes

One medium potato with skin contains about 161 kilocalories, 88 percent of which is carbohydrate, 10 percent of which is protein, and 1 percent of which is fat.^[1] Potatoes contain a broad array of vitamins and minerals but are particularly rich in potassium, manganese, vitamin C, and vitamin B6.^[1] On a calorie-for-calorie basis, potatoes contain about as much fiber as whole grains — 3.8 grams per medium potato with skin.^[1]

Among plant foods, potato protein stands out as being unusually complete and digestible.^[2] In other words, it has an amino acid profile similar to what the human body needs to maintain itself and build muscle, while most plant foods have to be combined with other plant or animal foods to achieve this. However, the total amount of protein in potatoes is modest at 4.3 grams per medium spud.^[1]

Potatoes contain a significant amount of non-essential phytochemicals. These include polyphenols, especially phenolic acids (also found in coffee) and, in purple potatoes specifically, anthocyanins (also found in blueberries),^[3] which are most concentrated in the skin but also present in the flesh.^[3] Observational research suggests that foods high in polyphenols, including anthocyanins, may reduce the risk of cardiovascular disease and type 2 diabetes^[4][5].

Randomized controlled trials report that these polyphenols found in potatoes reduce blood pressure and improve endothelial function, consistent with the idea that they may lower cardiovascular disease risk.^[6][7] However, there is no direct evidence that consuming potatoes prevents cardiovascular events.

Yellow-fleshed potatoes can also contain a significant amount of carotenoids, especially lutein (also found in green vegetables like spinach).^[8] Lutein plays a role in preventing and slowing the progression of macular degeneration, a common cause of visual impairment in the elderly.^[9]

Potatoes are one of the richest dietary sources of potassium, an important mineral for keeping blood pressure within a healthy range and preventing cardiovascular events like heart attack and stroke.^[10][11] A commonly-used dose in studies that report blood pressure reductions from potassium supplementation is 2.3 grams per day, approximately the amount in two medium potatoes.^[10][1]

One randomized controlled crossover trial compared the impact of non-fried potatoes, fried potatoes, potassium supplements, and usual diet on blood pressure over 17-day diet periods in people with high blood pressure.^[12] Systolic blood pressure tended to be lower on the non-fried potato diet vs. usual diet, but this didn’t reach statistical significance. In contrast, the decline in systolic blood pressure from baseline was significantly greater for the non-fried potato group vs. usual diet, but this was a secondary outcome. The decline in blood pressure did not reach statistical significance on the diet with fried potatoes or potassium supplements.

An additional small trial reports that eating eight small purple potatoes per day for four weeks reduces blood pressure in people with high blood pressure (hypertension), but the finding should be interpreted with caution due to major methodological weaknesses.^[13] For example, the paper doesn’t statistically compare blood pressure in the intervention group against the control group, which is the most important comparison in a controlled trial. Together, these two randomized controlled trials provide modest evidence that eating non-fried potatoes can lower blood pressure, consistent with the high potassium content of spuds.

In a study testing the satiety (fullness after a meal) effects of 32 commonly-eaten foods, boiled potatoes were the most sating per calorie, beating other high-satiety foods like fish, steak, fruit, and oatmeal.^[14] Baked potatoes are expected to be comparable due to their similar composition and palatability. This suggests that potatoes may be helpful for controlling calorie intake and body weight, although this hasn’t been directly tested. It’s also important to note that this study used plain potatoes, and the effects would likely be different with added butter, cheese or other calorie-dense toppings.

Potatoes are unusually nutritionally complete. Although a potato-only diet lacks significant quantities of vitamins A, E, and B12, most other essential nutrients are present at adequate or near-adequate levels. Small experiments in the early 20th century reported that people can eat almost nothing but potatoes for 5.5 to 10 months with no apparent ill effects.^[15][16]

Most types of potatoes, such as the common russet, have a high glycemic index. This means they increase blood glucose more than most other foods containing the same amount of carbohydrate. However, this varies by potato type and processing method. For example, frying potatoes, or cooling them after cooking, tends to lower their glycemic index.^[17] Potatoes also have a high insulin index, meaning they increase insulin secretion more than most other foods.^[18] The health implications of this aren’t entirely clear. Observational studies report no consistent association between the habitual glycemic index of the diet and body mass index, a measure of body fatness. Similarly, randomized controlled trials report no consistent effect of glycemic index on body weight.^[19] In contrast, observational studies report that diets higher in glycemic index tend to be associated with a higher risk of developing type 2 diabetes,^[20][21] and a higher risk of cardiovascular disease in women but not men.^[22][23][24] In addition, people with diabetes may have a harder time controlling their blood sugar levels when they eat high-glycemic foods.^[25]

When considering potatoes specifically, there is no consistent association between the intake of boiled, baked, or mashed potatoes and cardiovascular risk in observational studies, but they are correlated with a slightly higher risk of type 2 diabetes. Intake of fried potatoes is more strongly associated with the risk of cardiovascular disease and type 2 diabetes in these studies, despite the lower glycemic index of fried potatoes.^[26][27]

Potatoes contain oxalates, which can contribute to the formation of kidney stones in susceptible people.^[28][29]

Potatoes also contain the toxic glycoalkaloids solanine and chaconine, which can cause digestive distress and in very rare cases can be fatal. These are only present in potentially dangerous amounts in potatoes that are green, damaged, diseased, and potato sprouts. Peeling potatoes removes most of their glycoalkaloid content.^[30]

Per calorie, potatoes are not as dense in vitamins and minerals as low-calorie vegetables like greens, broccoli, and carrots. This isn’t necessarily a problem if potatoes are eaten as a starch alongside vegetables, as one would eat rice or bread. But if they’re viewed as a vegetable and eaten instead of low-calorie vegetables, they may lead to a lower intake of vitamins and minerals and a higher calorie intake.

Potatoes are commonly eaten baked, boiled, mashed, and fried. Relative to the other three preparation methods, frying results in a lower glycemic index, higher calorie density, greater palatability, and lower satiety per calorie.^[17][14] This is likely to increase calorie intake and contribute to weight gain. Consistent with this, an observational study reported that people who increase their intake of French fries and potato chips experienced much more weight gain than people who increased their intake of baked, boiled, or mashed potatoes.^[31] This must be interpreted with some caution due to the possibility of confounding by other diet and lifestyle factors. Adding calorie-dense toppings or ingredients like butter and cheese to baked, boiled, and mashed potatoes is expected to make them less filling per calorie.

Cooling potatoes after cooking tends to reduce their glycemic index and insulin index, even if they are subsequently reheated, although this is not always the case.^[32][33] To the extent that dietary glycemic index and insulin index may impact health, cooling potatoes prior to eating may make them healthier.

High-temperature cooking of some foods creates a carcinogen called acrylamide, and fried potatoes are one of the largest dietary exposures to this compound.^[34] Although dietary acrylamide is a theoretical concern, observational studies have not reported consistent links between dietary acrylamide intake and the risk of cancer at any site, with the possible exception of kidney cancer.^[35] Soaking potatoes prior to frying reduces the formation of acrylamide.