Why should we eat at gaps of 2-3 hours?

Do you know our metabolism is like a car engine.It needs fuel in the form of food to keep burning the calories.This is the reason,we should keep eating something at least every three hourly.But that something should be nutritious and healthy.Like you can have three complete major meals and few snacks in between .Healthy snacking options can be a whole fruit,sprouts,dry fruits,roasted chana,rice puffs,unsalted popcorns,whole wheat based grilled sandwich,besan chilla,fruit smoothies,buttermilk,coconut water etc.So tell me how frequently do you eat and which snacks are there usually in our diet?