Wow . That ' s harsh . <| sep |> Because they can ' t realistically get any smaller than their useful variations . The stuff we use is basically the base building block of every biological organism or material . For example We use iron in its smallest form , a single atom of Fe , in our red blood cells . We use amino acids in their base form , in proteins . We use fatty acids in their base form , in . fat . Most of the other materials are just their base atoms or ions , such as Na , K , Ca , etc . The digestive enzymes are highly specific and only break down the molecules they ' re designed to break down , such as proteins and fatty acids . The acid in our stomach doesn ' t really damage our food , it just makes it a bit more susceptible to digestion and kills some organisms that happen to come down with it .