Abstract
‘According to conventional wisdom, nutritional requirements increase dramatically during pregnancy due to the rapid growth of the fetus.’
According to conventional wisdom, nutritional requirements increase dramatically during pregnancy due to the rapid growth of the fetus. Adequate nutrition is therefore paramount to a healthy pregnancy. On the other hand, there are several food-related risks that may hinder the ability of a pregnant woman to choose a wide variety of foods and achieve sufficient nutrition. Media coverage of diet in pregnancy has also tended to create confusion for both the public and health professionals. Fortunately, Harvey and Ricciotti, 1 in this issue of American Journal of Lifestyle Medicine, provide a clear, up-to-date, and comprehensive review of various nutrition-related issues faced by pregnant women. They begin with an overview of one of the biggest public health issues of the century that also has critical ramifications for pregnancy—obesity. Overweight and obesity rates around the world have remained high and show no sign of declining, meaning many women will be overweight or obese prior to conception. An overweight or obese mother-to-be has a much higher risk of developing complications such as preeclampsia and gestational diabetes mellitus (GDM). Her offspring have a 2- to 3-fold increased risk of being overweight and obese even as children, thereby creating a vicious cycle. If we are to make any progress in the war against obesity, interventions must begin before conception.
It is not uncommon for women of normal weight prior to pregnancy to gain excessive weight during pregnancy. This may be partly due to current dietary guidelines for pregnancy and the widespread belief (even among health professionals) that women need to eat significantly more to provide adequate energy for the growth of the fetus. Theoretically, the total energy cost of pregnancy is estimated to be about 300 MJ over 9 months or 1.1 MJ per day (about 10% to 15% above the prepregnant level). But careful studies in well-nourished women have revealed either no change in energy intake or only a minor increase from early to late pregnancy that is insufficient to explain the large amount of energy deposited in new tissues. While it can be argued that food records underestimate true energy intakes, it is also possible that pregnant women naturally reduce their energy expenditure by an amount equivalent to around 1 MJ per day. A recent study 2 used a multiple-accelerometer-based system to measure time spent sitting down, lying, standing, walking, or running and estimate the pace at which these activities are performed. The researchers found that pregnant women spent significantly more time in less demanding activities (eg, reclining and sitting), equivalent to a total of 0.9 MJ per day lower in pregnant than nonpregnant women. Clearly, we need more well-designed studies using appropriate methodologies with sufficient power to detect meaningful differences in energy intake and energy expenditure during pregnancy. The findings could well have important implications for pregnancy guidelines3,4 as well as assumptions about excessive food intake among normal people who have gained excessive weight.
One of the most common pregnancy-related complications associated with obesity is GDM, defined as diabetes first diagnosed during pregnancy. Women with GDM will have elevated blood glucose levels, which contributes to the main adverse pregnancy outcomes associated with GDM, that is, excessive fetal growth, eventually leading to increased birth weight. The latter have been shown to be associated with various forms of chronic disease later in life, such as diabetes, cardiovascular diseases, and obesity. The prevalence of GDM around the world is increasing, not only because of higher body mass index among reproductive-age women but also because of changing diagnostic criteria that recognize the risk associated with “mild hyperglycemia.” Even within the normal physiological range, elevated blood glucose levels are still associated with an increased risk of high birth weight. 5 This suggests that postprandial hyperglycemia also deserves more consideration because it is the principal determinant of average blood glucose levels in healthy individuals. The glycemic index (GI) of a food describes how quickly the carbohydrates are digested, absorbed, and raise blood glucose. A food with a lower GI will be digested and absorbed more slowly, and vice versa. Harvey and Ricciotti 1 provide an informative overview of the current evidence supporting the use of a low GI diet to improve pregnancy outcomes. It resonates with the finding of 2 of our more recently published studies6,7 that following a low GI diet during GDM pregnancy results in similarly improved outcomes as a conventional, high-fiber diet and that a low glycemic load (GL; defined as glycemic index [as %] multiplied by total available carbohydrate) diet in GDM pregnancy is more likely to be nutritionally adequate than one with a higher GL.
The importance of postpartum weight loss and whether breastfeeding plays a role recognizes the newest research in this arena. The concept of fetal origins of adult disease has also been clearly summarized, indicating that intrauterine nutrition had a much more important role in long-term health of the unborn than we have previously understood. Pregnancy-related food-borne illness and pathogens are discussed, including a succinct description of the risk of mercury poisoning, Toxoplasmosis, Listeriosis, as well as Salmonellosis, the 4 most common types of food-related risks in pregnancy. Practical suggestions on how to reduce these risks are provided to help the readers answer any questions for women in their care. Bisphenol A (BPA) had become a “hot” public health topic because of its pseudo-estrogenic activity. The authors provided a brief review of the effects of BPA in pregnancy and advise pregnant women to avoid exposure.
Due to the rapid growth of the fetus, micronutrient requirements in pregnancy increase dramatically, and supplementation is usually recommended to help pregnant women meet the increased needs. The authors provide an excellent summary of the implications and potential risks of supplementation of folic acid, iron, vitamin D, iodine, vitamin A, and docosahexaenoic acid. To complete this comprehensive review, the effects of smoking, alcohol, and caffeine in pregnancy; herbal medications; as well as the benefits of exercise and information related to nutritional requirements in special situations such as multiple pregnancy, vegetarianism, and the newly minted eating disorder “pregorexia” are also discussed.
As nicely concluded by Harvey and Ricciotti 1 in their review, “Pregnancy is a time of dynamic physiological change and development.” Their review is a valuable and informative document for doctors and health care providers managing the nutritional needs of healthy pregnant women.