In 2016, the long-standing limit on cholesterol intake was lifted with the release of the 2015-2020 Dietary Guidelines for Americans, a decision based on years of research suggesting the connection between dietary and plasma cholesterol is minimal. This was welcome news for egg-enthusiasts everywhere, but came with one caveat: a compound called trimethylamine-N-oxide (TMAO) that appears to increase risk for heart disease. TMAO is a byproduct of choline, an important nutrient of which eggs are an excellent source. The prevailing hypothesis is that choline-containing foods, such as eggs, may elevate plasma TMAO. The good news is that its not quite so straightforward.
Most of the choline found in eggs isnt free, but rather in a bound form that changes how the nutrient is digested and absorbed. A recent study by Miller, et al. found that only 14% of choline from eggs is converted to TMAO. Furthermore, the body is efficient at excreting TMAO, meaning the compound doesnt accumulate in the bloodstream.
To test the effects of regular egg intake on plasma TMAO and other heart disease risk factors, young healthy adults consumed 1, 2, and 3 eggs/day for 4 weeks each. Egg intake increased HDL good cholesterol but did not raise LDL bad cholesterol, meaning that the LDL/HDL ratio an important predictor of heart disease risk went down. In addition to transporting cholesterol, LDL and HDL have other important functions which were improved by egg intake.
But, most relevant to the current controversy, TMAO did not increase. That eggs provide choline without increasing fasting plasma TMAO is especially important in light of a recent survey showing that nearly 90% of Americans do not meet recommendations for choline consumption. Choline is an essential nutrient and two eggs provide approximately 50% of the daily recommendation. Consuming up to 3 eggs/day appears to be an effective strategy for young, healthy adults to increase choline intake without elevating their risk for heart disease.
Diana M. DiMarco, MS is a recipient of the Egg Nutrition Center Young Investigator Award.
References
Carolyn A Miller, Karen D Corbin, Kerry-Ann da Costa, Shucha Zhang, Xueqing Zhao, Joseph A Galanko, Tondra Blevins, Brian J Bennett, Annalouise OConnor, and Steven Zeisel (2014) Effect of egg ingestion on trimethylamine-N-oxide production in humans: a randomized, controlled, dose-response study. American Journal of Clinical Nutrition, 100:3, 778-786, DOI: 10.3945/ajcn.114.087692
Diana M DiMarco, Amanda Missimer, Ana Gabriela Murillo, Bruno S Lemos, Olga V Malysheva, Marie A Caudill, Christopher N Blesso, and Maria Luz Fernandez (2017) Intake of up to 3 Eggs/Day Increases HDL Cholesterol and Plasma Choline while Plasma Trimethylamine-N-oxide is Unchanged in a Healthy Population. Lipids, DOI: 10.1007/s11745-017-4230-9
Diana M DiMarco, Gregory H Norris, Courtney L Millar, Christopher N Blesso, and Maria Luz Fernandez (2017) Intake of up to 3 Eggs per Day Is Associated with Changes in HDL Function and Increased Plasma Antioxidants in Healthy, Young Adults. Journal of Nutrition, DOI: 10.3945/jn.116.241877
Taylor C. Wallace & Victor L. Fulgoni III (2016) Assessment of Total Choline Intakes in the United States. Journal of the American College of Nutrition, 35:2, 108-112, DOI: 10.1080/07315724.2015.1080127