Which organisms must obtain cholesterol or related sterols from their diets?

While many organisms are capable of synthesizing cholesterol or related sterols, certain groups lack this metabolic pathway and must obtain these essential compounds through their diets. Specifically, the following organisms are known to require dietary sources of cholesterol or related sterols:

• Insects: These organisms cannot synthesize cholesterol and must acquire it from their food to support vital biological processes, such as the production of molting hormones like ecdysone.12
• Certain Mollusks: Specific members of this phylum lack the ability to produce these sterols internally.1
• Annelids: Like insects and certain mollusks, these segmented worms must obtain necessary sterols from their environment.1
• Some Protozoa: Certain single-celled organisms within this group also rely on dietary intake rather than endogenous biosynthesis.1

In contrast, most vertebrates and many other invertebrates possess the metabolic machinery to synthesize cholesterol via a pathway involving terpenoid precursors.13