Once maligned for raising plasma cholesterol levels, eggs are gaining favor as an inexpensive dietary source of protein, antioxidants, vitamins and minerals and are now considered a safe addition to a healthy diet.
Diana DiMarco, PhD candidate in the Department of Nutritional Sciences, completed a clinical study on egg consumption involving thirty-seven healthy adults between the ages of eighteen and thirty, both male and female with varying diet and exercise habits. The study was funded through the Esperance Family Foundation and the Egg Nutrition Center.
“Our goal of the study was to look at a number of biomarkers for cardiovascular disease,” DiMarco says. “We wanted to get an overall picture of what was happening while eating these different numbers of eggs.”
The study began with a two-week wash-out period where participants did not consume eggs. After that, they were instructed to eat one egg per day for four weeks, two eggs per day for four weeks, and three eggs per day for four weeks. Blood was drawn at each interval and tested for HDL and LDL cholesterol, triglycerides, glucose, antioxidants lutein and zeaxanthin, free choline and TMAO (Trimethylamine-N-oxide), a metabolite derived from gut bacteria. Blood pressure was also monitored.
Egg consumption did not appear to raise total cholesterol levels. Plasma LDL cholesterol (known as the “bad” cholesterol) concentrations slightly decreased, and HDL cholesterol (“the good” cholesterol) concentrations increased. HDL is thought of as the good cholesterol because it helps to rid the body of excess cholesterol and is involved in antioxidant transportation. The ratio of LDL to HDL, which is also considered a predictor of heart disease, decreased as well. Blood pressure improved.
Other measured biomarkers were plasma concentration of both choline and TMAO. TMAO is thought to be a biomarker for cardiovascular disease while choline is an essential nutrient. In some instances, choline can be metabolized into TMA by gut bacteria and then into TMAO within the liver. In this study, egg consumption did not increase TMAO concentration.
“I think a general trend is that eggs are getting to be more favorable in the public eye,” DiMarco says. “The cholesterol controversy concerning eggs has been taken out of the dietary recommendations. Recently, the TMAO issue crept up, but with our study we didn’t see any effect on TMAO levels from eating eggs. This continues to support the idea that perhaps eggs have been unfairly vilified over the past few years.”
Working with DiMarco on this study was her faculty advisor, Maria-Luz Fernandez, professor of nutritional sciences, Christopher Blesso, assistant professor of nutritional sciences, as well as fellow graduate students in the Fernandez lab. Collaborating with DiMarco during the data analysis was Marie Caudill, professor in nutritional sciences at Cornell University, and Olga Malysheva, research support specialist at Cornell.
DiMarco will present their findings at the Experimental Biology Conference in Chicago, April 22-26. She will complete her PhD degree this May and hopes to find a summer internship toward her RD (Registered Dietitian) certification. Her long-term goal is a position in teaching.
In a continuation of DiMarco’s research, Fernandez is working with PhD student Bruno Lemos on a new project funded through the Egg Nutrition Center. In the study, they will further examine the connection between choline and increased TMAO levels. This study will compare what happens to plasma TMAO after consuming choline from eggs versus consuming choline from a dietary supplement. As mentioned before, choline can be converted to TMA by the gut bacteria in the large intestine, and then into TMAO by the liver.
“Our hypothesis is that you might have an increase in TMAO if you take choline as a supplement, but not when eating eggs,” says Fernandez. “This is because we think that for the choline in eggs to be converted into TMAO, it needs to reach the large intestine, but we think the choline that occurs in eggs will be absorbed in the small intestine, never to reach the large intestine.”