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The Good, The Bad & The Egg

Are eggs bad because their fat content increases cholesterol or they are good because they are packed with nutrients? Or are they both?

Studies have suggested that egg consumption may lead to increased LDL cholesterol (“bad” cholesterol) and inflammatory markers linked to heart disease and diabetes. However, other research highlights the potential benefits of eggs due to their rich nutrient profile.

Traditionally, research on egg health benefits has focused on specific clinical measures. These studies often isolate biomarkers for heart disease, diabetes, body composition, inflammation, immune function, and anemia, rather than examining them comprehensively. Additionally, participants in these studies frequently have pre-existing chronic disease risk factors and may be following dietary interventions like weight loss plans. These factors make it difficult to determine the isolated impact of eggs on health markers in the general population, particularly young, healthy individuals

The Study

A more comprehensive study was conducted by Catherine J. Andersen and colleagues, focusing on clinical measurements typically assessed during a routine physical. This approach aimed to provide a clearer picture of egg consumption’s effects on a young, healthy population using standard clinical biomarkers.

The study design involved comparing three groups: those consuming no eggs, those eating three egg whites daily, and those consuming three whole eggs daily. Participants were given freedom in how they prepared the eggs.

Analysis of blood samples revealed a significant increase in choline, a vital nutrient found in egg yolks, among participants who consumed whole eggs daily. While choline intake has been linked to elevated TMAO levels, a metabolite associated with heart disease, this study by Andersen did not observe any changes in TMAO despite the choline increase.

This outcome is considered highly positive. The goal is to maintain sufficient levels of this crucial nutrient without triggering a potential rise in TMAO, which could contribute to cardiovascular disease development.

Furthermore, the research did not identify any negative effects on inflammation or blood cholesterol levels. Additionally, consuming whole eggs appeared to have a less detrimental impact on markers linked to diabetes risk compared to consuming only egg whites.

Study Analysis

A key finding of the study was the increased dietary nutrient density observed in participants consuming whole eggs. Additionally, whole egg consumption led to a higher hematocrit, a measure of red blood cell concentration in the blood that can be low in individuals with anemia.

“Our comprehensive measurement approach offers a more complete picture of the overall effects of egg intake. It’s crucial to consider potential changes in multiple markers. If one marker shows a less favorable shift, others might exhibit beneficial changes, providing valuable context.”

Catherine J. Andersen

The study included participants of both genders, with roughly half the female participants using a combined oral contraceptive pill. This design allowed researchers to investigate potential discrepancies in nutritional outcomes between women taking the pill and those who weren’t.

“These medications are widely used, yet research on their interaction with dietary interventions remains limited,”

Catherine J. Andersen

While not all observations reached statistical significance, some differences were noted within this subgroup. Blood samples from female participants not taking the pill displayed a larger increase in the ratio of total cholesterol to HDL-cholesterol, a factor associated with heart disease risk.

An unexpected outcome emerged concerning hormonal birth control. These medications are often linked to negative metabolic changes, but in this study, they appeared to offer a more protective effect in response to egg consumption.

Blood tests revealed greater increases in monocytes, a type of white blood cell crucial for initial immune defense, among female participants not taking the pill compared to those using it. Interestingly, changes observed in whole-egg consumers’ clinical immune profiles, regardless of medication use, correlated with several clinical HDL measures.

This research represents the first installment in a series by Andersen investigating the mechanisms underlying the relationship between egg intake and HDL function in the immune system. Her lab is currently exploring additional questions, such as the composition of HDL particles and their influence on immune cell activity. Recent discoveries indicate that HDL carries far more than just cholesterol – hundreds of proteins, in fact. Additionally, Andersen plans to investigate potential variations in nutritional outcomes based on participant age when consuming eggs.

“The field of nutrition is increasingly focused on establishing a framework for personalized dietary recommendations. Researchers are actively exploring how factors like age, sex, genetics, gut microbiome composition, and others can influence an individual’s response to dietary interventions. This is certainly a growing area of investigation within my lab and our department.”

Catherine J. Andersen


Eggs—particularly egg yolks—are a rich source of bioactive nutrients and dietary compounds that influence metabolic health, lipid metabolism, immune function, and hematopoiesis. We investigated the effects of consuming an egg-free diet, three egg whites per day, and three whole eggs per day for 4 weeks on comprehensive clinical metabolic, immune, and hematologic profiles in young, healthy adults (18–35 y, BMI < 30 kg/m2 or <30% body fat for men and <40% body fat for women, n = 26) in a 16-week randomized, crossover intervention trial. We observed that average daily macro- and micronutrient intake significantly differed across egg diet periods, including greater intake of choline during the whole egg diet period, which corresponded to increased serum choline and betaine without altering trimethylamine N-oxide. Egg white and whole egg intake increased serum isoleucine while whole egg intake reduced serum glycine—markers of increased and decreased risk of insulin resistance, respectively—without altering other markers of glucose sensitivity or inflammation. Whole egg intake increased a subset of large HDL particles (H6P, 10.8 nm) and decreased the total cholesterol:HDL-cholesterol ratio and % monocytes in female participants using combined oral contraceptive (COC) medication (n = 11) as compared to female non-users (n = 10). Whole egg intake further increased blood hematocrit whereas egg white and whole egg intake reduced blood platelet counts. Changes in clinical immune cell counts between egg white and whole egg diet periods were negatively correlated with several HDL parameters yet positively correlated with measures of triglyceride-rich lipoproteins and insulin sensitivity. Overall, the intake of whole eggs led to greater overall improvements in micronutrient diet quality, choline status, and HDL and hematologic profiles while minimally—yet potentially less adversely—affecting markers of insulin resistance as compared to egg whites.

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