Sweet leaf

Sweet leaf (Sauropus androgynus (L.) Merr.) belongs to the family Phyllanthaceae and is a perennial, multi-stemmed shrub 1–2.5 m tall, occasionally up to 3 m, with smooth wood at the base and round, fleshy green young branches. The alternate leaves are ovate to oblong, 2–6 cm long and 1–3 cm wide, glossy dark green above and paler beneath, with entire margins; they rarely drop, so the plant stays green year-round. The tiny flowers are arranged along short axillary stalks and are greenish (dark-red-flowered forms are also recorded); the fruit is a small depressed-globose berry 5–7 mm across, whitish at first and turning dark purple when ripe, containing a few seeds.

According to Plants of the World Online (Kew, 2025) the native range is tropical and subtropical Asia: from India, Bangladesh, Assam and the East Himalaya, Sri Lanka, through Indochina (Myanmar, Thailand, Laos, Cambodia, Vietnam) to Malaya, Indonesia (Java, Sumatra, Sulawesi, Maluku, the Lesser Sunda Islands), Borneo, the Philippines and New Guinea, as well as southern China and Hainan. PROSEA notes that the exact origin is unknown and records that it is not present in New Guinea. Today the plant is widely cultivated across Southeast Asia and other tropical regions — Vietnamese rau ngót, Indonesian katuk, Malaysian cekur manis — mostly in home gardens and small commercial plots.

The leaves contain the isoquinoline alkaloid papaverine — the most characteristic constituent, reported at about 580 mg/100 g in fresh leaves by the Journal of Ethnic Foods review (2022); it is a smooth-muscle relaxant and underlies the safety warning about overusing raw juice. Flavonoids are abundant: among 11 Indonesian vegetables compared, sweet leaf had the highest flavonoid content (Andarwulan et al., Food Chemistry, 2010), including kaempferol (and its glycoside 3-O-β-D-glucosyl-(1→6)-β-D-glucosyl-kaempferol, GGK), quercetin, myricetin, luteolin and apigenin, plus the phenolic acids chlorogenic, caffeic and ferulic. The leaves are also rich in β-carotene (provitamin A), vitamin C (about 239 mg/100 g), protein (about 4.8 g/100 g), and contain sterols, triterpenoids, lignan glycosides, squalene and phytol (Zhang et al., Journal of Ethnopharmacology, 2020).

In Vietnamese cuisine the leaves and shoot tips are cooked in soup with minced pork, crab or dried shrimp, or stir-fried with egg; in Malaysia the leaves are eaten as a 'multivitamin' vegetable (salads, curries, stir-fries) and in Indonesia as katuk dishes and the herbal drink jamu to support lactation. In research, leaf extracts show antioxidant, anti-inflammatory, anti-ulcer, skin-whitening, hypoglycaemic (α-glucosidase inhibition was documented among Vietnamese vegetables — Mai et al., J. Nutr. Sci. Vitaminol., 2007) and immunomodulatory activities (Zhang et al., 2020). The flavonoid GGK isolated from the leaves reduced food intake by 15% in rats on a high-fat diet (60 mg/kg) without histopathological changes, pointing to anti-obesity research. On lactation, papaverine raises oxytocin and prolactin in mice studies (Soka et al., 2010), and human studies report that leaf juice increases breast-milk production in postpartum mothers.

An important safety warning: in Taiwan in 1996 several hundred women who drank raw-leaf juice or extracts for weight loss developed bronchiolitis obliterans, reported in The Lancet (Lai et al., 1996); similar cases were recorded in Japan in 2005. The mechanism is still unclear: a rat study dosing the leaves and papaverine did not reproduce the lung injury (Lai, Wang & Lee, Chinese Medical Journal, 2000), so other compounds or factors may be involved. Sweet leaf should therefore be eaten cooked, raw weight-loss juice avoided, intake kept moderate (the 2022 review warns of symptoms with prolonged consumption above 131 g/day), and caution exercised in pregnancy. For conservation, the IUCN lists the species as Least Concern (assessed 2021) and it is not in CITES; the plant is widely cultivated across the tropics so populations are stable, although Singapore records it as Vulnerable at the local level.