ReviewEgg consumption and heart health: A review
Introduction
Cardiovascular disease (CVD) accounted for $444 billion in healthcare expenditures in 2010 and remains the leading cause of death in the United States [1], [2]. Until recently, reducing dietary cholesterol has been part of the American Heart Association (AHA) and American College of Cardiology (ACC) guidelines on lifestyle management, despite inconclusive evidence to support the recommendation. The current AHA/ACC guidelines [3] now recommend dietary patterns that emphasize fruits, vegetables, whole grains, low-fat dairy products, poultry, fish, and nuts, rather than strictly limiting cholesterol intake, as an approach to decrease serum low-density lipoprotein-cholesterol (LDL-C) and hypertension. Considering approximately one third of the US population has been diagnosed with hypertension and hypercholesterolemia, the AHA/ACC recommend the Therapeutic Lifestyle Changes (TLC) and the Dietary Approaches to Stop Hypertension (DASH) diet to help attenuate development of CVD. The TLC and the DASH diet recommended consuming less than 200 mg and 150 mg of cholesterol per day [4], [5], respectively. Of note, the 2015–2020 Dietary Guidelines for Americans [6] have removed the recommendation of limiting cholesterol intake to no more than 300 mg/d; however, the guidelines state that “individuals should eat as little dietary cholesterol as possible while consuming a healthy eating pattern.”
Considering eggs are a rich source of dietary cholesterol (typically containing 141–234 mg per egg, depending on size), individuals with increased risk for CVD are often advised not to consume eggs. Moreover, based on the 2012 AHA/ACC guidelines [3], individuals with lower risk for CVD have previously been advised to avoid consuming eggs due to the high content of dietary cholesterol. The purpose of this review is to summarize the documented health risks of egg consumption in individuals with low and high risk for CVD and determine whether current recommendations (Table 1) are warranted based on the available literature. Furthermore, considering insulin resistance places an individual at increased risk for development of CVD and stroke [7], we describe the effect of eggs on glucose metabolism. Lastly, we aim to provide guidance for future studies that will help further elucidate the health modulating effect of eggs.
Section snippets
The relationship between serum cholesterol and CVD risk
Elevated serum LDL-C is a long-established risk factor for the development of heart disease; however, the relationship between serum concentrations of LDL-C and dietary cholesterol is not clear. Researchers from the Framingham Heart Study were among the first to demonstrate increased CVD risk with elevations in serum cholesterol [8]. They suggested limitations on cholesterol intake, yet no association between cholesterol intake and elevated serum cholesterol had been reported. An early
Eggs and CVD risk: Prior conceptions and current evidence
As previously mentioned, cholesterol intake reduction in recent times has been a unifying characteristic of the DASH, TLC, and AHA/ACC diets. Since a single egg yolk typically contains between 141 mg and 234 mg of cholesterol, the TLC and DASH diets recommend no more than two or four egg yolks per week, respectively. In early research, elevations in serum TC concentrations were detected following whole egg consumption; however, the concentration of cholesterol among lipoproteins was not
Egg consumption by individuals at lower risk for CVD
In the past, limiting egg consumption has frequently been recommended as a means of decreasing CVD risk in the population rather than only for individuals at higher risk. Multiple groups of researchers have examined the potential lipid modulating effects of eggs in low- and high-risk individuals alike. Here we describe the available research conducted with respect to the impacts of egg intake (with and without simultaneous exercise intervention) on lipid profiles of individuals at low risk for
Egg consumption by individuals at higher risk for CVD
Cardiovascular disease is progressive, slow to develop, and various comorbidities increase risk of CVD [45]. Targeting comorbidities such as obesity, insulin resistance, and metabolic syndrome (MetS) is a key avenue of research regarding CVD prevention. Considering obesity, insulin resistance and MetS increase risk for CVD, it would be beneficial to further evaluate the effects of egg intake in these specific at-risk populations. Following, we present a discussion of dietary intervention trials
Modulation of lipoprotein metabolism: The potential mechanism linking eggs to heart health
HDL-C is a key biomarker for protection against cardiovascular disease. Low circulating concentrations of HDL-C place an individual at elevated risk for developing CVD [56]. Higher HDL-C has been linked to cardiovascular health through the capacity of HDL particles to facilitate acquisition of lipids from macrophage foam cells within the arterial wall for promotion of reverse cholesterol transport [49]. Antiinflammatory properties of HDL particles further attenuate atherogenesis [57]. It is
Relationship between egg intake and glucose metabolism
Insulin resistance is an independent predictor of coronary heart disease, hypertension, as well as stroke, and over time can lead to type 2 diabetes mellitus (T2 DM) [7]. Insulin resistance is defined by the inability of the hormone, within its physiological range, to elicit its effect on target tissues (skeletal muscle, adipose tissue, and liver) [63]. Glucose uptake is one the primary roles of insulin across its target tissues [64]; thus, studying glucose metabolism allows for direct and
Egg consumption and stroke risk
In the United States, stroke is the fourth leading cause of mortality, with an estimated stroke incidence of 795 000 [17]. Increased risk of stroke has been reported in individuals with poor cardiovascular health, and is commonly associated with suboptimal diet quality [17]. Risk factors are categorized as either modifiable or non-modifiable, with diet considered a modifiable risk factor [71]. Between 2009 and 2012, greater than 100 million US adults ages 20 y or older were reported to have
Future directions
Future research should consider the effects of egg consumption on CVD risk in individuals classified as hyper-responders, as this cohort has been identified but not extensively studied. Furthermore, gene expression of ABCG5 and ABCG8 have been associated with an individual's ability to absorb cholesterol [74], [75] and may serve as an important target to better understand potential genetic influences on egg metabolism in the future. To date, only 2 studies [74], [75] have been conducted to
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