Adherence and success in long-term weight loss diets: the dietary intervention randomized controlled trial (DIRECT)

Data are limited as to whether participants in diet trials truly adhere to their assigned diet and the factors that affect their adherence.

We evaluated success and adherence in a two-year dietary intervention randomized controlled trial (DIRECT) in which 322 moderately obese participants (mean age 52 yrs, mean body-mass-index (BMI) 31 kg/m(2), 86% men) were randomized to one of three groups: low-fat, Mediterranean, or low-carbohydrate diets.

Overall compliance at month-24 was 85%, with 90% in low-fat, 85% in Mediterranean, and 78% in low-carbohydrate diet (p = .042 between groups). Attrition was higher in women (29% vs. 14% men, p = .001) and current smokers (25% vs. 14% among maintainers, p = 0.04). In a multivariate model, independent predictors of dropping-out were: higher baseline BMI (OR = 1.11; CI: 1.03-1.21) and less weight loss at month-6 (OR = 1.20; CI: 1.1-1.3). In a multivariate model, greater weight loss achieved at month-6 was the main predictor associated with success in weight loss (> 5%) over 2 years (OR = 1.5; CI: 1.35-1.67). Self-reported complete adherence score to diet was greater on low-carbohydrate diet (p < .05 compared to low-fat) until month-6, but dropped overall from 81% at month-1 to 57% at month-24. Holidays were a trigger to a significant decrease in adherence followed by a partial rebound. Changes in diet composition from month-1 to month-12 were more pronounced in the multi-stage low-carbohydrate diet-group (p < .05). Generally, the most irresistible restricted food items were cookies (45% of dieters) and fruits (30%). Among the physically active (n = 107), 44% reported a tendency to eat less after exercising compared to 10% who tended to eat more.

Initial 6-month reduction in weight is the main predictor of both long-term retention and success in weight loss. Special attention is needed for women, current smokers, and during holidays. Physical activity is associated with subsequent reduction in energy intake.