Here’s an interesting study, dubbed the DIABEGG trial, in which a group of Australian researchers explored whether overweight people with Type 2 diabetes would benefit from eating more eggs to boost satiety and improve weight management. The only concern was, what would happen to their cholesterol levels?
Although the average hen’s egg contains around 200 milligrams of cholesterol, their total fat content isn’t high (5.2 grams) and is predominantly in the form of monounsaturated fats (51 percent) or polyunsaturated fats (16 percent) rather than the saturated fats, which are widely demonized (although steadily gaining admirers).
One hundred forty volunteers with a diagnosis of poor glucose tolerance (prediabetes) or Type 2 diabetes were recruited, with an average age of 60 years and an average BMI of 34 (obese). Half were randomly assigned to eat 12 eggs a week (2 for breakfast on six days out of seven) for three months.
The other half were asked to match the protein intake of the high-egg group by eating 10 grams of lean protein from meat, chicken, fish, legumes, or reduced-fat dairy products for breakfast, but to eat fewer than two eggs a week.
At the beginning of the study, there were no significant differences between the two groups in age, fasting glucose, glucose control (as measured by HbA1c), blood pressure, or total body fat, although those in the high-egg group weighed an average of 98 kilograms versus 93.3 kilograms for those in the low-egg group.
Both groups were instructed to maintain their body weight, which they successfully managed to do (gaining or losing less than 1 kilogram on average).
At the end of the study, there were no significant differences between the two groups in their levels of total cholesterol, “bad” LDL-cholesterol, “good” HDL-cholesterol, or triglycerides.
This was despite the fact that food-diary analysis showed those eating 12 eggs a week increased their total daily cholesterol intake by 281 milligrams, compared with a reduction of -36 milligrams cholesterol for those on the low-egg diet, giving an average difference between the two groups of 337 milligrams dietary cholesterol intake per day. But hang on.
Why Didn’t Their Lipids Change?
At first sight, these findings seem extraordinary. Eating 12 eggs a week didn’t raise blood cholesterol levels any more than a similar group eating fewer than two eggs a week. Really?
Much as I like eggs and would love to pounce on this wonderful finding with glee, the baseline total cholesterol levels of both groups were also extraordinarily good, almost too good to be true, in fact: total cholesterol 5 millimole/liter or less; LDL cholesterol 2.9 millimole/liter or less, HDL cholesterol 1.2 millimole/liter or greater and triglycerides not too shabby at 1.8 millimole/liter or lower, on average.
These are stunning baseline results, given that only 56 percent of those assigned to the high-egg group and 52 percent of those allocated to the low-egg group were taking a statin. I’ll say that again. Only 56 percent of those assigned to the high-egg group were taking a statin.
Statins are usually dished out like Smarties [candy] to people who are obese with Type 2 diabetes or prediabetes. If they’re not on a statin, yet have pretty perfect lipid profiles, what’s going on?
The most likely explanation is that almost half the 140 people in the DIABEGG trial happen to have inherited cholesterol-friendly genes. If you inherit “good” genes, the amount of LDL-cholesterol that’s synthesized by your liver reduces as your dietary intake of cholesterol increases.
If you inherit “bad” genes, on the other hand, this negative feedback mechanism malfunctions, so your liver keeps churning out cholesterol even though you get plenty in your diet and have plenty in your circulation.
As all these study volunteers were recruited from around Sydney, the capital of New South Wales, I wondered what average cholesterol levels are like in this part of the world. Imagine my surprise to find that cholesterol levels vary significantly from state to state in Australia and are, in fact, lowest in New South Wales (NSW, the last column in the table below).
So what we are left with is a group of people who are either taking a statin, or who have naturally good cholesterol control, for whom eating 12 eggs a week does not significantly affect their blood lipids.
Before I feel comfortable recommending that overweight or obese people with Type 2 diabetes can start to eat lots more eggs (whether or not they are on a statin), this study needs to be replicated in a group of volunteers who have naturally poor cholesterol control to see what happens—although I doubt such a study would gain ethical approval.
This is such a confusing area. What’s healthier? Eating more or fewer eggs, eating more or fewer carbohydrates, or eating more or less saturated fat? Even national guidelines vary widely.
The Australian National Heart Foundation currently recommends a maximum of six eggs per week for healthy people and those with Type 2 diabetes. U.S. guidelines recommend that people with Type 2 diabetes limit their dietary cholesterol intake to 300 milligrams per day (one egg contains around 200 milligrams of cholesterol) and no more than four eggs per week, while in the U.K., there is no suggested limit on the number of eggs consumed, and emphasis is placed instead on reducing dietary saturated fats.
I’m now more confused than when I started writing this article. Can anyone shed some light?
By Dr Sarah Brewer, originally published on www.drsarahbrewer.com. Twitter: @DrSarahB