Gac

Gac is a dioecious climbing vine, meaning male and female flowers appear on separate plants. The fruit is oval, about the size of a large grapefruit, covered in soft spines and turning from green to deep orange or red when ripe. Inside, the flesh holds rows of flat, dark brown, ridged seeds, each surrounded by a bright, sticky red aril that has a mild, slightly nutty and earthy taste. The seeds themselves are hard and bitter. Dried seeds are sold whole or sliced in Chinese and Vietnamese herb shops, while the aril is sold as a pulp, frozen or as a processed oil and powder. The seeds are not normally eaten raw.

Gac is native to tropical southern China, Southeast Asia and northern Australia, and it has long been grown in home gardens in Vietnam, Thailand, Laos and southern China. The botanical name refers to Cochinchina, the old European name for southern Vietnam. The genus Momordica comes from the Latin for to bite, because the seeds of some species look as though they have been bitten. The word gac is Vietnamese. In Chinese the seeds are called mu bie zi, meaning wood turtle seeds, a reference to their flattened shell-like shape.

In Vietnam gac has been tied to celebration and good fortune for generations. The red sticky rice called xoi gac is cooked for weddings, the Lunar New Year and other festivals, because the colour is considered lucky. The fruit is seasonal, appearing mostly in the cooler months, and families grow the vine on trellises beside houses.

In traditional Chinese medicine the seeds, known as mubiezi, have been used for centuries, mainly in external preparations for swellings and sores. They are described in historic materia medica texts. In Southeast Asia, aril and leaves were also used in home cooking and folk remedies.

Gac drew international attention in the 2000s when researchers reported unusually high levels of lycopene and beta-carotene in the aril, and companies began selling gac juice and oil as a superfruit product. Studies on its nutrient and phytochemical composition followed, along with efforts to encourage cultivation in other countries, including Australia, where the plant also grows wild. Much of the commercial claim-making has run ahead of clinical evidence, and gac remains mainly a cultural food in its home region and a niche supplement elsewhere.

The red aril, scraped from the seeds, is cooked with glutinous rice to produce xoi gac, or stirred into soups and curries for colour. It is also pressed into an orange oil sold as a carotenoid-rich supplement, or dried to a powder. Young leaves and shoots are cooked as greens in some regions. The seeds are used in traditional Chinese medicine, usually after processing, and are not a common food. The fruit has also been used as a natural food colourant. Frozen aril pulp is exported for use in smoothies and cosmetics.

The aril is notable for its carotenoids, particularly lycopene and beta-carotene, and it also contains fats that help the body absorb them. Laboratory studies describe antioxidant activity, while human evidence for specific health benefits is limited. The seeds contain bioactive proteins and saponin-type compounds that have been studied in laboratory settings, mainly for anti-tumour and anti-inflammatory activity, but these are not established treatments. As with any carotenoid-rich food, gac can be part of a varied diet but should not be viewed as a medicine.