A health study came to the defence of certain dietary fats on Tuesday, adding fuel to a scientific row over low-fat guidelines that have bedevilled dieters for nearly half-a-century. The low-fat movement has not prevented a global epidemic of obesity linked to health concerns such as diabetes, heart attacks and stroke, said researchers who probed whether fat in olive oil and nuts pile on the pounds. “Our trial demonstrates that a high-fat, high vegetable diet such as (a) Mediterranean diet does not promote weight gain,” study author Ramon Estruch of the University of Barcelona told AFP.