While turnips and potatoes share some similarities -- the former is a type of taproot, while the latter is an edible tuber -- the vegetables have some differences. Turnips and potatoes are both healthy foods, but the two vegetables offer dramatically different nutritional profiles. Because of this, you may find one food or the other inappropriate for your dietary needs. You should note that cooking these foods can alter the nutritional content.
Potatoes are significantly higher in calories than turnips, as a 100 gram potato contains 77 calories, a 100 gram turnip just 28 calories. If you're trying to lose weight, turnips would be the preferable choice, given the same serving size. It would take 14 more minutes of weightlifting to burn the calories gleaned from a 100 gram potato than a 100 gram turnip.
Turnips and potatoes both contain very little fat, with turnips providing .1 gram per 100 grams, and potatoes just .09 grams in each 100 gram serving. While dietary fat is high in calories, it can be beneficial, as it promotes the absorption of some vitamins and helps you feel full after meals.
Turnips are considerably lower in carbohydrates than potatoes. Each 100 gram serving of turnips contains 6.4 grams of carbohydrates, while 100 grams of potatoes comes with 17.5 grams. Carbohydrates are your body's primary source of energy, so potatoes may be more suitable for pre-exercise meals.
Turnips and potatoes contain roughly the same amount of fiber. A 100 gram serving of turnips contains 1.8 grams, compared to the 2.2 grams you get from potatoes. Fiber is a vital nutrient that promotes feelings of fullness, prevents constipation and aids in digestion.
Both turnips and potatoes are low in protein. Potatoes are slightly higher in this nutrient, as potatoes contain 2 grams of protein, while turnips contain .9 grams. Protein is important because it helps build and repair your body's tissues.
Potatoes and turnips have dramatically different mineral contents. Potatoes are much higher in potassium, while turnips contain more calcium. Turnips are also higher in sodium, which can be a drawback, as too much sodium can lead to water retention and high blood pressure.
Neither potatoes nor turnips are particularly rich in vitamins, but they do contain some. Turnips have slightly more vitamin C, while potatoes provide you with more folate and choline, which are both B vitamins. Neither vegetable is a significant source of vitamins A, D or E.