To our knowledge, the present investigation is the first to report the short-term effects of LGL meals in obese Latino children and adolescents. The purpose of this study was to examine the metabolic, hormonal, and appetite responses of obese Latino youth to a LGL or a HGL meal. The HGL and LGL meals in our study were carefully constructed to be comparable in palatability, and to consist of food items with which participants were familiar.
Contrary to our hypotheses, we found no significant differences between the LGL and HGL groups in the energy consumed from the post-lunch ad libitum
snack platter. Neither the percentage of energy consumed from the total offered at each of the three randomized meals, nor the cumulative energy consumption over the entire study were significantly different between the two groups. We also found no significant differences in the reported perception of hunger, fullness, or satiety between the two dietary groups. Several adult (4
) and two pediatric (5
) studies reported decreased hunger, increased satiety, and decreased voluntary intake in response to LGI/LGL meals. Ludwig et al (5
) reported significantly higher ratings of hunger and greater ad libitum
energy intake after a HGI meal in a randomized crossover study comparing HGI and LGI meals in 12 adolescent boys. Ball et al (10
) reported a 48-minute prolongation of satiety after a LGI versus a HGI supplement in a similar crossover study of 16 adolescents, but found no differences in hunger ratings or changes in actual energy intake. Such crossover meal studies have the advantages of a within-subjects design that controls for many extraneous factors that may complicate human studies. However, because the actual characteristics of the foods or supplements consumed during both conditions are experienced by subjects, such studies may be affected by carryover effects. In addition, it is conceivable that subjects in the crossover studies are more likely than in parallel designs to compare the items consumed under the two conditions and respond to the demand characteristics of the experiment so as to seek to confirm what they believed were the investigator's hypotheses. The present study, which used a randomized, between-subjects design, would be anticipated to be less susceptible to such confounding.
Other possible explanations for the negative findings observed in the present study and the positive findings of other pediatric investigations (5
) include differences in study population and other design considerations. All our study participants considered themselves Hispanic, whereas predominantly Caucasian youth participated in the previous studies. It is conceivable that the degree of baseline insulin resistance was greater in our cohort and could have blunted the impact of differences in meal GL. Diet-phenotype interactions have been reported in some earlier studies (24
). The participants in our study were also somewhat younger, with a mean age of 12 years compared to a mean age of 16 years in Ludwig et al (5
) and 14 years in Ball et al (10
). Another distinction between the current study and the two previous pediatric studies lies in the presentation of the ad libitum
platters to the participants. In the earlier studies, adolescents had to request a platter, an approach intended to give them the opportunity to pay attention to their internal hunger cues. In the current study, the platters were left in the participants’ rooms 30-minutes post-lunch without requiring a request for food. It is conceivable that participants may have consumed what was given to them without necessarily feeling hungry. The composition of the ad libitum
snack platter was also different from the two earlier pediatric studies. It consisted of food items considered highly palatable and familiar to the study participants. One possible explanation for our findings is that our toxic food environment may so dominate eating behavior that altering factors such as the GI of prior meals may have little effect for those exposed to the highly palatable foods found in many households.
Finally, although the current study was adequately powered to find the previously reported (5
) differences in energy intake, it was not powered to detect small energy differences. shows the energy differences that would have been detectable between the two groups in the present study of 88 subjects at 80%, 90%, and 95% power. The LGL group consumed only 5% less energy than the HGL group in contrast to the 81% greater energy consumption in the HGI group reported by Ludwig et al (5
). Based on the large standard deviation for energy intake from the ad libitum
snack platter, a sample size of 1906 participants would have been required to detect the observed 5% difference in intake with 80% power (26
). Large standard deviations in parallel-design studies of this nature reflect the large inter-individuals differences in metabolic requirements and feeding behavior among a heterogeneous population.
Appendix Table 1
Detectable difference at various levels of Statistical Power, 2-tailed type 1 error of 5%*
Consistent with findings from other laboratory studies (10
), the obese youth in the present investigation consumed large quantities of food from the post-lunch snack platter despite consuming adequate energy at lunch for metabolic needs, demonstrating that deficiencies in meal intake regulation are common in obese children. In addition to the physiologic factors regulating the desire to eat, however, it is important to note that hunger and satiety may be affected by learned behaviors (27
). It is possible that obese study participants have also learned to override their internal hunger and satiety cues. It has been suggested that the desire to eat is regulated more by external cues than by actual hunger, particularly in obese individuals (27
Study strengths and limitations
The strengths of this study include the relatively large sample size, the broad age range of participants that may increase its generalizability, and the well-controlled study design. However the study was carried out only among obese Hispanic youth and was not powered to detect smaller differences in energy consumption. The sample size however was adequate to detect differences in the appetitive responses between the two dietary groups. in the appendix shows the detectable differences for hunger, fullness, and satiety ratings at 80%, 90%, and 95% power. This indicates that the study was capable of detecting quite small differences in hunger, fullness, and satiety ratings between the two dietary groups and would not miss very modest differences in these outcomes. Therefore, it is unlikely that the study's failure to detect such differences was due to inadequate power.