The effect of goal difficulty on self-efficacy, dietary intake and clinical outcomes in adults with type 2 diabetes

Epidemiologic evidence suggests that low glycemic index (GI) and glycemic load (GL) diets are associated with reduced risk for type 2 diabetes and associated comorbidities. Goal setting theory postulates that increasing goal difficulty should increase self-efficacy and performance. However, there are no studies implementing goal setting theory in a population with type 2 diabetes to help lower the overall GI of the diet. This study randomized adults with type 2 diabetes to two groups; either a diet with an easier goal of consuming 6 low GI food servings/day (the 6 group) or a diet with a more difficult goal of consuming 8 low GI food servings/day (the 8 group). We hypothesized individuals assigned to the 8 group would have greater changes in overall dietary GI/GL, measures of glycemic (HbA1C) and weight control, goal satisfaction, and potential mediating variables (goal commitment and self-efficacy). Adults aged 40-65 with diagnoses of type 2 diabetes ≥ 1 year completed the study (n = 35). Participants met in groups with the study dietitian for 5 weekly lessons about GI and self-monitoring. After the nutrition intervention, participants were randomized to the easier or more difficult goal and entered a period of self-monitoring for approximately 8 weeks. Outcomes of interest were measured at baseline, following nutrition education, following goal assignment and at study end.;At baseline there were no significant differences in any of the outcome measures between groups or between those who did or did not complete the intervention. Within group (mean +/- SD) reductions in GI and GL for the 6 group were (GI = -6.78 +/- 5.92; GL = -37.38 +/- 38.01; p<0.01) and for the 8 group were (GI = -4.56 +/- 4.19; GL = -38.52 +/- 35.64; p<0.001). Within group changes (all p<0.05) in energy, carbohydrate (% of energy and total grams), total and insoluble fiber, added sugars, calcium, vitamin C, beta-carotene and magnesium were noted in the 6 or the 8 group. Within group increases in total low GI food servings for the 6 group were (1.73 +/- 3.17 servings; p<0.05) and for the 8 group were (1.85 +/- 3.04 servings; p<0.05). Small weight losses were noted for both groups; reductions in HbA1C were 0.38 +/- 1.25% in the 6 group and 0.73 +/- 1.28% (p<0.05) in the 8 group. Self efficacy for making lower GI food choices increased in both groups over the course of the study (all p<0.05); correlation analyses revealed that with increasing goal difficulty, commitment decreased in both treatment groups. When grouped by commitment, greater changes (p.0.05) in energy, % energy from protein and GL were noted for those with higher commitment. The results from this study illustrate that implementing the components of goal setting theory in combination with a low GI diet can facilitate beneficial dietary change, weight loss and improve glycemic control in individuals with type 2 diabetes. Future research should focus on determining individualized, appropriately difficult goals and building commitment for dietary behavior change.