Abstract:
In contemporary society, adult individuals tend to consume minimal amounts of food in the morning, shifting the majority of their energy intake to later in the day. Current dietary recommendations for body weight management generally rest on the assumption that the total energy intake is what matters, regardless of when it is consumed during the day. However, recent dietary intervention studies challenge this assumption, indicating that the timing of energy intake—particularly the meal during which the majority of energy is consumed—can have significant effects on body weight, appetite, glucose, and lipid metabolism, even when energy intake is iso-caloric. This study was designed to examine the effects of consuming half of daily energy intake either at breakfast or dinner on anthropometric measurements, certain metabolic parameters, and subjective appetite. The study was conducted with 28 overweight or obese (Body Mass Index (BMI) ≥ 25 kg/m²), premenopausal adult women (ages 20-45) who were healthy and free from any gastrointestinal disorders, and who voluntarily participated in the study at the Gastroenterology Clinic of Ba?kent University Ankara Hospital between November 2023 and March 2024. In this randomized, open-label, parallel-group study, participants were assigned to one of two dietary groups through simple randomization: the 'Breakfast Group' (BG)(n=14)(total dietary energy: B:%50; L:%35; D:%15) or the 'Dinner Group' (DG) (n=14)(total dietary energy: B:%15; L:%35; D:%50), to follow their respective diets for a period of 6 weeks. The diets implemented during the study were hypocaloric (with a 20% reduction in total energy expenditure), individually designed, and ensured the same macronutrient composition. Anthropometric measurements and body composition were assessed at the beginning, the third week, and the end of the study. Metabolic parameters were evaluated at the start and the end of the study. Subjective appetite was assessed using a Visual Analog Scale (VAS) on the first day, the last day of the third week, and at the study's conclusion. No significant differences were observed between the groups in terms of anthropometric measurements or body composition changes (p>0,05), except for hip circumference, which differed significantly (p<0,05). The BG group experienced a greater reduction in hip circumference (2,7 cm) compared to the DG group. Additionally, significant differences were found between groups regarding HDL cholesterol, fasting blood glucose, and HbA1c changes. HDL cholesterol and HbA1c (%) decreased more in the DG group (p<0,05). Fasting blood glucose levels decreased more in the BG group (6,7 ± 6,01 mg/dL) compared to the DG group (0,5 ± 5,68 mg/dL) (p<0,05). Throughout the study, appetite scores were higher in the BG group compared to the DG group (p<0,05). The BG group reported greater appetite in the evening, while the DG group reported higher appetite in the morning. Appetite scores at midday were similar between groups. Although consuming a larger portion of daily energy intake at breakfast, as opposed to dinner, did not result in significant effects on anthropometric measurements or appetite, it had a positive effect on fasting blood glucose. Future studies are needed to further elucidate the impact of breakfast-based energy intake on body weight management and metabolic health
