Effect of a North American Diet on Cardiometabolic Risk Factors in Women with Obesity and with or without Insulin Resistance: Preliminary Analysis of the NutrIMM Study

Introduction: Heart disease is the primary cause of mortality in women in North America. Diet quality plays an important role in cardiovascular diseases. High-fat diets, usually low in fruits and vegetables, are associated with the development of obesity and insulin resistance (IR). No studies to date have evaluated the effects of a North American diet, under controlled feeding conditions, on cardiometabolic risk factors in women. This study aimed to investigate the effect of consuming an isocaloric North American high-fat diet on cardiometabolic risk factors in women.
Methods: This is a 3 parallel-arm trial in controlled feeding conditions being conducted at the Human Nutrition Research Unit, at the University of Alberta. Three groups of women (Lean-normoglycemic (lean-NG; n=2), Obese-NG (n=6) and Obese-IR; n=3) consumed a diet containing 35% fat (12.5% saturated fat), 48% carbohydrates (mainly refined), and 17% protein for 4 weeks. All food/meals were provided to participants for the duration of the study. Blood samples were collected in the fasting state before and after the dietary intervention and cardiometabolic risk factors were measured. Paired t-test was used to assess differences in variables before and after the intervention and one-way ANOVA was used to compare changes among the three groups.
Results: After the intervention, reductions in IR parameters were observed for HbA1c (-0.10±0.14), insulin (-2.81±3.21), and homeostatic model assessment (HOMA) (-0.65±0.73) (all p<0.05). The magnitude of the change within each group (i.e. delta pre-post) for HOMA index tended to be higher in Obese-IR (-1.37±0.61) compared with Obese-NG (-0.48±0.63) and lean-NG (-0.01±0.06) groups (p=0.07). Except for a reduction in high-density lipoprotein cholesterol levels (-0.14±0.09; p<0.01), no other effect was observed on the lipid profile of women consuming a North American diet. Conclusion: In conclusion, our preliminary data show that a North American diet, under isocaloric controlled feeding conditions, improved IR parameters in women with obesity and IR while having a minor effect on the lipid profile. Our findings should be interpreted cautiously due to the small sample size. Keywords: cardiovascular risk; insulin resistance; women; North American diet.