A Low Glycemic Diet for Optimal Pregnancy Weight

Learn how to manage your pregnancy weight gain with a low glycemic diet.
August 2013
Pregnant women instructed to follow a low GI diet gained significantly less weight during pregnancy than those given no dietary advice.

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The Low GI Eating Plan for an Optimal Pregnancy (The Experiment, 2012)—written by the world's leading experts on the glycemic index (GI), Dr. Jennie Brand-Miller, Dr. Kate Marsh and Dr. Robert Moses—will help you to clearly understand the connection between the food you eat, your blood glucose levels and your baby's future health. In this excerpt from chapter 4, “Ideal Weight Gain,” discover the average weight gain during pregnancy and how a low glycemic diet can assist you with your optimal pregnancy weight goals.

You can purchase this book from the Mother Earth Living store: The Low GI Eating Plan for an Optimal Pregnancy.

Ideal Weight Gain

This chapter doesn’t beat around the bush. Pregnancy is a time when many women gain more than enough. Traditionally, dietary advice for pregnancy has focused on making sure there’s adequate intake of all the essential nutrients. That’s not surprising, considering the fact that the requirements for many nutrients are higher than at any other time in life. Unfortunately, weight gain during pregnancy, despite its importance, is not given the emphasis that it deserves. In this chapter, we show you how to calculate your ideal weight gain (depending on your height and pre-pregnancy weight), and how to monitor and keep it under your control.

As a routine part of care, many obstetric care providers will keep an eye on your weight gain, but most will steer away from discussing it for fear of causing embarrassment or needless anxiety. Women will often discuss the subject among themselves, especially if it’s faster and greater than they expected. Many will tell you that even after the birth, they retained a few pounds, and found them difficult to budge. While their experience is common, we want to assure you that weight gain during pregnancy is under your control and, indeed, it’s good practice for you to monitor it yourself, so that you gain the ideal, or optimal, amount.

Okay, so what’s ideal? The optimal amount of weight gain over pregnancy is one that results in a “desirable pregnancy outcome.” That means a healthy baby, born at full term (about forty weeks, or nine months plus one week, gestation) with a birth weight of 6–9 pounds. In women from affluent countries like the United States, who start pregnancy weighing 140–160 pounds, the average weight gain over pregnancy is about 28 pounds, and the average infant birth weight is 7 pounds, 8 ounces. But these are averages only. You’ll be pleased to hear that there’s a range of weight gains that are considered ideal. The desired amount depends to a large extent on your pre-pregnant weight. For a woman who is underweight, a higher weight gain is desirable, while an overweight mom should gain less.

Of increasing concern, the average weight gain during pregnancy has increased over the past few decades. From the 1940s to the 1960s, weight gain tended to hover around 22 pounds. The recommendation to all pregnant women at the time, irrespective of their starting weight, was to restrict their weight gain to just 15 pounds. This advice stemmed largely from the observation that increased weight gain was directly related to higher birth weight, and higher risk of pregnancy complications. In 1970, however, the Institute of Medicine (IOM) determined that restriction of weight gain during pregnancy was likely to be harmful, and the weight gain recommendations were eased to a range of 20–26 pounds. Nonetheless, by 1980, the average weight gain in American women had increased to 33 pounds. In the US, up to 40 percent of women gain more weight than is recommended during pregnancy. The increase has occurred in women of all shapes and sizes, including the slimmest and the heaviest, with far-reaching consequences.

Why Does Weight and Weight Gain Matter?

Weight gain in pregnancy is an excellent predictor of the baby’s weight at birth. This, in turn, predicts how well your baby copes in the first days and months of life. That’s the reason for the proud tradition of announcing not only the baby’s sex but its birth weight as well. Like many things in life, however, there is a happy medium. If you gain too little, it can mean a small baby who has been born too lean with little body fat. Small babies, defined as those born weighing less than 5 pounds, 8 ounces, have a higher chance of having poor outcomes during and after birth. Paradoxically, they are more likely to become overweight as adults and have a greater risk of high blood pressure and heart disease. On the other hand, a baby that grows too big or too fast also has poor outcomes. Excessive weight gain during pregnancy and high birth weight (greater than 9 pounds) are both linked to complications at birth, such as emergency Caesarean delivery, fetal macrosomia (a baby having excess fat), physical injury and postpartum hemorrhage. Just as importantly, excess weight gain also predicts the future health of both mother and baby. In the long run, excessive weight gain in pregnancy has contributed to the current epidemic of obesity in women and children. A woman who gains too much during pregnancy gives birth to an overweight daughter, who in turn is more likely to be an overweight child and young adult, who is then more likely to gain excessive weight during her first pregnancy and give birth to a child with excess fat, and the cycle repeats itself.

Body Fat in Babies—The Studies

The most concerning aspect of excessive weight gain in pregnancy is the body fat of the baby. The Southampton Women’s Study in the UK found that almost half the children in the study were born to women who gained excessive weight during pregnancy, resulting in greater body fat mass at birth, as well as at four years of age and again at six years of age. In contrast, appropriate pregnancy weight gain as defined by the IOM was linked to lower levels of fat in the children. In Sweden, a study of nearly 150,000 male army recruits found that their BMI (body mass index) at eighteen years of age was directly linked to their mother’s pregnancy weight gain—but only if their mother had been overweight or obese at the start of pregnancy. If she was normal weight, her pregnancy weight gain did not predict her son’s future BMI. Excessive weight gain also worsens the mom’s state of insulin resistance, which is an otherwise normal physiological adaptation to pregnancy. However, in excess, insulin resistance has adverse effects on blood fats and on other metabolic markers, including blood glucose levels, blood pressure and inflammatory factors.

Recommended Guidelines for Weight Gain

In 1990, the IOM established the first set of guidelines for weight gain in pregnancy. In 2009, these guidelines were updated to take into account the larger number of women who entered pregnancy with excess body fat. The new recommendations are shown in the box below. Most developed countries around the world use these guidelines.

IOM Guidelines for Pregnancy Weight Gain 2009
The BMI here refers to your BMI at the start of pregnancy

BMI less than 18.5 (underweight); 28 – 40 pounds
BMI of 18.5–24.9 (normal weight); 25 – 35 pounds
BMI of 25–29.9 (overweight); 15 – 25 pounds
BMI of 30 or greater (obese); 11 – 20 pounds

How to Calculate Your BMI

Your BMI is a rough guide to your body fat mass relative to your height. To calculate yours, you need to know your pre-pregnancy weight in pounds without clothing and your height in inches without shoes.

BMI = weight (pounds) divided by the square of your height in inches (that is, height squared) multiplied by 703

An example:
If your weight is 140 pounds and your height is 64 inches, then your BMI is (140 /[64 x 64]) x 703 = 24

Rate of Weight Gain

Your rate of weight gain (that is, pounds per week) over the course of pregnancy varies according to trimester. Very little is usually gained in the first trimester. Indeed, the developing embryo weighs only .04 ounces and is not quite three-quarters of an inch long at eight weeks of age: It’s about the size of a bean. During those first critical weeks and months, the rapidly multiplying cells have differentiated into various tissues and tiny organs, which is why the quality of the diet, not the quantity, is so important at this stage. From 12 weeks onward, however, you can expect to gain steadily at a rate of about 3/4 to 1 pound until the baby is delivered at around 40 weeks gestation (38–42 weeks is considered within the range of normal gestation).

It is interesting to look at the makeup of the pregnancy weight gain. Much of it is water (about 60 percent), 30 percent is fat and only 8 percent is protein. For a woman who gains the typical 28 pounds, about 5–10 pounds represents a natural increase in her own fat stores. Your blood volume also increases, as does the weight of your uterus and breast tissue. The baby weighs on average 6 1/2 to 8 1/2 pounds at birth and the placenta that is delivered after the baby weighs about 1 1/2 pounds. The components of pregnancy weight gain are shown in the box below.

Not surprisingly, the biggest variation among different women is in the amount of fat stored. It ranges from no increase at all in some developing countries to 11 pounds or more in affluent countries.

Components of Weight Gain in Pregnancy (in pounds)

Results of Conception – 11
    Baby – 7.7
    Amniotic fluid – 1.8
    Placenta – 1.5

Maternal Tissues  9.4
    Water – 3.7
    Uterus and breasts – 3.1
    Blood – 2.6

Fat Stores – 7.1

Total Weight Gain – 27.5

Using the figures above, we can calculate that about 70,000 additional calories are needed to grow these new tissues over a period of about nine months, equivalent to roughly 240 calories per day. An average woman normally eats about 2,100 calories per day, so the extra 240 calories is about 10 percent above pre-pregnant needs. But interestingly, careful studies in well-nourished women reveal either no change in energy intake during pregnancy or only a minor increase, so small that it simply can’t explain all the extra energy deposited in new tissues. Scientists have long been puzzled as to why this is so. Some suspect that physical activity declines and others suspect that absorption of nutrients increases, but at the present time, we really don’t know why most women do not appear to eat more energy during pregnancy. So much for the old saying “eating for two”!

The Best Diet for Optimizing Pregnancy Weight Gain

At the present time, we believe that low GI diets are the healthiest and safest diets for optimizing pregnancy weight gain. In non-pregnant overweight and obese women, low GI diets are linked to improved sense of fullness, greater weight and body fat loss and a better capacity to prevent weight regain after a large weight loss. It is therefore reasonable to expect that low GI diets might help prevent excess pregnancy weight gain. This proved to be the case in a recent study in 800 Irish women (the ROLO Study) who were at risk of delivering overly large babies. Those instructed to follow a low GI diet gained significantly less weight during pregnancy than those given no dietary advice. Importantly, this study showed that a low GI diet significantly reduced the risk of developing glucose intolerance during the third trimester, a potential harbinger of type 2 diabetes later in life.

A low GI diet may reduce the risk of giving birth to a large baby without increasing the risk of a small baby.

Dr. John Clapp III, a Californian obstetrician, found that a low GI diet that was initiated at around 12 weeks gestation reduced both weight gain and birth weight in a small group of women. The six women allocated the higher GI diet gained an average of 44 pounds compared with only 26 1/2 pounds in the low GI group.

Although more research is needed, low GI diets might also improve glucose metabolism during pregnancy. Remember, pregnancy can be likened to a metabolic stress test. Low GI diets reduce the levels of insulin in the blood after meals and also improve insulin sensitivity in people with type 2 diabetes. Higher insulin sensitivity is likely to reduce the chance of excess weight gain. In fact, high insulin concentrations in the mother’s blood are linked to greater weight gain during pregnancy and a greater tendency to retain the weight after pregnancy. While increasing insulin resistance in pregnancy is a normal physiological consequence of pregnancy, in excess it can cause impaired glucose tolerance and gestational diabetes.

Food Supplements and Pregnancy Weight Gain

Many studies have examined whether food supplementation (for example, milk powders and other supplement drinks) during pregnancy is helpful or not, particularly in undernourished women with a low BMI. Food supplements containing calories and protein in normal proportions were found to increase total pregnancy weight gain and increase the birth weight of the baby. Importantly, the food supplements reduced the chances of having a small baby (under 5 pounds, 8 ounces) and perhaps the chance of premature delivery. When the mothers were followed up with later, supplemented mothers were the same weight as unsupplemented mothers, and there were no differences in the children’s heights, BMI or body fat levels as teenagers. If your BMI is in the underweight range, consult your doctor about whether you may need a food supplement.

High-Protein Diets and Supplements

Some studies have specifically examined the efficacy of high-protein supplements. A large trial in Harlem, New York, found that adding daily protein shakes did not increase the mother’s weight gain or the infant’s birth weight. Indeed, there was a tendency for the babies to be born lighter (the opposite of the investigators’ expectations) and an increased risk of stillbirth.

Similarly, some trials have looked at whether a high-protein diet (as opposed to high-protein supplements) is beneficial. They found a small increase in weekly weight gain and birth weight, but unfortunately, there may have been an increased risk of having a small baby, too.

To sum up, health authorities believe there’s no justification for prescribing high-protein supplements to pregnant women. Not only do these products lack evidence of benefits, they may even be harmful. This applies to both undernourished and well-nourished women. Even in overweight women, who may be gaining weight too fast, there is nothing to suggest that they are helpful, and there may even be a small chance that they may limit the growth of your developing baby.

Excerpted from The Low GI Eating Plan for an Optimal Pregnancy: The Authoritative Science-Based Nutrition Guide for Mother and Baby, copyright © Dr. Jennie Brand-Miller, Dr. Kate Marsh, and Dr. Robert Moses, 2013. Reprinted by permission of the publisher, The Experiment. Buy this book from out store: The Low GI Eating Plan for an Optimal Pregnancy.