The lychee seed can cause death due to highly toxic compounds concentrated within it and the flesh of unripe fruit. The danger is not physical but chemical. When consumed under adverse conditions, these natural toxins can trigger a severe, life-threatening metabolic disorder. The risk is significantly heightened when the fruit is eaten on an empty stomach, particularly by individuals with poor nutrition.
The Toxic Compounds in Lychee Seeds
The lychee contains two naturally occurring amino acid derivatives responsible for its toxicity: Hypoglycin A and methylenecyclopropylglycine (MCPG). These chemicals are considered protoxins, meaning they are metabolized into highly poisonous compounds once ingested. They are structurally similar to a toxin found in the ackee fruit.
The concentration of these toxins is highest in the lychee seed, but they are also present in the fruit’s pulp. Unripe, green lychees contain substantially higher levels of both Hypoglycin A and MCPG compared to fully ripened fruit. The presence of these compounds in the unripe fruit flesh is the primary source of mass poisonings, not solely the ingestion of the seed itself.
How These Toxin Affect the Body
Once consumed, Hypoglycin A and MCPG are metabolized into compounds that interfere with the body’s energy production system. Their toxic metabolites block two fundamental processes: gluconeogenesis and fatty acid beta-oxidation. Gluconeogenesis is how the liver creates new glucose, and fatty acid oxidation is how the body breaks down fats for energy when glucose stores are depleted.
By inhibiting these two pathways, the toxins severely impair the body’s ability to maintain a steady blood sugar level. This metabolic disruption leads to acute, severe hypoglycemia, or dangerously low blood sugar. Since the brain relies on glucose for fuel, this drop can rapidly cause neurological symptoms. Symptoms often begin with vomiting, followed by seizures, an altered mental state, and potentially a coma and death, a condition known as hypoglycemic encephalopathy.
Vulnerable Populations and Historical Events
The risk of severe illness or death from lychee consumption is concentrated within specific vulnerable populations. Children are the most susceptible group because they have smaller reserves of stored liver glycogen compared to adults. When a child eats lychees on an empty stomach, their existing low sugar stores are quickly depleted. The toxins then prevent the body from initiating the backup process of converting fat into glucose, leading to a catastrophic drop in blood sugar.
These toxic effects have been linked to recurrent, seasonal outbreaks of acute neurological illness in lychee-growing regions of Asia, including India and Vietnam. In India’s Bihar state, outbreaks occurred annually during the lychee harvest season. Investigations confirmed the illness was a hypoglycemic encephalopathy associated with children consuming large amounts of unripe lychees without having had an evening meal. Public health advisories now focus on ensuring children eat an evening meal and limit their intake of the fruit.
Safe Ways to Consume Lychees
To enjoy lychees safely, focus on minimizing exposure to the concentrated toxins. The most direct preventative measure is to always discard the seed completely, as it contains the highest concentration of Hypoglycin A and MCPG. Consumers should only eat lychees that are fully ripe, indicated by a bright reddish-pink color. Unripe, greenish fruit must be avoided entirely due to their significantly higher toxin content.
Another safety factor is ensuring that lychees are not consumed on an empty stomach, especially by children. Eating the fruit as part of a meal or after a meal helps to maintain adequate blood glucose levels. This practice reduces the risk that the body will need to rely on the toxin-inhibited energy pathways. By selecting only ripe, seedless fruit and consuming them with food, individuals can effectively mitigate the danger.