Cardio­metabolic Health

Cardiometabolic health is a relatively new term that encompasses cardiovascular and metabolic diseases, including type 2 diabetes and metabolic syndrome. Collectively, such conditions are the leading cause of preventable death worldwide. They all share similar risk factors (e.g., overweight/obesity, elevated blood pressure) which can be modified by diet and lifestyle choices. The available evidence indicates that eggs, when consumed as part of an overall healthy diet pattern, do not affect risk factors for cardiometabolic disease. Recent recommendations from the American Heart Association, American College of Cardiology and American Diabetes Association do not limit egg or cholesterol intake, a change from earlier guidance from these organizations. In fact, several global health organizations, including Health Canada, the Canadian Heart and Stroke Foundation, the Australian Heart Foundation and the Irish Heart Foundation, promote eggs as part of a heart-healthy diet.

Given the public health significance of understanding cardiometabolic diseases, research on risk reduction remains an active area of pursuit. For example:

  • A randomized controlled study in people with metabolic syndrome showed that those consuming three whole eggs per day as part of a reduced carbohydrate diet experienced favorable changes in HDL-cholesterol, insulin sensitivity, and other aspects of the lipoprotein lipid profile
  • A randomized controlled weight loss trial in people with diagnosed type 2 diabetes showed improved lipid and glucose markers following consumption of 2 eggs per day for 12 weeks.
  • An egg-based breakfast, rich in protein (35% energy; 26.1 g egg protein), promoted glycemic control in people with type 2 diabetes and pre-diabetes relative to a high-carbohydrate breakfast.

Eggs and Heart Disease: New study in line with broader science

A new study published last week in the American Heart Association journal Circulation adds more data to the mix on egg consumption and risk for heart disease1. Recall just a few weeks ago, a study published in the Journal of the American Medical Association (JAMA) made headlines when it seemed to reverse the course of the latest dietary recommendations to say that, once again, eggs and dietary cholesterol were linked with increased heart disease risk2. Now, just a few weeks later a new study says exactly the opposite.

In the new study, researchers from Oxford University in the U.K. analyzed data from over 400,000 men and women in Europe over an average follow up of 12 years. The authors reported a small but statistically significant decrease in risk for ischemic heart disease with every 20 gram increment of egg intake (about ½ an egg per day). The researchers also reported similar favorable results for yogurt and cheese consumption, while consumption of red and processed meats was associated with increased risk for heart disease.

Does this mean the science on eggs has changed yet again, just within a matter of weeks? No, it doesn’t. What it does mean is that the science never actually changed with the publication of the study in JAMA. As with any study, it is important to not view it in isolation, but rather in the broader context of the total scientific literature. This is particularly true with studies that are observational in nature, because in this type of research there are often outlier studies that deviate from the clear majority.

Furthermore, if you read the details of the new study the authors rightly pointed out that, as with any new observational study, there are several important factors to consider when interpreting these results:

  • The beneficial associations eggs and yogurt may be influenced by reverse causation bias.
  • There will always be residual confounding in observational studies that cannot be eliminated; even though the investigators statistically adjusted for many potential confounders including lifestyle factors.
  • The results may not be generalizable to populations outside this European cohort.
  • Associations with eggs and yogurt were no longer significant after excluding the first 4 years of follow-up.

Importantly, these are factors that should be considered in any observational study, whether the results are favorable or unfavorable to a dietary or lifestyle factor.

That said, these latest findings published in Circulation are more in line with previous meta-analyses of observational cohorts that reported either no relationship with egg consumption and cardiovascular risk3,4 or small decreases in cardiovascular risk5. Given all the caveats and confounding factors that are involved in observational studies, consistency across many studies over time is important.

It’s easy to get wrapped up in the day to day headlines from the next big study, and view the latest study as the next “game changer”. But the truth is science doesn’t change all that quickly, especially nutrition science. Many studies over the course of years or even decades are needed to achieve consensus. This is in fact what happened when the 2015 Dietary Guidelines for Americans no longer listed dietary cholesterol as a nutrient of concern. The evidence required to do so involved 16 studies over the course of many years3.

Lastly, as these studies are all observational in nature it is important to remember that we cannot infer a cause and effect relationship, no matter if the result is favorable or unfavorable to heart disease risk.  Therefore, it is important to view these results in the context of existing randomized controlled trials that consistently show egg intake does not negatively impact cardiovascular disease risk factors, and in some cases, has shown to improve risk factors such as HDL, or “good” cholesterol6.

References

  1. Key et al. Consumption of Meat, Fish, Dairy Products, Eggs and Risk of Ischemic Heart Disease: A Prospective Study of 7198 Incident Cases Among 409,885 Participants in the Pan-European EPIC Cohort. Circulation. 2019 Apr 22. [Epub ahead of print]
  2. Zhong et al. Associations of dietary cholesterol or egg consumption with incident cardiovascular disease and mortality. JAMA. 2019;321(11):1081-1095.
  3. Shin JY, Xun P, Nakamura Y, He K. Egg consumption in relation to risk of cardiovascular disease and diabetes: a systematic review and meta-analysis. Am J Clin Nutr. 2013 Jul;98(1):146-59.
  4. Rong Y, Chen L, Zhu T, Song Y, Yu M, Shan Z, Sands A, Hu FB, Liu L. Egg consumption and risk of coronary heart disease and stroke: dose-response meta-analysis of prospective cohort studies. BMJ. 2013 Jan 7;346:e8539.
  5. Alexander DD, et. al. Meta-analysis of egg consumption and risk of coronary heart disease and stroke. J Am Coll Nutr. 2016. 6:1-13.
  6. Blesso CN, Fernandez ML. Dietary Cholesterol, Serum Lipids, and Heart Disease: Are Eggs Working for or Against You? Nutrients. 2018 Mar 29;10(4). pii: E426. doi: 10.3390/nu10040426. Review.

Eggs and Cholesterol: New study, old story

A new study1 published in the Journal of the American Medical Association examining the relationship between dietary cholesterol and egg consumption with regard to cardiovascular disease risk provides interesting new data to consider as part of the broader context of the scientific literature in this area.

The authors report:

  • Small but statistically significant increases in cardiovascular risk with dietary cholesterol and egg consumption in six U.S.-based cohorts totaling over 29,000 participants.
  • These findings contrast with previous meta-analyses2,3 of observational cohorts not included in the present study that reported no relationship with egg consumption and cardiovascular risk in cohorts totaling almost 350,000 participants.
  • Furthermore, additional studies have shown small but statistically significant favorable relationships with egg consumption and cardiovascular risk in non-U.S. cohorts4,5, while randomized controlled trials consistently show egg intake does not negatively impact cardiovascular disease risk factors6.

The inconsistency of this new study with that of other recent studies demonstrates the importance of additional research to further explore this area, including the need to understand the unique contribution of eggs as part of healthy eating patterns set forth in the Dietary Guidelines for Americans.

The fact that studies outside the U.S. appear to show favorable relationships with egg intake and cardiovascular risk may speak to the importance of what other foods are consumed with eggs as part of the overall diet pattern, as recent research has demonstrated the importance of separating eggs from other foods to understand their independent impact on health outcomes7.

References

  1. Zhong et al. Associations of dietary cholesterol or egg consumption with incident cardiovascular disease and mortality. JAMA. 2019;321(11):1081-1095.
  2. Shin JY, Xun P, Nakamura Y, He K. Egg consumption in relation to risk of cardiovascular disease and diabetes: a systematic review and meta-analysis. Am J Clin Nutr. 2013 Jul;98(1):146-59.
  3. Rong Y, Chen L, Zhu T, Song Y, Yu M, Shan Z, Sands A, Hu FB, Liu L. Egg consumption and risk of coronary heart disease and stroke: dose-response meta-analysis of prospective cohort studies. BMJ. 2013 Jan 7;346:e8539.
  4. Qin C, Lv J, Guo Y, Bian Z, Si J, Yang L, Chen Y, Zhou Y, Zhang H, Liu J, Chen J, Chen Z, Yu C, Li L; China Kadoorie Biobank Collaborative Group. Associations of egg consumption with cardiovascular disease in a cohort study of 0.5 million Chinese adults. Heart. 2018 Nov;104(21):1756-1763.
  5. Virtanen JK, Mursu J, Virtanen HE, Fogelholm M, Salonen JT, Koskinen TT, Voutilainen S, Tuomainen TP. Associations of egg and cholesterol intakes with carotid intima-media thickness and risk of incident coronary artery disease according to apolipoprotein E phenotype in men: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J Clin Nutr. 2016 Mar;103(3):895-901.
  6. Blesso CN, Fernandez ML. Dietary Cholesterol, Serum Lipids, and Heart Disease: Are Eggs Working for or Against You? Nutrients. 2018 Mar 29;10(4). pii: E426. doi: 10.3390/nu10040426. Review.
  7. Sabaté J, Burkholder-Cooley NM, Segovia-Siapco G, Oda K, Wells B, Orlich MJ, Fraser GE. Unscrambling the relations of egg and meat consumption with type 2 diabetes risk. Am J Clin Nutr. 2018 Nov 1;108(5):1121-1128.

Daily Consumption of Eggs Increase Plasma Choline Without Affecting Risk for Heart Disease in Healthy Individuals

Featured article in the March, 2019 Issue of Nutrition Research Update; written by Bruno S. Lemos, PhD

Currently one in every four deaths in the United States is from cardiovascular disease (CVD)1. The major cause of CVD is atherosclerosis due to cholesterol accumulation in the arterial wall, building up to form a plaque that upon rupturing, can lead to major cardiovascular events such as stroke, heart attack and sudden death2. With that, consumption of cholesterol-rich foods have historically been a concern to the American population in regards to association with CVD risk. Continue reading “Daily Consumption of Eggs Increase Plasma Choline Without Affecting Risk for Heart Disease in Healthy Individuals”

Egg Metabolites Lower Type 2 Diabetes Risk: Insights into a Potential Mechanism

New egg nutrition research was making the headlines once again recently with the news of a new study that showed consumption of one egg every day is associated with a blood metabolite profile that would indicate a lower risk of type 2 diabetes.

The study1, published in the journal Molecular Nutrition and Food Research, examined 2,682 men aged 42-60 years of age as part of the Kuopio Ischemic Heart Disease (KIHD) Risk Factor Study in Finland. Dietary intakes were assessed with 4-day food records at baseline while type 2 diabetes incidence was assessed at 4, 11, and 20 years. Researchers compared the metabolic profile of individuals with higher egg intake – about one egg per day – to the metabolic profile of those with lower egg intake – about two eggs per week on average. The authors then took this information and looked for any relationships between those who developed type 2 diabetes or those who otherwise remained healthy during a follow-up period of almost 20 years. Continue reading “Egg Metabolites Lower Type 2 Diabetes Risk: Insights into a Potential Mechanism”

Eggs, Diabetes, and the Current Scientific Evidence

The Dietary Guidelines for Americans no longer provide a limit for dietary cholesterol for healthy people,1  however, some questions remain about the cardiovascular impact in people with diabetes or impaired fasting glucose.  This Nutrition Research Update highlights new evidence that supports eggs can be included in a healthy dietary pattern without adverse cardiovascular effects linked to diabetes, and in some cases, can be linked to beneficial outcomes. Continue reading “Eggs, Diabetes, and the Current Scientific Evidence”