There are actually two stages that the coconut can be eaten at. Young or mature. Young coconuts are green and have softer meat inside and more water. Brown-haired and more firm, the mature coconut is slightly unhealthier and the one most people are used to seeing.
The water from young coconuts is full of electrolytes, which keep the body hydrated and functioning well. It is much more hydrating than normal water. This water is also almost fully fat free and has hardly any carbs, calories, or sugars but is full of vitamin B and protein.
The flesh of the coconut may be quite fatty, but it is healthy fat, like the fat found in avocados and has lots of protein as well as numerous vitamins and minerals. Eating it can also reduce some kinds of tissue damage and help the body repair itself.