Caloric restriction (CR) has been shown to retard aging processes in many species. We investigated effects of CR on plasma low density lipoproteins (LDL), a major risk factor for the age-associated process of atherosclerosis. Studies emphasized effects of CR on LDL composition and their interaction with arterial proteoglycans (PG). Rhesus monkeys were fed a control diet (n=13) or subjected to CR (n=12 fed 30% less calories) for > 5 years. Plasma LDL cholesterol concentrations were similar for control and CR groups (82+/-8 vs 72+/-6 mg/dL, mean+/-SEM). LDL was isolated by ultracentrifugation and HPLC. LDL particles from CR animals had a lower molecular weight (2.9+/-0.1 vs 3.2+/-0.1 g/micromol, p < .05) and were depleted in triglyceride (249+/-16 vs 433+/-49 mol/particle, p < .005) and phospholipid (686+/-20 vs 837+/-33 mol/particle, p <.001). Lower PG binding was measured for LDL from CR animals (10.1+/-0.8 vs 15.6+/-1.1 microg LDL cholesterol/microg PG, p <.005). This was associated with the lower triglycerides (r=.76, p < .0005) and phospholipids (r=.48, p < .01). Thus, a dietary intervention which may retard aging inhibits a proposed mechanism of atherogenesis.