This study showed that, during a single multi-item meal, subjects who were born at HR for obesity self-selected a more energy-dense meal compared to subjects born at LR for obesity. This association remained significant when adjusting for current BMI z-score. Energy intake from food, beverages, or food and beverages combined, however, when expressed as a percentage of subjects’ daily energy requirement, did not differ between risk groups.
It is possible that familial influences, genetic or environmental in nature, may have affected HR subjects’ susceptibility to select foods of higher ED. For example, the home food environments in which HR and LR teens were raised may have been very different (Davison & Birch, 2001
). In households with a family history of obesity teens may have had easier access to more energy-dense foods during their upbringing which in turn may have helped shape their preferences for those foods. Given that parents, and mothers in particular, serve as important role models for eating behavior and food choices (Brown & Ogden, 2004
; Cutting, Fisher, Grimm-Thomas, & Birch, 1999
; Faith, 2005
; J. Fisher, Mitchell, Smiciklas-Wright, & Birch, 2001
; Longbottom, Wrieden, & Pine, 2002
; Vauthier, Lluch, Lecomte, Artur, & Herbeth, 1996
), it furthermore is conceivable that mothers of youth born at HR for obesity may have passed on to their children some of their own food preferences. It is also possible that, during their upbringing, parents of HR youth may have restricted access to energy-dense foods more than parents of LR youth, which in turn may have enhanced HR teens’ preference for these types of foods.
Another interesting finding was that the association between meal ED and risk group was independent of subjects’ weight status. This suggests that teens’ food choices (with respect to ED) were different for HR subjects compared to LR subjects regardless of whether HR subjects were of normal-weight or overweight. If sustained, the susceptibility of HR subjects to select a more energy-dense diet may predispose these subjects to negative long-term health consequences, such as development of obesity and related chronic diseases. Cross-sectional data from adults have shown that diets that are higher in ED also tend to be of lower diet quality (Ledikwe, Blanck, Khan et al., 2006
). Poor diet quality has been associated with adverse health consequences in U.S. adolescents such as the metabolic syndrome (Pan & Pratt, 2008
Another interesting finding was that energy intake from foods, energy intake from beverages, and total energy intake, when expressed as a percentage of youths’ estimated daily energy requirement, did not significantly differ between HR and LR subjects. This finding, combined with the significant risk group effects for ED, suggests that HR and LR subjects may have consumed different amounts (by weight) of foods and beverages. Given that the weight of food per volume differed for the various food items (e.g., 1 cup of fruit salad and mixed salad weigh approximately 175g and 55g, respectively), it would have been necessary to develop a single, composite variable (e.g., z score) to standardize and hence compare the amount of food consumed (McConahy, Smiciklas-Wright, Birch, Mitchell, & Picciano, 2002
). However, the small sample size precluded us from computing a composite variable and hence analyzing the weight of food that was consumed. Because the beverages that we served in this study had a more similar weight per volume, we were able to compare HR and LR subjects in the amounts of caloric and non-caloric beverages they consumed. The finding of a trend for HR subjects to consume more caloric beverages than LR subjects warrants additional research.
Our findings also point to important sex differences in intake during early adolescence. With respect for meal ED, there was a significant association between meal ED and sex such that males selected a more energy-dense meal than did females (model adjusted for risk group). Data from the Continuing Survey of Food Intakes by Individuals (CSFII, 1994 - 1996), which were based on two 24-h dietary recalls, showed significant sex differences in dietary ED among adults (> 19 years of age) (Ledikwe et al., 2005
). In this analysis, women consumed a diet that was significantly lower in ED compared to that of men. On the other hand, when the CSFII (1994 - 1996, 1998) data were analyzed for children (mean age 9.3 years), no sex differences were found in dietary ED (Mendoza et al., 2006
). It is possible that sex differences in dietary ED start to emerge during early puberty perhaps to support the higher energy needs for growth and development in males.
With respect to energy intake, males, independent of their risk status to obesity consumed an overall greater percentage of their daily energy requirement during lunch (from food, beverages, and food and beverages combined) than did females. It remains unclear what may have contributed to these differential intakes among males and females. It is possible that the laboratory conditions or other factors such as, for example, dieting behaviors or social desirability may have affected females’ and males’ eating behavior differently.
The strengths of this study include the precise measurement of teens’ intake under controlled laboratory conditions and use of an obesity risk design. Limitations are also associated with this experiment. The sample of teens was homogeneous with respect to race (i.e., all children were Caucasian) which precludes generalization of the findings to others. Second, this study cannot discern to what extent differences in the amounts of foods consumed may have contributed to differences in dietary ED between risk groups and males and females. Third, teens were videotaped during the lunch meal which could have affected both the amount of food consumed as well as their food choices. Fourth, the study used an estimated, rather than observed, measure of physical activity for the computation of participants’ EER. Finally, the study could not disentangle genetic from environmental influences on eating behavior phenotypes.
In summary, teens with a familial predisposition to obesity self-selected a more energy dense lunch meal than did teens without a familial predisposition. Future studies should determine the extent to which the consumption of higher energy-dense foods may foster normal growth patterns, particularly among males, or may instead represent one of the pathways involved in the development of obesity and related chronic diseases.