A study published in the British Medical Journal showed that women who ate nuts more than five times a week were about one third less likely to suffer from coronary heart disease as those who ate no nuts at all.
你这道题我是这么理解的: 比较的对象不是 吃坚果的女性 和 不吃坚果的女性, 而是 吃坚果女性患冠心病的可能性(women who ate nuts ... were ... less likely to suffer from coronary heart disease) 和 不吃坚果的女性患冠心病的可能性(than were those who ate no nuts at all).
than were those ...中的were是很关键的,补全了就是were likely to suffer...