Your post scratches at some scientific-sounding ideas of the involvement of genetics, but fails to cite any definitive research into inheritable weight-control issues. The mathematics behind maintaining a healthy weight are startlingly simple, and the mythology of “fat genes” and thyroid problems and impossible to shed pounds is merely there to sell books and gym memberships.
The body is a closed system and cannot create additional weight without an over consumption of calories. Joel S is correct — it’s literally impossible to gain weight by eating your “maintenance” number of calories without violating the first law of thermodynamics.
So there are a couple of issues here. One is on whether or not genetics can make a difference. Are there “fat genes?” Does the thyroid matter? The second is whether or not First Law solves the obesity question. I’ll do this in two posts.
I’ll post a couple of links on genetics of obesity and one chart
The chart comes from a paper I am writing on obesity and is based off of data organized by Bruce Scaredote and first used in his paper What Happens When We Randomly Assign Families.
The red dots show the the BMI of mothers plotted against that of their birth children. The blue dots show the BMI of the mothers plotted against that of their adopted children. As you can see the correlation for adopted children is very slight. While the correlation for birth children has a steeper slope.
In both cases we are dealing with heights and weights for all persons reported by the mother. This will tend to introduce measurement error and cause the correlations to be less than the true correlation.
I think its important to note that almost all of the adopted children of morbidly obese mothers, BMI over 40, were normal weight. While the birth children of morbidly obese women tended to be at least overweight if not morbidly obese themselves.
We should also consider the possibility of response anchoring. That is giving a high or low weight for one child will influence the mother’s estimation of the weight for the other child. This will tend to introduce correlation between adopted and birth weights. Which will mean that the two correlations with Mother’s BMI will be closer together than reality. Because the adopted correlation is slight and the birth small, this should lead us to believe that the adopted correlation is even smaller and the birth even larger.
The take home here is that the tendency for whole families to be overweight or normal weight at least seems to work through genetic as opposed to environmental channels.
Other work on obesity and heritability