An interesting study, dubbed the DIABEGG trial, 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 – would their cholesterol levels climb through the roof?
Although an average hen’s egg contains around 200mg cholesterol, their total fat content isn’t high (5.2 g) and is predominantly in the form of monounsaturated fats (51%) or polyunsaturated fats (16%) rather than the saturated fats which are widely demonised (although steadily gaining admirers).
The DIABEGG study involved 140 Australians, with an average age of 60 and an average BMI of 34 (obese), who also had poor glucose tolerance (prediabetes) or type 2 diabetes. Half were randomly assigned to eat 12 eggs a week (two for breakfast on six days out of seven) for 3 months while the other half were asked to match the protein intake of the high egg group by eating 10g lean protein from meat, chicken, fish, legumes or reduced-fat dairy products for breakfast but to eat less than 2 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 98kg versus 93.3kg 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 1kg 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 281mg, compared with a reduction of -36mg cholesterol for those on the low-egg diet, giving an average difference between the two groups of 337mg dietary cholesterol intake per day.
But wait a minute …
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 less than two eggs a week. Really?
Much as I like eggs, and would love to pounce on this fabulous 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 mmol/L or less; LDL cholesterol 2.9 mmol/L or less, HDL cholesterol 1.2 mmol/L or greater and triglycerides not too shabby at 1.8 mmol/L or lower, on average.
Source: Fuller NR et al. Am J Clin Nutr. 2015 Apr;101(4):705-13.
These are stunning baseline results, given that only 56% of those assigned to the high-egg group and 52% of those allocated to the low egg group were taking a statin. I’ll say that again. Only 56% of those assigned to the high-egg group were taking a statin. Statins are usually dished out like Smarties 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 synthesised 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 continues churning out cholesterol even though you get plenty in your diet, and have plenty in your circulation.
Maybe this part of Australia is different
As all these study volunteers were recruited from around Sydney, 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).
Source: Carrington M & Stewart S, 2010. Baker IDI Heart & Diabetes Institute, Melbourne, Australia.
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.
How many eggs per week?
Before I feel comfortable recommending that overweight or obese people with type 2 diabetes can start eating a lot 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 easy ethical approval.
This is such a confusing area relating to type 2 diabetes. What’s more healthy? Eating more or fewer eggs, eating more or less carbohydrates or eating more or less saturated fat? Even national guidelines vary widely.
The Australian National Heart Foundation currently recommends a maximum of 6 eggs per week for healthy people and those with type 2 diabetes; US guidelines recommend that people with type 2 diabetes limit their dietary cholesterol intake to 300 mg/day (one egg contains around 200 mg cholesterol) and no more than 4 eggs per week, while in the UK, there is no suggested limit on the number of eggs consumed and emphasis is placed instead on reducing dietary saturated fats.
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