Wednesday, May 1, 2013

The Incredible, Edible Egg or Not?

Eggs have long been part of the traditional American diet especially when it comes to a hearty breakfast. Gym junkies also swear by eggs, highlighting the egg whites as a perfect low-fat, low-calorie source of protein. Others say eggs are an essential food for good health citing the fact they are an excellent source of vitamin A, B-complex vitamins (specifically choline), and two carotenoids (lutein and zeaxanthin) which are important for healthy vision. Along with these health claims proponents also often say you should limit egg consumption. The Mayo Clinic states to consume no more than 4 eggs per week to avoid increasing cholesterol levels.

So are eggs really the perfect food? Are there any downsides to eating eggs? Should you eat eggs or not eat eggs? What does the science say about eating eggs?

Eggs - The Evidence vs. What They "Say"


Egg advocates often highlight a few vitamins and antioxidants contained in the egg to help boost the case of them being a health food.  The cholesterol and fat content is usually downplayed as a source of concern when it comes to egg's overall effect on health by these same proponents. I believe it's important to look at the actual evidence when contemplating whether or not to eat eggs before making your decision. Relying on hearsay is of little benefit when it comes to your individual health.

Below is a look at the evidence (not funded by the egg industry) on egg consumption and health:

Cardiovascular Disease

- A 2008 study in The Journal of the American Dietetic Association concluded that a greater dietary intake of eggs (1 egg/day) was associated with a 23% increased risk of incident heart failure (death or hospitalization) independent of energy intake, demographic characteristics, physical activity level, smoking, drinking status, and prevalent status of cardiovascular disease, diabetes, and hypertension [1]. The study followed a total of 14,153 African-American and white adults for a period of 13.3 years.

- The 2008 Harvard Physicians' Health Study published in the journal Circulation found an increased risk of heart failure and egg consumption [2]. This study followed 21,275 physicians for a period of 20.4 years. After adjusting for age, body mass index, smoking, alcohol consumption, and history of diabetes, atrial fibrillation, and hypertension the study found the following increased risk in heart failure with regards to egg consumption - 2-4 eggs/week (2%), 5-6 eggs/week (1%), 1 egg/day (27%), 2+ eggs/day (61%). A review in the American Journal of Clinical Nutrition of this same study also found an increased risk of stroke with higher egg consumption - 2-4 eggs/week (7%), 5-6 eggs/week (13%), 7+ eggs/week (6%) [5]. The same review found the overall risk of death was also higher in individuals who consumed more eggs - 2-4 eggs/week (1%), 5-6 eggs/week (3%), 7+ eggs/week (27%).

Type 2 Diabetes

- A 2012 study published in the Public Health Nutrition journal found an increase risk of type 2 diabetes with increased egg consumption [3]. A 2-fold increased risk was found in individuals consuming 3-5 eggs/week and a 3-fold increased risk was found for those consuming 5+ eggs/week compared to those eating < 1 egg/week. These findings came after adjusting for body mass index, family history of diabetes, smoking, education level, morning exercise, and plasma triglyceride levels.

- A 2009 article in Diabetes Care journal concluded there was an increased risk of type 2 diabetes in men and women as egg consumption increased [4]. The study followed 1,921 men for an average of 20.0 years and 2,112 women for 11.7 years. After adjusting for age, body mass index, smoking, alcohol consumption, exercise, and history of hypercholesterolemia and hypertension the following increased risk of type 2 diabetes was found:
      - Men - 1 egg or less/week (9%), 2-4 eggs/week (18%), 5-6 eggs/week (46%), 7+ eggs/week (58%)
      - Women - < 1 egg/week (6%), 2-4 eggs/week (19%), 5-6 eggs/week (18%), 7+ eggs/week (77%)

Cancer

- A 2009 study published in the Asian Pacific Journal of Cancer Prevention found an increased risk in several cancers with higher egg consumption [6]. These findings were after adjusting for age, sex, residence, education, income, interviewer, smoking, alcohol consumption, body mass index, calorie intake, and consumption of other food groups. The following increased risks of cancer (broken down by type) were found in those consuming 3.5 eggs or more per week compared with those consuming no eggs in their diet:
       - Oral cavity/pharynx cancer - 102% (> 2-fold increase)
       - Head and neck cancer - 67%
       - Colon cancer - 221% (> 3-fold increase)
       - Breast cancer - 186% (nearly 3-fold increase)
       - Prostate cancer - 89%
       - Bladder cancer - 123% (> 2-fold increase)
       - All cancers combined - 71%
The study went on to state that a plausible explanation of egg intake and cancer risk could be the high cholesterol content of eggs. In addition to this, the researchers also stated the following, "Our finding that adjustment for cholesterol slightly strengthened the association between egg intake and cancer risk suggests that other factors than cholesterol may account for the positive associations we observed." Given the fact that animal proteins increase the risk of cancer growth it may also be plausible that this could account for the increased association of egg intake and cancer risk while adjusting for cholesterol intake. So eating just egg whites rich in animal protein is not necessarily the recipe for great health.

Nutritional Content - Eggs vs. Plant-Based, Whole Foods


To be fair, we should not forego comparing the health claims in regards to vitamins and other nutrients egg proponents say they provide. In some areas eggs do provide more of a single nutrient than other foods, but in others the marketing doesn't meet the hype. In either case, one has to decide whether the above health risks (cancer, heart disease, type 2 diabetes) are worth consuming eggs for the one or two individual nutrients found in higher amounts in eggs.

Choline Content

Choline is an essential nutrient for many different metabolic functions including cell membrane functions, normal muscle functioning, and liver health [7]. Eggs provide some of the highest amounts of choline of any food in the diet. However, the amount of choline humans actually need has not been well studied. The Institute of Medicine didn't even have enough scientific evidence to create a Recommended Dietary Allowance (RDA) for choline when it set out to provide the general public guidelines for the prevention of a dietary choline deficiency [8]. Instead, they opted for creating an Adequate Intake (AI) level, which is basically their best educated guess based on the scant science available. The AI for men is 550 mg/day of choline and for women 425 mg/day. However, no study has ever nailed down an absolute minimum amount for avoiding a deficiency, and one study actually showed as little as 138 mg/day may be enough for some males to prevent a deficiency [9]. Furthermore, most studies testing a choline deficiency in humans found that symptoms didn't present themselves until choline intake was less than 50 mg/day. What's even more concerning is that recent data over the past few years has been increasingly showing that too much choline can lead to heart disease, cancer, and death (see video below).


The U.S. government has created a database for the choline content of different foods here - USDA Database for the Choline Content of Common Foods. Two hardboiled eggs (approximately 100 grams) provides 230 mg of choline. Two thirds of a cup of uncooked, unprocessed soybeans (approximately 100 grams) delivers 120 mg of choline. Using the Nutritiondata.com database 1 cup of cooked quinoa provides 119 mg of choline. Unprocessed soybeans and quinoa (a whole grain) are two health-promoting plant foods that are viable alternatives to eggs (along with many other plant-based foods) for dietary choline sources. These plant foods have also not been shown in multiple studies to increase the risk of cardiovascular disease, type 2 diabetes, and cancer like eggs have. Definitely something to think about when considering how to construct a health-promoting diet.

For more information on choline in the human diet, specifically as it relates to plant-based nutrition, please read this article by registered dietitian Jack Norris, RD.

Vitamin A

Vitamin A has long been known for its health benefits, especially when it comes to the eyes or vision health [10]. Beta-carotene (converted into vitamin A by the human body) is the most commonly recognized carotenoid and also plays an important role in preventing cancer due to its ability to counteract free radical damage in the body [11].

The egg industry touts the abundance of vitamin A in eggs to promote their product. However, a quick look at the USDA National Nutrition Database for Vitamin A contents in various foods shows that eggs are far down the line in terms of providing generous amounts of vitamin A. Carrots, pumpkin, sweet potatoes, spinach, and a variety of other dark leafy greens top the list as these items fill the first several pages of foods highest in vitamin A. In fact, you have to scroll all the way down to page 6 before eggs even make the list. When you do get there you'll find that one fried egg provides a total of 362 International Units of vitamin A. Compare this to one sweet potato (baked) which provides 28,058 International Units of vitamin A. The notion that eggs are a good source of vitamin A is overhyped at best and used simply as a marketing tool to get more people to buy them instead of eating healthier alternatives such as dark leafy greens.

Lutein and Zeaxanthin

Lutein and zeaxanthin are two more carotenoids highlighted for their role in healthy vision. Once again eggs are marketed as being rich sources of these two carotenoids. This video sums up the evidence nicely:


Protein

One of the most important highlighted nutrients in eggs is protein. Eggs are revered as an excellent source of a perfect protein for human beings. This benefit is especially supported by many individuals who workout and frequent the gym on a regular basis. Protein is a must for working out and repairing muscle. This is true as it provides the building blocks for muscle growth and repair, but not all is that meets the eye when it comes to this highly valued (and commercially marketed) macronutrient.

The human body has been shown to need as little as 30 grams of protein per day to meet its basic needs [12]. In those leading a sedentary life this amounts to as little as 5-10% of total daily calories. The need for protein obviously increases for athletes or persons participating in a regular, vigorous strength training workout program. Up to 1.41 grams/kg/day of protein or roughly 10-15% of total daily calories has been recommended in these cases [13]. This works out to be approximately 110 grams/day for a 175 pound athlete. One large fried egg provides 6 grams of protein. One cup of cooked quinoa provides 8 grams of protein. Eggs are praised for being the perfect source of protein. As far as the human body is concerned the "perfect" source of protein would contain all 9 essential amino acids (amino acids the body cannot make on its own). Quinoa would also then be considered the perfect source of protein as it contains all 9 essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine). While eggs come along with the health risks noted earlier (heart disease, type 2 diabetes, and cancer), quinoa (like many other whole plant foods) has never been shown in studies to increase these diseases or any other chronic disease that's prevalent in Western cultures.

The notion that eggs are the perfect source of protein and encouraged by many in the fitness world as part of a healthy diet just doesn't hold true when it comes to looking at the scientific evidence. Protein is important when vigorously training your body, but there are much better options healthwise to choose from that do not increase your risk of chronic illnesses later in life.

For more information on protein as it relates to athletic performance read this article - Fueling the Vegetarian (Vegan) Athlete.

For more information on complete and "incomplete" proteins read this article - When Friends Ask: Where do You Get Your Protein?

Conclusion


Eggs are often promoted as a health food through a confusion of misleading information highlighting the few nutrients and vitamins contained within them shown to be important to human health. Unfortunately, these claims are overstated while important scientific data on the health risks associated with egg consumption go unspoken, especially in terms of long term health.

When looking at the evidence more closely eggs become one of those individual food items where we humans can get away with eating a few (1 or 2 per week at the very most) without suffering major health consequences. However, foods that truly promote health should never show up in numerous scientific studies reporting an increase risk of developing potential debilitating diseases in those who consume them. It is this fact that should prompt anyone eating any food item (including eggs) to take a step back and evaluate whether or not the benefits/risks are worth it. Is there another way to accomplish what you want from a nutritional standpoint while improving your health instead of rolling the dice when it comes to certain foods? The choice is always yours in the end. Ultimately, you are in charge of your health. What you eat today will surely affect you tomorrow. Make the most of your choices.







Photo credit: Freedigitalphotos.net


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References:
1 Nettleton JA, Steffen LM, Loehr LR, et al. Incident heart failure is associated with lower whole-grain intake and greater high-fat dairy and egg intake in the Atherosclerosis Risk in Communities (ARIC) study. J Am Diet Assoc. 2008 Nov;108(11):1881-7.
2 Djousse L, Gaziano JM. Egg consumption and risk of heart failure in the Physicians’ Health Study. Circulation. 2008;117:512–516.
3 Radzevičienė L, Ostrauskas R. Egg consumption and the risk of type 2 diabetes mellitus: a case-control study. Public Health Nutr. 2012 Aug;15(8):1437-41. doi: 10.1017/S1368980012000614.
4 Djoussé L, Gaziano JM, Buring JE, et al. Egg consumption and risk of type 2 diabetes in men and women. Diabetes Care. 2009 Feb;32(2):295-300. doi: 10.2337/dc08-1271.
5 Djoussé L, Gaziano JM. Egg consumption in relation to cardiovascular disease and mortality: the Physicians' Health Study. Am J Clin Nutr. 2008 Apr;87(4):964-9.
6 Aune D, De Stefani E, Ronco AL, et al. Egg consumption and the risk of cancer: a multisite case-control study in Uruguay. Asian Pac J Cancer Prev. 2009;10(5):869-76.
7 Zeisel SH. Choline: Critical Role During Fetal Development and Dietary Requirements in Adults. Annu Rev Nutr. 2006;26:229-50. Review.
8 Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic A Report of the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its Panel on Folate, Other B Vitamins, and Choline and Subcommittee on Upper Reference Levels of Nutrients, Food and Nutrition Board, Institute of Medicine. 1998:390-422.
9 da Costa KA, Badea M, Fischer LM, Zeisel SH. Elevated serum creatine phosphokinase in choline-deficient humans: mechanistic studies in C2C12 mouse myoblasts. Am J Clin Nutr. 2004 Jul;80(1):163-70.
10 Manzi F, Flood V, Webb K, Mitchell P. he intake of carotenoids in an older Australian population: The Blue Mountains Eye Study. Public Health Nutr. 2002 Apr;5(2):347-52.
11 Paiva SA, Russell RM. Beta-carotene and other carotenoids as antioxidants. J Am Coll Nutr. 1999 Oct;18(5):426-33. Review.
12 Rose W. The amino acid requirements of adult man. Nutritional Abstracts and Reviews. 1957;27:631.
13 Fuhrman J, Ferreri DM. Fueling the Vegetarian (Vegan) Athlete. Curr Sports Med Rep. 2010 Jul/Aug;9(4):233-241.

3 comments:

  1. Why can't you just throw the yolk?

    ReplyDelete
    Replies
    1. Please see the section on protein and choline... animal-based proteins promote cancer and choline is now shown to increase one's risk of heart disease, cancer, and mortality rates.

      Delete
  2. Thanks for this.

    Chicken and eggs are the top sources of arachidonic acid in the diet, an omega 6 fatty acid involved in our body’s inflammatory response.

    http://www.youtube.com/watch?v=-0ap3dVC-LM

    ReplyDelete