Objective: Recent reports have suggested that a low glycemic index (GI) diet may have a role in the management of obesity through its ability to increase the satiety value of food and modulate appetite. To date, no long-term clinical trials have examined the effect of dietary GI on body weight regulation. The majority of evidence comes from single-day studies, most of which have been conducted in adults. The purpose of this study was to investigate the effect of 3 test breakfasts-low-GI, low-GI with 10% added sucrose, and high-GI-on ad libitum lunch intake, appetite, and satiety and to compare these with baseline values when habitual breakfast was consumed.
Methods: A 3-way crossover study using block randomization of breakfast type was conducted in a school that already ran a breakfast club. A total of 37 children aged 9 to 12 years (15 boys and 22 girls) completed the study. The proportion of nonoverweight to overweight/obese children was 70:30. Children were divided into 5 groups, and a rolling program was devised whereby, week by week, each group would randomly receive 1 of 3 test breakfasts for 3 consecutive days, with a minimum of 5 weeks between the test breakfasts. Participants acted as their own control. The 3 test breakfasts were devised to match the energy and nutritional content of an individual's habitual breakfast as far as possible. All test breakfasts were composed of fruit juice, cereal, and milk with/without bread and margarine; foods with an appropriate GI value were selected. After each test breakfast, children were instructed not to eat or drink anything until lunchtime, except water and a small serving of fruit supplying approximately 10 g of carbohydrate, which was provided. Breakfast palatability, satiation after breakfast, and satiety before lunch were measured using rating scales based on previously used tools. Lunch was a buffet-style meal, and children were allowed free access to a range of foods. Lunch was served in the school hall where the rest of the schoolchildren were eating. Food intake at lunch was unobtrusively observed and recorded. Leftovers and food swapping were recorded, and plate waste was estimated. Lunch intakes were analyzed using a multilevel regression model for repeated measures data. The likelihood ratio statistic was used to determine whether the type of breakfast eaten had a significant effect on lunch intake after allowing for sex and weight status.
Results: The type of breakfast eaten had a statistically significant effect on mean energy intake at lunchtime: lunch intake was lower after low-GI and low-GI with added sucrose breakfasts compared with lunch intake after high-GI and habitual breakfasts (which were high-GI). Overweight and sex did not have a significant effect on lunch intake. Pairwise comparisons among the 3 types of test breakfasts and between each test breakfast and habitual breakfast were made. Lunch intake after the high-GI breakfast was significantly higher than after the low-GI breakfast and low-GI breakfast with added sucrose. The details of the pairwise comparisons were as follows: high-GI versus low-GI = 145 +/- 54 kcal; high-GI versus low-GI plus sucrose = 119 +/- 53 kcal; low-GI plus sucrose versus low-GI = 27 +/- 54 kcal. Lunch intake after the low-GI breakfast and the low-GI breakfast with added sucrose was significantly lower than after the habitual breakfast. The details of the pairwise comparisons were as follows: low-GI versus habitual = -109 +/- 75 kcal; low-GI plus sucrose versus habitual = -83 +/- 75 kcal; high-GI versus habitual = 36 +/- 75 kcal. There were no significant differences between the test breakfasts in immediate satiation. The high-GI breakfasts were rated to be more palatable than the low-GI breakfasts. At lunchtime, hunger ratings were greater after the high-GI breakfast compared with the other 2 test breakfasts on 2 of the 3 experimental days. Prelunch satiety scales were inversely related to subsequent food intake.
Conclusions: These results suggest that low-GI foods eaten at breakfast have a significant impact on food intake at lunch. This is the first study to observe such an effect in a group of normal and overweight children and adds to the growing body of evidence that low-GI foods may have an important role in weight control and obesity management. The potentially confounding effect of differences in the macronutrient and dietary fiber content of the test breakfasts warrants additional study. In addition, the impact of GI on food intake and body weight regulation in the long term needs to be investigated.