Adherence to protein restriction in patients with type 2 diabetes mellitus: a randomized trial

Objective: To describe the extent to which diet counselling can decrease protein intake, and to identify predictors of adherence. Design: (1) Randomized trial; (2) observational longitudinal study. Subjects: (1) 125 type 2 diabetic patients in primary care; (2) 59 patients in the experimental group. Intervention: For a period of 12 months, dieticians provided guidance on protein restriction (experimental group, n = 59) or the usual dietary advice (control group, n = 66). Outcome measures: Adherence was estimated primarily from urinary urea excretion (UUE), but also from food-frequency questionnaires (FFQ). Results: After 6 months protein intake was, according to the WE and the FFQ, respectively, 8 g/day (95% CI -2, 13) (8%) and 15 g/day (95%-CI 9, 22) (16%) lower in the experimental than in the control group. After 12 months these differences were smaller. Linear regression analysis indicated that protein restriction was greater in patients who were well satisfied with their pre-existing diet (r = 0.32, b(per 1/10) = 3.6 (1, 6) g), in patients who were less overweight (r = 0.32, b(per) (kg.m-2) = 1.1 (0.2, 2.0) g), and in patients living alone (r = 0.22, b = 7.7 (-2, 17) g). These combined factors explained only 11% of variation in adherence. Adherence was not predicted by the number of barriers reported by the patients or by coinciding changes in diet satisfaction. Conclusions: The diet counselling resulted in a very moderate degree of protein restriction only. Predictors of adherence could be identified, but only a few, and their predictive power was limited.