Objective versus Self-Reported Energy Intake Changes During Low-Carbohydrate and Low-Fat Diets

Objective This study aimed to compare self-reported with objective measurements of energy intake changes ( increment EI) during a 1-year weight-loss intervention with subjects randomized to low-carbohydrate versus low-fat diets. Methods Repeated body weight measurements were used as inputs to an objective mathematical model to calculate increment EIModel and to compare with self-reported energy intake changes assessed by repeated 24-hour recalls ( increment EIRecall). Results increment EIRecall indicated a relatively persistent state of calorie restriction of similar to 500 to 600 kcal/d at 3, 6, and 12 months with no significant differences between the diets. increment EIModel demonstrated large early decreases in calorie intake > 800 kcal/d followed by an exponential return to similar to 100 kcal/d below baseline at the end of the year. Accounting for self-reported physical activities did not materially affect the results. Discrepancies between increment EIModel and increment EIRecall became progressively greater over time. The low-carbohydrate diet resulted in increment EIModel 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 thereafter. Conclusions Self-reported increment EI measurements were inaccurate. Model-based calculations of increment EI 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.