CHICAGO — A study has found states with more strict school meal nutrition standards have better weight status with students who receive free or reduced-prices lunches compared with students who do not eat school lunches, according to a study published by the Journal of the American Medical Association Pediatrics.

“In states that did not exceed U.S.D.A. standards, students who obtained free/reduced-price lunches were almost twice as likely to be obese than students who did not obtain school lunches (26% and 13.9%, respectively), whereas the disparity between groups was markedly reduced in states that exceeded U.S.D.A. standards (21.1% and 17.4%, respectively),” the study reported.

Overall, the difference in obesity rates between students who received free or reduced-price lunches and students who did not get lunches was 12.3 percentage points smaller compared with states that did not exceed U.S.DA. standards.

Daniel R. Taber of the University of Illinois at Chicago headed the study and used a sample of 4,870 students in 40 states. Student data were obtained from the Early Childhood Longitudinal Study, Kindergarten Class, which began collecting data from a nationally representative sample of kindergarten students in the fall of 1998.

The National School Lunch Program has faced criticism that lunches do not meet U.S.D.A. standards and may be a missed opportunity to help students manage weight and reduce obesity.

“The evidence in this study suggests that ongoing changes to school meal standards have the potential to reduce obesity, particularly among students who are eligible for free/reduced-price lunches, though additional longitudinal research is needed to confirm this,” the study said.