A sweet potato is neither a potato nor a yam. It is the root of a plant in the morning glory family, while the white potato is a nightshade. True yams (Dioscorea) are a third group, mostly grown in Africa, with rough, scaly skin.
What US stores sell as a yam is usually a soft, orange sweet potato. The USDA (US Department of Agriculture) requires the words “sweet potato” on the label beside it.
The sweet potato genome even carries bacterial genes. Researchers found a stretch of DNA from Agrobacterium in all 291 cultivated types they examined. The authors call it a naturally transgenic food crop.
The orange kind tops our beta-carotene ranking: 9,444 µg (micrograms) per 100 g boiled, first of 85 foods. Gram for gram, only 1 of 93 foods has more vitamin A.
That is why it has been used against vitamin A deficiency in Africa, where most sweet potatoes grown were white-fleshed. Breeders there developed 42 orange varieties. Trials in Mozambique, Uganda and Kenya found that growing and eating them raised vitamin A intake.
Sweet potato is not an efficient source, though. Men in one trial needed about 13 µg of its beta-carotene to make 1 µg of retinol, against about 6 µg for pure beta-carotene. Retinol is the body’s ready-made vitamin A.
How you cook it matters for blood sugar. In a test of ten varieties in ten healthy adults, boiled sweet potato had a glycemic index of 41 to 50. Baked and roasted ones ran from 79 to 94. The glycemic index measures how quickly a food raises blood sugar.
Our nutrition table lists 46 for boiled. Many of the studies below used extracts, drinks or leaves, so they say less about a plate of sweet potatoes than they seem to.
Health benefits of sweet potatoes
The top findings from 26 studies, strongest evidence first
What the stars mean
- Strong. Several randomized trials, pooled in a meta-analysis, point the same way, or regulators (FDA or EFSA) have approved the claim.
- Moderate. Good randomized trials support it, but there are fewer of them, or their results vary.
- Limited. Small, short or single trials, or mixed results. Promising, but it needs confirmation.
Population and lab studies get no stars: they show a link or a mechanism, not proof.
How we rate evidence →- ★★More vitamin A from orange-fleshed typesIn 180 children, 125 g a day of orange-fleshed sweet potato raised liver vitamin A more than white-fleshed. In Ugandan families, it cut inadequate vitamin A intake by over 30 percentage points in young children.
- ★Slightly lower HbA1c with an extractA Cochrane review found a 4 g daily preparation lowered HbA1c (average blood sugar over months) by 0.3 points in 2 trials with 122 people. Evidence was insufficient, and none tested the cooked vegetable.
- ★Boiling gave a lower glycemic indexBoiled sweet potato had a glycemic index (how fast a food raises blood sugar) of 41 to 50, against 82 to 94 baked. That was in 10 healthy adults; nobody with diabetes took part.
- ★Weight fell with sweet potato meal replacementIn 58 overweight workers, 132 g of white sweet potato a day as a meal replacement for 8 weeks cut weight by about 5%. A normal-diet group lost weight too.
- ★Less constipation in leukemia patientsIn 120 leukemia patients on first chemotherapy, 200 g of sweet potato a day eased constipation by day 5 compared with routine care. The result may not apply to healthy adults.
All 26 studies, strongest evidence first
Orange-fleshed sweet potato raised children’s liver vitamin A more than white
This randomized trial included 180 dewormed children aged 5 to 10 years, 90 in each group. For 53 school days they ate 125 g a day of boiled, mashed sweet potato, orange-fleshed or white-fleshed. The orange kind supplied 1,031 retinol activity equivalents (RAE, a measure of vitamin A) a day as beta-carotene; the white kind has none. The share with normal vitamin A status tended to rise from 78% to 87%, but the study was not designed to test that.
Orange sweet potato cut inadequate vitamin A intake in Ugandan families
This 2-year randomized, controlled study covered 265 children aged 6 to 35 months, 578 aged 3 to 5 years and 573 women. Inadequate intake fell over 30 percentage points in young children and over 25 in women, and the two programs (intensive and reduced) did not differ. In the intensive program, low blood retinol fell 9.5 percentage points in the 3- to 5-year-olds with complete data (396). Orange sweet potato supplied 44 to 60% of vitamin A intake at follow-up.
Promotion raised women’s vitamin A intake by 492 µg a day
This randomized, controlled study in rural Mozambique compared a 1-year and a nearly 3-year training model for orange sweet potato. It included women and children aged 6 to 35 months or 3 to 5.5 years. Under the first model, net intake rose by 263 and 254 µg RAE a day in the two child groups, similar for both models. Orange sweet potato gave 80% of vitamin A intake among the reference children, and the study measured intake, not blood levels.
Promoting orange sweet potato raised child blood retinol by 0.10 µmol/L
This quasi-experimental study (not randomized) ran for two years in a very poor area of rural Mozambique, with 741 children of mean age 13 months. Intervention children were more likely to eat it 3 or more days in the last week (55% against 8%). Their median vitamin A intake was 426 against 56 µg retinol activity equivalents. Blood (serum) retinol did not clearly rise in the control children.
Orange sweet potato for Kenyan women cut low retinol-binding protein odds 45%
Eight health facilities in western Kenya were allocated to a program with nutrition counseling, support groups and vouchers for vine cuttings, or to counseling alone. In all, 505 women in early or mid pregnancy took part. By 9 months after birth, vitamin A intake was 297 retinol activity equivalents higher in the program group (206 women assessed). Retinol-binding protein is a marker of vitamin A status, and only eight clinics were compared.
Puréed sweet potato did not clearly raise vitamin A stores
For 60 days, 14 Bangladeshi men per group added 750 µg retinol equivalents a day to a low-vitamin A diet. On cooked, puréed sweet potato, vitamin A stores rose by 0.029 mmol, which could be chance. The other sources, Indian spinach, retinyl palmitate and synthetic beta-carotene, raised stores clearly. The authors estimate that about 13 µg of beta-carotene from sweet potato gave 1 µg of retinol, against about 6 µg for synthetic beta-carotene.
Promotion led 61 to 68% of farmers to adopt orange sweet potato
This analysis of two randomized field experiments in Mozambique and Uganda asked how the projects worked. Children’s vitamin A intake doubled, and two models with different training intensity and cost had similar effects. The gain came mostly from growing the crop, not from the nutrition knowledge people gained. So the authors say smaller trainings could have worked as well.
Boiled sweet potato’s glycemic index was far below baked or roasted
Ten healthy adults (5 men and 5 women, average age 27) ate ten sweet potato varieties common in Jamaica, boiled, baked, roasted or fried. Boiled ones had a glycemic index of 41 to 50, baked ones 82 to 94 and roasted ones 79 to 93. The cooking method mattered more than the variety. The authors suggest boiled sweet potato may help limit blood sugar spikes in type 2 diabetes, but nobody with diabetes took part.
Cochrane: sweet potato preparation cut HbA1c 0.3 points; evidence insufficient
This Cochrane review covered 3 randomized trials in type 2 diabetes (140 people, 6 weeks to 5 months). All were by the same trialist and used a preparation; HbA1c measures average blood sugar over months. At 3 to 5 months, 4 g a day lowered HbA1c by 0.3% in 2 trials with 122 people. Risk of bias was unclear or high, no serious side effects were reported, and none tested the cooked vegetable.
White sweet potato extract lowered HbA1c from 6.46% to 6.25%
This randomized trial included 61 people with type 2 diabetes treated with diet only. For 5 months, 27 took 4 g a day of the extract Caiapo and 34 took a placebo (dummy pill). In the placebo group, HbA1c rose from 6.25% to 6.50%. Insulin sensitivity improved, fasting glucose fell from 138 to 128 mg/dL and fibrinogen fell, but this was an extract, not the cooked vegetable.
White sweet potato extract lowered HbA1c from 7.21% to 6.68%
This placebo-controlled trial included 61 people with type 2 diabetes managed with diet. Of these, 30 took 4 g a day of the extract Caiapo for 12 weeks and 31 took placebo. HbA1c did not change on placebo (7.04% to 7.10%), and fasting glucose fell from 143.7 to 128.5 mg/dL on the extract. It was well tolerated, but it tested an extract, not the cooked vegetable.
Sweet potato meals went with about 5% lower weight; controls lost too
In 58 overweight white-collar workers, an 8-week randomized trial tested 132 g of white sweet potato a day as a meal replacement. Body weight, body fat and BMI fell clearly in both this group and a normal-diet group. The sweet potato group had drops of about 5% in each, and 3.5% in HbA1c. A meal replacement is not the same as adding sweet potato to a usual diet.
Sweet potato daily eased constipation in leukemia patients on first chemotherapy
In this randomized trial of 120 patients, 57 ate 200 g of sweet potato a day from admission to discharge and 63 had routine care. By day 5, almost all measures of defecation had improved, though two of the Rome III items (standard constipation criteria) did not. These were patients on chemotherapy, so the result may not apply to healthy adults.
Purple sweet potato drink lowered GGT about 28 IU/L versus placebo
In this randomized, double-blind trial, 38 Japanese men aged 30 to 60 with borderline liver tests finished; none had hepatitis virus. They drank two 125 mL bottles a day for 8 weeks, each with about 200 mg of anthocyanins (purple plant pigments). The liver enzymes GGT, AST and ALT were all lower than on placebo. It tested a drink rich in anthocyanins, not the whole root.
Purple sweet potato drink lowered AST and ALT in borderline hepatitis
In this double-blind trial, 40 Caucasian adults aged 41 to 69 with borderline hepatitis drank three 125 mL bottles daily for 8 weeks, or placebo. Of them, 39 finished, and each bottle held 177 mg of anthocyanins. GGT was clearly lower on day 43 but not clearly on day 15. It was a small pilot with a drink, not the whole food.
Purple sweet potato leaves cut a urine DNA-damage marker 36.7%
In this randomized crossover trial, 16 healthy adults aged 20 to 22 ate 200 g a day of the leaves for 2 weeks. The leaves (902 mg of polyphenols) were compared with a low-polyphenol diet, and the marker drop was seen at day 7. LDL lag time, a sign of how well LDL resists oxidation, rose 15.0% and red cell glutathione 33.3%. These are markers, not illness, and the leaves are a different part of the plant from the root.
Top third: 13% lower fatty liver risk in men, not women
This cohort of 15,787 adults used a food questionnaire and an ultrasound at annual health checks. Men had 0.87 times the risk; women had 1.05 times, which was no clear link. A link is not proof of cause.
More sweet potato went with 0.33 times the odds of gallbladder cancer
This small case-control study compared 64 people with gallbladder cancer and 101 with gallstones, using diet recall. Case-control studies look back at the diets of people with and without a disease. Radish, green chili and several fruits showed similar links, so sweet potato is one of many foods. Recalling past diet can be unreliable.
Japanese eating more starchy roots had lower risk of kidney cancer death
This Japanese cohort followed 47,997 men and 66,520 women aged 40 and over for about 10 years. There were only 48 kidney cancer deaths. Taro, sweet potato and potato were studied together, so sweet potato was not looked at alone. The authors say more research is needed because the number of deaths was small.
Top leaf eaters had 35 to 57% lower lung cancer odds
This case-control study in Taiwan compared 301 people with lung cancer with 1,204 controls (602 from hospitals and 602 from the neighborhood). This is about the leaves, not the root. Vegetables overall and garland chrysanthemum showed weaker links, and diet was recalled from a questionnaire.
Traditional Okinawan eating went with less age-related disease and longer lives
This review of population data covered older Okinawans, who lived on a traditional, mildly calorie-restricted diet (10 to 15% less). The authors name sweet potatoes, marine carotenoid-rich foods and turmeric as foods that may mimic calorie restriction. The data cannot separate sweet potato from everything else in that diet.
Lab digestion: industrial puree released over ten times the beta-carotene of homemade
This lab test ran smooth, industrially heated orange sweet potato purees and homemade puree through a digestion model. Heat processing destroyed 16 to 32% of the beta-carotene, most with sterilization. Yet 0.50% was released from the homemade puree, against 5.3 to 6.2% from the sterilized and commercial ones. The authors calculate that 115 g of sterilized puree with 2% oil gives 31.4% of a young child’s daily vitamin A need, against 3.5% homemade.
Blanching and soaking before frying cut fries’ acrylamide about sevenfold
This lab study measured acrylamide, a compound that forms when starchy food is fried, in sweet potato French fries. Untreated strips fried at 165°C for 2, 3 and 5 minutes had 124.9, 255.5 and 452.0 ng/g of acrylamide. After water blanching and a soak in sodium acid pyrophosphate, they had 16.3, 36.9 and 58.3 ng/g. A calcium chloride soak lowered it further, and it measured food, not health in people.
Mold-infected sweet potatoes built up a toxin, even in healthy-looking parts
This lab study looked at roots infected with the fungus Rhizopus stolonifer, a common mold. The toxin ipomeamarone reached toxic levels in the healthy-looking parts of some roots. It has long been linked to cattle deaths in rotting sweet potatoes. The authors say the effect on human health needs assessing.
Mice on high-fat food gained less with 30% sweet potato
This study was in mice, not people. Obese mice ate a high-fat diet with 15% or 30% sweet potato or purple sweet potato for 12 weeks. The 30% dose of either lowered weight and fat, improved blood lipids and changed energy expenditure. The purple type also helped liver and kidney function.
Cell and animal studies: sweet potato lowered blood sugar, regulated blood fats
This systematic review chose 23 of 2,491 articles published from 2011 on. It covered lab-dish and animal studies of Ipomoea batatas in high blood sugar and abnormal blood fats. It did not test people.
Who should be careful with sweet potatoes
Most people can eat sweet potatoes freely. Take a little care if one of these applies:
- Kidney disease. The National Kidney Foundation lists sweet potatoes among the higher-potassium root vegetables. Most people with early-stage kidney disease or a transplant do not need to limit them. If your blood potassium is high, or you are on hemodialysis, ask your kidney dietitian how much to eat.
- Irritable bowel syndrome. Monash University lists sweet potato as low FODMAP (low in carbohydrates that can trigger gut symptoms) in a standard serve of 75 g. It says that a typical, larger serve is moderate or high. Start small if your gut is touchy.
- Moldy or rotting roots. A lab study found that roots infected with a common mold built up a toxin, ipomeamarone, even in parts that looked healthy. Throw out sweet potatoes with mold or soft rotten spots rather than cutting them away.
How to choose, store and eat sweet potatoes
- Boiled: the lowest glycemic index in the test, 41 to 50, against 82 to 94 baked and 79 to 93 roasted.
- Orange flesh with a little fat: 125 g a day of boiled, mashed orange sweet potato improved vitamin A status in children. A review of biofortified crops says fat helps the body absorb provitamin A carotenoids.
- Fried: in a lab test, fries held 125 ng/g of acrylamide after 2 minutes at 165°C and 452 ng/g after 5, so shorter frying and blanching first help.
Choose firm roots with no mold or soft spots. Keep them in a cool, dark place at about 55 to 60°F (13 to 16°C), not in the refrigerator. Below 50 to 55°F they can suffer chilling injury.
Residues are no reason to skip them. In USDA tests of 701 sweet potato samples in 2017, only one had a residue above the legal limit.
Sources
- Root vegetables and kidney disease. National Kidney Foundation. 2022.
- Low FODMAP shopping list. Monash University FODMAP blog.
- Serving size and FODMAPs. Monash University FODMAP blog.
- Wamalwa LN, Cheseto X, Ouna E, et al. Toxic ipomeamarone accumulation in healthy parts of sweetpotato (Ipomoea batatas L. Lam) storage roots upon infection by Rhizopus stolonifer. J Agric Food Chem. 2015.
- Bahado-Singh PS, Riley CK, Wheatley AO, Lowe HI. Relationship between processing method and the glycemic indices of ten sweet potato (Ipomoea batatas) cultivars commonly consumed in Jamaica. J Nutr Metab. 2011.
- van Jaarsveld PJ, Faber M, Tanumihardjo SA, et al. Beta-carotene-rich orange-fleshed sweet potato improves the vitamin A status of primary school children assessed with the modified-relative-dose-response test. Am J Clin Nutr. 2005.
- Bechoff A, Dhuique-Mayer C. Factors influencing micronutrient bioavailability in biofortified crops. Ann N Y Acad Sci. 2017.
- Truong VD, Pascua YT, Reynolds R, et al. Processing treatments for mitigating acrylamide formation in sweetpotato French fries. J Agric Food Chem. 2014.
- Sweetpotato curing and storage. Penn State Extension.
- Pesticide Data Program annual summary, calendar year 2017. USDA Agricultural Marketing Service. 2018.
- Carotenemia. Cleveland Clinic.
History of sweet potatoes
The sweet potato is a crop of tropical America. It was domesticated in Central or South America, and domesticated plants were present in Central America at least 5,000 years ago. A 2018 study of 199 specimens found that its closest relative is the wild Ipomoea trifida, which was also its progenitor.
The crop also crossed the Pacific, and how it got there is still argued. A 2013 study of modern and herbarium samples supported a transfer from the Peru and Ecuador region into Polynesia before Europeans arrived. The 2018 study instead found evidence that the plant was in Polynesia before people were, which would make a human voyage unnecessary. Wikipedia notes that the Polynesian word kumara may be related to the Quechua k’umar.
Europeans met it in 1492, when members of Columbus’s expedition were the first to taste it. The Taíno word for it was batata, which Spanish speakers kept. Spain carried the plant across the Pacific to the Philippines on the Manila galleons.
Around 1594 it reached Fujian in China from Luzon during a major crop failure, and a governor there encouraged people to grow it. In 2020, China produced about 55% of the world’s sweet potatoes.
In Japan, the Portuguese brought it to the Ryukyu Kingdom, now Okinawa, in the early 1600s. In the 18th century the scholar Aoki Konyō helped spread it, and the shogun Tokugawa Yoshimune grew it in his private garden.
The yam mix-up comes from the United States. “Yam” or “nyam” means “to eat” or “to taste” in several West African languages. Food historian Jessica B. Harris suggests that enslaved Africans gave the sweet potato the name of the true yam they knew.
In 1937 a researcher, Julian C. Miller, developed a new variety at the Louisiana Experiment Station. The trade group Louisiana Sweet Potatoes branded it the “Louisiana yam.”
In Africa, sweet potato research turned to vitamin A. In 1995 researchers saw that orange varieties could help against deficiency, and a program launched in 2009 has since reached 2.8 million households.
Sources
- Sweet potato. Wikipedia.
- What’s the difference between sweet potatoes and yams? University of Illinois Extension. 2019.
- I am what I nyam. 64 Parishes, Louisiana Endowment for the Humanities.
- Kyndt T, Quispe D, Zhai H, et al. The genome of cultivated sweet potato contains Agrobacterium T-DNAs with expressed genes: an example of a naturally transgenic food crop. Proc Natl Acad Sci U S A. 2015.
- Muñoz-Rodríguez P, Carruthers T, Wood JRI, et al. Reconciling conflicting phylogenies in the origin of sweet potato and dispersal to Polynesia. Curr Biol. 2018.
- Roullier C, Benoit L, McKey DB, Lebot V. Historical collections reveal patterns of diffusion of sweet potato in Oceania obscured by modern plant movements and recombination. Proc Natl Acad Sci U S A. 2013.
- Low JW, Mwanga ROM, Andrade M, Carey E, Ball AM. Tackling vitamin A deficiency with biofortified sweetpotato in sub-Saharan Africa. Glob Food Sec. 2017.
- Haskell MJ, Jamil KM, Hassan F, et al. Daily consumption of Indian spinach (Basella alba) or sweet potatoes has a positive effect on total-body vitamin A stores in Bangladeshi men. Am J Clin Nutr. 2004.
Frequently asked questions about sweet potatoes
Are sweet potatoes good for you?
For most people, yes. Boiled sweet potato has 76 kcal, 2.5 g of fiber and 787 µg of vitamin A (87% of the Daily Value) per 100 g. The best evidence is for the orange kind: in trials in Uganda, Mozambique and Kenya, it raised vitamin A intake in children and women.
Findings on blood sugar, weight and liver tests come from small trials, and none here reaches strong evidence.
Are sweet potatoes and yams the same thing?
No. Sweet potatoes are the roots of a plant in the morning glory family from tropical America. True yams are Dioscorea from Africa and Asia, with rough, scaly skin.
In the US, “yam” on a label is usually a soft orange sweet potato, a habit that goes back to Louisiana marketing in 1937. The USDA requires the words “sweet potato” on the label beside it.
Is a sweet potato healthier than a white potato?
No study here compares them, so neither wins on evidence. They are unrelated plants, a morning glory and a nightshade.
The clear difference is beta-carotene. Boiled sweet potato has 9,444 µg per 100 g on this page, against 1 µg in raw white potato with skin on our potatoes page. Cooking method and portion matter for both.
Is sweet potato good for diabetes?
It can fit, but the evidence is thin. Boiled sweet potato had a glycemic index of 41 to 50 in ten healthy adults, against 82 to 94 baked. But nobody with diabetes was tested.
The trials that lowered HbA1c used a white sweet potato extract at 4 g a day, not the vegetable. A Cochrane review called the evidence insufficient. Check portions and choices with your care team.
Is it better to boil or bake sweet potatoes?
For blood sugar, boiling came out best: glycemic index 41 to 50 against 82 to 94 baked and 79 to 93 roasted. No study here compares the vitamin A you absorb from each method. A review says fat helps absorb provitamin A carotenoids, so a little oil on boiled sweet potato is a sensible pairing.
How many calories and carbs are in a sweet potato?
One medium boiled sweet potato (151 g, without skin) has 115 kcal, 26.8 g of carbohydrate, 3.8 g of fiber and 2.1 g of protein. That leaves 23 g of net carbs (carbohydrate minus fiber). Per 100 g it is 76 kcal, 17.7 g of carbohydrate and 2.5 g of fiber.
These are USDA values for boiled sweet potato without skin, so baked or fried ones will differ.
Can you eat too many sweet potatoes?
In very large amounts they can turn your skin yellow-orange, called carotenemia, which Cleveland Clinic calls temporary and not dangerous. It is linked to about 20 to 50 mg of beta-carotene a day for a few weeks. A medium boiled sweet potato has about 14 mg (14,260 µg).
See a provider if the color lasts after you cut back, and ask your kidney team about portions if you have kidney disease.
Are sweet potatoes good for weight loss?
No study here tested sweet potato for weight loss on its own. In an 8-week trial in 58 overweight workers, a white sweet potato meal replacement (132 g a day) went with about 5% lower weight. But weight also fell in the group on a normal diet.
Boiled sweet potato has 76 kcal and 2.5 g of fiber per 100 g, so it fills a plate cheaply. That is a swap effect, not a proven effect of the food itself.