What are the toxic compounds in lychee?
The toxins found in lychee fruit are amino acid analogs named Hypoglycin A (HGA) and Methylenecyclopropylglycine (MCPG). While similar to the compound found in the related ackee fruit, the combination of these two compounds in lychees can disrupt the body's natural metabolic processes.
The role of hypoglycin A
Hypoglycin A, a compound also found in unripe ackee fruit, is a potent inhibitor of several enzymes in the body's metabolic pathways. It is converted into a substance that interferes with the beta-oxidation of fatty acids, a process the body uses to generate energy when glucose levels are low. In a state of fasting, the body relies on stored fat for energy. When HGA is present, this crucial metabolic pathway is blocked.
The role of MCPG
Methylenecyclopropylglycine, or MCPG, is a homologue of hypoglycin A and acts synergistically to increase toxicity. It is known to be present in higher concentrations in the seeds and unripe fruit. MCPG further suppresses gluconeogenesis, the process by which the liver produces glucose from non-carbohydrate sources. When combined with HGA, this leads to a dangerous drop in blood sugar levels, or hypoglycemia.
Why does it primarily affect malnourished children?
The lychee toxins primarily affect malnourished children because of their depleted glycogen stores. Well-nourished individuals have sufficient glycogen reserves in their liver to maintain blood glucose levels during short periods of fasting. When they consume lychees, the impact of the toxins is usually negligible or mild. However, for a malnourished child, these reserves are already low. Consuming lychees, especially unripe ones, on an empty stomach and then skipping an evening meal, means the child's body cannot compensate for the dual assault on its energy production pathways.
- Impact on Glucose Production: The liver's ability to produce glucose is severely impaired. The combination of HGA and MCPG blocks both fatty acid oxidation and gluconeogenesis, removing the body's backup energy sources.
- Rapid Blood Sugar Drop: With no viable energy source, blood sugar levels plummet rapidly, leading to severe hypoglycemia. This is particularly dangerous for the brain, which relies heavily on a constant supply of glucose for function.
- Development of Encephalopathy: The metabolic derangement can cause acute encephalopathy, or swelling of the brain, leading to seizures, coma, and sometimes death.
Symptoms of lychee toxicity
Symptoms of lychee toxicity, often described as Acute Encephalitis Syndrome (AES), typically appear in the early morning after a child has eaten lychees on an empty stomach the previous day.
- Initial Symptoms: Early signs include fever, vomiting, and loss of consciousness.
- Neurological Symptoms: As the illness progresses, seizures and severe brain inflammation (encephalopathy) can occur.
- Hypoglycemia: Low blood sugar is a hallmark symptom of the condition, and rapid glucose correction is a critical part of treatment.
How to prevent lychee toxicity
Prevention is the most effective way to combat lychee toxicity. Since the risk is highly correlated with consumption patterns and nutritional status, simple precautions can significantly reduce the danger.
- Eat Ripe Fruit Only: Unripe lychees contain the highest concentration of toxins. Always ensure the fruit is fully ripe before consumption.
- Avoid Fasting Consumption: Do not eat lychees on an empty stomach, especially large quantities.
- Ensure Proper Nutrition: For children in high-risk areas, a nourishing evening meal is crucial to maintain glycogen stores and prevent nighttime hypoglycemia.
- Monitor Consumption: Moderation is key. Both adults and children should consume lychees in limited amounts. The toxins also tend to be more concentrated in the seeds, which should not be consumed.
Comparing Lychee Toxins (HGA & MCPG) to Ackee Toxin (HGA)
While both lychee and ackee fruits belong to the same botanical family and contain hypoglycin A, there are key differences in their toxic profiles and effects.
| Feature | Lychee Fruit (Litchi chinensis) | Ackee Fruit (Blighia sapida) |
|---|---|---|
| Primary Toxin(s) | Hypoglycin A (HGA) and Methylenecyclopropylglycine (MCPG) | Hypoglycin A (HGA) |
| Toxic Part | Higher concentration in seeds and unripe fruit, but also present in pulp | Entire unripe fruit is toxic; only the fleshy aril of properly ripe fruit is edible |
| Clinical Manifestation | Acute Encephalitis Syndrome (AES) often linked to fasting-induced hypoglycemia in malnourished children | Jamaican Vomiting Sickness, characterized by severe vomiting and hypoglycemia |
| Mechanism of Toxicity | HGA inhibits fatty acid oxidation, while MCPG suppresses gluconeogenesis, synergistically causing severe hypoglycemia and encephalopathy | HGA inhibits fatty acid oxidation, leading to a profound drop in blood sugar |
| Prevention | Focus on eating ripe fruit in moderation and ensuring an evening meal, especially for children | Wait for the fruit to fully ripen and open naturally on the tree; discard the inedible parts and cook the edible aril |
Conclusion
While the sweet and juicy flesh of ripe lychee is generally safe for consumption in moderation, the fruit contains potent toxins, Hypoglycin A and MCPG, that can be dangerous under specific conditions. These toxins inhibit the body's ability to produce glucose, a process that is critical when blood sugar levels are low. The risk is most pronounced in malnourished individuals, particularly children, who consume unripe fruit on an empty stomach. The tragic outbreaks of Acute Encephalitis Syndrome in countries like India and Vietnam serve as a powerful reminder of this risk. To prevent illness, it is vital to only eat ripe lychees, consume them in moderation, and always ensure a proper meal has been eaten, particularly for children. The seeds of the lychee fruit are especially high in toxins and should never be consumed. By being aware of the science behind lychee toxicity, you can enjoy this delicious fruit safely.
