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
]. 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
] 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
] 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 66th
percentile for BMI) or lean (<33rd
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
] 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
] while two found such a relationship [42
]. 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.