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Summary

To obtain a comprehensive view of the impact of women's diet and physical activities on pregnancy outcome, lactation, and health, the Subcommittee on Diet, Physical Activity, and Pregnancy Outcome of the Committee on International Nutrition Programs examined the available data on the patterns of physical activity of women in developing countries and the variations that occur during pregnancy and lactation. The goals were to provide descriptive information as a basis for the interpretation of other data and to determine the extent to which women in the developing world are known to reduce or otherwise alter their activities and diets as a result of childbearing.

Although the interest in this subject arose from the desire to address the problems of women whose work requires them to perform heavy physical labor during pregnancy, the committee defined its task in terms of women's physical activities, rather than work, for several reasons. In developing countries, women's occupational roles are often multiple and difficult to define. Women may spend substantial amounts of time in agricultural work; however, if this is not paid labor or cash cropping, it may not be defined as work or employment. In addition, routine household tasks, such as pounding and grinding grain, carrying water, or washing clothes by hand, which are often not defined as work in employment studies, may be very strenuous physically and may require a prolonged energy expenditure. For this reason, the subcommittee was charged to focus on the physical activity encompassed in all of these activities. Psychological stress is highly relevant to women in poor circumstances in developing countries, and although its effects were considered important, they were judged to be beyond the scope of this review.



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Nutrition Issues in Developing Countries: Part I: Diarrheal Diseases - Part II: Diet and Activity During Pregnancy and Lactation 1 Summary To obtain a comprehensive view of the impact of women's diet and physical activities on pregnancy outcome, lactation, and health, the Subcommittee on Diet, Physical Activity, and Pregnancy Outcome of the Committee on International Nutrition Programs examined the available data on the patterns of physical activity of women in developing countries and the variations that occur during pregnancy and lactation. The goals were to provide descriptive information as a basis for the interpretation of other data and to determine the extent to which women in the developing world are known to reduce or otherwise alter their activities and diets as a result of childbearing. Although the interest in this subject arose from the desire to address the problems of women whose work requires them to perform heavy physical labor during pregnancy, the committee defined its task in terms of women's physical activities, rather than work, for several reasons. In developing countries, women's occupational roles are often multiple and difficult to define. Women may spend substantial amounts of time in agricultural work; however, if this is not paid labor or cash cropping, it may not be defined as work or employment. In addition, routine household tasks, such as pounding and grinding grain, carrying water, or washing clothes by hand, which are often not defined as work in employment studies, may be very strenuous physically and may require a prolonged energy expenditure. For this reason, the subcommittee was charged to focus on the physical activity encompassed in all of these activities. Psychological stress is highly relevant to women in poor circumstances in developing countries, and although its effects were considered important, they were judged to be beyond the scope of this review.

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Nutrition Issues in Developing Countries: Part I: Diarrheal Diseases - Part II: Diet and Activity During Pregnancy and Lactation The subcommittee included several kinds of data in its review. Studies that have focused on women's employment rather than physical activity per se were reviewed, and their relevance to the subcommittee's task was assessed. then, to have a broad perspective, reports of energy expenditure research were examined for pregnant and nonpregnant women in developing countries, and to the extent that data were available, consideration was given to the type and duration of physical activity performed. Information on the dietary, metabolic, physiological, and endocrine adaptations to pregnancy in well-nourished women was also reviewed as they pertain to energy expenditure and physical activity. Most of the data on maternal work and employment were from developed countries. there are some problems in extrapolating these data to developing countries as the kinds of work that are most taxing would be most relevant and would differ from that in developed countries. Data on the impact of physical activity on cardiovascular and placental function were examined to determine their significance for the mother, the fetus, and the newborn infant. Animal studies and epidemiological research pertaining to gestational duration, fetal growth, fetal loss, and congenital malformations were also included. The subcommittee also reviewed the available data on the impact of physical activity on lactation as an outcome of pregnancy and on maternal postpregnancy nutritional status. In general, the subcommittee concluded that field-based studies are needed to quantify the intensity, frequency, and effort of physical activity under natural conditions during pregnancy. These studies should include changes that occur during the course of pregnancy, including their effect on different outcome measures such as maternal and infant morbidity and mortality. Presently, very few studies on humans or even animals shed any light on this topic. Many women in developing countries are chronically malnourished, as demonstrated by stunting, low weight-for-height, and low fat stores. They are also more likely to have iron deficiency anemia. In part because of increases in maternal weight during pregnancy, the energy cost of weight-bearing tasks also increases. These findings are highlighted throughout the report. It is intriguing to find that pregnant women in developing countries seem to achieve energy balance despite limited diets and high levels of physical exertion. It is not known if this is due to some adaptive mechanism or to measurement error. Socioeconomic status, women's employment in rural and urban environments, consequent physical activity, and its effect on the outcome of pregnancy are reviewed in Chapter 2. It is pointed out that both pregnant and nonpregnant women in developing countries perform physical work for prolonged periods of time under unfavorable environmental conditions.

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Nutrition Issues in Developing Countries: Part I: Diarrheal Diseases - Part II: Diet and Activity During Pregnancy and Lactation The physiology of pregnancy and nutritional status is reviewed in Chapter 3. Some of the existing human data indicate that mild physical activity does not adversely influence the outcome of pregnancy in well-nourished populations. However, animal studies employing a combination of severe and acute exercise and severe undernutrition, reviewed in Chapter 3, have shown that these result in a decrease in uterine blood flow and could result in fetal compromise. It should be noted, however, that the results from animal models cannot always be extrapolated to humans. Many of these studies were performed on sheep, and quadrupeds have less of a problem returning blood from the limbs to the heart, and placenta transfer is often different. In Chapter 4, the subcommittee reviews the data on physical activity, productivity, and physical work capacity and how they affect gestation and the outcome of pregnancy. The subcommittee also looks at the effect of chronic and acute maternal undernutrition on the metabolic adaptations to pregnancy and, consequently, its outcome. As discussed in Chapter 5, the subcommittee concludes that low energy intake during pregnancy has detrimental effects on fetal growth and possible negative effects on gestational duration. The detrimental effects of decreased energy intake on fetal growth are exacerbated in women with poor prepregnancy nutritional status. Available epidemiological data as described in Chapter 5 do not permit firm conclusions about the effects of physical activity on the duration of gestation. The evidence (from developed countries) regarding strenuous exercise and prolonged mild exertion suggests a possible deleterious effect on gestational duration. Although a negative impact on fetal growth is less well documented, some evidence suggests that it may be greater in undernourished women. In Chapter 6, the impact of physical activity and diet on lactation is reviewed. The influences of physical activity and fat storage are reviewed as functional aspects of energy stores. Some field studies of lactation performance are described. There are few epidemiological data on the level and type of interaction (i.e., simply additive or synergistic) of physical activity and nutrition as they affect pregnancy and its outcome. Women in the developing world, including those who are pregnant and lactating, are frequently engaged in moderate to high levels of physical activity that are not offset by increases in energy intake. This imbalance appears to be reflected by low weight gain during pregnancy, impairment of intrauterine growth, and decreased ability to sustain milk production. Further studies are needed to more fully clarify this relationship. These and other conclusions and recommendations are summarized in Chapter 7.

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Nutrition Issues in Developing Countries: Part I: Diarrheal Diseases - Part II: Diet and Activity During Pregnancy and Lactation Gestational weight gain represents a balance between nutrient intake and energy expenditure. Supplementation programs seem to be most effective in poorly nourished women; however, research should focus on what groups may most benefit from supplementation programs or a reduction in physical activity. The epidemiological evidence is very strong that fetal growth increases with increasing gestational weight gain. Physical activity, particularly heavy work, appears to exacerbate the adverse effects of poor nutritional status on lactation. the subcommittee knows of no information on how various physiological adjustments to physical activity influence lactation performance. It is recommended that studies should be undertaken to examine the effects on lactation as measured by milk volume, composition, feeding frequencies, and infant growth. Since there are so few data available addressing women's postpartum health and nutrition, the conclusions of the subcommittee are based almost exclusively on complications and immediate outcomes of pregnancy. The subcommittee recommends that future studies include outcome variables related to women together with those related to infants. Additional studies should also be carried out to explore the possible association between malnutrition and physical activity during pregnancy with complications of delivery. These complications may include the outcome of Caesarean section, maternal mortality, and congenital anomalies. Implementation of health care services geared toward women's health, including prepregnancy and pregnancy nutritional status and health care, would also be helpful. These services should be able to monitor women who have had complicated pregnancies and deliveries, particularly those who have previously given birth to low-birthweight infants. These services should also support breastfeeding, while considering both the infant's growth and the mother's nutritional status. Current evidence suggests that programs to reduce physical activity would also be most effective in this group; however, more research needs to be done in this area. Many other of the most obviously needed measures fall outside the realm of this report. Some of these are increased access to education (both formal and informal), support for child care (especially for women who are heads of households), improved opportunities for employment, access to technology that saves time and heavy physical activity, and more legislation to protect pregnant women from strenuous physical activity.