3-hydroxy-3-methylglutaric acid is a dicarboxylic acid that is glutaric acid in which one of the two hydrogens at position 3 is substituted by a hydroxy group, while the other is substituted by a methyl group. It has been found to accumulate in urine of patients suffering from HMG-CoA lyase (3-hydroxy-3-methylglutaryl-CoA lyase, EC 4.1.3.4) deficiency. It occurs as a plant metabolite in Crotalaria dura. It has a role as an antimetabolite, an EC 1.1.1.34/EC 1.1.1.

Citric acid is a natural preservative and food tartness enhancer, it is also an Al-chelating substance and a natural antioxidant. Citric acid (1-2 g/kg) can decrease brain lipid peroxidation and inflammation, liver damage, and DNA fragmentation. Citric acid has phytoremediation of heavy metal contaminated soil; citric acid can decrease the adsorption of both lead and cadmium. Dietary citric acid can effectively improve phytate P utilization in chicks. Citric acid is a tricarboxylic acid that is propane-1,2,3-tricarboxylic acid bearing a hydroxy substituent at position 2. It is an important metabolite in the pathway of all aerobic organisms. It has a role as a calcium chelator, an antimicrobial agent, a chelator, a food acidity regulator and a fundamental metabolite. It is a conjugate acid of a citrate anion and a citrate(1-).