Circulating IGF binding protein (IGFBP)-1 levels have been associated with insulin sensitivity, the metabolic syndrome, several cardiovascular risk factors, and possibly with cancer. We examined long-term nutrient intake and metabolic and anthropometric factors in relation to IGFBP-1 levels in 226 men, 42-76 yr old, who completed 14 24-h diet recall interviews. Spearman rank correlation coefficients were calculated. Serum IGFBP-1 levels were significantly inversely correlated with insulin, homeostasis model assessment-insulin resistance, and IGF-I and positively correlated with age. Furthermore, IGFBP-1 was inversely correlated with anthropometric measures reflecting obesity, somewhat stronger in middle-aged (<65 yr) than in older men. Serum IGFBP-1 increased with higher energy and carbohydrate intake but only in the younger age group. The difference in mean IGFBP-1 levels comparing men in the top quartile of carbohydrate intake with those in the bottom quartile was 45% in men of age 42-54 yr (P = 0.01). Insulin, body mass index, and carbohydrate intake together explained 39% of the variability in IGFBP-1 levels in men 42-54 yr of age, 27% in men 55-64 yr, and 6% in men 65 or more years old. Our data suggest that metabolic, anthropometric, and nutritional factors are important determinants of IGFBP-1 levels in healthy men.