comida* it's a familiar term (also it's the past participle of the verb "comer") alimento* it's a concrete noun which means "food" (this term is fomal/neutral) alimentación* is the abstract noun

in general you should think about this definitions comida= something that you can eat alimento= something that you can eat and nurishes to you alimentacion= in general, this word refers to the set of food that you often intake as a source of materials to nourish the body Of course there are exceptions, but you can consider these definitions as a practical rule to understand their meaning in context.

más informal? no estoy seguro...