Yes, I am retarded, using logic and science to explain why identical twins can have different body types.>>188586559
There are countless examples of twins having different body types due to diet. They are the perfect example of nature vs. nurture.
Genes do have a strong effect on where your body will be, a woman whose genes tell her she will be flat won't have huge breasts no matter what. Now, let's do the opposite, a woman who has the genes to have large breasts. If she consumes lots of protein and has a nutrient-rich diet, she will have large breasts. Now, if she was poor and didn't have a good diet, the same woman would probably have very big breasts for her very skinny frame, but the physical size would be smaller than the person who has a good diet.
Twins are basically that concept but as two different people. If one twin girl kept on eating the protein from her sister's plate, nutrition and hormones will have an effect on both of them.