Can We Blame Our Parents If We Are Overweight?

If you are overweight, the problem isn't necessarily just your diet, but, in fact, also has something to do with your genetics. But the genes that make a difference in obesity may have been turned on or turned off, and knowing what can turn a gene on or off can actually make a noticeably big difference in your efforts to control your weight.

What do you need to know about how genes can affect your weight?

Fat Mouse, Skinny Mouse

Geneticist Dr. Randy Jirtle recently retired from Duke University after a long and fruitful career studying the ways that genes can act in the real world. Dr. Jirtle is a renowned expert in the study of epigenetics, how encounters with the environment can switch off and switch on your genes, creating an epigenome of activated DNA that can really determine how our bodies work. One of Dr. Jirtle's more interesting experiments involved studies of the agouti gene that sometimes determines your obesity — and sometimes does not.

Jirtle kept colonies of genetically identical mice, with each mouse carrying a copy of a gene which is commonly known as the agouti gene. Some of the genetically identical mice had brown coats and had a weight of about 30 grams (which is about an ounce), and had the capacity to scamper around their cages, while others of the genetically identical mice had yellow coats instead and weighed about 60 grams, which is twice as much compared to the first group, and were not capable of doing very much at all other than lounging around in their cages all day while waiting for the next feeding of mouse chow.

The difference between the mice wasn't in their genes. Their genes were, in fact, completely identical. So what could it be that made the mice so different? Did Dr. Jirtle perhaps put some of his mice on the Southbeach Diet and feed the other mice some burgers and fries? Did the skinny mice maybe spend their day running on a wheel to generate electricity to keep the lights in the lab on? Did the fat mice spend too much time watching the Food Network? What really happened?

Fat Genes Permanently "Switched Off"

The reason that some of the mice in this experiment were thin and healthy and others were fat and sick, Dr. Jirtle discovered, was that in the skinny mice, the agouti gene was permanently switched off. On a molecular level, a chemical marker known as a methyl group (-CH3) had attached to the agouti gene, so that it no longer coded the proteins that made the enzymes that led to obesity.

The deactivation of the agouti gene, Jirtle was among the first to explain this concept, was a little like having computer hardware without the computer software. While the obesity gene was still present in the skinny mice, it couldn't "run" anymore. And once the obesity gene had been switched off in a mother mouse, the gene was also switched off in its offspring, although there were some factors that could potentially turn the agouti gene back on.

Environmental toxins, it turns out, could actually switch on the obesity gene. And when the obesity gene was switched on in a mother or father of a generation of mice, it stayed switched on in all of their descendants. The right nutrition, however, could help switch the gene off.