Manzanilla, Kalamata, Niçoise—there are a ton of olive varieties out there, sourced from Europe to the Middle East to California and beyond.
And because of this, no two types will be exactly the same, nutritionally speaking. “Because raw olives are often bitter, they are cured and fermented before eating, which can make slight changes to the nutrient levels among different varieties,” says Brynn McDowell. But, in general, these changes aren’t significant enough to say one variety of olive is definitively healthier than another, she says.
Oh, and in case you were wondering, green olives are picked before they’re ripe, while deep purple-black ones ripen on the vine before being picked. (This doesn’t have any major bearing on their nutrient profiles, however.)
As for those mass-produced black olives that you see in the grocery store? They’re actually green olives processed with oxygen and iron so they darken.