As unlikely as it sounds, obesity and type 2 diabetes may not be caused by what you eat. They may be caused by what your father or grandfather didn't eat.
Scientists reporting research in the journal Cell have found that male mice who are starved activate certain genes in their livers that cause greater release of sugars from stored food. When they later mate and have offspring, the offspring also have these genes activated, even if they never have contact with their fathers, and even if they are not starved. When the offspring are given a normal diet, they become obese and diabetic. This effect is passed on at least to the third generation.
Studies of survivors of famine in World War II have also found greatly increased rates of diabetes in the children of people who had little to eat during their childhood, regardless of the diet eaten by the second generation. The effects are even greater in the grandchildren of World War II famine survivors. This does not mean that your diabetes may be your parents' or grandparents' fault, but it does mean that you may have to control it by very careful diet.
Benjamin R. Carone, Lucas Fauquier, Naomi Habib, Jeremy M. Shea, Caroline E. Hart, Ruowang Li, Christoph Bock, Chengjian Li, Hongcang Gu, Phillip D. Zamore, Alexander Meissner, Zhiping Weng, Hans A. Hofmann, Nir Friedman, Oliver J. Rando. Paternally Induced Transgenerational Environmental Reprogramming of Metabolic Gene Expression in Mammals. Cell, 2010; 143 (7): 1084-1096 DOI: 10.1016/j.cell.2010.12.008