Wish that were true for my sister who died of cancer years ago. She was a skinny child, a skinny teenager, and a skinny adult. I always envied her for that.
It is true as a RISK REDUCER in my opinion, there are no guarantees in any form to prevent cancer.
The most cancer I see is in people who have inherited cancer genes unless they have some habits like smoking or becoming fat. I have 60 close relatives, including first cousins, my mother had many brothers and sisters and they were all very fertile lol, and no one came down with cancer except one heavy smoker. Food was expensive in my home country so obesity was rare.
So sorry about premature loss of your sister.