A controlled clinical trial shows that what you eat at breakfast, not just how much, can shape appetite, weight loss and gut microbiota with implications for long-term nutritional strategies
Study: Composition of large breakfast meal affects appetite control and gut health: a randomized weight loss trial in overweight or obese adults. Image credit: An Dvi / Shutterstock
A recent study published in British Journal of Nutrition investigated the effects of breakfast composition in a calorie-restricted weight loss diet with a large breakfast on appetite, energy balance, and markers of gut health related to gut microbial flora.
Growing evidence shows that, in addition to meal composition, meal timing is a critical factor in healthy weight management. One study found that those who ate early had significantly greater weight loss (WL) from late eaters. Morning calorie intake is associated with improved blood glucose control and lower hunger than evening intake.
A larger morning meal improves appetite control, while delayed eating has been associated with fat storage and increased hunger. Despite public health advice about the importance of breakfast in maintaining a healthy weight, little is known about what people eat in the morning. Furthermore, data on why and how meal timing, diet composition, and calorie distribution relate to appetite control remain limited.
Randomized Crossover Design and Nutritional Interventions
In the present study, researchers evaluated the impact of two calorie-restricted weight loss diets with identical calorie distribution in the rich breakfast but different macronutrient composition on appetite, energy balance, and gut microbiota composition and metabolites and not on clinical gastrointestinal outcomes. Healthy overweight or obese subjects aged 18-75 years were recruited. The team implemented a randomized crossover protocol involving a four-day ad libitum diet, a four-day maintenance (MT) diet and 28 days of high-fiber WL (HFWL) or WL with high protein content (HPWL) diet, separated by a washout period; participants served as their own controls. Resting metabolic rate (RMR) was measured by indirect calorimetry during a screening visit.
The MT diet (15% protein, 55% carbohydrate, and 30% fat) was fed at 1.5 times RMR to maintain body weight. WL diets were fed at 100% RMR to achieve a caloric deficit. Subjects consumed three meals per day, with 45%, 20%, and 35% of their calories in the morning, afternoon, and evening, respectively, with lunch allowed ad libitum within the prescribed dose. The HFWL diet (50% carbohydrate, 15% protein, and 35% fat) included a mixture of insoluble and soluble fiber sources, including lentils, fava beans, buckwheat, and wheat bran.
The HPWL diet (30% protein, 35% carbohydrate, and 35% fat) included fish, poultry, eggs, red meat, and dairy. Body density, thermic effect of food (TEF), waist and hip circumferences, RMR, total body water (TBW), subjective appetite and blood pressure were measured and blood samples were collected on test days after an overnight fast. Body weight was measured three times per week during the WL diet. Glucose, lipid profile and insulin were assessed as metabolic biomarkers and not as clinical disease outcomes.
Insulin and glucose results were used to calculate the homeostatic model of insulin resistance assessment (HOMA-IR) and β-cell function (SOIL-b), and the insulin to glucose ratio (IGR). TEF was assessed every 30 minutes for 4 hours after breakfast. Appetite was assessed using visual analog scales. TBW was measured by deuterium dilution. Fecal samples were collected for analysis of gut microbiota composition.
Weight loss, metabolic indices and energy expenditure
The study involved 19 participants, two of whom were women, with a mean age of 57.4 years and a body mass index of 33.3 kg/m.2indicating a predominantly male cohort and potentially limited generalizability to wider populations. Energy intake did not differ significantly between the two WL diets. Mean WL was 4.87 kg on the HFWL diet and 3.87 kg on the HPWL diet. Both diets also significantly reduced fat mass and fat-free mass (FFM) relative to the MT diet. However, the reduction in FFM was significantly greater after the HFWL diet.
The HFWL diet resulted in reduced TBW volume relative to the MT diet, while no differences were observed after the HPWL diet. Hip and waist circumference, and waist-to-hip ratio, were significantly reduced after both WL diets compared to the MT diet. The HPWL meal maintained satiety, whereas the HFWL meal reduced postprandial satiety. A significant reduction in RMR was observed after both WL diets relative to the MT diet.
TEF was significantly lower with the HFWL diet than with the HPWL and MT meals. Both WL diets resulted in significant decreases in lipid levels from baseline, with no difference between the HPWL and HFWL diets. Fasting and postprandial glucose levels were 10.2% and 10% lower after the HFWL diet and 8.4% and 6.9% lower after the HPWL diet compared with the MT diet, respectively. Fasting insulin, HOMA-IR and IGR were significantly lower after both WL diets compared to the MT diet.
Meanwhile, HOMA-β decreased significantly more after the HPWL diet than after the MT diet, with no difference after the HFWL diet. Although total bacterial loads in faecal samples were not significantly different between WL diets, α-diversity was lower with the HPWL diet compared to the HFWL diet. In addition, significant differences in microbiota composition were observed between WL diets, although individual variation remained a key determinant of microbial profiles, and diet effects explained only part of the observed variability.
Gut Microbiota and Short Chain Fatty Acid Differences
Buttermilk producers, such as e.g Anaerostipes hadrus, Roseburia faecisand Faecalibacterium prausnitziiwere associated with the HFWL diet. At the genus level, Streptococcus was associated with the HPWL diet and Bifidobacterium, Faecalibacterium and Roseburia with the HFWL diet. In addition, total short-chain fatty acids (SCFA) and the major faecal SCFAs, such as acetate, butyrate and propionate, were significantly lower with the HPWL diet than with the HFWL diet.
Interpretation and implications for long-term compliance
Overall, the findings suggest that within a calorie-restricted eating pattern, the composition of the morning meal is an important factor in improving WL and metabolic health biomarkers during the short intervention period studied. While both WL diets resulted in a significant reduction in body weight, they had distinct effects on gut microbiota and appetite. Specifically, the HPWL diet resulted in greater satiety and may be helpful for long-term dietary compliance. In contrast, the HFWL diet yielded a superior microbial profile and may support long-term gut health as reflected by microbial composition and SCFA production rather than direct clinical gut health outcomes. However, long-term studies are needed to confirm the prolonged effects.
