A Scientific Comparison: Potato, Sweet Potato and Purple Potato

All three grow in the ground and serve as a starchy side dish, but botanically they are not related at all: the potato belongs to the nightshade family (along with tomato and eggplant), and the sweet potato to the morning glory family. The similarity between them is purely functional.

The short answer to “which is healthier”: the sweet potato wins on vitamin A and fiber, the potato wins on potassium and satiety, and the purple potato wins on antioxidants. The difference between them is much smaller than the difference created by the cooking method — a boiled and cooled potato is far healthier than a fried sweet potato.

1. White/Yellow Potato

One of the most common carbohydrates in the world, and one that gets undeservedly bad press.

• Benefits:
  • Potassium: 535 mg per 100 grams baked with the skin — more than a banana (358 mg). A critical mineral for regulating blood pressure.
  • Exceptional satiety: On the Satiety Index, boiled potato ranks first among all the foods tested — three times higher than white bread for the same number of calories.
  • Resistant starch: Cooking and then cooling in the fridge turns some of the starch into “resistant starch,” which behaves like dietary fiber, doesn’t raise blood sugar and feeds gut bacteria. Reheating doesn’t completely cancel the effect.
  • Vitamin C: About 10 mg per 100 grams — not something to take for granted in a root vegetable.
• Downsides:
  • High glycemic index: Especially as hot mashed potatoes or baked.
  • Solanine: Green skin or sprouts contain solanine, a toxic alkaloid. Remove green parts and sprouts, and store potatoes in the dark.
  • Cooking method: Fried French fries double or triple the calories and add acrylamide.

2. Sweet Potato

• Benefits:
  • Vitamin A: Orange sweet potato provides about 380% of the daily intake per 100 grams, in the form of beta-carotene. This is the biggest nutritional gap between the three vegetables.
  • More fiber: 3.3 grams per 100 grams, compared with 2.2 in potato.
  • Lower glycemic index — but only when boiled in water. See the explanation below; this is a point most sources miss.
  • Vitamin C: About 20 mg per 100 grams, double that of potato.
• Downsides:
  • More sugar: About 4–6 grams per 100 grams, compared with less than a gram in potato.
  • Less potassium than potato (475 mg compared with 535).
  • Oxalates: A relatively high amount, relevant for people prone to calcium oxalate kidney stones.

3. Purple Potato (Vitelotte)

An ancient variety that originates in the Andes mountains, where hundreds of colorful potato varieties are grown.

• Benefits:
  • Anthocyanins: The purple pigment belongs to the same family of antioxidants found in blueberries and red cabbage. The antioxidant content of purple potatoes is 2–3 times higher than that of white potatoes.
  • Blood pressure: A small controlled study found a slight drop in blood pressure after eating purple potatoes twice a day, without weight gain.
  • Lower glycemic index than white potato — the polyphenols slow down starch breakdown.
  • The color holds up in cooking, unlike many purple vegetables.
• Downsides:
  • Price and availability — expensive and not always available.
  • Less vitamin A than sweet potato — it doesn’t replace it.
  • Drier texture, less suitable for mashing.

Comparison table (100 grams, baked with the skin)

The glycemic index — the point most sources miss

The claim that “sweet potato has a lower glycemic index than potato” is only partly true, and depends entirely on the cooking method:

Two practical conclusions:

1. Baked sweet potato is not a “low glycemic index sweet potato.” Long baking breaks the starches down into simple sugars — that’s why baked sweet potato is sweet and caramelized — and its glycemic index jumps to a level similar to that of a baked potato.
2. Cooling lowers the glycemic index of both thanks to the formation of resistant starch. A cold potato salad is an inherently different dish from hot mashed potatoes.

Note: Glycemic index values vary greatly between varieties, measurement sources and cooking times. Treat them as an order of magnitude, not an exact number.

So which is healthier — sweet potato or potato?

The answer depends on what you’re missing:

• For vitamin A, eyesight and skin → sweet potato, by a huge margin.
• For potassium, blood pressure and maximum satiety → potato.
• For antioxidants → purple potato.
• For blood sugar balance → boiled sweet potato, or boiled and cooled potato.
• For athletes after a workout → potato, thanks to the readily available carbohydrate and potassium.
• For weight loss → both are similar in calories. Potato leads in satiety, so it has a slight advantage.

The most important conclusion of all: the difference between sweet potato and potato is negligible compared with the difference between one cooking method and another. A deep-fried sweet potato is less healthy than a boiled potato, by a wide margin. Details on baking methods are on the baked potato page.

Summary and conclusions

There is no absolute winner. The white potato is an excellent source of potassium — more than a banana — and the most satiating food ever measured; just prefer it boiled and cooled over hot mashed. The sweet potato is an exceptional supplier of vitamin A and contains more fiber, but it only keeps a low glycemic index when boiled in water. The purple potato provides 2–3 times the antioxidants, at a higher price.

The best approach is to vary between them — and to put more thought into the cooking method than into the choice of variety.