Abstract
Objective To examine objective versus self-reported energy intake changes (ΔEI) during a 12-month diet intervention.
Methods We calculated ΔEI in subjects who participated in a 1-year randomized low-carbohydrate versus low-fat diet trial using repeated body weight measurements as inputs to an objective mathematical model (ΔEIModel) and compared these values with self-reported energy intake changes assessed by repeated 24-hr recalls (ΔEI24hrRecall).
Results ΔEI24hrRecall indicated a relatively persistent state of calorie restriction ≥500 kcal/d throughout the year with no significant differences between diets. ΔEIModel demonstrated large early decreases in calorie intake >800 kcal/d followed by an exponential return to approximately 100 kcal/d below baseline at the end of the year. The low-carbohydrate diet resulted in ΔEIModel that was 162±53 kcal/d lower than the low-fat diet over the first 3 months (p=0.002), but no significant diet differences were found at later times. Weight loss at 12 months was significantly related to ΔEIModel at all time intervals for both diets (p<0.0001).
Conclusions Self-reported measurements of ΔEI were inaccurate. Model-based calculations of ΔEI found that instructions to follow the low-carbohydrate diet resulted in greater calorie restriction than the low-fat diet in the early phases of the intervention, but these diet differences were not sustained.
What is already known about this subject?
Diet assessments that rely on self-report, such as 24hr dietary recall, are known to underestimate actual energy intake as measured by doubly labeled water. However, it is possible that repeated self-reported measurements could accurately detect changes in energy intake over time if the absolute bias of self-reported of measurements is approximately constant for each subject.
What this study adds
We compared energy intake changes measured using repeated 24hr dietary recall measurements collected over the course of the 1-year Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS) trial versus energy intake changes calculated using repeated body weight measurements as inputs to a validated mathematical model.
Whereas self-reported measurements indicated a relatively persistent state of calorie restriction, objective model-based measurements demonstrated a large early calorie restriction followed by an exponential rise in energy intake towards the pre-intervention baseline.
Model-based calculations, but not self-reported measurements, found that low-carbohydrate diets led to significantly greater early decreases in energy intake compared to low-fat diets, but long-term energy intake changes were not significantly different.
Footnotes
Funding: KDH and JG were supported by the Intramural Research Program of the National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases. JLR and CG were supported by Grant 1R01DK091831 from the NIDDK, Grant 1K12GM088033 from the NIH (CTSA) and the Nutrition Science Initiative.
Conflict of interest disclosure statement: None of the authors have conflicts of interest