Upon giving yourself Leather horse armor with proper components the player is unable to eat it regardless if they should be able to. 
To recreate in game run these commands 

/give @p leather_horse_armor[food =

{nutrition:4,saturation:6,can_always_eat:true,eat_seconds:2}

] 1

Notice how you cannot eat this item, however if you replace the item with stone for example

/give @p stone[food=

{nutrition:4,saturation:6,can_always_eat:true,eat_seconds:2}

] 1 

This command will properly produce an item that can be consumed despite no component changes

{EDIT] the horse armor command sometimes has an arbitrary \ before the equal sign for a reason beyond me as i cannot remove it no matter what i try due to it being a bug on the site itself. Please remove the \ before testing in game