In this study, we investigated the effect of 2 breakfast meals differing in GL on satiety after breakfast, hunger prior to lunch, and energy intake at lunch in pre-school children aged 4-6 y old. We observed that children were less hungry in the LGL intervention compared to the HGL intervention group. However, this reduced hunger prior to lunch in the LGL intervention group did not result in a significant reduction either in energy intake or in the quantity of food consumed at lunch. Also, there was no significant difference in satiety ratings after breakfast between the LGL and HGL intervention groups. Additional analysis revealed no correlation between pre-lunch hunger scores and subsequent energy intake for either of the test breakfast meals (data not shown), suggesting that the pre-lunch hunger had no significant effect on lunch energy intakes in preschool children.
In contrast, recently, Fajcsak et al  in Hungarian pre-pubertal overweight/obese children aged 11 y found that the self-reported hunger was significantly reduced after consumption of diets high in GL. A few other studies have reported on the effect of GI on food intake and hunger. Ludwig et al  found that obese teenagers not only had an increase in hunger before lunch following consumption of the high-GI breakfast, but that they also consumed significantly more energy at lunch following the high-GI breakfast in comparison to the medium GI breakfast (P < 0.05) and the low-GI breakfast (P = 0.01). Warren et al  found that after consumption of the high-GI breakfast meal, energy intake at lunch was 145 kcal higher than the low-GI breakfast meal and 119 kcal higher than the low-GI plus sucrose breakfast meal (P ≤ 0.05). In contrast, Ball et al  found no significant difference in energy intake at the subsequent meal between those on the high-GI meal replacement and those on the low-GI meal replacement or the low-GI whole foods meal. Alfenas and Mattes  found no significant difference in food intake between persons consuming low and high GI foods. These observations are in line with our findings, although we studied the impact of GL rather than GI on food intake in a subsequent meal.
The increased hunger that is experienced with the HGL meal may be related to the hormonal and metabolic consequences of HGL foods. Consumption of a HGL meal leads to rapid absorption of glucose because HGL foods are more readily digestible . The counter regulatory hormone, glucagon is inhibited by elevated glucose and gut hormones, while release of insulin is stimulated . The high insulin concentration promotes glucose uptake by liver and muscle, while suppressing lipolysis in adipoctyes and reducing the release of glucose from the liver into the circulation [13, 34]. As a result, the blood glucose concentration is rapidly decreased following a HGL meal when compared to a LGL meal . Thus, the hunger response occurs faster with a HGL meal than with a LGL meal . This increased hunger may or may not lead to increased energy intake in subsequent meal. In the present study, greater energy intake at lunch after consuming the HGL test breakfast meal did not occur indicating that the association between hunger and energy intake is much more complicated than a simple linear association.
Additional analysis revealed no correlation between intake of breakfast GL value and satiety after breakfast, hunger prior to lunch, or energy intake at lunchtime during either of the test breakfast interventions. This led us to believe that the significantly greater hunger we observed before lunch after consumption of HGL breakfast was due to factor(s) other than the GL of the breakfast meal consumed. Although attempts were made to match macronutrient contents of the two test breakfast meals, children were allowed to consume as they desired, therefore macronutrient intake varied from child to child. In the LGL intervention group, children consumed significantly more protein and fat compared to HGL group at the breakfast. Protein and fat are known to trigger the release of cholecystokinin (CCK) from I cells of the duodenal and jejunal mucosal cells. CCK activates CCK receptor-1 in the pyloric sphincter leading to pyloric sphincter contraction and decreased gastric emptying . This further leads to decreased hunger. Dietary fiber could not have played a role in decreased hunger in the LGL intervention group because the dietary fiber intake was significantly lower in the LGL than in the HGL intervention group. Therefore, the significant difference observed between the test breakfast meals in hunger before lunch may be due to significant differences in the macronutrient intakes associated with two test breakfast meals.
Despite the lack of significant difference observed in hunger before breakfast for the two test breakfast meals, significantly more energy was consumed by children at breakfast when the HGL test breakfast was served. However, no significant difference was found in the amount of food consumed at breakfast between the LGL and HGL intervention groups. This can be attributed to the greater energy density of the HGL test breakfast meal than the LGL test breakfast meal. The energy density of the food consumed by the HGL intervention group was ≈0.4 kcal/g higher than the energy density of the food consumed by the LGL group. Foods with high GL tend to have a greater energy density due to the fact that they are usually processed as convenience-type foods and also often have greater sugar contents [3, 36].
In conclusion, this study suggests that when pre-school aged children consumed breakfast meals with differing GLs, a significant difference in hunger before lunch resulted. However, the observed difference in hunger prior to lunch did not have an impact on energy intake at lunch. It is possible that the significant difference observed in huger prior to lunch was due to difference in micronutrient intakes from these test meals. One limitation of this study was that the children regularly chose extreme ratings due to their inability to fully understand the meaning of hunger, satiety, or palatability. Another limitation of this study is that the results may have been confounded by the energy content, carbohydrate quantity and quality, fiber content, and glycemic index of breakfast meals. In this study, participants were not required to consume the entire portion of the breakfast. However, it is not known how this affected the study outcomes. Studies are needed to validate hunger, satiety, and palatability scales in pre-school age children. More research is needed to establish a clear role of GL in hunger and satiety, and its eventual relation with obesity in various stages of life.