Egg consumption and insulin metabolism in the Insulin Resistance Atherosclerosis Study (IRAS)

Egg and saturated fat containing breakfasts have no acute effect on acute glycemic control in healthy adults: a randomized partial crossover trial

BACKGROUND/OBJECTIVES

High egg consumption is associated with poor glycemic control. Considering the widespread consumption of eggs, it is crucial to determine causality in this association. We tested if egg consumption acutely alters glucose disposal in the absence or presence of saturated fat, which is frequently consumed with eggs.

SUBJECTS/METHODS

In a randomized partial crossover clinical trial, 48 subjects (consuming ≥ 1 egg/week) received two of four isocaloric, macronutrient-matched breakfasts. The groups were defined based on the main ingredient of the breakfasts offered: eggs (EB); saturated fat (SB); eggs and saturated fat (ES); and control, which included a cereal based breakfast (CB). The breakfasts were offered in two testing sessions spaced seven days apart. Six blood samples (pre breakfast (fasting); 30, 60, 90, 120, and 180 minutes post breakfast) were collected to measure glucose and insulin levels. Area under the curves (AUC) were analyzed controlling for the baseline concentrations using mixed-effects models accounting for within-subject dependencies to compare these across breakfast assignments.

RESULTS

Forty-eight patients (46% males, age 25.8 ± 7.7 years, BMI 25.7 ± 4.6 kg/m²) were included. Neither EB, SB nor ES was associated with a significant difference in AUC of glucose or insulin compared to CB (p > 0.1).

CONCLUSIONS

Acutely, consumption of egg breakfast with or without accompanying saturated fat does not adversely affect glucose disposal in healthy adults. While this is reassuring for continued egg consumption, a long-term evaluation of egg intake with or without saturated fat would be the next step.

The Debate Over Egg Consumption and Incident Cardiovascular Disease

There is a great debate regarding the association of cholesterol intake from egg consumption and the incidence of cardiovascular disease (CVD). Most studies show that moderate egg consumption is not associated with a significant increase in CVD, stroke, heart failure, and type 2 diabetes mellitus (T2DM), whereas others dispute this fact and state that there is an association with increased egg consumption, especially if they are consumed with saturated fats. In addition, the recent relaxation of cholesterol intake to greater than 300 mg/d by the American College of Cardiology/American Heart Association Nutritional Guidelines has fueled this debate. In order to get a current perspective on the significance of moderate egg consumption with the primary incidence of CVD, a focused Medline search of the English language literature was conducted between 2010 and March 2020 using the terms, cholesterol intake, egg consumption, coronary artery disease, CVD, and T2DM. Nineteen pertinent articles were retrieved, and these, together with collateral literature, will be discussed in this review article. The analysis of data from the articles retrieved indicated that several studies showed that moderate egg consumption (1 egg/d) is not associated with adverse cardiovascular effects in subjects free of CVD or T2DM, whereas other studies showed a positive association, especially in patients with preexisting CVD or T2DM. Therefore, at present, there is no unanimous agreement on this subject, and the controversy will continue until new confirmatory evidence becomes available.

Whole Egg Consumption Impairs Insulin Sensitivity in a Rat Model of Obesity and Type 2 Diabetes

BACKGROUND

The literature regarding the relation between egg consumption and type 2 diabetes (T2D) is inconsistent and there is limited evidence pertaining to the impact of egg consumption on measures of insulin sensitivity.

OBJECTIVES

The aim of this study was to investigate the effect of dietary whole egg on metabolic biomarkers of insulin resistance in T2D rats.

METHODS

Male Zucker diabetic fatty (ZDF) rats (n = 12; 6 wk of age) and age-matched lean controls (n = 12) were randomly assigned to be fed a casein- or whole egg-based diet. At week 5 of dietary treatment, an insulin tolerance test (ITT) was performed on all rats and blood glucose was measured by glucometer. After 7 wk of dietary treatment, rats were anesthetized and whole blood was collected via a tail vein bleed. Following sedation, the extensor digitorum longus muscle was removed before and after an intraperitoneal insulin injection, and insulin signaling in skeletal muscle was analyzed by Western blot. Serum glucose and insulin were analyzed by ELISA for calculation of the homeostatic model assessment of insulin resistance (HOMA-IR).

RESULTS

Mean ITT blood glucose over the course of 60 min was 32% higher in ZDF rats fed the whole egg-based diet than in ZDF rats fed the casein-based diet. Furthermore, whole egg consumption increased fasting blood glucose by 35% in ZDF rats. Insulin-stimulated phosphorylation of key proteins in the insulin signaling pathway did not differ in skeletal muscle of ZDF rats fed casein- and whole egg-based diets. In lean rats, no differences were observed in insulin tolerance, HOMA-IR and skeletal muscle insulin signaling, regardless of experimental dietary treatment.

CONCLUSIONS

These data suggest that whole body insulin sensitivity may be impaired by whole egg consumption in T2D rats, although no changes were observed in skeletal muscle insulin signaling that could explain this finding.

Unscrambling the relations of egg and meat consumption with type 2 diabetes risk

Background

Meat intake is associated with increased risk of type 2 diabetes (T2D). It is not clear if egg intake is associated with T2D risk because purported associations may be due to concurrent consumption of eggs with meat.

Objective

Our aim was to differentiate any associations between meat and egg consumption and the risk of T2D.

Design

In this longitudinal study, 55,851 participants of the Adventist Health Study 2 who were free of diabetes provided demographic, anthropometric, and dietary data at baseline. Meat and egg intakes were assessed with a validated quantitative food-frequency questionnaire. Responses to 2 follow-up questionnaires determined incident T2D cases. Multivariate-adjusted logistic regression was used to determine relations between meat and egg intake and incident T2D.

Results

T2D cases identified during a mean 5.3 y of follow-up totaled 2772. Meat intake of >0 to <25 g/d, ≥25 to <70 g/d, and ≥70 g/d significantly increased the risk of T2D compared with no meat intake (OR: 1.29; 95% CI: 1.16, 1.44; OR: 1.42; 95% CI: 1.25, 1.61; and OR: 1.65; 95% CI: 1.39, 1.96, respectively; P-trend < 0.0001). Egg intake compared with no egg intake was not associated with T2D risk. A significant meat-egg interaction (P = 0.019) showed that within every category of egg intake, there was an incremental rise in T2D risk as meat intake increased. However, within categories of meat intake, increasing egg intake did not increase the risk of T2D except among nonmeat-eaters consuming ≥5 eggs/wk (OR: 1.52; 95% CI: 1.09, 2.12).

Conclusions

Meat consumption, but not egg consumption, is independently associated with T2D risk. Egg intake seems not to increase T2D risk further with meat intake. Our findings suggest that the purported egg-T2D risk relation in US populations may be biased due to failure to investigate egg-meat interactions. Further investigations are needed to ascertain T2D risk among nonmeat-eaters with high egg intakes.

The Impact of Egg Nutrient Composition and Its Consumption on Cholesterol Homeostasis

Nutrient deficiencies and excess are involved in many aspects of human health. As a source of essential nutrients, eggs have been used worldwide to support the nutritional needs of human societies. On the other hand, eggs also contain a significant amount of cholesterol, a lipid molecule that has been associated with the development of cardiovascular diseases. Whether the increase of egg consumption will lead to elevated cholesterol absorption and disruption of cholesterol homeostasis has been a concern of debate for a while. Cholesterol homeostasis is regulated through its dietary intake, endogenous biosynthesis, utilization, and excretion. Recently, some research interests have been paid to the effects of egg consumption on cholesterol homeostasis through the intestinal cholesterol absorption. Nutrient components in eggs such as phospholipids may contribute to this process. The goals of this review are to summarize the recent progress in this area and to discuss some potential benefits of egg consumption.

Dietary habits associated with reduced insulin resistance: The Nagahama study

AIMS

To investigate the association between insulin resistance assessed by a homeostasis model and dietary habits.

METHODS

Cross-sectional analysis using a community-based cohort, the Nagahama Prospective Cohort for Comprehensive Human Bioscience. Multiple linear regression analysis was performed with log HOMA-IR or log HOMA-β as the dependent variable and 20 dietary habits, tobacco smoking, medical history, family medical history of diabetes, age and BMI as the simultaneous independent variables in each sex separately.

RESULTS

Females (n = 2956) eating fish dishes every day had a HOMA-IR 0.90 times that of the reference group (P = 0.043). Females eating miso-soup every day had a HOMA-IR 0.95 times that of the reference group (P = 0.038). Males (n = 1371) eating vegetable dishes every day had a HOMA-IR 0.91 times that of the reference group (P = 0.003). Males eating egg dishes 4 to 5 times per week had a HOMA-IR 1.14 times that of the reference group (P = 0.011). Males eating fruits every day had a HOMA-IR 1.13 that of the reference group (P = 0.008).

CONCLUSIONS

Dietary habits associated with lower insulin resistance were eating fish dishes, miso soup or vegetable dishes every day and eating staple foods for dinner, egg dishes or fruits less frequently.