High-fat diets and stress responsivity

Adult male rats were fed one of five diets varying in fat composition (Purina Chow or soy bean oil, corn oil, menhaden oil, or olive oil added to chow) for 10 weeks. After 3 days of access, no differences between groups were found in plasma corticosterone measured at light onset and light offset. During Week 2, restraint stress tests were performed. High-fat diets promoted significantly higher stimulated corticosterone levels. During Week 6 all rats were given an oral glucose tolerance test. Rats fed the corn and soybean oil diets had significantly elevated blood glucose 2 h after glucose intubation. Euglycemia was restored after 3 hours in all but the soybean oil group. During Week 9, a second stress test was performed. No differences in initial stress responsivity was observed, but groups fed the menhaden, soybean and olive oil diets had significantly higher corticosterone 1 h after the end of restraint. The corn oil, olive oil and soybean oil diets promoted transient hyperphagia. By the end of the experiment, the group fed the menhaden oil diet weighed significantly less and ate less than the remaining groups. These data demonstrate that stress responsivity is briefly enhanced during initial access to the high-fat regimens. Continued high-fat feeding results in an impaired ability to restore basal corticosterone following stress.