A new study says Americans' eating habits have improved - except among the poor.

Those results show a widening wealth gap when it comes to diet. Yet even among wealthier adults, food choices remain far from ideal.

The 12-year study used an index of healthy eating where a perfect score is 110. U.S. adults averaged just 40 points in 1999, and that climbed to 47 points in 2010. Scores for low-income adults were lower than the average and barely budged during the years studied.

Higher scores mean greater intake of heart-healthy foods including vegetables, fruits, whole grains and healthy fats. Low scores mean less of those foods and a greater chance for diet-related illnesses including diabetes, heart problems and obesity.

The study was published Monday in JAMA Internal Medicine.