Effects of Higher Dietary Protein and Fiber Intake at Breakfast on Postprandial Insulin and Glucose Responses in Overweight Adults

BackgroundDietary protein and fiber independently influence insulin‐mediated glucose control. However, the potential additive or synergistic effects of higher protein and fiber intake on postprandial insulin and glucose responses are not known.PurposeThis study assessed the effects of protein and fiber intakes at breakfast on postprandial insulin and glucose responses.MethodsMen and women [n = 20; age: 26 ± 5 y; body mass index: 26.1 ± 0.2 kg/m2; means ± SEM] consumed provided breakfast meals with varying protein (high = 25 g vs. normal =12.5 g) and fiber (high= 8 g vs. normal = 3 g) amounts during 4, 2‐week interventions (randomized crossover experimental design). Each 2‐week period was separated by a 2‐week washout period. The breakfast variations included: normal protein and fiber (NPNF), normal protein and high fiber (NPHF), high protein and normal fiber (HPNF), or high protein and fiber (HPHF). Breakfast was provided with fixed energy (400 kcal) and digestible carbohydrate (50 g) on each day, and the remainder of daily energy intake was self‐selected. On the last day of each intervention period, a meal tolerance test was completed to assess serum glucose and insulin concentrations at fasting and hourly for 4 hours (240 min). Repeated measures ANOVA was applied for data analyses.ResultsThere were no differential responses among breakfast meals on composite postprandial insulin and glucose (240‐min total areas under the curve (AUC)) after adjusting for fasting values, sex, and breakfast treatment order. Analysis of the 0–120 min and 120–240 min AUCs supported that higher protein and/or fiber did not influence glucose responses. Further, differential responses were not observed for insulin AUC at 0–120 min but were for 120–240 min. The 120–240 min insulin AUC was numerically lowest after NPHF (880 ± 103 μU/mL) and was statistically different from HPNF (1228 ± 104 μU/mL) but not HPHF (1004 ± 104 μU/mL) or NPNF (1049 ± 108 μU/mL).ConclusionDoubling the amount of protein from 12.5 g to 25 g/meal and increasing fiber from 3 to 8 g/meal did not additively or synergistically affect postprandial insulin and glucose responses. These results do not support increasing dietary protein and fiber at breakfast as an effective strategy for modulating insulin‐mediated glucose responses in young, overweight adults.Support or Funding InformationSupport: American Egg Board‐ Egg Nutrition Center; NIH UL1TR0001108; USDA‐NIFA 2011‐38420‐20038