Orange sweet potatoes are an exceptional source of beta carotene – but don’t mistake them for yams.zeleno/Getty Images/iStockphoto
Potatoes are often dismissed as a starchy indulgence, and one that’s inferior in nutrients to many other vegetables.
Yet the much-maligned potato is far more nutritious than its reputation suggests. That includes white potatoes, too.
From white and yellow to orange and purple, here’s how potatoes stack up nutritionally – and why they’re worthy of a place in your regular diet, not just the Thanksgiving meal.
White potato nutrition
When it comes to their nutrient profiles, white potatoes, including russet, Yukon Gold, red and new, are very similar.
All provide fibre, vitamin B6, folate, vitamin C and magnesium, along with smaller amounts of other vitamin and minerals.
And they’re an excellent source of potassium, a mineral that helps regulate blood pressure and is needed for muscle contraction and nerve transmission.
A medium-sized, white-fleshed potato supplies 600 to 900 mg of potassium, depending on how it’s prepared. Baked potatoes retain more potassium than boiled potatoes because some of the mineral leaches into cooking water.
A medium baked russet potato, for example, serves up 952 mg of potassium, more than twice the amount found in two bananas. Women and men are advised to consume 2,600 and 3,400 mg of potassium daily, respectively.
The glycemic index of white potatoes varies
Potatoes differ in how quickly they raise blood glucose levels, which is indicated by their glycemic index (GI) value.
Foods with a high GI cause a sharp increase in blood glucose that declines rapidly. Foods with a low GI, on the other hand, are digested more slowly producing a smaller, steadier rise in blood glucose.
A low-glycemic diet is thought to support metabolic health by improving glucose control and insulin sensitivity.
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Russet potatoes, the highest in starch of white potatoes, have a high GI value.
Yukon Gold and red potatoes contain less starch than russets and generally have a medium GI.
New potatoes, because they’re harvested before fully maturing, are less starchy than mature potatoes and often have a low GI value.
Keep in mind, though, a potato’s glycemic index can vary depending on how it’s prepared.
How do sweet potatoes rate?
All sweet potatoes, including orange-, yellow- and white-fleshed varieties, are good sources of fibre, vitamin C and potassium.
A medium-sized (114 g) baked sweet potato, for instance, provides 4 g of fibre, 22 mg of vitamin C and 542 mg of potassium.
Where sweet potatoes differ, though, is their level of beta-carotene, a phytochemical associated with protection from Type 2 diabetes and cardiovascular disease.
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Orange sweet potatoes are an exceptional source; a medium baked sweet potato provides an impressive 13 mg.
Yellow sweet potatoes contain some beta-carotene, but much less than orange sweet potatoes, while white sweet potatoes have very little.
There is no official recommended intake for beta-carotene, but observational studies suggest that consuming 3 to 6 mg daily is associated with a lower risk of chronic disease.
What about purple sweet potatoes?
Purple-fleshed potatoes are similar to other sweet potatoes when it comes to fibre, vitamin C, B vitamins and potassium.
What makes them stand out, however, is their exceptional content of anthocyanins, phytochemicals that give many fruits and vegetables their deep purple, blue and red hues, including blueberries, cherries, eggplant and purple cabbage.
Depending on the variety, one half-cup of cooked purple potato can provide anthocyanin levels comparable with those found in three-quarters of a cup of blueberries.
Anthocyanins have antioxidant and anti-inflammatory properties that are thought to support healthy blood vessel function, the heart and the brain as we age.
Are yams nutritious?
The terms “yam” and “sweet potatoes” are often used interchangeably but they’re two different vegetables with distinct nutrient profiles.
Yams belong to the lily family, while sweet potatoes are related to the morning glory. The flesh of yams can vary from ivory to yellow to purple.
Yams contain a negligible amount of beta-carotene, but are very rich in potassium, with one cup of cooked yams offering 911 mg.
One cup of baked or boiled yams also supplies 5 g of fibre, 16.5 mg of vitamin C, B vitamins and some magnesium.
Beyond nutrients: appetite control, gut health
According to a landmark study published in 1995, researchers from the University of Sydney found that boiled potatoes were the most filling food of 38 foods tested.
Potatoes ranked higher than oatmeal, whole wheat pasta, apples, oranges and protein-rich foods such as beef and fish.
Researchers believe potatoes owe their satiety factor to their high water and fibre content, making them particularly filling for the number of calories they provide.
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A medium-sized baked white or sweet potato is about 75 per cent water and contains 4 g of fibre.
Potatoes also contain resistant starch, a prebiotic fibre that escapes digestion in the small intestine. Once in the large intestine beneficial gut bacterial ferment it and use it as a fuel source.
Cooking and cooling potatoes increases their resistant starch content compared with freshly cooked potatoes. Sweet potatoes have less resistant starch than white potatoes.
Sliced cold roasted potatoes with leftover turkey, anyone?
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan.