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A yam is the starchy tuber of a Dioscorea plant, a climbing vine grown as a staple food across West Africa, Asia, the Caribbean and the Pacific. True yams usually have rough, bark-like brown skin and white, cream or purple flesh, and they are drier and starchier than the soft orange roots many US stores label as yams, which are actually sweet potatoes. In USDA data, a cup of cooked yam has about 158 calories, 5.3 grams of fiber and close to a fifth of the Daily Value for potassium, with almost no sugar. Below: what is a yam, yam nutrition per cup, how yams compare with other starchy roots, cooking safety, and what the evidence says about wild yam creams and pills.
Peptide Labs does not sell yams or wild yam products. This article is general nutrition information, not medical advice.
Key Takeaways
- True yams belong to the genus Dioscorea; the orange roots sold as yams in most US stores are sweet potatoes, according to the Library of Congress.
- One cup of cooked yam cubes (136 g) has about 158 calories, 37 grams of carbohydrate, 5.3 grams of fiber (19% DV) and 911 milligrams of potassium (19% DV) in USDA data.
- Yams have very little vitamin A and under a gram of sugar per cup, unlike orange sweet potatoes.
- Yams are eaten cooked; case reports link undercooked bitter yam to poisoning.
- Wild yam creams contain diosgenin, but there is no evidence the body turns it into progesterone, and small studies found no change in progesterone or DHEA sulfate levels.
What is a yam?
Botanically, yams are monocots in the family Dioscoreaceae and are native to Africa and Asia, the Library of Congress explains. Yam is a major staple in Nigeria and much of sub-Saharan Africa, and a 2026 review of cultivated yams singles out Dioscorea rotundata, Dioscorea cayenensis and Dioscorea alata as key species. Dioscorea alata, known as water yam or purple yam, is widely grown in Asia and the Pacific Islands and gets its violet color from anthocyanin pigments. In East Asia, yam has a long history as a food and a traditional remedy.
In US supermarkets, true yams are mostly found in African, Caribbean, Latin and Asian grocery stores. The rough skin is peeled before cooking, and the starchy flesh can be boiled, steamed, roasted, fried or mashed and pounded.
Why US stores call orange roots yams
The soft, orange-fleshed roots labeled yams in most US grocery stores are sweet potatoes (Ipomoea batatas), a dicot in the morning glory family that is not related to true yams. According to the Library of Congress, growers used the word yam to set the softer orange type apart from firmer sweet potatoes, and USDA requires labels that say yam to also say sweet potato. So when a recipe for candied yams calls for canned yams, it means orange sweet potatoes. Our sweet potato guide covers those roots, including the full comparison most shoppers are looking for; this article is about true yams.
Yam nutrition per cup
The table uses the USDA FoodData Central SR Legacy entry for yam, cooked, boiled, drained or baked, without salt (FDC 170072), per 100 grams and per cup of cubes (136 grams). The percent Daily Value (%DV) uses the FDA Daily Values printed on Nutrition Facts labels.
| Nutrient (cooked yam, FDC 170072) | Per 100 g | % DV | 1 cup cubes (136 g) | % DV |
|---|---|---|---|---|
| Calories | 116 | Not applicable | 158 | Not applicable |
| Carbohydrate | 27.5 g | 10% | 37.4 g | 14% |
| Fiber | 3.9 g | 14% | 5.3 g | 19% |
| Total sugars | 0.5 g | No DV | 0.7 g | No DV |
| Protein | 1.5 g | 3% | 2.0 g | 4% |
| Potassium | 670 mg | 14% | 911 mg | 19% |
| Vitamin C | 12.1 mg | 13% | 16.5 mg | 18% |
| Vitamin B6 | 0.23 mg | 13% | 0.31 mg | 18% |
| Manganese | 0.37 mg | 16% | 0.50 mg | 22% |
| Copper | 0.15 mg | 17% | 0.21 mg | 23% |
| Thiamin (vitamin B1) | 0.10 mg | 8% | 0.13 mg | 11% |
| Magnesium | 18 mg | 4% | 24 mg | 6% |
| Vitamin A | 6 mcg RAE | 1% | 8 mcg RAE | 1% |
Three things stand out in the yam nutrition numbers. Potassium is high for a single food, which is why yams appear in our guide to potassium in foods. Fiber is solid at 5.3 grams per cup, covered in our guide to fiber-rich foods. And yams are almost all starch: total sugars are under a gram per cup, while vitamin A is close to zero because true yams do not carry the orange beta-carotene of sweet potatoes. Raw yam (FDC 170071) lists slightly more potassium and vitamin C per 100 grams than cooked yam in USDA data, a common pattern when vegetables are boiled, but yams are not eaten raw.
Yams compared with other starchy roots
The Dietary Guidelines for Americans count yam as a starchy vegetable, alongside potatoes, taro, cassava and plantains. Per 100 grams cooked, here is how yam compares with roots people often swap for it.
| Per 100 g, cooked (USDA FDC ID) | Calories | Carbohydrate | Fiber (% DV) | Total sugars | Potassium (% DV) | Vitamin A (% DV) |
|---|---|---|---|---|---|---|
| Yam (170072) | 116 | 27.5 g | 3.9 g (14%) | 0.5 g | 670 mg (14%) | 6 mcg RAE (1%) |
| Orange sweet potato, baked (168483) | 90 | 20.7 g | 3.3 g (12%) | 6.5 g | 475 mg (10%) | 961 mcg RAE (107%) |
| Potato, baked with skin (170093) | 93 | 21.2 g | 2.2 g (8%) | 1.2 g | 535 mg (11%) | 1 mcg RAE (0%) |
| Taro (168486) | 142 | 34.6 g | 5.1 g (18%) | 0.5 g | 484 mg (10%) | 4 mcg RAE (0%) |
Yam is denser in calories and carbohydrate than baked potato or sweet potato per 100 grams and carries more potassium than either. Taro, covered in our sibling guide to taro root, is denser still. Orange sweet potato is the clear vitamin A source in the group. Our starchy vegetables guide lists the whole group, and our low glycemic foods guide explains why cooking method and what you eat alongside a starchy food change how it affects blood sugar. People managing diabetes can include yams but should ask their clinician or dietitian how they fit a plan.
Yam research: what has been studied
Yam is studied far more in the lab than in people. A 2025 systematic review of yam and digestive function found 27 studies, but only 2 were human trials and 25 were animal experiments; the authors named the lack of high-quality human studies, small samples and differences in plant parts and extracts as limits. A 2026 review of Dioscorea alata described saponins and anthocyanins with antioxidant and other activities in lab work and said clinical studies are still needed. Neither review shows that eating yam produces a specific health effect, so read headlines about yam and hormones, blood sugar or weight with caution.
Wild yam creams and pills: the diosgenin claim
Wild yam (Dioscorea villosa) is sold as creams and capsules, often marketed as natural progesterone or a natural source of DHEA. The idea comes from diosgenin, a plant compound in wild yam. Memorial Sloan Kettering Cancer Center’s herb database explains that diosgenin has been used as a raw material to make synthetic progesterone in a lab, but there is no evidence that the human body can convert diosgenin into progesterone.
- Menopause cream trial (2001): a double-blind crossover study gave 23 women with menopausal symptoms a wild yam cream and a placebo cream for 3 months each. Serum and salivary progesterone, estradiol and FSH did not change, and symptom scores did not differ between creams.
- DHEA study (1996): in volunteers aged 65 to 82, three weeks of a dioscorea extract had no effect on blood levels of DHEA sulfate.
- Mixed small studies: MSKCC notes one small study where an oral Dioscorea alata formula did better than placebo for menopausal symptoms and another where a topical wild yam formula did not work.
- Caution: MSKCC says wild yam has estrogenic effects, so people with hormone-sensitive cancers should talk to their physicians before using it. Anyone pregnant, nursing or using hormone therapy should ask a clinician first.
Supplement quality also varies; our guide to third-party tested supplements explains what a testing seal does and does not mean. Eating yam as food is a different matter from wild yam extracts, and none of the hormone claims apply to a bowl of boiled yam.
How to cook yams safely
- Always cook: yams are eaten cooked. A 2025 report from Nigeria described two men who had seizures and lost consciousness after eating undercooked bitter yam (Dioscorea dumetorum); both recovered with hospital care. A 2026 review of yam species stresses that processing has a critical role in reducing potential toxic effects.
- Peel and cut: scrub, peel the thick skin and cut the flesh into even chunks so it cooks through.
- Cooking methods: boil, steam, roast or fry until tender all the way through.
- Potassium limits: yams are high in potassium in USDA data. Kidney disease and some medicines change how much potassium is right for you; ask your care team and see our potassium guide.
- Allergy: yam is not one of the nine major food allergens that US labels must declare, but any food can cause a reaction. Get urgent care for swelling or breathing trouble, and see an allergist for unclear symptoms.
Frequently Asked Questions
What is a yam?
A yam is the starchy tuber of a Dioscorea vine, with rough brown skin and white, cream or purple flesh. It is a staple in West Africa, Asia, the Caribbean and the Pacific.
Are the yams in US grocery stores real yams?
Usually not. The orange roots labeled yams are sweet potatoes, and USDA requires those labels to say sweet potato too. True yams are sold mostly in international markets.
How many calories are in a cup of yams?
About 158 calories per cup of cooked yam cubes (136 grams) in USDA data, with 5.3 grams of fiber.
Are yams healthy?
Yams supply fiber, potassium, vitamin C, vitamin B6, manganese and copper with very little sugar or fat. They are also starchy and calorie-dense, so portion size matters.
Can you eat yams raw?
Yams are eaten cooked. Undercooked bitter yam has been linked to poisoning cases, so cook yams until tender throughout.
Does wild yam cream contain progesterone?
No. Wild yam contains diosgenin, which labs can use to make progesterone, but there is no evidence the body converts it, and a small trial found no change in progesterone levels.
Questions about a label? Contact us or read our Buyer’s Guide. Food comes first; follow the label and ask a healthcare provider before starting a supplement, especially if you take medicines, are pregnant or have a food allergy. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Last reviewed October 2026.
Related guides: Taro Root: Taro Nutrition, Poi, Leaves and Cooking Safety, Sweet Potato Nutrition: Calories, Vitamin A and Sweet Potato vs Potato, Starchy Vegetables: List, USDA Nutrition and Non-Starchy Swaps.