Energy requirements during pregnancy is the energy intake from food that balances energy expenditure when the woman has a body composition and physical activity level consistent with good health [1, 2]. The primary energy requirements of pregnancy provide a mean for adequate maternal weight gain to ensure growth of the fetus, placenta and associated maternal tissues [2, 3]. Secondary energy requirements must allow for increased metabolic demands in addition to the energy necessary to maintain adequate maternal weight, body composition and physical activity throughout gestation, as well as providing energy stores to assist in lactation after delivery [2, 3]. The additional energy required for pregnancy is estimated to be negligible during the first trimester, 1646 kJ/day in the second trimester and 2092 kJ/day in the third trimester [4]. By balancing energy intake with energy requirements for fetal growth and activity, energy balance will be reached where energy intake equals energy expenditure [2]. Energy balance during pregnancy can be achieved by various methods, including decreasing resting energy expenditure, mobilizing maternal fat stores, decreasing physical activity or increasing energy intake by increasing food intake [3, 5–8].
From a systematic review, it was found that energy intake during pregnancy in developing countries was 8971 ± 1034 kJ/day, with the authors reporting a significantly higher energy intake in the third trimester compared to the first trimester [3]. However, in another study, it was found that healthy pregnancies can be achieved without significant increases in energy intake [9]. Women eat significantly more than is required to meet the energy requirements for a healthy pregnancy and therefore gain, on average, excess weight of more than 12 kg [10]. Excessive energy intake that contributes to excessive weight gain may increase the risk of developing pregnancy-induced hypertension [11] and increase the risk of caesarean birth, macrosomia [12], postpartum weight retention and gestational diabetes [13]. Therefore, the belief that increasing dietary energy intake will lead to an improved pregnancy outcome has no evidence-base [3, 14]. Energy intake guidelines should, therefore, be individually adjusted to meet variations in basal metabolic rate, body composition before and during pregnancy, gestational weight gain and physical activity [15].
In conjunction with energy intake, maternal macronutrients (carbohydrates, lipids, and protein) influence fetal growth (3,16,17)]. The recommended percentage energy distributions of macronutrients during pregnancy are similar to those for healthy women, with the assumption that dietary energy intake is sufficient to maintain current body weight [3, 18]. In addition, dietary intakes of pregnant women do not align with country-specific energy and macronutrient recommendations [3]. More specifically, total fat and saturated fat intake were generally higher than the recommended guidelines, while carbohydrates and poly-unsaturated fatty acid intake were lower than recommended [3].
During pregnancy, total energy expenditure increases due to the energy required for fetal growth, development of the placenta and various maternal tissues, as well as changes in maternal metabolism and the increase of energy expended during movement and activities of daily living resulting from weight gain (1,2,9,19)]. Total energy expenditure consists of basal metabolic rate, dietary-induced thermogenesis and energy expended during daily living activities and physical activity [2].
Basal metabolic rate—the primary component (60%) of total energy expenditure—refers to the lowest level of energy expended at rest [20]. Basal metabolic rate tends to increase during pregnancy due to increased tissue mass and thus increased energy cost for maintenance [1, 9, 21]. Increases in both total energy expenditure and resting energy expenditure are more pronounced in the second and third trimesters [1, 21]. According to Butte & King [1], on average, there is an increase of basal metabolic rate of 4.5% for the first, 10.8% for the second and 24.0% for the third trimesters, respectively.
Diet-induced thermogenesis is the energy required to digest and assimilate food and is considered to be small—about 5–10% of total energy expenditure [8]. However, little scope exists for energy savings concerning diet-induced thermogenesis during pregnancy, but there is considerable scope for adaptations in basal metabolism [22].
Any changes that occur in physical activity levels during pregnancy will have important implications for maternal energy requirements [23]. Energy expended during physical activity or activity energy expenditure refers to any energy expended above resting level, due to bodily movement [24]. Activity energy expenditure contributes to about 25–30% of total energy expenditure [25] in a developed world context. Energy expended during physical activity tends to decline during pregnancy due to decreases in habitual physical activity [1, 26–28], which are likely due to minor discomforts such as leg cramps, swelling, fatigue, shortness of breath, difficulties in movement due to weight gain and perceptions that physical activity might pose risks for the fetus [29, 30]. Physical activity may be reduced during pregnancy by selecting less demanding activities or decreasing the pace of activities [19].
Broad variations in energy requirements during pregnancy exist between well-nourished women in developed countries compared to women from low-income, developing societies, where the availability of nutritious foods is limited [1, 2, 6, 13]. Special consideration should be given to the women with low and high Body Mass Index (BMI) as energy adaptations or responses to pregnancy may not reflect optimal nutritional conditions [4].
Underweight (BMI < 18.8 kg/m2) Gambian women living under constraints of limited food supply and obligatory intense physical activity reduced their resting energy expenditure to allow the delivery of a viable infant who may or may not be small for gestational age, depending on the severity of the energy imbalance [5]. Normal-weight women in developing countries with unlimited food availability tend to conserve energy by reducing physical activity [5, 28]. However, this is not always the case, since hormonal changes facilitate fat deposition and due to non-restrictive energy supply, these women tend to gain additional fat stores [5]. With regards to overweight women (BMI > 25 kg/m2) in developed countries with free access to food, ample energy reserves are present at conception to protect fetal growth. Therefore, there is no need to accumulate fat [5, 19].
The possibility to offset the potential for further increases in energy storing, basal metabolic rate increases in overweight and obese women [5, 31]. However, if excessive energy storage occurs, despite increases in basal metabolic rate, the excessive weight gain can be detrimental for both mother and infant [5, 17]. Promoting methods to increase energy expenditure in overweight, pregnant women can be extremely valuable to promote energy balance and a good pregnancy outcome by reducing excessive weight gain [17, 32].
In South Africa, the prevalence of obesity, especially among women, has increased due to urbanization, increased wealth, increased dietary intake and decreased physical activity [33]. Furthermore, cultural factors shape South African (SA) women’s eating habits, such as overeating at social gatherings where food is abundant, associating particular foods with social status, being more accepting of being overweight and relating thinness with illness and HIV/AIDS [34]. It was found SA black women living in an urban towns in South Africa to have a diverse eating pattern, which leads to the consumption of an energy-dense diet that is high in proteins and fat [35]. Another study from non-pregnant SA women found total energy expenditure to be lower in black than white women, due to the lower measured activity energy expenditure and smaller fat-free mass in black women [36]. Preventing excessive weight gain and treating obesity in young black women by propagating a healthy lifestyle [37] is essential during the reproductive period.
Energy requirements during pregnancy should be derived based on healthy populations with favorable outcomes [1, 4]. As stated by Löf [19], if the energy expended on physical activity is unknown, pregnant women may be encouraged to increase their energy intake above the required levels, potentially leading to an increased risk of excessive weight gain. Both sides of the energy balance equation—energy intake and expenditure—should be accounted for in relation to gestational weight gain and birth weight [3,38]. Therefore, this paper aims to determine the changes that occur in energy intake and expenditure from the first to the third trimester of pregnancy in women from the Tlokwe Municipal area of South Africa. It was hypothesized that both energy intake and energy expenditure would increase significantly from the first to the third trimester of pregnancy in women from the Tlokwe Municipal area of South Africa.
Benefits of the study include objective measurements of energy expenditure in combination with energy intake, which would lead to a more accurate determination of energy balance. If energy imbalances occur, corrective measurements can be taken by means of nutritional and physical activity guidelines during pregnancy.