If you are thinking about getting pregnant, you probably know that smoking is harmful for your baby.  But did you know that being overweight or even eating a high-fat diet during pregnancy may put your child at increased risk for obesity, diabetes, and heart disease when they grow up?

For a number of years, nutrition researchers have studied what is called “fetal programming.”  One of the first clinical examples of fetal programming was seen by British researchers studying malnourished pregnant women in developing countries. These women gave birth to smaller-than-normal babies but, paradoxically, the babies were at greater risk for obesity and diabetes when they grew up.  This effect was eventually traced to changes in insulin and appetite hormone regulation due to being under-nourished in the womb.

More subtle effects of fetal programming have since been discovered – ones that occur even when nutrition is adequate during pregnancy.  One investigator found that feeding high-fat diets to pregnant rats resulted in baby rats who became obese, even when they were fed low-fat, healthy diets as adults.  Another researcher found that when monkeys were fed a high fat diet during pregnancy, their babies were born with fatty livers and an increase is blood markers of inflammation, both risk factors for diabetes and metabolic syndrome.  In a recently reported study in the American Journal of Physiology (October, 2008), researchers at the University of Buffalo reported that fetuses of obese mother rats were “programmed” to become obese when they grew up, an effect again tied to abnormal insulin and appetite hormone regulation during fetal growth.

Fortunately, there is a lot you can do to prevent these problems if you are planning to become pregnant.  First and most important, if you are overweight, try to lose some weight before you get pregnant.   Dr. John Kral and his colleagues at the State University of New York reported that children born to mothers who had lost weight from gastric bypass surgery had a significantly lower risk of becoming obese compared to their siblings who were born before the mother’s surgery.  This protective effect was seen even though the mothers were still classified as obese after the surgery, so every bit of excess weight you can lose before you become pregnant is probably helpful.  You don’t want to try to lose weight after you become pregnant so this takes some planning ahead!

Second, make sure you eat a healthy diet during your pregnancy – one that is rich in whole foods like fruits, vegetables and whole grains, and low in fat.  While we don’t know yet whether high-fat diets during pregnancy have the same harmful effects in humans as they do in monkeys and rats, we do know that high-fat diets contribute to excess weight gain and tend to be pro-inflammatory so there are plenty of reasons to limit fat intake during pregnancy.

Finally, with your doctor’s approval, make sure you maintain regular, moderate physical activity during your pregnancy.  Taking a 30 minute walk every day will not only help you stay fit and handle the stresses of motherhood, it may prevent you from giving birth to a son or daughter who’s “programmed” for excess weight gain.