DNC NEWs: Eggs: go ahead and eat them….
April 2, 2005
Subject: Eggs have little effect on heart disease risk.
Ever since the Framingham studies linked cholesterol levels to heart disease, people have been afraid to eat foods containing cholesterol. There is no evidence to support this.
This is the case particularly with eggs. Eggs are an inexpensive source of high quality protein. Egg protein, in fact, is so high quality that it is used as the standard to which the amino acid profiles of all other proteins are compared.
Despite being so nutritious many people try to avoid eating eggs or will separate the eggs prior to cooking and discard the yolks. They are convinced that the yolks are bad for them, “something to do with cholesterol.” This is a myth, I suspect dreamed up and perpetuated by a food industry which wants to sell Eggbeaters.
Plenty of epidemiological studies have asked whether there was a connection between eggs eaten and heart disease or stroke and found nothing to worry about. In a 1999 JAMA article, Hu and his colleagues reported on data from the Health Professionals and the Nurse's Health studies. They analyzed data from 37, 851 men and 80,082 women. To quote their paper, “After adjustment for age, smoking, and other potential CHD risk factors, we found no evidence of an overall significant association between egg consumption and risk of CHD or stroke in either men or women.” [i]
Another epidemiological study published in the Journal of the American College of Nutrition found a modest increase in cardiovascular risk with high egg consumption but when confounding factors were accounted for this increased risk disappeared. In other words eating bacon with eggs, toast and coffee and a cigarette afterwards may raise the risk, but they could not prove it was the eggs causing the problem. “When dietary confounders were considered, no association was seen between egg consumption at levels up to 1 + egg per day and the risk of coronary heart disease in non-diabetic men and women.” [ii]
There was a theory kicking around for awhile that eating eggs increased the amount of HDL, the good cholesterol, more than total cholesterol so that the ratio of total to good would decrease, lowering heart disease risk. This idea has been dropped based on more recent research. A Dutch meta analysis published in 2001 in the American Journal of clinical Nutrition compiled data from 17 separate epidemiological studies and found that, “The addition of 100 mg dietary cholesterol/day increased the ratio of total to HDL cholesterol by 0.020 units and total cholesterol concentrations by 0.056 mmol/L (2.2 mg/dL)” [iii] Although this data shows a statistically significant increase in cholesterol, it is not clear that these meager changes are actually clinically significant for our patients.
Another epidemiological study published in the same American Journal of Clinical Nutrition in 2004 reviewed Japanese data. [iv] Rather than just looking at cholesterol levels or heart disease rates they also reviewed overall mortality rates. The number of eggs people ate was statistically tied to their chance of dying. Women who ate more than 2 eggs per day had almost half the mortality rate of women who seldom ate eggs. Women who averaged about ½ an egg per day had the lowest mortality rate, about ¼ of the rate women who rarely ate eggs had.
These studies I've mentioned so far are epidemiological studies. They examine data collected for large numbers of people and try to finesse out information. These sorts of studies are famous for producing misleading information. Studies which set up clinical experiments produce more reliable information.
In a 2004 study published in Metabolism , researchers watched what an egg a day for a month did to the blood chemistry of volunteers with special focus on the lipoprotein particles that increase risk for heart disease. Even if eggs don't raise blood cholesterol, reasoned the scientists, perhaps they change something else that would put egg-eaters at greater risk. They demonstrated some changes: the effect was different between men and women, some people responded to the egg cholesterol while others did not. In the end the researchers concluded, “…these data indicate that the consumption of a high-cholesterol diet does not negatively influence the atherogenicity of the LDL particle.” [v]
The most recent study I've come across and probably the most accurate was published in March, 2005 in the International Journal of Cardiology. [vi] It was a randomized crossover trial. A group of 49 volunteers ate either two eggs a day for six weeks or oatmeal. After the six weeks their diets were switched, or crossed over. The six weeks of egg eating had no effect on total cholesterol. The six weeks of daily oatmeal did lower total cholesterol significantly, both statistically and clinically, from a baseline of 204 to 194.
If worried about heart disease, this study would say, “don't worry about how many eggs you eat. Instead make sure you eat your oatmeal.”
There is another element that must be mentioned. Good research suggests that eating fish or nuts protects people from heart disease. [vii] This benefit is attributed to the omega-3 fatty acids both contain. These specific fats also prevent breast and prostate cancer and are needed for brain development in infants.
In the United States no dietary standards have been set for how much of these fats we should consume. In Canada , the government has set dietary standards suggesting that 0.5% of a person's daily calories should come from omega-3 fats.
The amount of omega-3 fats in eggs varies a great deal depending on what the hens are fed. Feeding the hens either fish oil, flax seeds, or canola seed increases the amount of these fats in the eggs by about 400%. In an experiment where volunteers ate four omega-3 enriched eggs for a month, no significant increase in total cholesterol or LDL was detected but triglycerides and blood platelet aggregation both decreased significantly. This suggests that eating these special Omega-3 enriched eggs may be protective against heart disease. [viii]
So what's the bottom line?
Eating up to two eggs a day does not appear to cause a measurable increase in heart disease but it may lower the risk of overall mortality.
Eating the omega-3 enriched eggs theoretically may lower risk of heart disease; eating a bowl of oatmeal with a few nuts thrown in certainly will.
[i] JAMA. 1999 Apr 21;281(15):1387-94.
A prospective study of egg consumption and risk of cardiovascular disease in men and women.
Hu FB, Stampfer MJ, Rimm EB, Manson JE, Ascherio A, Colditz GA, Rosner BA, Spiegelman D, Speizer FE, Sacks FM, Hennekens CH, Willett WC.
Department of Nutrition, Harvard School of Public Health, Boston , Mass 02115, USA . Frank.firstname.lastname@example.org
CONTEXT: Reduction in egg consumption has been widely recommended to lower blood cholesterol levels and prevent coronary heart disease (CHD). Epidemiologic studies on egg consumption and risk of CHD are sparse. OBJECTIVE: To examine the association between egg consumption and risk of CHD and stroke in men and women. DESIGN AND SETTING: Two prospective cohort studies, the Health Professionals Follow-up Study (1986-1994) and the Nurses' Health Study (1980-1994). PARTICIPANTS: A total of 37851 men aged 40 to 75 years at study outset and 80082 women aged 34 to 59 years at study outset, free of cardiovascular disease, diabetes, hypercholesterolemia, or cancer. MAIN OUTCOME MEASURES: Incident nonfatal myocardial infarction, fatal CHD, and stroke corresponding to daily egg consumption as determined by a food-frequency questionnaire. RESULTS: We documented 866 incident cases of CHD and 258 incident cases of stroke in men during 8 years of follow-up and 939 incident cases of CHD and 563 incident cases of stroke in women during 14 years of follow-up. After adjustment for age, smoking, and other potential CHD risk factors, we found no evidence of an overall significant association between egg consumption and risk of CHD or stroke in either men or women. The relative risks (RRs) of CHD across categories of intake were less than 1 per week (1.0), 1 per week (1.06), 2 to 4 per week (1.12), 5 to 6 per week (0.90), and > or =1 per day (1.08) (P for trend = .75) for men; and less than 1 per week (1.0), 1 per week (0.82), 2 to 4 per week (0.99), 5 to 6 per week (0.95), and > or =1 per day (0.82) (P for trend = .95) for women. In subgroup analyses, higher egg consumption appeared to be associated with increased risk of CHD only among diabetic subjects (RR of CHD comparing more than 1 egg per day with less than 1 egg per week among diabetic men, 2.02 [95% confidence interval, 1.05-3.87; P for trend = .04], and among diabetic women, 1.49 [0.88-2.52; P for trend = .008]). CONCLUSIONS: These findings suggest that consumption of up to 1 egg per day is unlikely to have substantial overall impact on the risk of CHD or stroke among healthy men and women. The apparent increased risk of CHD associated with higher egg consumption among diabetic participants warrants further research.
PMID: 10217054 [PubMed - indexed for MEDLINE]
[ii] J Am Coll Nutr. 2000 Oct;19(5 Suppl):549S-555S.
Egg consumption and coronary heart disease: an epidemiologic overview.
Kritchevsky SB, Kritchevsky D.
Department of Preventive Medicine, University of Tennessee Health Sciences Center , Memphis 38105 , USA .
Serum cholesterol has been established as a modifiable risk factor for coronary heart disease. Experimental feeding studies show that saturated fat and cholesterol increase serum cholesterol levels; thus, dietary recommendations for lowering the risk of heart disease proscribe the intake of both substances. Recommendations have also included limits on the intake of eggs because of their high cholesterol content. In free-living populations, diet reflects a pattern of associated choices. Increases in one food may lead to changes in the consumption of other foods that may modulate disease risk. Epidemiologic data are helpful in assessing the importance of foods and nutrients in the context in which they are actually consumed. We review epidemiologic data relating dietary cholesterol and eggs to coronary disease risk. Cholesterol intake was associated with a modest increase in the risk of coronary events. The true magnitude of the association is difficult to estimate because most studies fail to account for potential confounding by other features of the diet. When a full-range of confounding factors was considered, the association between cholesterol intake and heart disease risk was small (6% increase in risk for 200mg/1,000kcal/day difference in cholesterol intake). Several studies have examined egg intake and its relationship with coronary outcomes. All but one failed to consider the role of other potentially confounding dietary factors. When dietary confounders were considered, no association was seen between egg consumption at levels up to 1 + egg per day and the risk of coronary heart disease in non-diabetic men and women.
PMID: 11023006 [PubMed - indexed for MEDLINE]
Link to full text of article: http://www.jacn.org/cgi/content/full/19/suppl_5/549S
[iii] Am J Clin Nutr. 2001 May;73(5):885-91.
Dietary cholesterol from eggs increases the ratio of total cholesterol to high-density lipoprotein cholesterol in humans: a meta-analysis.
Weggemans RM, Zock PL , Katan MB .
Division of Human Nutrition and Epidemiology, Wageningen University , Wageningen , Netherlands .
BACKGROUND: Several epidemiologic studies found no effect of egg consumption on the risk of coronary heart disease. It is possible that the adverse effect of eggs on LDL-cholesterol is offset by their favorable effect on HDL cholesterol. OBJECTIVE: The objective was to review the effect of dietary cholesterol on the ratio of total to HDL cholesterol. DESIGN: Studies were identified by MEDLINE and Biological Abstracts searches (from 1974 to June 1999) and by reviewing reference lists. In addition, we included data from a more recently published study. Studies were included if they had a crossover or parallel design with a control group, if the experimental diets differed only in the amount of dietary cholesterol or number of eggs and were fed for > or =14 d, and if HDL-cholesterol concentrations were reported. Of the 222 studies identified, 17 studies involving 556 subjects met these criteria. RESULTS: The addition of 100 mg dietary cholesterol/d increased the ratio of total to HDL cholesterol by 0.020 units (95% CI: 0.010, 0.030), total cholesterol concentrations by 0.056 mmol/L (2.2 mg/dL) (95% CI: 0.046, 0.065 mmol/L; 1.8, 2.5 mg/dL), and HDL-cholesterol concentrations by 0.008 mmol/L (0.3 mg/dL) (95% CI: 0.005, 0.010 mmol/L; 0.2, 0.4 mg/dL). CONCLUSIONS: Dietary cholesterol raises the ratio of total to HDL cholesterol and, therefore, adversely affects the cholesterol profile. The advice to limit cholesterol intake by reducing consumption of eggs and other cholesterol-rich foods may therefore still be valid.
PMID: 11333841 [PubMed - indexed for MEDLINE]
Link to full text: http://www.ajcn.org/cgi/content/full/73/5/885
[iv] Am J Clin Nutr. 2004 Jul;80(1):58-63.
Egg consumption, serum cholesterol, and cause-specific and all-cause mortality: the National Integrated Project for Prospective Observation of Non-communicable Disease and Its Trends in the Aged, 1980 (NIPPON DATA80).
Nakamura Y, Okamura T, Tamaki S, Kadowaki T, Hayakawa T, Kita Y, Okayama A, Ueshima H; NIPPON DATA80 Research Group.
Division of Cardiology, Department of Medicine, Shiga University of Medical Science, Shiga , Japan . email@example.com
BACKGROUND: Because egg yolk has a high cholesterol concentration, limited egg consumption is often suggested to help prevent ischemic heart disease (IHD). OBJECTIVE: We epidemiologically examined the validity of this recommendation. DESIGN: We analyzed the relations of egg consumption to serum cholesterol and cause-specific and all-cause mortality by using the NIPPON DATA80 (National Integrated Project for Prospective Observation of Non-communicable Disease And its Trends in the Aged, 1980) database. At the baseline examination in 1980, a nutritional survey was performed by using the food-frequency method in Japanese subjects aged > or =30 y. We followed 5186 women and 4077 men for 14 y. RESULTS: The subjects were categorized into 5 egg consumption groups on the basis of their responses to a questionnaire (> or =2/d, 1/d, 1/2 d, 1-2/wk, and seldom). There were 69, 1396, 1667, 1742, and 315 women in each of the 5 groups, respectively. Age-adjusted total cholesterol (5.21, 5.04, 4.95, 4.91, and 4.92 mmol/L in the 5 egg consumption categories, respectively) was related to egg consumption (P < 0.0001, analysis of covariance). In women, unadjusted IHD mortality and all-cause mortality differed significantly between the groups [IHD mortality: 1.1, 0.5, 0.4, 0.5, and 2.0 per 1000 person-years, respectively (P = 0.008, chi-square test); all-cause mortality: 14.8, 8.0, 7.5, 7.5, and 14.5 per 1000 person-years, respectively (P < 0.0001, chi-square test)]. In men, egg consumption was not related to age-adjusted total cholesterol. Cox analysis found that, in women, all-cause mortality in the 1-2-eggs/wk group was significantly lower than that in the 1-egg/d group, whereas no such relations were noted in men. CONCLUSION: Limiting egg consumption may have some health benefits, at least in women in geographic areas where egg consumption makes a relatively large contribution to total dietary cholesterol intake.
PMID: 15213028 [PubMed - indexed for MEDLINE]
[vi] Int J Cardiol. 2005 Mar;99(1):65-70.
Egg consumption and endothelial function: a randomized controlled crossover trial.
Katz DL, Evans MA, Nawaz H, Njike VY, Chan W, Comerford BP, Hoxley ML.
Yale Prevention Research Center , 130 Division Street, Derby , CT 06418 , USA .
Background: Because of egg cholesterol content, reduction in egg consumption is generally recommended to reduce risk of cardiovascular disease. Recently, however, evidence has been accumulating to suggest that dietary cholesterol is less relevant to cardiovascular risk than dietary saturated fat. This randomized controlled crossover trial was conducted to determine the effects of egg ingestion on endothelial function, a reliable index of cardiovascular risk. Methods: Forty-nine healthy adults (mean age 56 years, 40% females) underwent a baseline brachial artery reactivity study (BARS), and were assigned to two eggs or oats daily for 6 weeks in random sequence with a 4-week washout. A BARS was done at the end of each treatment phase, measuring flow-mediated vasodilation (FMD) in the brachial artery using a high-frequency ultrasound. Results: FMD was stable in both egg and oat groups, and between-treatment differences were not significant (egg -0.96%, oatmeal -0.79%; p value >0.05). Six weeks of egg ingestion had no effect on total cholesterol (baseline: 203.8 mg/dl; post-treatment: 205.3) or LDL (baseline: 124.8 mg/dl; post-treatment: 129.1). In contrast, 6 weeks of oats lowered total cholesterol (to 194 mg/dl; p=0.0017) and LDL (to 116.6 mg/dl; p=0.012). There were no differences in body mass index (BMI), triglyceride, HDL or SBP levels between egg and oat treatment assignments. Conclusion: Short-term egg consumption does not adversely affect endothelial function in healthy adults, supporting the view that dietary cholesterol may be less detrimental to cardiovascular health than previously thought.
[vii] JAMA. 2002 Apr 10;287(14):1815-21.
Fish and omega-3 fatty acid intake and risk of coronary heart disease in women.
Hu FB, Bronner L, Willett WC, Stampfer MJ, Rexrode KM, Albert CM, Hunter D, Manson JE.
Department of Nutrition, Harvard School of Public Health, 665 Huntington Ave, Boston, MA 02115, USA. Frank.firstname.lastname@example.org
CONTEXT: Higher consumption of fish and omega-3 fatty acids has been associated with a lower risk of coronary heart disease (CHD) in men, but limited data are available regarding women. OBJECTIVE: To examine the association between fish and long-chain omega-3 fatty acid consumption and risk of CHD in women. DESIGN, SETTING, AND PARTICIPANTS: Dietary consumption and follow-up data from 84 688 female nurses enrolled in the Nurses' Health Study, aged 34 to 59 years and free from cardiovascular disease and cancer at baseline in 1980, were compared from validated questionnaires completed in 1980, 1984, 1986, 1990, and 1994. MAIN OUTCOME MEASURES: Incident nonfatal myocardial infarction and CHD deaths. RESULTS: During 16 years of follow-up, there were 1513 incident cases of CHD (484 CHD deaths and 1029 nonfatal myocardial infarctions). Compared with women who rarely ate fish (<1 per month), those with a higher intake of fish had a lower risk of CHD. After adjustment for age, smoking, and other cardiovascular risk factors, the multivariable relative risks (RRs) of CHD were 0.79 (95% confidence interval [CI], 0.64-0.97) for fish consumption 1 to 3 times per month, 0.71 (95% CI, 0.58-0.87) for once per week, 0.69 (95% CI, 0.55-0.88) for 2 to 4 times per week, and 0.66 (95% CI, 0.50-0.89) for 5 or more times per week (P for trend =.001). Similarly, women with a higher intake of omega-3 fatty acids had a lower risk of CHD, with multivariable RRs of 1.0, 0.93, 0.78, 0.68, and 0.67 (P<.001 for trend) across quintiles of intake. For fish intake and omega-3 fatty acids, the inverse association appeared to be stronger for CHD deaths (multivariate RR for fish consumption 5 times per week, 0.55 [95% CI, 0.33-0.90] for CHD deaths vs 0.73 [0.51-1.04]) than for nonfatal myocardial infarction. CONCLUSION: Among women, higher consumption of fish and omega-3 fatty acids is associated with a lower risk of CHD, particularly CHD deaths.
PMID: 11939867 [PubMed - indexed for MEDLINE]
[viii] Poult Sci. 2000 Jul;79(7):971-4.
Enriched eggs as a source of N-3 polyunsaturated fatty acids for humans.
Lewis NM, Seburg S, Flanagan NL.
Department of Nutritional Sciences and Dietetics, University of Nebraska , Lincoln 68583-0806 , USA . email@example.com
Dietary intake of omega-3 fatty acids (n-3 PUFA) decreases the risk of heart disease, inhibits the growth of prostate and breast cancer, delays the loss of immunological functions, and is required for normal fetal brain and visual development . The US has not established a recommended daily intake for n-3 PUFA. However , Canada has established the Canadian Recommended Nutrient Intake (CRNI) at 0.5% of energy . Dietary sources of n-3 PUFA include fish, chicken, eggs, canola oil, and soybean oil. Food consumption studies in the US indicate that the majority of Americans do not meet the CRNI for n-3 PUFA. Mean n-3 PUFA consumption was 78% of the CRNI for Midwestern women during pregnancy. In Midwestern women at risk for breast cancer, the mean n-3 PUFA consumption is approximately 50% of the CRNI . Increased consumption of n-3 PUFA requires identification of a food source that the public would eat in sufficient amounts to meet recommended intake. N-3 PUFA-enriched eggs can be produced by modifying hens diets. When 70 g/kg of cod liver oil, canola oil, or linseed oil are added to a commercial control diet, the n-3 PUFA are increased from 1.2% of egg yolk fatty acids to 6.3, 4.6, and 7.8%, respectively . Feeding flaxseed increases linolenic acid in the egg yolk about 30-fold, and docosahexaenoic acid (DHA) increases nearly fourfold. When individuals are fed four n-3 PUFA-enriched eggs a day for 4 wk, plasma total cholesterol levels and low-density lipoprotein cholesterol (LDL-C) do not increase significantly. Plasma triglycerides (TG) are decreased by addition of n-3 PUFA-enriched eggs to the diet. N-3 PUFA may influence LDL particle size, causing a shift toward a less atherogenic particle. Blood platelet aggregation is significantly decreased in participants consuming n-3 PUFA-enriched eggs. Overall results of studies to date demonstrate positive effects and no negative effects from consumption of n-3-enriched eggs. Three n-3 PUFA-enriched eggs provide approximately the same amount of n-3 PUFA as one meal with fish. It is recommended that n-3 PUFA-enriched eggs be used as one source of n-3 PUFA to increase individual consumption to meet the current Canadian recommendations.