The water solubility of the polyphenol curcumin was enhanced by preparing pea protein isolate nanoparticles loaded with curcumin using a well-established pH-driven method. This process generated supersaturated nanoparticles, with 96% of the solubilised curcumin precipitating within 24 h. The supersaturated and stable mass concentrations were 1.39 ± 0.093 mg/mL and 0.0528 ± 0.0088 mg/mL, respectively. The study assessed the kinetics, stability, and adsorption and desorption behaviour of curcumin with these nanoparticles, comparing the supersaturated and stable states. A schematic mechanism encompassing all steps from nanoparticle preparation to curcumin precipitation is proposed. The phenomenon is explained by the aggregation or isomerisation of tightly packed curcumin molecules attached to the nanoparticle surface. The precipitation kinetics are influenced by stirring, temperature, and lyophilisation, and are slowed by dilution and the addition of bisdemethoxycurcumin. The studied system is also evaluated from a pharmaceutical perspective and is proposed as a supersaturated drug-delivery system (SDDS).