Abstract MP63: Randomized Trials of Low-Fat vs. Other Diet Interventions on Weight Loss: A Meta-Analysis

Introduction: The effectiveness of low-fat diets for weight loss has been debated for decades. Dozens of randomized control trials (RCTs) have assessed whether decreasing the intake of total fat leads to weight loss, giving mixed results. Hypothesis: We hypothesized that low-fat dietary interventions do not lead to greater weight loss when comparator diet intervention intensity is considered. Methods: We conducted a systematic review and meta-analysis. RCTs were included if they compared a low-fat dietary intervention to any control diet with at least 1 year of follow-up. We estimated the combined fixed effect inverse variance weighted mean difference of low-fat vs. comparison diets. Several a priori stratified analyses were considered to explore heterogeneity. Results: Fifty studies met inclusion criteria, reporting 1-10 years of follow-up on 70,054 participants. Overall, low-fat dietary interventions resulted in 0.51kg greater weight loss compared to other diets (95% CI = -0.62, -0.40, p<0.001; I2 = 83%). However, when trials where greater attention was given to the low-fat group were excluded, comparator diets led to greater weight loss than low-fat diets (n=30; WMD=0.87, 95% CI=0.56, 1.17, p<0.001). Similarly, when the type of comparator diet was considered, low-fat diets were only beneficial compared to control groups who were simply asked to maintain their usual diet (n=18; WMD = -1.03, 95% CI = -1.18, -0.88, p<0.001). When equal attention was given to intervention groups, low-carbohydrate diets (n=15; WMD = 1.13kg, 95% CI = 0.53, 1.73, p<0.001) and other “healthy” diets without a low-fat component (n=20; WMD = 0.77kg, 95% CI = 0.42, 1.13, p<0.001) led to greater weight loss than low-fat diets. Comparison diets, irrespective of type, were associated with 1.30kg greater weight loss than low-fat diets when the interventions were intended to be isocaloric (n=19; 95% CI = 0.92, 1.69, p<0.001). Conclusions: Low-fat dietary interventions are not more effective than other diets for weight loss when differences in intervention intensity between treatment groups are considered. Rather, evidence from long-term (>=1 year) randomized trials indicates low-carbohydrate or other healthful dietary pattern interventions without a low-fat focus may be more effective for weight loss than low-fat dietary interventions. Further evidence is needed to establish the role of these interventions in longer-term weight loss and weight maintenance.