High blood cholesterol, particularly high low-density lipoprotein (LDL) cholesterol, is a well-known risk factor for cardiovascular disease (CVD). What is less clear is whether cholesterol from foods plays a role in raising blood cholesterol levels and CVD risk.
Cholesterol occurs only in animal foods, like beef, poultry, pork, seafood, eggs and dairy products. In addition to cholesterol, animal foods often contain saturated fat, which is linked to increasing blood cholesterol levels. Thus it can be challenging to tease out the separate impact dietary cholesterol has on blood cholesterol and risk for disease.
Dietary Cholesterol Guidelines
The American Heart Association (AHA) recommends limiting dietary cholesterol to:
- Less than 300 milligrams per day for most people
- Less than 200 milligrams per day for people who have coronary heart disease, are at a high risk of cardio-vascular disease, or have an LDL cholesterol level of 100 mg/dL or more
Enter eggs. Eggs are unique in that they are high in dietary cholesterol (186 milligrams per egg, nearly all in the yolk), but not in saturated fat. This makes whole eggs or egg yolks ideal for investigating the effects of di-etary cholesterol on the body and disease risk. Indeed, the research on eggs is extensive but the results are varied.
The egg debate. Do eggs raise cholesterol? Yes and no. “Two-thirds of the population does not experience any rise in blood cholesterol, even after a challenge of three eggs per day for four weeks,” asserts Maria Luz Fernandez, MS, PhD, Professor of Nutrition, University of Connecticut and author of several papers examining egg consumption on blood cholesterol and CVD risk. Fernandez says “The people who do respond, one-third of the population, raise both LDL (“bad” cholesterol) and HDL (“good” cholesterol). Thus the ratio of LDL to HDL ratio is maintained, which is a key marker for CVD risk.” She explains that the LDL/HDL ratio is an expression of how much “bad” (LDL) cholesterol you have compared to “good” (HDL) cholesterol. Since HDL carries cholesterol to the liver for elimination, effectively neutralizing it, as long as the ratio is maintained it doesn’t raise risk for heart disease.
What is Cholesterol?
Cholesterol is a sterol, one of three classes of lipids. Triglycerides (fats and oils) and phospholipids (e.g. lec-ithin) are the two other lipid classes. Cholesterol is a waxy substance manufactured by the liver and other or-gans. Cholesterol has many functions in the body; it serves as an important part of every cell as a component of cell membrane structure, and is a precursor for vitamin D, steroid hormones, and bile acids, which are necessary for the digestion of triglycerides. The bad side of cholesterol is that too much of it in your blood raises the risk for CVD. Cholesterol can collect in your arteries, and along with other substances, form plaques (A). Plaques narrow the arteries and cause them to be inflexible, increasing your risk for heart attacks and stroke.
The story doesn’t end there, says stroke researcher David Spence, MD, Professor of Neurology and Clinical Pharmacology at Western University, London Canada. He declares, “What matters more is that about four hours after a high cholesterol meal you have inflammation of the arteries, almost a 40 percent in-crease in oxidized LDL, endothelial dysfunction and increased oxidative stress.” These factors do not bode well for cardiovascular health, or consuming eggs.
Still, the egg debate continues. In 2013, both the American Journal of Clinical Nutrition (AJCN) and the British Medical Journal (BMJ) reported no elevated risk of CVD from egg intake in the general population. However, an analysis in Atherosclerosis in 2013 did, concluding that the more eggs consumed per week, the higher the CVD risk.
The cholesterol-diabetes link. There is more agreement regarding a connection between eggs and diabetes. The AJCN, BMJ and Atherosclerosis papers all concluded egg consumption raised CVD risk in people with diabetes. What’s more, both the AJCN and Atherosclerosis studies reported that more than one egg a day actually increased the risk for developing type 2 diabetes in the general population.
The bottom line. Dietary cholesterol from any food source may not be innocuous. Play it safe by sticking with the American Heart Association’s guidelines (see Dietary Cholesterol Guidelines). If you like eggs, it’s best to limit them to one a day, especially if you are at risk for vascular disease. You also may want to try an egg white substitute. If you do eat a whole egg or other cholesterol-containing foods, choose mainly plant-based foods for your other meals to stay within the guidelines.
— Andrea N. Giancoli, MPH, RD