Obesity is a complex disease resulting from the interactions of a wide variety of hereditary and environmental factors. The combined progress in quantitative genetics, genomics and bioinformatics has contributed to a better understanding of the genetic and molecular basis of obesity. Hormones are chemical messengers that regulate processes in our body. They are one factor in causing obesity. Excesses or deficits of hormones can lead to obesity and, on the other hand, obesity can lead to changes in hormones.