To determine which established diet quality indices best predict weight-related outcomes in young women.

In this cross-sectional analysis, we collected dietary information using the Harvard FFQ and measured body fat percentage (BF%) by dual-energy X-ray absorptiometry. We used FFQ data to derive five diet quality indices: Recommended Food Score (RFS), Healthy Eating Index 2015 (HEI-2015), Alternate Healthy Eating Index 2010 (AHEI-2010), alternate Mediterranean Diet Score (aMED) and Healthy Plant-Based Diet Index (HPDI).

University of Massachusetts at Amherst.

Two hundred sixty healthy women aged 18–30 years.

The AHEI-2010 and HPDI were associated with BMI and BF%, such that a ten-point increase in either diet score was associated with a 1·2 percentage-point lower BF% and a 0·5 kg/m2 lower BMI (P < 0·05). Odds of excess body fat (i.e. BF% > 32 %) were 50 % lower for those in the highest v. lowest tertile of the AHEI-2010 (P = 0·04). Neither the RFS nor HEI-2015 was associated with BMI or BF%; the aMED was associated with BMI but not BF%.

These results suggest that diet quality tends to be inversely associated with BMI and BF% in young women, but that this association is not observed for all diet quality indices. Diet indices may have limited utility in populations where the specific healthful foods and food groups emphasised by the index are not widely consumed. Future research should aim to replicate these findings in longitudinal studies that compare body composition changes over time across diet indices in young women.