...and the potassium.

Rats concerned about avoiding cardiovascular disease might want to monitor their potassium intake. Studies on species of rats prone to hypertension-related strokes show that a diet high in potassium protects them against strokes. The finding, says Louis Tobian of the Univeristy of Minnesota in Minneapolis, could very well apply to humans as well.

He and his colleagues found that 20 of 24 stroke-prone rats died after four months on a diet that contained the normal amount of potassium for rat food. When 50 of their cousins were fed a high potassium diet, only one was dead after four months. The blood pressure in each group was the same, so the reduction in the death rate -- from 83 percent to 2 percent -- could be ascribed to potassium, Tobian says. When they found similar results in further studies, they took a close look at the condition of the arteries.

"The classic thing about high blood pressure is that it thickens the walls of the arteries," says Tobian. But with sufficient potassium, he says, "the walls didn't get thicker even though the rats still had high blood pressure. Something about potassium allows that artery to not have problems. It seems to protect the wall of the artery against the damage of carrying high blood pressure."

The low potassium diets of many blacks in the southeastern United States may explain that group's 18-fold increased incidence of strokes, he says. While he doesn't recommend that people take megadoses of potassium (too much of the element can be lethal), he does believe a dietary change is in order. The diet of our hunter-gatherer forebears -- lots of fruit and vegetables -- is the way to go, he says.

"We were gradually designed to run perfectly on this," says Tobian, "just as some cars are designed to run on diesel, and some on no-lead."