Eggs have been a dietary staple around the world for centuries. Not only are eggs delicious, but they also offer a rich source of essential nutrients. However, concerns have been raised about their impact on cholesterol levels and heart disease.

Eggs are a dietary source of cholesterol, with approximately 186 mg of cholesterol per egg. Due to this, eggs have been implicated in raising LDL cholesterol levels, leading to an increased risk of heart disease. However, recent scientific research has challenged this traditional belief.

In this article we will provide you an insightful exploration of the longstanding debate surrounding eggs and cholesterol, particularly the relationship between egg consumption, cholesterol levels, and heart health.

Before we dive into the research, let’s learn what cholesterol is and what the nutritional benefits of eggs are.

What is Cholesterol?

Cholesterol is a waxy, fat-like substance that is substantial for many physiological functions in the human body. While cholesterol holds a negative connotation due to its relation to heart diseases, it is important to understand its role and different types within the body.

Cholesterol is an essential lipid molecule that is involved in various biological processes in the body. It plays a vital role in the structure and function of cell membranes, as well as in the synthesis of certain hormones and bile acids. Cholesterol can be obtained from two main sources: dietary intake and endogenous production in the liver.

1. Dietary Cholesterol:

   Dietary cholesterol is found in animal-based foods such as meat, eggs, and dairy products. When you consume foods containing cholesterol, it is absorbed in the small intestine and transported into the bloodstream in the form of chylomicrons, which are large lipoprotein particles. Chylomicrons deliver cholesterol to various tissues throughout the body, including the liver.

   The liver can regulate the absorption and synthesis of cholesterol based on the body’s needs. When dietary cholesterol intake is high, the liver decreases its production of cholesterol to maintain balance. Conversely, if dietary cholesterol intake is low, the liver increases its synthesis to meet the body’s demands.

2. Liver Cholesterol Production:

   The liver is the primary site of cholesterol synthesis in the body. It synthesizes cholesterol through a complex series of enzymatic reactions known as the mevalonate pathway. The liver uses acetyl-CoA, a product of carbohydrate, protein, and fat metabolism, as a precursor for cholesterol synthesis.

   The production of cholesterol in the liver is regulated by a feedback mechanism. When cellular cholesterol levels are low, the liver increases its synthesis by upregulating the expression of enzymes involved in the mevalonate pathway. On the other hand, when cellular cholesterol levels are high, the liver reduces cholesterol synthesis by downregulating these enzymes.

   Furthermore, the liver also plays a crucial role in regulating cholesterol levels in the body through the production of two key lipoproteins: VLDL and HDL.

   VLDL carries cholesterol from the liver to peripheral tissues, while HDL helps remove excess cholesterol from tissues and transports it back to the liver for processing and elimination. VLDL delivers cholesterol and triglycerides to tissues, and as it undergoes metabolic changes in the bloodstream, it is converted into LDL. Through the production and metabolism of VLDL and HDL, the liver maintains a delicate balance in cholesterol levels, ensuring proper distribution, utilization, and elimination of cholesterol in the body.

Types of Cholesterol

1. High-Density Lipoprotein (HDL) Cholesterol

   High-density lipoprotein (HDL) cholesterol is often referred to as “Good Cholesterol” as it helps remove excess cholesterol from the blood and carries it back to the liver for its elimination from the body. High levels of HDL are associated with a reduced risk of cardiovascular disease.
   

2.  Low-density lipoprotein(LDL) cholesterol

   A commonly used term for low-density lipoprotein (LDL) cholesterol is “Bad Cholesterol”. Elevated levels of LDL cholesterol in the bloodstream can result in its accumulation within the arterial walls, leading to the formation of plaque. This process can contribute to the development of atherosclerosis, a condition characterized by the narrowing and hardening of arteries, thereby increasing the risk of heart disease.

3.  Triglycerides

   Triglycerides are a type of fat that circulates in the bloodstream and serves as a source of energy for the body. They can be obtained through the foods we consume or produced by the liver. Elevated levels of triglycerides are often associated with obesity, heart disease, and diabetes.

   High triglyceride levels, combined with low HDL cholesterol and high LDL cholesterol levels, can increase the risk of heart disease.

Are Eggs bad for cholesterol?

For many years, eggs have been wrongly criticized for their cholesterol content and their association with increased blood cholesterol levels. However, scientific research has provided a better understanding of the relationship between egg consumption and blood cholesterol.

The body tightly regulates cholesterol levels, and dietary cholesterol has less influence than previously thought. The liver produces cholesterol adequately to fulfill the body’s requirements. However, If someone consumes foods high in cholesterol, their liver responds by slowing down cholesterol production. This maintains a cholesterol balance, ensuring stability in levels and minimizing the influence of dietary sources of cholesterol, such as eggs, on blood cholesterol.

Studies done on people with metabolic syndrome have shown that consuming eggs may cause a moderate increase in LDL cholesterol levels, however, this increase is usually accompanied by an increase in HDL cholesterol in people with metabolic syndrome. The overall impact on the LDL-to-HDL cholesterol ratio, which is a more important marker of heart health, tends to be promising.

Nevertheless, it’s important to note that having higher HDL levels alone doesn’t mean you can consume unlimited eggs without any potential drawbacks. Maintaining a balanced diet remains crucial, considering your overall cholesterol intake from various sources, including foods that contain cholesterol and saturated fats.

While dietary cholesterol has a limited impact on blood cholesterol levels for most people, saturated fat is known to raise LDL cholesterol.
While egg yolks are high in cholesterol but low in saturated fat, Saturated fat is primarily found in animal products like meat, and dairy, and has a more significant impact on blood cholesterol levels than dietary cholesterol present in eggs.

Most foods that are high in cholesterol are also high in saturated fatty acids and thus may increase the risk of heart disease due to the saturated fatty acid content. The exceptions are eggs(1.56 g/egg). A diet high in deep-fried foods and processed junk foods can lead to weight gain, obesity, and metabolic disorders, including elevated triglyceride (TGL) levels. Excessive calorie intake, coupled with a lack of nutrient-dense foods, can disrupt lipid profiles and contribute to cardiovascular problems.

Deep-fried foods and processed junk foods, in addition to their saturated fat content, are often high in unhealthy fats overall, including trans fats. Trans fats, commonly found in partially hydrogenated oils used in frying and processed foods, not only raise LDL cholesterol levels but also lower the beneficial HDL cholesterol levels. Consuming these unhealthy fats can increase the risk of developing heart disease.

To prioritize heart health and reduce the risk of high TGL and cholesterol levels, it is advisable to limit the consumption of saturated and trans fats. Instead, focus on incorporating healthier fats, such as monounsaturated and polyunsaturated fats found in avocados, nuts, seeds, fatty fish, and olive oil, into your diet. Adopting a well-balanced diet plan that includes ample fruits, vegetables, whole grains, and lean proteins, along with regular physical activity, can support weight management and overall cardiovascular well-being.

Egg’s Nutritional Profile

According to the USDA (United States Department of Agriculture), a single hard-boiled egg weighing approximately 50 grams (g) offers the following nutritional content:

Energy: 78 calories

Macronutrients
Protein: 6.29 grams
Fat: 5.3 grams
Carbohydrate: 0.56 grams
Sugars: 0.56 grams
Dietary Fiber: 0 grams

Minerals:
Calcium: 25 milligrams
Iron: 0.59 milligrams
Phosphorus: 86 milligrams
Potassium: 63 milligrams
Zinc: 0.53 milligrams

Vitamins:
Cholesterol: 186 milligrams
Folate: 22 micrograms
Vitamin A: 260 international units
Vitamin D: 44 international units

The nutritional benefits of eggs

1. Eggs are a complete source of protein as they contain all 9 essential amino acids required by the body.
2. Eggs are rich in vitamins and minerals. They contain vitamin A, which supports vision, vitamin D, which helps in calcium absorption and bone health, vitamin E, an antioxidant with anti-inflammatory properties, and vitamin B such as riboflavin, folate, and B12 that play essential roles in energy production, brain function, and red blood cell formation.
3. Eggs are a good source of choline which is crucial for brain development and function.
4. Eggs are a natural source of antioxidants like lutein and zeaxanthin which helps protect against age-related macular degeneration and cataract.
5. Including eggs in your diet can help in weight management as eggs are highly satiating due it’s high protein content which helps you feel full for longer. It can aid in reducing hunger pangs and curbing overeating.

How many eggs can we eat every day?

No study tells you exactly how many eggs to eat in a day. It depends on a lot of factors such as your overall calorie intake and requirements. On average, a healthy individual can consume up to 2-4 whole eggs per day. That being said, there are some limitations to those with medical health conditions such as any existing heart disease, high cholesterol, or type 2 diabetes. In such medical conditions, the egg intake should be limited to 6 per week.

Factors influencing cholesterol metabolism

1.)Diet- When eggs are cooked in high-fat oils, such as butter, lard, or hydrogenated oils, the overall fat content of the meal increases. These added fats are a source of saturated and trans fats, which have been shown to raise LDL cholesterol levels. Consuming foods high in saturated and trans fats can have a more significant impact on blood cholesterol levels compared to the cholesterol content of the eggs.
Similarly, if bacon or other processed meats are consumed with eggs, it adds a significant amount of saturated and often trans fats to the meal. Processed meats like bacon are typically high in saturated fats and may also contain trans fats from the processing methods used.

2.) Medical condition-
There are several medical conditions that can affect cholesterol metabolism. Here are a few examples.

A.) Diabetes- In diabetes, insulin resistance and elevated blood sugar levels can disrupt normal cholesterol metabolism. Insulin resistance reduces the effectiveness of insulin in clearing LDL cholesterol from the bloodstream, leading to elevated LDL cholesterol levels. Additionally, high blood sugar levels can increase the production of triglycerides in the liver, contributing to elevated triglyceride levels.
There are two types of fatty liver disease: alcoholic fatty liver disease and non-alcoholic fatty liver disease.Here’s a brief summary of how each type affects cholesterol metabolism:

B.) Fatty Liver-
– Alcoholic Fatty Liver Disease: Chronic alcohol consumption stimulates the liver to produce more very low-density lipoprotein (VLDL) cholesterol, which can contribute to higher levels of LDL cholesterol in the bloodstream. Alcohol disrupts lipoprotein metabolism, leading to increased LDL cholesterol levels and decreased HDL cholesterol levels.

-Non-Alcoholic Fatty Liver Diseases: NAFLD is a condition characterized by the accumulation of excess fat in the liver in individuals who consume little to no alcohol. NAFLD is associated with insulin resistance, which can result in decreased levels of HDL cholesterol and increased levels of triglycerides and LDL cholesterol.

3.) Physical activity: Regular physical activity and exercise can positively affect cholesterol metabolism. Exercise can raise HDL cholesterol levels and promote the clearance of LDL cholesterol from the bloodstream, thus improving the overall cholesterol profile.

4.)Individual response: Some individuals, known as “hyperresponders,” may experience a more significant increase in blood cholesterol levels when they consume dietary cholesterol. These individuals may need to be more attentive about their dietary cholesterol intake, including eggs, to manage their cholesterol levels effectively. Additionally, people with certain medical conditions, such as diabetes or familial hypercholesterolemia, may be more sensitive to dietary cholesterol and need to be mindful of their egg consumption.

5.)Body weight and body composition: Being overweight or obese can disrupt cholesterol metabolism. Excess body fat, particularly around the abdominal area, can increase LDL cholesterol levels and reduce HDL cholesterol levels. Losing weight and maintaining a healthy body weight can help improve cholesterol levels.

6.) Hormonal factors: Hormones can impact cholesterol metabolism. For example, estrogen has been shown to increase HDL cholesterol levels and lower LDL cholesterol levels, which somewhat explains why premenopausal women have a lower incidence of heart attacks as compared to men. Hormonal changes during menopause can lead to adverse changes in cholesterol levels.

Conclusion

The longstanding belief that eggs are bad for heart health and increases cholesterol levels has been challenged by scientific research.

As with any food, moderation is key. It is recommended to consume eggs as part of a balanced diet that includes a variety of other nutrient-dense foods, such as fruits, vegetables, whole grains, lean proteins, and healthy fats. It’s essential to focus on overall dietary patterns rather than fixating on individual foods or nutrients

For the majority of individuals, moderate egg consumption as part of a balanced diet does not significantly impact blood cholesterol levels or increase the risk of heart disease. However, individual responses may vary, and those with specific medical conditions should consult healthcare professionals for personalized advice. It’s time to embrace the nutritional benefits of eggs and include them in our diets without undue concern about cholesterol.

References:
Blesso CN, Andersen CJ, Barona J, Volek JS, Fernandez ML. Whole egg consumption improves lipoprotein profiles and insulin sensitivity to a greater extent than yolk-free egg substitute in individuals with metabolic syndrome. Metabolism. 2013 Mar;62(3):400-10. doi: 10.1016/j.metabol.2012.08.014. Epub 2012 Sep 27. PMID: 23021013.
https://pubmed.ncbi.nlm.nih.gov/23021013/

Ma Z, Wu W, Zhang D, Wu P, Guo Y, Li D, Yang F. Daily intake of up to two eggs for 11 weeks does not affect the cholesterol balance of Chinese young adults. Food Sci Nutr. 2022 Jan 17;10(4):1081-1092. doi: 10.1002/fsn3.2734. PMID: 35432976; PMCID: PMC9007305.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9007305/

Larsson SC, Åkesson A, Wolk A. Egg consumption and risk of heart failure, myocardial infarction, and stroke: results from 2 prospective cohorts. Am J Clin Nutr. 2015 Nov;102(5):1007-13. doi: 10.3945/ajcn.115.119263. Epub 2015 Sep 23. PMID: 26399866.
https://pubmed.ncbi.nlm.nih.gov/26399866/&sa=D&source=docs&ust=1688579300376191&usg=AOvVaw0H5x2y-BpnfdbV3mEBKukn