You've heard of the dangers of childhood obesity, but you probably never thought that your baby could be born overweight. A 2006 study by researchers at the Harvard School of Public Health however has found that overweight newborns are on the increase—and that these obese babies are turning into chubby children.

The study, which examined health records for over 100,000 babies over 20 years, revealed that the number of overweight infants under 6 months old increased more than 70 percent from 1980 to 2001. Researchers note that high infant weights are associated with obesity throughout childhood and adulthood.

Why the boost in baby BMIs? A breastfed baby doesn't eat doughnuts or watch too much TV—and you can't put tots on a treadmill. The puzzling rise in infant weight and body mass appears to begin at birth and can't be explained by diet and exercise. That's why researchers have started to look at the environment—and many of them have decided that obesogens could be to blame.

What's an obesogen? The term obesogen—coined by Dr. Bruce Blumberg—refers to chemicals in the environment that might contribute to higher birth weights and excessive weight gain in infants. Through his research, Dr. Blumberg found that prenatal exposure to a common chemical, tributyltin, caused mice to be born with more fat cells—almost as if they were "programmed" to be fat. Unsurprisingly, these lab mice then grew up obese. Blumberg says that chemical and environmental factors are "a possible model both in terms of prenatal exposure and early life exposure," but he cautions that hard evidence for humans is still scant.

Dr. Robert Lustig, a pediatric endocrinologist who studies the obesogen phenomenon, says that "There are a lot of studies correlating obesogen levels to adiposity [obesity] in children. The problem is that these studies show correlation, not causation. The best we can do is 'predictive studies', where obesogen levels in the pregnant mother predict adiposity [fatness] in the offspring in later life." In other words, there are strong hints that something is up with the environment and infant obesity, but the facts are still being uncovered.

While the hypothesis is still evolving, a number of scientific studies have found definite associations between specific chemicals and early weight gain. Some of the likely chemical culprits are:

  • DDT/DDE. These chemicals are an ingredient in pesticides, and the toxins persist in the environment for decades without degrading. A study of women in Michigan who ate fish contaminated with DDT/DDE showed that prenatal exposure to these chemicals significantly increased BMI in babies.
  • Phthalates. Phthalates are a chemical found in items that we use everyday like cosmetics, soaps, plastics and paint. Most adults in the modern world have phthatlates in their system. Studies have shown a correlation between phthalates and obesity in adults.
  • Bisphenol A (BPA). BPA is a chemical used primarily in plastics. Baby bottles, water bottles, juice boxes and food containers all contain BPA. Animal studies show an association between body mass and BPA levels.
  • Estrogenic Compounds. Many everyday drugs contain synthetic estrogen-like chemicals that have been linked to weight gain in animal studies. These substances mimic the hormone estrogen in your body. Exposure to artificial estrogens has been linked to weight gain in animal studies.

So what can you do to protect yourself and your child both before birth and after? The first step is raising your awareness of the substances that surround you. You can also follow these sensible steps.

  • Fresh Food. Eat fresh and unprocessed food, advises Dr. Blumberg. Because we don't know what specific chemicals cause our cells to morph into fat cells, it's best to avoid as many artificial ingredients as possible. Fresh veggies, fruits, legumes and whole grains are perfect for pregnant and nursing mamas, since chemicals may be transmitted through breast milk. Feed your baby unprocessed, whole food—such as puréed sweet potatoes or soft avocado—when she starts solids.
  • Paper or Plastic? Minimize plastic in your life, especially for food consumption. Avoid water bottles and plastic food storage containers, as they're a major source of BPA. Drink out of a glasses, and look for BPA-free bottles for your little one. Store leftovers in glass or metal containers.
  • Protect Against Pesticides. Eating low on the food chain while pregnant and nursing can help protect against pesticides in your food. Persistent pesticides like DDT/DDE are "bio-magnified" in food products—meaning that if the chemical is present in small amounts in a plant food and the plant is eaten by an animal, the chemical gets concentrated and you ingest more of it. So skip copious amounts of animal products, and substiute with lots of fruits, vegetables and grains—preferably organic.
  • Smoke and Pollution. You know not to smoke while pregnant, but you should also avoid places where you are exposed to second-hand smoke. Be aware of the air quality both inside and outside of your home.
  • Hormone Havoc. Avoid drugs and pharmaceuticals that contain synthetic estrogens that might cause hormone disruption. Messing with your hormonal profile while pregnant or nursing could impact your infant's weight.

Above all, don't panic. Chemicals are everywhere in our modern world, and you can't raise your child in a bubble. Obesogens are only one piece of the puzzle of childhood obesity. Be sensible and continue eating healthy foods and limiting sugar intake for yourself and your child. In addition, be a smart mom and mom-to-be and minimize your chemical exposure for a happy and healthy baby.