In a recent study of more than 400 North American men and women whose previous heart attack put them at risk for a second heart attack, about half were told to switch to a “Mediterranean-type diet”—one rich in fish, vegetables, olive oil, and grains—while the other half were advised to eat a more traditional “Western” diet but to limit their fat intake. Those following the Mediterranean diet were significantly less likely than those in the other group to have a second heart attack. But the Mediterranean diet includes a fair amount of fat from fish and olive oil, so the research suggests that a diet may not have to be extremely low in fat in order to protect the heart.

Which one of the following, if true, most strengthens the argument?