Totally gut bacteria. I have 2 brothers, both weigh well over 300-350+lbs at 5'9" and 5'11", mom is 5'2"-5'4" at probably 180ish, and my deceased father was 350lbs at 6' (pre-colon cancer weight roughly). Meanwhile I (male) sit here at 6'0" 165-167lbs. Genetics, right? (wrong).