The insulin-like growth factor pathway plays a central role in the normal and abnormal growth of tissues; however, nutritional determinants of insulin-like growth factor I (IGF-I) and its binding proteins in healthy individuals are not well defined. Three test diets-high-fat diet (40% energy as fat), low-fat diet (LF; 20% energy as fat), and a diet with low fat and high omega-3 fatty acid (LFn3; 23% energy as fat)-were tested in a randomized crossover designed controlled feeding trial in healthy postmenopausal women. Plasma IGF-I, IGF binding protein-3 (IGFBP-3), insulin, glucose, and ratio of IGF-I/IGFBP-3 concentrations were measured in response to diets. Insulin sensitivity was calculated using the homeostatic model assessment of insulin resistance We hypothesized that IGF-I, insulin, and glucose concentrations would decrease and IGFBP-3 concentration would increase in response to the low-fat diets. Eight weeks of the LFn3 diet increased circulating IGF-I (P < .001) and IGFBP-3 (P = .01) and the LF diet increased IGFBP-3 (P = .04), resulting in trends toward an increased IGF-I/IGFBP-3 ratio with the LFn3 diet and a decreased IGF-I/IGFBP-3 ratio with the LF diet (P = .13 for both comparisons). No statistically significant differences were detected between treatments at baseline or 8 weeks for IGF-1, IGFBP-3, or the ratio of IGF-1/IGFBP-3. Insulin, glucose, and the homeostatic model assessment of insulin resistance were not altered by the interventions. Low-fat diet with high n-3 fatty acids may increase circulating IGF-I concentrations without adversely affecting insulin sensitivity in healthy individuals.
Bibliographical noteFunding Information:
We would like to thank the participants for their serious commitment to this study and the General Clinical Research Center staff for their assistance with clinical work and preparation of the study diets. We thank Douglas Yee for his comments and review of the manuscript. Funding for this work was provided by grants from the Department of Defense ( W81XWH-04-1-0448 and W81XWH-06-1-0778 ) and the National Center for Research Resources, National Institutes of Health ( Mo1-RR00400 ). Salmon of the Americas, Inc, donated salmon fillets for the controlled diets. The authors declare no conflict of interest.
- Dietary fat
- IGF binding protein-3 (IGFBP-3)
- Insulin-like growth factor I (IGF-I)
- Omega-3 fatty acids