Many people have not studied nutrition, or not studied it properly, and associate fats as in lipids with fat as in being overweight when this is in fact not the case and the various types of fats are both essential and provide energy to become an active person. Like you, I run 20+ miles a week, eat beef everyday and I'm the skinniest person I know.
There are many considerations to take into account. Nutrition is not one size fits all, but the general rule which does apply is moderation and balance. A completely sedentary lifestyle would have higher risk for disease if they had the same diet as, for example, a professional athlete.
