Low-fat dietary pattern and change in body-composition traits in the Women's Health Initiative Dietary Modification Trial

Abstract

Background: The Women's Health Initiative Dietary Modification (DM) Trial was a randomized controlled trial that compared the effects of a low-fat (≤20% of total energy) or a usual diet in relation to chronic disease risk in postmenopausal women.

Objective: We characterized long-term body-composition changes associated with the DM trial and potential modifiers of these associations.

Design: In the DM trial, 48,835 women aged 50-79 y were randomly assigned to intervention (40%) or comparison (60%) groups. We studied a subset with whole-body dual-energy X-ray absorptiometry scans at baseline and during follow-up. Changes in fat mass (FM), lean mass (LM), and percentage body fat between the intervention (n = 1580) and comparison (n = 2731) groups at years 1, 3, and 6 were compared. By using generalized estimating equations, we calculated overall differences between groups and tested for interactions with age, diabetes, race-ethnicity (white, black, and Hispanic), body mass index (BMI), and hormone therapy (HT).

Results: The intervention women experienced significantly greater reductions in percentage body fat, FM, and LM at years 1 and 3 than did women in the comparison group (all P < 0.05). At year 6, only the FM change was significantly different between groups. Overall, the intervention was associated with reductions in percentage body fat (-0.8%; 95% CI: -1.0%, -0.6%), FM (-1.1 kg; 95% CI: -1.3, -0.8 kg), and LM (-0.17 kg; 95% CI: -0.28, -0.06 kg) during follow-up (all P < 0.003). Intervention associations varied by race-ethnicity, BMI, diabetes, and HT and remained significant after adjustment for physical activity.

Conclusion: This intervention was associated with modest long-term body-composition changes; the findings were more robust in years 1 and 3. This trial was registered at clinicaltrials.gov as NCT00000611.

FIGURE 1.

Mean changes in percentage body fat from baseline to years 1, 3, and 6. P values (2-sided t test) indicate the difference between the intervention and comparison groups at years 1, 3, and 6. With the use of generalized estimating equation models, interaction between the intervention and visit year was tested. The interaction term was significant, P < 0.001 (Wald test), suggesting that the association between the intervention and change in percentage body fat varied over time.

FIGURE 2.

Mean changes in fat mass from baseline to years 1, 3, and 6. P values (2-sided t test) indicate the difference between the intervention and comparison groups at years 1, 3, and 6. With the use of generalized estimating equation models, interaction between the intervention and visit year was tested. The interaction term was significant, P < 0.001 (Wald test), suggesting that the association between the intervention and change in fat mass varied over time.

FIGURE 3.

Mean changes in lean mass from baseline to years 1, 3, and 6. P values (2-sided t test) indicate the difference between the intervention and comparison groups at years 1, 3, and 6. With the use of generalized estimating equation models, interaction between the intervention and visit year was tested. We found that the association between the intervention and change in lean mass did not significantly vary over time, P = 0.92 (Wald test).