The term "inversely related" is used primarily in research. It means that when two variables (things for simplicity sake) are examined, one variable causes a reduction in the other. In your example, it appears like the risk of stroke is reduced if one eats more nuts. Another example, as exercise increases, depression decreases (one has an opposite effect on the other).

As far as I know, inversely related means that the more you do A, the less chance for B. So, in this example, if you eat more nuts, you are less likely to suffer from a stroke.

Inversely related means opposite proportion of both actions. More nuts you eat, less risk of heart disease.