Tracking of an energy-dense, high saturated fat, low-fibre dietary pattern, foods and nutrient composition over 10 years in the severely obese

Abstract

Background: The consideration of dietary changes over time, or tracking, is important in studies of diet and disease risk. However, there has been no work carried out on dietary tracking in obese adults, who may be prone to weight loss attempts and changes in their dietary intake. The aim of this study was to investigate tracking of a dietary pattern (DP), food groups and macronutrient intake in a severely obese population over a 10-year period. Methods: Dietary intake was assessed nine times over 10-years using a dietary questionnaire in the control group of the Swedish Obese Subjects (SOS) study. At registration (t = R), a DP was derived using reduced rank regression (RRR), based on intakes of 39 food groups with dietary energy density, saturated fat and fibre density as response variables. Exploratory RRR analyses resulted in a similar DP that was high in energy density and saturated fat and low in fibre. To assess real change in this DP over time, confirmatory RRR analysis was applied to calculate a score for the DP identified at registration at each of the subsequent follow-ups. Average daily intakes of food groups and macronutrients were calculated at each follow-up and standardised in relation to intakes at registration. A tracking coefficient for the DP was calculated using generalised estimating equations (GEE) (Twisk et al., 1996) falling between 0 (no tracking) and 1 (perfect tracking). The models were adjusted for age at registration. Further GEE analyses were carried out to calculate tracking coefficients for selected food group intakes and response variables. These models included adjustment for age and total energy intake. Results: The control group contained 2037 severely obese individuals [mean (SD) body mass index 41 (4) kg m−2] who reported total mean (SD) energy intakes of 13 045 (6146) kJ [3118 (1469) kcal] and 10 614 (5096) kJ [2537(1218) kcal] for men and women respectively at t = R. The tracking coefficient for this DP from study registration to 10 years was 0.38 for men and 0.40 for women (Table 1). The DP tracking coefficients were stronger when follow-up time was shorter (Table 1). For both men and women, the strongest tracking coefficients were for vegetable intake [β1 = 0.52 (95% confidence interval [CI], 0.48–0.56); β1 = 0.37 (95% CI, 0.35–0.39), respectively] and fruit intake [β1 = 0.46 (95% CI, 0.43–0.49); β1 = 0.36 (95% CI, 0.34–0.38)]. We observed significantly lower tracking coefficients for less healthy food groups in men and women respectively, including fast food [β1 = 0.25 (95% CI, 0.22–0.27); β1=0.14 (95% CI, 0.13–0.15)] and candy [β1 = 0.10 (95% CI, 0.08–0.12); β1 = 0.18 (95% CI, 0.17–0.20)]. Of the three response variables, fibre density displayed the greatest tracking coefficient. Table 1. Tracking coefficient and 95% CI of a standardised dietary pattern score of 2037 severely obese Swedish men and women over an average 11 years of follow-up Dietary pattern score (time points) Men Women Tracking coefficient 95% CI Tracking coefficient 95% CI All coefficients are significantly different from zero (P < 0.01). *Adjusted for age and smoking. All other coefficients are adjusted for age, smoking and total energy intake. (R-10) 0.38* 0.35–0.41 0.40* 0.38–0.42 (0–10) 0.39* 0.36–0.41 0.45* 0.43–0.47 (2–10) 0.45* 0.31–0.49 0.50* 0.44–0.55 (6–10) 0.47* 0.38–0.57 0.53* 0.46–0.61 Discussion: In this novel analysis, low to moderate tracking of the identified DP, as well as food group and nutrient intakes, was observed over a 10-year period. As such, baseline diet may be a poor reflection of dietary intake over a prolonged follow-up in the severely obese. GEE uses all available data; considers between and within person differences; and accounts for repeated observations from the same individual. If the prevalence of under-reporting increased during the 10 years, then the tracking coefficient may be affected, and is a limitation of this method. Conclusions: Dietary intake in severely obese adults is not fixed over time and is likely susceptible to dietary change. Furthermore, the observed differences in tracking between some food groups suggest that particular foods may be better targets for dietary change. Reference: Twisk, J.W.R., Kemper, H.C.G., Mellenbergh, G.J., Van Mechelen, W. & Post, G.B. (1996) Relation between the longitudinal development of lipoprotein levels and lifestyle parameters during adolescence and young adulthood. Ann. Epidemiol.6, 246–256.