No, Crab and Persimmon Won’t Turn Into Arsenic in Your Stomach

Another message came through the family group chat. Crab and persimmon. A skull. The text: equals white arsenic.

Autumn arrives, and the message arrives with it. It sounds like a chemical formula. Persimmon has vitamin C. Crab has arsenic. Vitamin C reduces pentavalent arsenic to trivalent arsenic. Trivalent arsenic is white arsenic.

The formula looks clean. The body does not work that way.

The arsenic in crab is not the arsenic in white arsenic

Arsenic takes many forms. Inorganic arsenic is highly toxic. Organic arsenic has low toxicity. Most arsenic in seafood is organic, such as arsenobetaine. The body excretes most of it quickly. Crab, shrimp, and shellfish all follow this pattern.

China sets limits on inorganic arsenic in aquatic products. Crab from legitimate channels has inorganic arsenic far below dangerous levels.

Vitamin C is not magic

Vitamin C can reduce pentavalent arsenic to trivalent arsenic under certain conditions. “Can react” and “can poison a person in the stomach” are different claims.

The reaction needs concentration, an acid-base environment, and time. In the stomach, persimmon’s vitamin C is diluted by gastric acid. The arsenic content in crab is extremely low. The reaction time is limited. Synthesizing white arsenic on the spot by eating crab and persimmon is impossible.

Dose is a wall

Talking about toxicity while ignoring dose is scare-mongering.

Suppose all the arsenic in crab were inorganic pentavalent arsenic, and all of it were reduced by vitamin C to trivalent arsenic. To reach a toxic dose, you would need to eat dozens of kilograms of crab at one time. Dozens of kilograms, not a few crabs or a few jin. The stomach cannot hold that.

In 2018, CCTV’s 315 Gala looked into food incompatibility. Associate Professor Fan Zhihong and others from the College of Food Science and Nutritional Engineering at China Agricultural University ran an experiment. They put crab and persimmon into simulated digestive fluid and tested the forms of arsenic. Toxic trivalent arsenic did not increase.

Where the rumor came from

In 1984, researchers at the University of Illinois ran an animal experiment. It involved an organic arsenic feed additive for chickens, roxarsone, and vitamin C. Under the experimental conditions, pentavalent arsenic was reduced to trivalent arsenic, and chick mortality rose.

The subjects were chicks. The arsenic came from a feed additive. The exposure was injection, not eating.

In 1985, the Chicago Tribune reported it under the headline “Don’t mix vitamin C, shellfish.” The chick experiment became human diet. The feed additive became arsenic in seafood.

In 1986, a Chinese medicine scholar published an article in Jiangxi Journal of Traditional Chinese Medicine. The title: “Eating Crustaceans While Abusing Vitamin C Can Be Fatal.” The article said that when certain crustaceans are taken with large amounts of vitamin C, pentavalent arsenic can become trivalent arsenic, or white arsenic.

Later, persimmon is rich in vitamin C, and crab is a crustacean. The rumor became: crab plus persimmon equals white arsenic.

Why the ancients said it caused abdominal pain

The Compendium of Materia Medica quotes Su Song: “Whenever persimmon is eaten with crab, it causes abdominal pain and diarrhea; both things are cold in nature.”

The ancients had no cold chain. Live crabs, kept in bamboo baskets with wet grass, could live only two or three days. If they spoiled, eating them caused diarrhea. Persimmons that were not fully ripe were high in tannic acid. Eating a lot of them on an empty stomach also caused abdominal pain. The ancients could not tell whether the cause was stale crab, unripe persimmon, overeating, or bacterial infection. They explained it with cold and heat: both are cold, cold added to cold.

Similar entries include rabbit meat with ginger, lamb liver with Sichuan pepper, and shrimp with chicken or pork. Guiding modern life by these theories would leave little to eat.

If you feel unwell after eating them together, the problem is mostly the persimmon

Persimmons, especially unripe, unpeeled, astringent ones, contain a large amount of soluble tannic acid. When tannic acid enters the stomach, gastric acid makes it denature and coagulate into a water-insoluble gel. The pectin, fiber, and residues in the persimmon wrap around it layer by layer. It hardens as it accumulates. The result is a gastric persimmon stone, also called a phytobezoar.

Even without crab, eating a large amount of raw persimmon on an empty stomach carries the same risk. Hawthorn and black jujube are similar.

The Chinese Medical Association Digestive Endoscopy Branch’s Expert Consensus on Endoscopic Management of Upper Gastrointestinal Foreign Bodies in China (2015, Shanghai) says the key to preventing phytobezoars is to avoid eating large amounts of persimmons, hawthorn, black jujube, and similar foods on an empty stomach.

A gastric persimmon stone may cause upper abdominal pain, bloating, nausea, and vomiting. In severe cases, it can lead to obstruction, ulcers, and bleeding.

So the thing to remember is not that crab cannot be paired with persimmon. Do not eat large amounts of raw persimmon on an empty stomach. Eat fully ripe, de-astringented persimmons, in moderation, peeled.

Is the black membrane on a crab’s abdomen a heavy metal hotspot?

No. The black membrane outside the crab roe is mainly collagen, connective tissue that wraps the internal organs. It is not toxic. If you dislike the texture, tear it off. Calling it a heavy metal hotspot has no basis.

The parts of a crab that may accumulate heavy metals are the gills, hepatopancreas, and similar organs. Crab from standard aquaculture, standard channels, and passing inspection is safe. Buy live crabs. Cook them thoroughly. Do not eat ones that have been dead for a long time.

How to eat in autumn

Steam crab and serve it with ginger vinegar. Choose soft, fully ripe persimmons. Do not eat them on an empty stomach. Do not eat several at a time. Eating the two together is fine, but do not overdo it. People with sensitive stomachs should adjust according to their own condition.

If you feel unwell after eating, check whether the crab was fresh, whether it was cooked through, whether the persimmon was raw, and whether you ate too much.

To that message in the family group chat, reply: It will not turn into white arsenic. Then send this article.