Background:
Reducing excess body fat is important for overall health, but individual success at reducing body fat varies considerably. Because dietary modification plays a key role in reducing body fat and maintaining a healthy body weight, there has been speculation if one particular dietary pattern is superior to another for losing weight. Previously we reported no significant differences in the effectiveness of either a low-carbohydrate diet or a low-fat diet for weight loss in the DIETFITs Trial. However, there is less literature that has specifically focused on body fat reduction. Therefore the purpose of this study was to assess if 12-month dietary changes were associated with body fat reduction.
Methods:
Participants were men and women with overweight or obesity that participated in the DIETFITS trial, a randomized clinical trial comparing the effectiveness of a healthy low-fat diet to a healthy low-carbohydrate diet for weight loss. The primary outcome was body fat percent loss, which was measured with dual-energy x-ray absorptiometry (DEXA) scans. Demographic information was collected from online surveys at baseline, dietary data were assessed from participants 24-hour recalls, and physical activity was assessed with the Stanford Seven-Day Physical Activity Recall questionnaire. Linear regression models were conducted to assess the association between changes in energy intake, dietary fat, and carbohydrates with body fat reduction, while controlling for demographic variables and physical activity.
Results:
Data were available for 272 participants with DEXA scans and dietary data. In the main model both baseline physical activity (coef = -0.26, p = 0.016) and changes in physical activity (coef = -0.36, p < 0.01) were significantly associated with body fat reduction. When stratified by dietary assignment, changes in physical activity remained significant for each group (low-carb group: coef = -0.30, p = 0.002 and low-fat group coef = -0.35, p = 0.006), while changes in dietary fat, as a percentage of energy intake, was associated with body fat reduction in the low-fat group only (coef = 0.15, p = 0.006). Race was also significantly associated with body fat reduction in all models, indicating non-White participants gained more body fat at the end of the intervention compared to Whites.
Conclusions:
The reduction in body fat appears to be mostly driven from participants increasing their physical activity levels. Identifying other predictors of body fat reduction warrant further study.
Obesity [Abridged]