studies show saturated fats increase LDL cholesterol
A => B
People who get heart disease are more likely to have high LDL cholesterol
C => B
> Researchers have thus drawn a logical conclusion: a lot of saturated fat in the diet produces more cholesterol, which in turn increases the risk of heart disease.
A => B /\ B => C
> But this has been surprisingly difficult to prove.
The author wrote "People who get heart disease are more likely to have high LDL cholesterol". Had she written "People who have high LDL cholesterol are more likely to get heart disease" then the argument would have been valid.
You don't say?