No we don't. While one gene has been isolated and studied, according to the programme to which Alice linked, there are over 400 genes directly related to body weight of which we know relatively little and we also don't know much about the function of the "brain" in our gut. BTW, thanks for the link to the video Alice.

I have two adult daughters very close in age. One is very svelt and slender and the other isn't and they have been that way since early elementary school.

One weighed 8lbs 6 oz at birth and looked like the Michelan tire man, until she was about two or three. The other weighed 7lbs. 4oz. and maintained a more normal body weight prior to school. One was a closet, junk food junkie, although they both were fed the same healthful diet at home and they were both physically active children. However, the outcome was decidedly different for each.

The child junk food junkie, Michelan tire baby, to this day remains slim, while her sister is not and hasn't been, since about the age of seven. Go figure.