Here we go again. There's another study about eggs that might make some of you swap sunny-side up for a whites-only omelette.
The good news: Eating an egg a day – yolk included – did not increase the risk of cardiovascular disease in healthy people. The bad news: Egg eaters were more likely to develop type 2 diabetes. And among people who already had diabetes, an egg-a-day habit substantially upped the likelihood of a heart attack or stroke.
Eggs have long been vilified for their high cholesterol content. One large egg has 183 milligrams of cholesterol, almost an entire day's worth (200 milligrams) for someone with heart disease, diabetes or high blood cholesterol. Healthy people are advised to limit their daily cholesterol intake to 300 milligrams.
Although high blood cholesterol is an established risk factor for a heart attack and stroke, the link between cholesterol in foods and cardiovascular disease remains unclear. Most studies have found that dietary cholesterol has little, if any, impact on blood-cholesterol levels.
The new report, published online in the American Journal of Clinical Nutrition, combined the results of 16 studies, lasting seven to 20 years, which included participants ranging in number from 1,600 to 90,735.
The researchers found that eating one or more eggs a day did not increase the risk of heart disease or stroke among healthy people. It did, however, increase the odds of developing type 2 diabetes, a major risk factor for heart disease and stroke. Participants who ate at least one egg each day were 42 per cent more likely to develop type 2 diabetes compared with people who never ate eggs or ate less than one per week.
When the researchers analyzed studies conducted in people with diabetes, they found that daily egg eaters – versus those who did not eat eggs or ate less than one per week – had a 69-per-cent increased risk of cardiovascular disease.
While eggs may have little effect on your fasting blood-cholesterol level, that may not be the case for your "after-meal", or postprandial, blood cholesterol. (Fasting blood cholesterol is measured after consuming no food or drinks, with the exception of water, for nine to 12 hours.)
There is mounting evidence that, depending on what you eat, postprandial blood fats can damage blood vessels and promote atherosclerosis (hardening and narrowing of the arteries). Small studies have shown that eating a cholesterol-rich meal can enhance the blood-cholesterol-raising effects of saturated (animal) fat and increase the chance that your LDL (bad) blood cholesterol becomes oxidized. Once oxidized, LDL cholesterol can cause inflammation in blood vessels. These harmful "after-meal" changes can persist for at least four hours after eating.
Postprandial impairments to blood fats appear to be more frequent in people with diabetes, which may help to explain the higher risk of cardiovascular disease associated with diabetes. There is also speculation that individuals with diabetes absorb higher amounts of cholesterol from foods. As well, animal studies suggest that high cholesterol intakes impair the pancreas's ability to release insulin, the hormone that removes excess sugar from the bloodstream.
Eggs have not been getting good press lately, that's for sure. In 2012, Canadian researchers likened blood-vessel damage associated with eating egg yolks to cigarette smoking. While the study – widely picked up by the media – found increasing carotid artery plaque as more eggs were eaten, it did not prove that eating eggs caused this.
It also did not account for physical inactivity and other dietary factors that could promote plaque build-up. (The carotid arteries supply blood to your brain and head; a build-up of fatty plaque can impede blood flow and increase the risk of stroke.)
More recently, a report published in April in The New England Journal of Medicine found that eating two eggs a day increased blood levels of TMAO (trimethylamine-N-oxide), a compound linked to a greater risk of heart disease. Bacteria in the digestive tract make TMAO from choline, a B vitamin-like compound plentiful in egg yolks.
The researchers did not say choline should be avoided – a certain amount is essential to health – but rather that excessive intakes should be avoided.
So what are we to make of all this? Are eggs off the menu? In my opinion, people at high risk for cardiovascular disease – e.g. people with diabetes, high cholesterol, and/or hypertension and smokers – should definitely limit their intake of egg yolks, and some experts advise avoidance.
Instead of eating a two-egg omelette with 266 milligrams of cholesterol, have a cholesterol-free white-only omelette for a good source of protein, riboflavin (a B vitamin) and selenium. Try a cholesterol-free egg product sold in the egg case at grocery stores.
Keep in mind that there are variables we do not yet know. It's possible that consuming antioxidant-rich foods (e.g. berries, citrus fruit, red peppers, spinach, green tea) or anti-inflammatory foods (e.g. salmon, chia seeds, ground flax, walnuts) with an egg could mitigate the harmful postprandial blood fat effects.
But most of all, let's not forget that preventing cardiovascular disease is about a whole lot more that cutting back on egg yolks. Limiting refined (white) starchy foods and added sugars, reducing saturated and trans fats, emphasizing monounsaturated fats (e.g. olive oil, avocado, almonds), increasing omega-3 fats from fish oil, limiting sodium intake, getting regular exercise and maintaining a healthy weight are key strategies to guard against heart disease and stroke.
Leslie Beck, a registered dietitian, is the national director of nutrition at BodyScience Medical. She can be seen Thursdays at noon on CTV News Channel's Direct. Lesliebeck.com