Although the exact mechanism isn’t clear, many health experts believe that each person is born with a genetically predetermined weight range that the body strives to maintain. Human bodies used this system to protect them from starvation when access to food wasn’t as easy as a trip to the drive-through or a dash to the corner mini-mart.

According to the set point theory, your body has a set point: the weight your body naturally and easily maintains. This is generally within a healthy weight range for most people. Unfortunately, this level is generally higher than most people like, cosmetically speaking, and may explain why reaching a desired weight goal — especially dropping those pesky 5 or 10 pounds — can be so difficult.

Laboratories do plenty of research on mice genes. The research is promising and fast developing. For example, a gene called ob is responsible for the production of leptin, a hormonelike substance that helps the brain regulate appetite. Leptin, which is made in fat cells, travels to the brain, signaling to the brain that the cells have enough fat so that the appetite mechanism can be turned off. Another gene, known as db, also regulates leptin to reduce appetite, but it cranks up metabolism as well to control how fast or slowly calories are used.

Another family of genes called FOX has been found in mice that don’t gain weight, regardless of how much they pig out. The PPARd gene that’s activated in thin mice helps them burn calories faster than mice whose PPARd wasn’t active. Scientists have found only similar genetic material in human DNA; unfortunately, they haven’t yet found exactly the combination of genes or their structure that leads to obesity in humans — but they’re working on it.

Researchers suspect that the cells of obese people have diminished gene activity in much the same way that people with diabetes have reduced sensitivities to insulin.