Why are women and men shaped differently?
HOW BELLY FAT IS DIFFERENT FROM THIGH FAT
The answer isn't clear, but it’s worth looking into because belly fat comes with a greater risk of heart disease and diabetes - whereas both hip and thigh fat don't seem to. Also, men tend to store abdominal fat, while women are often pear-shaped and store more fat on their hips and thighs.
A recent study carried out at Sanford-Burnham Translational Research Institute for Metabolism and Diabetes looked at how belly and thigh fat differ at the genetic level and may provide a first step toward treatments aimed at specific body regions that contribute most towards the complications associated with obesity.
In this study, the research team compared genes that were most active in belly fat to those most active in thigh fat in samples taken from men and women.
Much to their surprise, they found that active thigh fat genes were significantly different from active belly fat genes. What’s more, variations in genetic activity were gender specific.
In men, 125 genes were expressed differently in their belly compared to their thigh fat. On the other hand in women, 218 genes - most unique to women, with 59 genes the same as in males - were expressed differently in belly relative to thigh fat.
The most noteworthy of the genes that differed were the so-called ‘homeobox’ genes, which play a dominant role in embryo development. Many homeobox genes are influenced by sex hormones such as estrogen and progesterone, so the researchers in this study concluded that homeobox genes may be programming fat cells to respond differently to hormones and other signals.
Even when the research team isolated stem cells from belly and thigh fat and grew them in laboratory dishes, they still saw the same location-specific differences in genetic activity in fat that developed from these stem cells.
This means belly fat and thigh fat are genetically pre-programmed for their final location during their development. It's not a difference that's acquired over time, as a result of diet or environmental exposure.
This suggests that the pear shape seen in women may actually reduce their risk of heart disease and diabetes. For instance, it’s well-known that women who have heart attacks tend to have more belly fat than thigh fat.
Clearly, the problem is not just about the fat but also the location. Future studies aimed at understanding critical differences between these fat storage areas is likely to lead to better, more specific treatments that are aimed at regions that contribute most to obesity complications in men and women.