BACKGROUND: Intensive dietary intervention programs may lead to benefits in vitality and other components of health quality. The Women's Health Initiative Dietary Modification (DM) intervention includes a large randomized controlled trial of an intensive intervention.

OBJECTIVE: To evaluate whether the intervention is associated with improved health-related quality of life (HRQoL) subscales, overall self-reported health, depression symptoms, cognitive functioning, and sleep quality.

DESIGN: This randomized controlled trial was analyzed as intent to treat.

PARTICIPANTS: Between 1993 and 1998, 48,835 women aged 50 to 79 years were recruited by 40 clinical centers across the United States. Eligibility included having fat intake at baseline > /=32% of total calories, and excluded women with any prior colorectal or breast cancer, recent other cancers, type 1 diabetes, or medical conditions with predicted survival < 3 years.

INTERVENTION: Goals were to reduce calories from fat to 20%, increase vegetables and fruit to 5+ servings, and increase grain servings to 6+ servings a day. During the first year, 18 group sessions were held, with quarterly sessions thereafter.

MAIN OUTCOME MEASURES: The RAND 36-Item Health Survey was used to assess HRQoL at baseline, Year 1, and close-out (about 8 years postrandomization), and estimate differential HRQoL subscale change scores.

STATISTICAL ANALYSES PERFORMED: Mean change in HRQoL scores (Year 1 minus baseline) were compared by randomization group using linear models.

RESULTS: At 1 year, there was a differential change between intervention and comparison group of 1.7 units (95% CI 1.5, 2.0) in general health associated with the intervention. DM intervention improved physical functioning by 2.0 units (95% CI 1.7, 2.3), vitality by 1.9 units (95% CI 1.6, 2.2), and global quality of life by 0.09 units (95% CI 0.07, 0.12). With the exception of global quality of life, these effects were significantly modified by body mass index at baseline.

CONCLUSIONS: DM intervention was associated with small, but significant improvements in three HRQoL subscales: general health, physical functioning, and vitality at 1 year follow-up, with the largest improvements seen in the women with the greatest baseline body mass index.