How does this work? Scientists have always thought that the genetic map, or the DNA, that we were born with was unchangeable - the genes you were born with determined what diseases you were at risk for.

Now genetic research is being turned upside down by a fascinating new field called epigenetics - the science of how the expression of some of our genes can be changed even if our basic DNA does not change.

What does epigenetics tell us? Certain chemicals and nutrients (or lack thereof) in our environment seem to be able to "tag" our DNA, which can then result in some of our genes being turned on or off, including certain genes that are known to increase our risk of cancer, obesity, heart disease and diabetes.

Epigenetics is also finding that certain protective nutrients in our food can keep these genes turned off and prevent them from causing illness.

Conversely, there are things that turn on those genes, such as nutritional deficiencies as well as exposure to certain environmental chemicals, resulting in illness. Americans are exposed to more than 100,000 chemicals every year that are used in household cleaners, plastics, food additives, food production, cosmetics, pesticides and yard-care products; more are added to the arsenal every year. Some of these industrial chemicals, such as benzene, formaldehyde and vinyl chloride, are known carcinogens; in many others, harm is suspected but difficult to prove.

Some of these substances probably exert their harmful effects via this process of epigenetics.

Recently, a chemical called bisphenol-A (BPA), which is found in hard plastics like water bottles and baby bottles, has come under fire for its epigenetic potential to cause harm. When pregnant mice are exposed to this chemical, some of the pups they give birth to are genetically at higher risk of obesity, diabetes, heart disease, and cancer. The good news is that certain nutrients and foods, particularly B vitamins, soy foods, cruciferous vegetables (including cabbage and broccoli), and green tea seem to protect against these changes, even if the BPA is still hanging around. This may explain why a healthy diet can help to protect us against diseases like cancer and obesity.

A recent expert panel of scientists from the National Toxicology Program came to the conclusion that BPA was not harmful to humans; however, another independent group of scientists criticized this position. They recommended that humans avoid exposure to BPA, stating that BPA was not safe and that this "expert" panel was influenced by industry to come to a benign conclusion about BPA.

So what is the average consumer to do with this information?

Given that pregnant women, infants and children may have the greatest threat of exposure to BPA, and that safe substitutes are available (e.g., stainless steel water bottles), we recommend that you avoid products with BPA if possible. You can also look for plastic bottles that are labeled as "BPA-free."