But the type of citrus matters. “You should eat the whole fruit and not [just] drink the juice," says Dr. Ana Baylin, an associate professor of nutritional sciences at the University of Michigan ...

A version of this story appears in the February 2017 issue of National Geographic magazine. Citrus, in many ways, stands alone. So many cultivated species have come from so few primary ancestors.

Add a little coconut milk to the lime pickle and stir through a curry or serve on the side as an accompaniment. This pickle has a slightly bitter flavour, but don't be tempted to add any more sugar.