Eggs are a cost-effective, nutrient-rich food source associated with satiety and potential weight loss benefits. Some studies indicate long-term egg consumption improves glycemic control, particularly with calorie restriction, in individuals with diabetes, metabolic syndrome, or obesity. However, other epidemiological studies suggest a link between high egg consumption and increased diabetes or cardiovascular disease risk. This ambiguity may be due to the frequent consumption of eggs with high-saturated fat foods, which is associated with insulin resistance. This study aimed to determine if egg consumption itself, or the combination of eggs and saturated fat, acutely alters glucose disposal. The hypothesis was that the association between egg consumption and poor glycemic control is due to saturated fat, not eggs themselves. Understanding the acute effects is a crucial first step in determining long-term effects and informing dietary management of conditions requiring tight glycemic control.

The literature on the effects of egg consumption on glycemic control is mixed. While some interventional studies show benefits, particularly with calorie restriction and in individuals with metabolic conditions, other epidemiological studies suggest an association with increased diabetes or cardiovascular disease risk. This discrepancy could be explained by the common pairing of eggs with high-saturated fat foods, known to negatively impact insulin sensitivity and glucose metabolism. Therefore, disentangling the effects of eggs from those of accompanying saturated fat is crucial.

This study employed a randomized partial crossover design. Forty-eight healthy adults (consuming at least one egg per week) were included. Participants received two of four isocaloric, macronutrient-matched breakfasts: an egg breakfast (EB), a saturated fat breakfast (SB), an egg and saturated fat breakfast (ES), and a control cereal-based breakfast (CB). The breakfasts were administered seven days apart. Six blood samples were collected (fasting and at 30, 60, 90, 120, and 180 minutes post-breakfast) to measure glucose and insulin levels. Area under the curve (AUC) analyses of glucose and insulin were performed using mixed-effects models, controlling for baseline concentrations and within-subject dependencies. The study was approved by the institutional review board and registered with Clinicaltrials.gov. Macronutrient composition of each breakfast was carefully controlled, and the ingredients are specified in Table 1 and Table 2. Statistical analysis utilized R software, with multiple imputations for missing data.

Forty-eight participants (46% male; mean age 25.8 ± 7.7 years; mean BMI 25.7 ± 4.6 kg/m²) completed the study. Mixed-effects model analyses revealed no statistically significant differences in the AUC of glucose or insulin between EB, SB, ES, and CB (p > 0.1 for all comparisons). Cohen's d values for all comparisons were small, ranging from 0.06 to 0.20 for glucose and 0.11 to 0.13 for insulin. These results indicate that, in the acute setting, consumption of egg breakfasts, with or without accompanying saturated fat, does not significantly affect glucose disposal in healthy adults.

This study's findings contradict some previous acute studies showing differences in glycemic response to egg vs. high-carbohydrate breakfasts. However, those studies did not control for macronutrient composition. The current study's rigorous macronutrient matching likely explains the discrepancy, suggesting that the impact of eggs on glycemic control is minimal when dietary context is controlled. The results align with some studies reporting long-term benefits of egg consumption on glycemic control, but those studies often involved carbohydrate restriction, unlike this study. While saturated fat is often associated with poor glycemic control, the type of fat (butter in this case) might play a role. Recent evidence suggests that dairy fat may even have beneficial effects on glucose homeostasis. The use of realistic breakfast meals and careful macronutrient matching are strengths of this study, although this naturally leads to some minor discrepancies in other variables such as fiber content and glycemic load. These are however unlikely to significantly influence the glycemic response.

In healthy adults, isocaloric, macronutrient-matched breakfasts containing eggs, saturated fat, or both do not acutely affect glucose disposal compared to a control breakfast. This challenges the notion that egg consumption per se negatively affects glycemic control. The findings support continued egg consumption but highlight the need for long-term studies to definitively assess the chronic effects of egg intake, with or without saturated fat, on glycemic control. Future studies should consider a larger, more diverse sample population, and incorporate factors such as physical activity and medication use.

The study's power was limited (5.7%, 5.5%, and 10.4% for EB vs CB, SB vs CB, and ES vs CB respectively), especially considering the anticipated small effect sizes. The sample primarily comprised of college students, limiting generalizability. Physical activity and medication use were not controlled for. The partial crossover design, necessitated by budgetary constraints, reduced statistical power. The acute nature of the study might not capture the effects of long-term consumption.