Q: I've been told by a doctor that I’m too big. Then my mother tells me to stop eating so much. I’m noticing that I’m starting to hate the way I look. Am I going to be this huge after my baby is born? Is it safe to diet when pregnant?
A: Many women start their pregnancy at weights that are higher than their ideal body weight. Although it is not ideal, pregnancy is not the right time to diet. All pregnant women need to gain weight, regardless of their pre-pregnancy weight. It is really important to determine what your BMI or body-mass index was prior to the start of your pregnancy. You can either ask your doctor or calculate it by going to nhlbisupport.com/bmi and plugging in your height and pre-pregnancy weight. It's confidential, so no cheating! Once your pre-pregnancy BMI is calculated, here is the estimated weight gain to aim for:
BMI < 18.5 (underweight) - 30-40 lbs. BMI 18.5—24.9 (healthy weight) - 25-35 lbs. BMI 25—29.9 (overweight) - 15-25 lbs. BMI > 30 (obese) - 11-20 lbs.
Here is why pregnant women should avoid dieting: A growing fetus requires a constant supply of glucose (from carbohydrates) to grow normally. Diets don’t provide enough carbohydrates or glucose for a growing baby. Glucose is the fuel for developing the brain and nervous system.
If a pregnant woman’s diet does not provide carbohydrates for her fetus, her body tries to use fats and protein for energy. Fat cannot be broken down into glucose. Instead, it breaks down into something called ketones. Normally, a small amount of ketones float around in the blood. But if a pregnant woman continually deprives herself of carbohydrates, large amounts of ketones accumulate.
Ketones can and do cross the placenta. This can result in fetal Ketoacidosis, which can lower the baby’s blood pressure and increase the baby’s heart rate. Many studies show elevated ketone levels stress the fetus (changing fetal vital signs) and put the baby at risk for health problems later in life, such as high blood pressure, heart disease, and diabetes. So the bottom line: pregnant women should still eat well-balanced meals but not for the purpose of losing weight.