Benefits
Vitamin C from fresh and dried lychee
USDA lists 71.5 mg of vitamin C per 100 g of raw lychee, which is about 10 peeled and pitted fruits (about 9.6 g each), and 183 mg per 100 g of dried lychee. This is a nutrient measurement from food composition data. No trial has tested lychee fruit against a control for vitamin C status or any health outcome.
Blood sugar response after eating lychees
In glycemic index testing, 20 healthy adults and 17 adults with type 2 diabetes ate a lychee portion supplying 25 g of carbohydrate. The glycemic index was about 48 in healthy adults and 60 in the diabetes group, the highest of six fruits tested in that group. Raw lychee has about 15 g of sugars per 100 g, so portion size matters.
Liver fat studied with a processed lychee polyphenol extract
This is a branded extract, not the fruit. In a 24-week placebo-controlled trial in 38 adults with fatty liver disease, Oligonol 100 mg twice daily lowered liver fat within its own group, but the difference from placebo at week 24 was not statistically significant, and the trial's main goal, a 30% or greater drop in liver fat, was not met. See the Oligonol page for that product's research.
Lychee pulp polyphenols in animal research
In a mouse study, a phenolic extract of lychee pulp given for 21 days before a stress test lowered blood liver enzymes and an oxidation marker and raised liver antioxidant levels. This is animal work with a concentrated extract; it has not been tested with lychee fruit in people.
Mechanism of action
Hypoglycin A and MCPG block backup fuel pathways
Hypoglycin A and MCPG, found in the aril and seed, block fatty acid beta-oxidation, which the body relies on for energy and glucose production once its glycogen stores run low. In children from the Muzaffarpur outbreak, abnormal blood acylcarnitine profiles were consistent with severely disrupted fat metabolism.
Why an empty stomach and undernutrition raise the risk
Reviews of the outbreaks describe three factors acting together: undernutrition, an overnight fast after a skipped evening meal, and eating many lychees. With little stored glycogen, the body turns to fat burning and glucose production, the pathways the toxins block, so blood sugar can fall sharply in the early morning.
Polyphenols and vitamin C as antioxidants
Lychee pulp contains phenolic compounds and vitamin C. In animal work, a pulp phenolic extract raised liver glutathione and antioxidant enzyme activity. These are lab and animal findings, not measured effects of eating the fruit.
Clinical trials
Hospital-based surveillance with a nested age-matched case-control study and laboratory testing of patient samples and local litchis, funded by the US CDC. (Shrivastava et al. 2017, Lancet Glob Health)
390 children aged 15 or younger admitted with new seizures or altered consciousness to two hospitals in Muzaffarpur, Bihar, from May to July 2014; 104 cases were compared with 104 age-matched hospital controls.
122 children (31%) died, and 62% of those tested had blood glucose of 70 mg/dL or less on admission. Eating litchis (matched OR 9.6) and missing the evening meal (matched OR 2.2) in the previous 24 hours were linked to illness; the litchi link was stronger without an evening meal. Toxin metabolites were found in 66% of case urine samples tested and none of 15 controls. Tests for infections and pesticides were negative. An observational study, not a trial.
Joint investigation by the Indian National Center for Disease Control and the US CDC, with clinical surveillance, a 2013 case-control study and laboratory testing. (Shrivastava et al. 2015, MMWR Morb Mortal Wkly Rep)
133 children admitted in 2013 and 390 in 2014 with seizures or altered consciousness in Muzaffarpur, mostly aged 1 to 5; the 2013 case-control study enrolled 101 cases and 202 controls.
The illness was a noninflammatory encephalopathy; in 2014, 204 of 327 children tested (62%) had blood glucose of 70 mg/dL or less on admission (20 of 94, or 21%, in 2013), and low glucose was linked to worse outcomes. Case fatality was 44% in 2013 and 31% in 2014, after rapid glucose testing and correction were recommended. Ill children had spent more time in fields or orchards, and those under 5 were more often wasted. The cause was still under study at the time.
Matched case-control study comparing sick children with household and neighborhood community controls. (Ponnaiah et al. 2023, Trans R Soc Trop Med Hyg)
61 children with acute encephalopathy syndrome and 239 controls in Muzaffarpur and nearby districts of Bihar, India, during the 2019 outbreak.
Compared with community controls, sick children were about five times more likely to have eaten litchi in the previous 7 days (adjusted OR 5.1, 95% CI 1.3 to 19) and to have skipped the previous evening meal (adjusted OR 5.2). Compared with household controls, they were more likely to be under 5 and to have skipped the evening meal. The wide confidence intervals reflect the small number of cases.
Outbreak investigation combining qualitative work with case-control analyses against village and neighborhood controls. (Islam et al. 2017, Am J Trop Med Hyg)
14 children who fell ill during the 2012 lychee harvest in a community in northern Bangladesh, 13 of whom died, with village and neighborhood controls.
Visiting a lychee orchard, family members working in orchards and visiting gardens while pesticides were applied were linked to illness. Eating lychees in the 24 hours before illness was not (57% of cases vs 71% of village controls). The authors linked this outbreak to orchard and agrochemical exposure rather than eating lychees, and noted the lack of acute specimens as a major limitation.
Glycemic index study using a standard protocol, with fruit portions supplying 25 g of carbohydrate compared with 25 g of glucose; funded by the National Science Council of Taiwan. (Chen et al. 2011, J Clin Biochem Nutr)
20 healthy young adults and 17 adults with type 2 diabetes in Taiwan.
The glycemic index of lychee was 47.9 in healthy adults and 60.0 in adults with type 2 diabetes; the difference between the two groups was not significant. In the diabetes group lychee had the highest value of the six fruits tested. This measures the short-term blood sugar response to one portion; it is not a health outcome trial and had no control food other than glucose.
Randomized, double-blind, placebo-controlled trial of Oligonol, a processed litchi-derived polyphenol product from Amino Up, 100 mg twice daily for 24 weeks. Branded extract, not the fruit. (Jinato et al. 2022, Nutrients)
38 adults in Thailand with fatty liver disease (liver fat of at least 11% on MRI), 19 per group.
Liver fat on MRI fell significantly within the Oligonol group but not within the placebo group; the difference between groups at week 24 was not statistically significant (p = 0.223 in the text, 0.215 in the table). A companion report of the same registered trial (TCTR20200814001; Chayanupatkul et al. 2022, J Integr Complement Med) found its primary endpoint, a 30% or greater drop in liver fat, was reached by 20% on Oligonol vs 15% on placebo (p = 0.50). Some gut bacteria differed between groups. The result applies to this extract, not to eating lychees.