Yam

What is Yam?

Yam is the starchy underground tuber of Dioscorea alata, a climbing vine. It is a staple food across the Caribbean and much of the tropics. Cooks know it as yanm in Haiti and ñame in Cuba and the Dominican Republic.

The tuber is boiled, roasted, fried or mashed. Some kinds have white or cream flesh. Others are deep purple, and these are often sold as purple yam or ube.

True yam is not the same plant as sweet potato, and not the same as the "wild yam" (Dioscorea villosa) sold in creams and capsules. Labels mix these names up often. Check the Latin name if you are buying a supplement.

In folk practice yam was eaten as a strengthening food, and as a food for women after childbirth. Long use in a tradition is not proof that something works, and it is not proof that it is safe. As a cooked food yam is well tolerated by most people; as a medicine, the human evidence is thin.

How does Yam work?

Most of what yam does in the body, it does as food. It is a source of starch, fibre and potassium.

Cooked and cooled yam holds resistant starch. This is starch that passes to the large bowel and feeds gut bacteria. Fibre of this kind is known to help bowel regularity in people.

Yam contains diosgenin, a plant steroid. Chemists can turn diosgenin into hormone drugs in a factory. Your body cannot do that step, so eating yam or rubbing on yam cream does not make progesterone.

Purple yam is rich in anthocyanins, the pigments that give the colour. In test-tube work these mop up reactive molecules. Whether that changes anything in a person who eats yam is not established.

In animal studies, yam extracts have lowered blood sugar and blood fats. These results have not been confirmed by good human trials.

Raw yam also holds saponins and needle-shaped oxalate crystals. These irritate the mouth and gut, which is why yam is always cooked.

What forms does Yam come in?

Fresh tuber is the main form. It is sold whole or in cut pieces in Caribbean, African and Asian markets.

Yam flour and dried flakes are used for porridge, dumplings and fufu-style dishes.

Purple yam powder is sold for baking, ice cream and drinks.

Capsules and tablets labelled "yam extract" or "diosgenin" exist. Quality and content vary a lot between brands.

Topical "wild yam" creams are marketed for menopause. These usually use Dioscorea villosa, a different plant, and the hormone claims are not supported.

Where it comes from:

Yam travelled from Asia and West Africa into the Caribbean and became a core food crop there. Enslaved and free communities grew it on provision grounds, and it stayed central to cooking and to holiday meals.

In Haitian, Cuban and Dominican home practice, yam was fed to people who were weak, recovering from illness, or newly delivered of a baby. It was seen as a food that builds back strength.

Some households also used the grated raw tuber or the slimy inner flesh as a poultice on sores and swellings. Folk texts record this use. It is described here as history, not as advice to try it.

What does Yam help with?

• Everyday nourishment and energy: This is what yam is good for, and it is not in doubt. It is a filling source of starch, fibre, potassium and vitamin C. It works as a staple food, not as a treatment.
• Bowel regularity: Yam adds fibre and resistant starch to a meal. Fibre-rich diets are known to help keep bowels regular in people. No trial has tested yam on its own for constipation.
• Recovery food after illness or childbirth (traditional): Caribbean households fed yam to people who were weak or recovering. The reasoning was that it is soft, filling and easy to eat. There are no trials testing yam for recovery, and it does not treat the illness behind the weakness.
• Menopause symptoms (claimed, not supported): Products trade on the fact that diosgenin can be turned into hormone drugs in a lab. Your body does not do that conversion. Trials of wild yam cream for hot flushes have not shown a clear benefit over placebo.
• Blood sugar and blood fats (early, unproven): Animal studies have shown lower blood sugar and lower blood fats with yam extracts. Human evidence is limited to one very small, uncontrolled feeding study. Do not treat yam as a way to manage diabetes or cholesterol.

Which foods are rich in Yam?

Yam is itself a food, so there is no need for a food source list. Look for Dioscorea alata in Caribbean, African, Latin American and Asian grocers. It may be labelled yanm, ñame, water yam, greater yam or ube.

What are the side effects of Yam?

• Gas, bloating or loose stools from a large portion
• Itching, burning or numbness in the mouth if the yam is undercooked
• Nausea and vomiting after eating raw or badly cooked tuber
• Itchy skin rash from handling the raw sap while peeling
• Allergic reaction, including rash, swelling or wheeze (uncommon)
• Oxalate load that may matter if you form kidney stones

Good to know:

Well-cooked yam is a safe everyday food for most people. Side effects are usually mild and come from eating a lot at once.

The real problems come from raw or undercooked tuber and from the sap on the skin. Allergy to yam is uncommon but does happen, and can be serious.

Supplement extracts and creams are less well studied than the food, so less is known about their effects.

How much Yam should you take?

• Recommended daily: Yam is a food, so there is no medicinal dose. A normal serving is roughly 100 to 200 grams of cooked tuber, as you would eat any starchy root. Supplement labels for yam or wild yam extract commonly list a few hundred milligrams per capsule. That figure reflects what is printed on packs, not a recommendation to you. There is no good human evidence behind any extract amount.
• Best time of day: Time of day does not matter. Yam is eaten with meals, most often as the starch on the plate.
• With or without food: Yam is food. Eat it cooked, as part of a meal. Never eat it raw, as the raw tuber irritates the mouth and gut.
• Time to effect: As a food, it fills you up within the meal. Fibre effects on bowel habit usually show over several days. For the hormone, blood sugar or menopause claims, there is no reliable time frame. It may do nothing at all for those.
• How long to take it: As an everyday food, yam can be part of the diet indefinitely, like potato or rice. For extracts and creams, no safe or useful length of use has been set. Long-term studies do not exist.