Changes in total energy intake and macronutrient composition after bariatric surgery predict long-term weight outcome: findings from the Swedish Obese Subjects (SOS) study

Background: Approximately 20-30% of obese patients do not achieve successful weight outcomes after bariatric surgery. Objective: We examined whether short-term changes (<= 0.5 y post-surgery) in energy intake and macronutrient composition after bariatric surgery could predict 10-y weight change. Design: Participants were recruited from the Swedish Obese Subjects (SOS) study, which was a matched (nonrandomized) prospective trial that compared bariatric surgery with usual care for obese patients. A total of 2010 patients who underwent bariatric surgery were included in the study. Physical examinations (e.g., weight) and questionnaires (e.g., dietary questionnaire) were completed before and 0.5, 1, 2, 3, 4, 6, 8, and 10 y after surgery. For the main analytic strategy, a linear mixed model was implemented, which included repeated measures with a random intercept and an unstructured covariance matrix. Results: Short-term changes in energy intake (P < 0.001) and in relative proportions of energy from carbohydrates (P < 0.001), fat (P < 0.001), and protein (P < 0.05) were associated with 10-y weight change after bariatric surgery. At the 10-y follow-up, men and women with the largest reductions in energy intake had lost 7.3% and 3.9% more weight, respectively, compared with that of subjects with the smallest intake reductions (P < 0.001). Greater weight loss was achieved in men and women who favored protein and carbohydrates over fat and in subjects who favored protein over carbohydrates than in individuals who favored the opposite changes in macronutrient composition (P < 0.05). Conclusions: The level of energy restriction that is achieved at 0.5 y after bariatric surgery predicts long-term weight loss. Weight loss is also associated with a changing dietary macronutrient composition.