Now a spate of new research, including a meta-analysis of nearly two dozen studies, suggests a reason why: investigators may have picked the wrong culprit. Processed carbohydrates, which many Americans eat today in place of fat, may increase the risk of obesity, diabetes and heart disease more than fat does—a finding that has serious implications for new dietary guidelines expected this year...

...These trends may be explained in part by the yo-yo effects that high glycemic-index carbohydrates have on blood glucose, which can stimulate fat production and inflammation, increase overall caloric intake and lower insulin sensitivity, says David Ludwig, director of the obesity program at Children’s Hospital Boston.