Fatsoluble

Fatsoluble refers to the property of a chemical substance to dissolve in fats or lipids rather than in water. In common usage, the term describes lipophilic compounds with low aqueous solubility, including many vitamins, lipids, and certain drugs. The degree of fat solubility is related to molecular polarity and is often summarized by lipophilicity measures such as the octanol–water partition coefficient (logP), with higher values indicating greater solubility in fats. Note that in scientific literature, fat solubility is more often described as lipophilicity or simply fat solubility, and the term fatsoluble is not uniformly used across disciplines.

In nutrition, fat-soluble vitamins A, D, E, and K illustrate the concept. Their absorption depends on dietary fat and bile salts; they are incorporated into micelles and absorbed by enterocytes, then transported via chylomicrons through the lymphatic system. Because they can be stored in liver and adipose tissue, they provide a reserve but also carry a risk of toxic accumulation if intake exceeds requirements.

In pharmacology and toxicology, many drugs and pollutants are fatsoluble, which influences distribution, storage, and elimination. Lipophilic substances tend to accumulate in fatty tissues and may exhibit longer half-lives, complicating dosing and leading to tissue-specific effects. Drug formulation often seeks to balance fat solubility to optimize absorption or to target fat-rich compartments, sometimes using emulsions or liposomal delivery.

Measurement and implications: fat solubility affects formulation, dietary requirements, and safety considerations. While water-soluble substances are readily excreted, fatsoluble compounds may require bile-mediated digestion, enterohepatic recirculation, and, in some cases, specialized excretion pathways for elimination.