One thing I find rather fascinating about all these types of threads is that no one ever mentions age!
When I was 28 I was very active and could drink and eat a lot of crap and it really didn't matter. Lots of women in their 20s are genetically gifted that way. Around mid 30s it starts to become apparent that oh sh*t I need to actually start paying attention to what I am eating. Now im in my mid to late 40s, it is more challenging. All the "genetically" thin people from my 20s have disappeared
I've come back into contact with friends who through their 20s were thin, thin skinny minnies. In their late 40s they have popped back into my life.... and they are obese. It's really disconcerting.
In your late 40s there is no such thing as a woman who can eat massive amounts of food and "genetically" stay thin.
However, there are women who stay thin naturally because they eat less. They may eat all sorts of things, but they just are able to eat a small to normal portion and that is it. They feel uncomfortably full and turned off to eat another bite. Most of us as we get older struggle with a strong desire to eat, eat, eat.
I've found that staying very low carb and walking and weights keeps me in good shape. I love to run, but its harder to control my appetite when I do.