A controlled clinical trial shows that what you eat at breakfast, not just how much, may shape appetite, weight loss, and gut microbiota with implications for long term dietary strategies
Study: Big breakfast diet composition impacts on appetite control and gut health: a randomized weight loss trial in adults with overweight or obesity. Image Credit: An Dvi / Shutterstock
A recent study published in the British Journal of Nutrition investigated the effects of breakfast composition within a calorie-restricted big-breakfast weight-loss diet on appetite, energy balance, and gut microbiota-related markers of gut health.
Growing evidence indicates that, in addition to meal composition, meal timing is a crucial factor for healthy weight management. One study found that early eaters had significantly more weight loss (WL) than late eaters. Morning intake of calories is associated with improved blood glucose control and lower hunger than evening intake.
A larger breakfast meal improves appetite control, while late eating has been associated with fat storage and increased hunger. Despite public health advice on the importance of breakfast for maintaining a healthy weight, little is known about what people eat in the morning. Moreover, data on why and how meal timing, diet composition, and calorie distribution relate to appetite control remain limited.
Randomized Crossover Design and Dietary Interventions
In the present study, researchers evaluated the impact of two calorie-restricted weight-loss diets with identical large-breakfast calorie distribution but different macronutrient composition on appetite, energy balance, and gut microbiota composition and metabolites rather than clinical gastrointestinal outcomes. Healthy overweight or obese individuals aged 18–75 years were recruited. The team implemented a randomized crossover protocol comprising a four-day ad libitum diet, a four-day maintenance (MT) diet, and a 28-day high-fiber WL (HFWL) or high-protein WL (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. The WL diets were fed at 100% RMR to achieve a caloric deficit. Subjects consumed three meals daily, with 45%, 20%, and 35% of their calories in the morning, afternoon, and evening, respectively, with lunch intake permitted ad libitum within the provided allowance. The HFWL diet (50% carbohydrate, 15% protein, and 35% fat) comprised a mix 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 following an overnight fast. Body weight was measured three times weekly during the WL diets. Glucose, lipid profile, and insulin were estimated as metabolic biomarkers rather than clinical disease outcomes.
Insulin and glucose results were used to calculate the homeostatic model assessment of insulin resistance (HOMA-IR) and β-cell function (HOMA-β), 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 analyzing gut microbiota composition.
Weight Loss, Metabolic Markers, and Energy Expenditure
The study included 19 participants, two of whom were female, with a mean age of 57.4 years and a body mass index of 33.3 kg/m2, indicating a predominantly male cohort and potentially limited generalizability to broader populations. Energy intake did not differ significantly between the two WL diets. The average WL was 4.87 kg with the HFWL diet and 3.87 kg with the HPWL diet. Both diets also significantly reduced fat mass and fat-free mass (FFM) relative to the MT diet. However, FFM reduction 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 circumferences, and the 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 HPWL and MT meals. Both WL diets resulted in significant reductions in lipid levels relative to 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 to 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 the total bacterial loads in fecal samples were not significantly different between WL diets, α-diversity was lower with the HPWL diet compared to the HFWL diet. Moreover, significant differences in microbiota composition were observed among the WL diets,, although individual variation remained a major determinant of microbiota profiles,, and diet effects explained only part of the observed variability.
Gut Microbiota and Short-Chain Fatty Acid Differences
Butyrate producers, such as Anaerostipes hadrus, Roseburia faecis, and Faecalibacterium prausnitzii, were associated with the HFWL diet. At the genus level, Streptococcus was associated with the HPWL diet, and Bifidobacterium, Faecalibacterium, and Roseburia were associated with the HFWL diet. Further, total short-chain fatty acids (SCFAs) and major fecal SCFAs, such as acetate, butyrate, and propionate, were significantly lower with the HPWL diet relative to the HFWL diet.
Interpretation and Implications for Long-Term Compliance
Taken together, the findings indicate that within a calorie-restricted big-breakfast eating pattern, breakfast meal composition is an important factor in improving WL and metabolic health biomarkers over 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. In particular, the HPWL diet led to greater satiation and may be helpful for long-term dietary compliance. In contrast, the HFWL diet yielded a superior microbiota profile and may support long-term gut health as reflected by microbial composition and SCFA production rather than direct clinical gut health outcomes. However, longer-term studies are needed to confirm sustained effects.