Asia Pac J Clin Nutr. 2008;17(4):635-43.
Consumption of guava (Psidium guajava L) and noni (Morinda citrifolia L) may protect betel quid-chewing Papua New Guineans against diabetes.
Owen PL, Martineau LC, Caves D, Haddad PS, Matainaho T, Johns T.

Epidemiological evidence indicates that chewing betel quid is associated with type 2 diabetes in Papua New Guinea populations.  But one specific community had lower incidence of type 2 diabetes, despite betel quid use. A neighboring and ethnically similar community had much higher incidence of type 2 diabetes even though they abstained from betel quid. A study of the diets of these two communities revealed that the population with the lower type 2 diabetes rates ate larger quantities of guava buds, noni fruit and noni leaf. Guava bud extract and noni fruit, noni leaf and commercial noni juice displayed significant insulin-mimetic and potentiating activity.  (view original abstract at