Relationship between maternal obesity and infant feeding-interactions

Childhood obesity is now recognized as a national health epidemic, doubling among children 6–11 years old between the last (1976–1980) and the present (1999–2000) National Health and Nutrition Examination Surveys. Obesity in early childhood leads to more severe adult obesity [1]. Overweight and obese children are facing adult onset disease type risk factors such as cardiovascular heart disease, elevated blood pressure and type II diabetes [2]. Presently, type II diabetes represents 8–45% of all new cases of diabetes diagnosed in children and adolescents [2]. This epidemic increase in childhood obesity can only lead to a lower quality and duration of life and increased health care costs [3, 4].

Many studies have identified the influence of genetics and environmental factors on potential causes of childhood obesity [5, 6] and [7]. Some of these include having obese biological parents [8] and biological mothers being of a low social economic status [9, 10]. There are other factors in early infancy that may also contribute to obesity in childhood. For example, being born small or large for gestational age [11], breast feeding less than three months [12], exposed to early introduction of complementary foods [13] and/or excess fruit juice consumption [14]. There may be many other potential factors that may contribute to childhood obesity but as yet undiscovered.

The relationship between maternal body composition and infant and maternal interaction and feedings have not been studied. Obese biological mothers may interact in such a way as to possibly contribute to greater energy intake in their infants earlier in life. Recently we published the results of 24-hour metabolic measurements in four-to-six month old infants in the Enhanced Metabolic Testing Activity Chamber (EMTAC) [15]. This study allowed collection of data to assess the relationship between maternal body composition and infant feeding and interaction patterns.

Height and age were similar among the normal weight and obese biological mothers. The latter had a greater body weight, BMI and percent body fat (Table 1) in comparison to their normal weight counterparts (p < 0.05). Furthermore no differences existed in regards to body weight, body composition and growth performance between infants of normal and obese biological mothers (Table 2). The similarity of the infants in terms of growth performance at the time of the study was further verified by the lack of significant differences in Z-scores obtained for weight for length, weight for age and length for age percentiles. None of the growth assessment parameters of the infants were more than 0.4 standard deviations from the mean.

Infants born to obese biological mothers consumed more energy, and energy as carbohydrate, than their normal weight counterparts (Table 3). Three, out of the four infants born to obese biological mothers consumed complementary foods. The amount of energy consumed from complementary foods by these infants of obese biological mothers was 18.3 ± 2.5 kcal/kg. This was in addition to the energy intake of 69.1 ± 20.3 kcal/kg from formula for these same infants. However, energy intake from protein and fat, for both complementary feedings and formula, were similar among the two groups (Table 3). The amount of formula intake was also similar (90.1 ± 16.3 vs. 98.9 ± 35.4 ml/kg) between the infants born to obese and the normal weight biological mothers. There was a significant (p < 0.05) correlation between total energy intake and maternal body weight (r = -0.73; p < 0.06; Figure 2a).

Obese biological mothers spent less time interacting and feeding their infants over the course of the 24-hour testing period (Table 3). There was a negative correlation between total 24-hour interaction time and both maternal body weight (r = 0.98; p < 0.01, Figure 3a) and body fat (r = 0.92; p < 0.01, Figure 3b). Moreover, overweight biological mothers spent less time interacting with their infants one hour prior to feeding (Table 3). The pattern of maternal interaction over the course of the 24-h testing period is shown in Figure 4. Normal weight biological mothers interacted with their infants more over the course of the 24-hour testing period than the obese biological mothers (Figure 4). When considering just the hour prior to each feeding, normal weight biological mothers interacted with their infants more than their obese counterparts (Table 3). The increased interaction was more significant (p < 0.05) during the day time hours (9:30 AM till 11:30 PM) while during the evening hours (11:31 PM till 5:30 AM) the difference in interaction time between normal and obese biological mothers was less significant (p < 0.10; Figure 4). Finally, infants of overweight biological mothers spent more time sleeping (Table 3) than their normal weight counterparts.

The number of feedings and the amount of time necessary for each meal tended to be less for the infants of obese biological mothers, however, these differences were not significant (Table 3). There was also a tendency for infants of obese biological mothers to consume more energy at each feeding in comparison to those of normal weight mothers. Furthermore, infants of obese biological mothers tended to allow more time in between feedings during the day and over the entire 24-hour testing period (Table 3).

There were no significant differences in any of the metabolic parameters between infants from obese and normal weight biological mothers (Table 4). However, there was a tendency for a higher respiratory quotient and a greater amount of physical activity in those infants born to obese biological mothers.

In this study we demonstrated through direct observation that infants born to obese biological mothers ingested more energy and a greater amount of that energy were derived from the carbohydrates present in complementary foods. Furthermore, increased maternal body weight and fatness were related to increased 24-hour energy intake. Moreover, increased body weight and fatness of the biological mothers resulted in a decline in the amount of time spent interacting with their infants during the 24-hour testing period. This included less time spent feeding the infant, and particularly a lower amount of interaction one hour prior to feedings.

The biological mothers were able to freely interact with their infants in a comfortable setting. However, none of the biological mothers reported being uncomfortable with their infant being in the EMTAC or staying at the laboratory during the metabolic testing. Furthermore, they did not report any difficulties in interacting or feeding their infant utilizing the hand access ports of the EMTAC. Nonetheless, it is possible that the unfamiliar surroundings of the metabolic laboratory might have contributed to some changes in infant feeding practices not present in their maternal home setups.

Excess energy consumption early in an infant's life of those born to obese mothers, possibly accelerated with complementary food intake, might set the stage for future childhood obesity. In this study, there were no significant differences in infant body weight or composition between four to six months of age among the two groups of infants studied. However, infants of obese biological mothers consumed an average of 19.7 kcal/kg body weight more than the infants born to normal weight mothers during this study. Assuming that approximately 4900 kilocalories are needed per kilogram of body weight gain [27], it would take the infants of obese biological mothers a considerable amount of time to become obese if they would continue ingesting this amount of excess calories each day. This might explain why investigators report that it takes up to two years before a noticeable gain of body fat is observed in young children [1, 28]. In overfed adults 66% of body weight gain is fat while the remainder is fat-free mass [29]. It is possible that overfeeding infants over a long period of time causes excess body weight gain of similar composition. However, no studies to date have quantified the composition of body weight gain in overfed infants from the time of birth.

Early introduction of complementary foods might increase body weight gain. In one study, early introduction of complementary foods was associated with greater infant body weight gain [30]. Other investigators [31] reported that complementary foods introduced to infants between 9 and 16 weeks showed a slight increase in weight gain velocity (g/week) in comparison to those infants who were introduced to these foods after 25 weeks. Both of these studies [30, 31] suggest that early introduction of complementary foods might increase body weight gain. Therefore, early introduction of complementary foods, coupled with the increased energy intake at each feeding in the infants from obese biological mothers, as seen in our study, might set the stage for future childhood obesity. However, we did not have data to ascertain why obese mothers started complementary feedings in their infants.

Infants may be introduced to complementary foods at different times. In the Feeding Infants and Toddlers Study (FITS), 71% of the parents reported introducing complementary foods to their infants between four and six months of age while the other 29% reported introducing these foods to their infants at less than four months [32]. In another study were the National Health and Nutrition Examination Survey (NHANES III) data were analyzed, less than 25% of the parents reported feeding complementary foods to their infants prior to four months of age [33]. Moreover, the parents in both of these studies [32, 33] were similar in regards to social economic status, age and ethnic background. In our study we did not have data on why obese biological mothers were feeding complementary foods to their infants. Moreover, neither the FITS [32] nor the NHANES III [33] studies related infant feeding practices to maternal body composition.

There were no significant differences in any of the metabolic parameters measured such as 24-hour energy expenditure, resting and sleeping metabolic rates, respiratory quotient and the index of physical activity. Moreover, there were no differences in any of the growth parameters (weight for length, weight for age and length for age percentiles) between the two groups of infants at the time of the study. Our results are in agreement with Stunkard et al [28] who found no differences in growth parameters, body composition, total energy expenditure by doubly labeled water, sleeping metabolic rate or physical activity in infants born to obese (greater than the 66^th percentile for BMI) or lean (<33^rd percentile for BMI) biological parents throughout the first year of life. In contrast to our results and those of Stunkard [28], Roberts et al [8] found reduced total daily energy expenditure in infants born to obese parents as determined by the doubly-labeled water method. The reduction of total daily energy expenditure was due to less physical activity in these infants [8]. It is possible that less interaction between obese mothers and their infants [8] accounted for the reduction in physical activity.

Since infants gain approximately 5 g/kg of body weight per day at four months of age [34], it is possible that constant additional caloric intake of those infants born to obese biological mothers will be manifested as additional daily body weight gain later in life. All these data suggest that maternal influences on infant body composition may not appear initially as obvious physical differences during the first six months of life. It is possible that the differences detected among biological obese mothers and their infants could affect the body composition of their infant as they age.

There may be other factors beginning in infancy that may be associated with the eventual increase in adiposity in later life. For example, fewer, but larger feeds and a higher sucking pressure were associated with greater adiposity in toddlers at two years of age [13]. This is in partial agreement with our results were we found that obese biological mothers spent less time interacting and feeding their infants. Moreover, infants from obese biological mothers consumed more energy in less time at each feeding. It is possible that the infants were hungrier due to the longer time between feedings.

Another study reported that greater maternal BMI during the first trimester of pregnancy was related to a higher prevalence of obesity in children from two to four years old. This is equivalent to 1 out of 4 children of obese mothers becoming obese as opposed to only 1 out of 10 children from normal weight mothers [35]. Moreover, it was also reported that a greater maternal BMI was a modest predictor of their daughter's relative weight at five years of age [36]. All of these studies [13, 28, 36] relate possible maternal influences upon future obesity of their infants. However, none eluted to the actual difference in the care of infants from either normal or obese mothers such as found in our analysis.

The association between the physical characteristics of biological mothers and their infants has not been ascertained. Six studies found no relationship between maternal BMI and infant's body weight after the first year of life [35, 37‐41] while two found such a relationship [42, 43]. None of these studies accurately measured maternal body composition and did not include direct observation of the interaction dynamics between mothers and their infants. This was done in our study using air displacement plethysmography for maternal body composition and direct observation of food intake and feeding patterns including the number and length of infant feedings and the amount consumed at each meal during the entire 24-hour period. Additionally the type and length of maternal interaction with their infants revealed significant differences between normal weight and obese biological mothers which may not have been elucidated by other means. Though there were a small number of infants studied the results suggest that differences do exist on how mothers interact with their infants, depending on their body composition.

This study provided some new insight as to possible influences, beginning in infancy, as to the possible causes of childhood obesity. We have found additional factors that may contribute to future childhood obesity. The ability to conduct 24-hour metabolic rate measurements and direct accurate recordings of the biological mother's interaction with their infants elucidated specific differences in the care of infants that were related to maternal body weight and adiposity.