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Chinese yam

Dioscorea polystachya

Also calledShan yao (Chinese) · Dioscoreae Rhizoma (pharmacy name)

In older monographsDioscorea opposita, Dioscorea batatas

A temperate East Asian yam whose mucilage-rich tuber is both an everyday food and shan yao, a gentle 'superior' tonic of Chinese medicine first recorded in the Shennong Bencao Jing. Human evidence is thin: one randomised trial of yam porridge after bowel-cancer surgery in people with diabetes, plus animal studies.

What it is used for

  • Eaten in East Asia as a medicinal food for digestive health. A 2025 systematic review found only two human studies (one randomised) and 25 animal studies, mostly favourable but small and heterogeneous.2,1

  • In a randomised trial of 92 people with type 2 diabetes having colorectal cancer surgery, adding 150 g/day of yam porridge for 3 weeks improved fasting and after-meal glucose, healing time (11.0 vs 13.9 days) and infection rate (6.8% vs 22.2%). Multi-herb Chinese prescriptions containing Dioscorea have also been tested in diabetes.2

  • Diarrhoea
    Traditional

    Chinese medicine uses it to tonify the spleen and stomach and to stop diarrhoea and discharges. Animal studies show protective effects on the gut lining, including in antibiotic-associated diarrhoea in mice.1,2

  • General tonic
    Traditional

    A superior-grade tonic in the Shennong Bencao Jing for the lungs, spleen and kidneys and the 'five fatigues'; used in formulas such as Liuwei Dihuang pills.1,4

How it is prepared

food

The fresh tuber cooked into porridge or other dishes; in TCM it is also cooked with astragalus as a medicinal porridge.

Liang et al. trial (as summarised by Lee 2025): yam porridge 150 g/day for 3 weeks.

Blood sugar and diabetes · Indigestion and dyspepsia

decoction

Dried sliced tuber simmered, usually within multi-herb Chinese formulas.

Diarrhoea · General tonic

Amounts are as recorded by the named source, not a recommendation.

Safety

Pregnancy
Insufficient data
Breastfeeding
Insufficient data

Do not use if

  • Yam allergy (dioscorin)

Side effects

  • Rare food allergy: anaphylaxis and oral allergy syndrome after boiled yam have been reported

Toxicity

Eaten widely as a food. The storage protein dioscorin (DB3S) survives cooking and caused anaphylaxis in three people who ate boiled yam; people with this allergy should avoid both raw and cooked yam.

In the healing traditions

  • Traditional Chinese Medicine

    Shan yao (Dioscoreae Rhizoma)

    Sweet and neutral, entering the lung, spleen and kidney meridians: tonifies the spleen and benefits the stomach, generates fluids and benefits the lungs, nourishes the kidneys and secures essence, and stops discharge and diarrhoea. Cooked with astragalus as a medicinal porridge, and an ingredient of Liuwei Dihuang and Shanyao Shenqi pills.

    Shennong Bencao Jing (superior grade)

  • Modern pharmacology

    Diosgenin source

    The tuber contains dioscin and its sapogenin diosgenin, the type of plant steroid used industrially (mostly from other yam species) as a starting material for cortisone, pregnenolone and progesterone.

Active compounds

mucilage polysaccharides
the main focus of research; immunomodulatory and gut-protective in animal studies
resistant starch
about half the dry weight of the tuber; raw yam starch lowered triglycerides and LDL cholesterol in rodents
dioscin and diosgenin
steroidal saponin and sapogenin; diosgenin is a precursor for semi-synthesis of steroid hormones
dioscorin
main storage protein, a carbonic anhydrase with antioxidant activity; also the heat-stable allergen behind yam anaphylaxis
allantoin
present in the tuber

History

Shan yao was recorded in the Shennong Bencao Jing as a superior herb, first as a wild plant, but has been almost entirely cultivated for about the last 400 years; Henan province is its main and most prized production area. It has been used in China for more than 2,000 years for diarrhoea, diabetes and asthma, and is now exported worldwide as a food.

Sources

  1. 1.Jia H et al. Preclinical research and potential clinical application of traditional Chinese medicine in cancer treatment: take Astragalus and Dioscorea opposita as an example. Front Pharmacol 2025
  2. 2.Lee JH et al. The effect of Dioscoreae Rhizoma on gastrointestinal function: a systematic review. Nutrients 2025;17:2943
  3. 3.Epping J, Laibach N. An underutilized orphan tuber crop — Chinese yam: a review. Planta 2020;252:58
  4. 4.Ren X et al. Botany, traditional applications, phytochemistry, pharmacologic activities, clinical application, and quality control of Dioscoreae Rhizoma: a comprehensive review. J Ethnopharmacol 2026 (abstract)
  5. 5.Xu YY, Yin J. Identification of a thermal stable allergen in yam (Dioscorea opposita) to cause anaphylaxis. Asia Pac Allergy 2018 (abstract)
  6. 6.GBIF: Dioscorea polystachya Turcz.

Reference, not prescription. Nothing here is medical advice. Herbs can interact with medicines and be dangerous in pregnancy; tell your doctor or pharmacist about anything you take.