Composition of dietary fat affects obesity-induced changes in blood pressure and insulin sensitivity

Lean mongrel female/spayed dogs (n=15) were overfed for five weeks on one of two high-fat, high-calorie diets: a saturated fat diet (SF; n=8; lard) or an unsaturated fal diet (UF; n=7; corn oil). Dogs were fed through stainless steel gastric tubes at a calorielevel 150% above their baseline ad lib intake. Fasted blood samples were collected each week during the experiment and analyzed for insulin and glucose. A frequently-sampled glucose tolerance test was administered both before and after overfeeding, and insulin and glucose concentrations were minimally modeled to calculate insulin sensitivit} (S,). Arterial blood pressure and heart rale were monitored continuously throughout the protocol by telemetry. Overfeeding increased body weight by 52.3 + 2.7% (p .01) and body fat mass by 198 25% (p<.01), but did not significantly affect lean hod> mass. Body weight and body fat did not differ between diet groups before or after overfeeding. Blood pressure was increased (p<.01) in both diet groups, but the magnitude of the increase \vas greater in the SF group (p<.01; 15.9-12.1 vs. 9.8i3.3 mmHg increase). Heart rate was increased in both groups (p<.01). although the magnitude of the increase was greater in the UF group (p<.05; 32.8±7.8 vs. 14.1±5.8 bpm increase). Circulating insulin increased from 0.6 ± 2 0 to 24 6 t fi.2 uU/ml. (p 01) in the SF group, but was unaffected by obesity in the UF group. S, did not differ between the two groups prior to overfeeding, however, the SF diet caused a decrease in S, (from 8.8± 1 5 lean to 2.95 ± 0.6 obese; p<.01). while S, in the UF group was unchanged (5.4±.8 lean and 4.7±.7 obese, NS). S_i in the lean animals was positively correlated with subsequent weight gain on a high-fat diet (R=.64; p<.01). however, when examined by diet group, this correlation only existed for the SF group (R=.69; p<.05) and not the UF group (R=-.37; p- 4) These data suggest the r>pe of dietar> fat producing obesity can affect insulin sensitivit> and blood pressure independent of the amount of body fat accumulation.