Among overweight or obese patients with prediabetes or type 2 diabetes, those who ate 12 eggs/week or more (high-egg diet) had similar blood levels of cardiovascular disease markers as those who ate fewer than 2 eggs/week (low-egg diet) in a year-long study.
"These findings suggest that it is safe for persons at high risk of [type 2 diabetes] and those with [type 2 diabetes] to include eggs, an acceptable and convenient food source, in their diet regularly," the researchers conclude.
The results, from the Diabetes and Egg (DIABEGG) study, by Nicholas R. Fuller, PhD, from the Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders at the University of Sydney, Australia, and colleagues, were published online May 7 in the American Journal of Clinical Nutrition.
Invited to comment, Jyrki K. Virtanen, PhD, adjunct professor of nutritional epidemiology at the University of Eastern Finland, Kuopio, who was not involved with the study, agrees.
This work isn't meant to imply "that people with diabetes (or any other people) should not worry about their blood cholesterol levels, it just shows that a rather high egg (and therefore cholesterol) intake did not have an adverse impact on blood cholesterol in this study," he told Medscape Medical News in an email.
In general, dietary cholesterol intake has a pretty small impact on serum cholesterol levels or most people, Virtanen explained, adding that dietary fat quality, for example, has a much greater impact.
The takeaway message, he says, is that "it is OK to include eggs in the diet, even if you have type 2 diabetes. Many people enjoy eating eggs, and eggs are used in many recipes and dishes, so it makes one's life easier if one doesn't have to severely restrict egg intake."
The ideal number of eggs per week for people to consume depends on genetics, overall health, and overall diet, he continued. According to most research, "one egg per day should be OK for most people, but like in the current study, even higher intake could be fine."
"And if we think about the environmental impact of food (as we should), eggs have one of the lowest impacts on greenhouse gas emissions among animal protein sources," he added.
However, another expert who has long been critical of egg marketing told Medscape Medical News this type of research is "propaganda" from the egg industry.
Reached by email, J. David Spence, MD, professor of neurology and clinical pharmacology at Western University and a researcher at the Stroke Prevention & Atherosclerosis Research Centre, in London, Ontario, did not specifically comment on this study.
But he reiterated his belief that there is no amount of egg yolk that is safe for people with diabetes, or at risk of cardiovascular disease, to eat. He did say, however, that egg whites are OK to consume.
Conflicting Research Findings, Guidelines
As previously reported, Fuller and colleagues presented partial findings from the DIABEGG study as a poster at the European Association for the Study of Diabetes 2014 Meeting.
They conducted the research because of conflicting research findings and differing national guidelines about egg consumption in diabetes.
In epidemiologic studies of people with type 2 diabetes (but not the general population), for example, higher egg intake has been associated with an increased risk of cardiovascular disease (CVD) and earlier mortality, Fuller and colleagues write.
But controlled studies in people with prediabetes or type 2 diabetes have shown predominantly favorable effects of higher egg intakes on cardiovascular and metabolic risk factors.
And to add to the confusion, different countries and societies have different recommendations. For example, in people with type 2 diabetes, the British Heart Foundation and Diabetes UK do not recommend limiting cholesterol or egg consumption, but the National Heart Foundation of Australia recommends a maximum of 6 eggs/week.
The American Diabetes Association used to recommend limiting total cholesterol consumption to 300 mg/day (one egg contains about 200 mg of cholesterol), but they recently removed this limit.
No Adverse Effects on CVD Markers in DIABEGG
In DIABEGG, 128 adults aged 18 years and older with type 2 diabetes or prediabetes and a body mass index (BMI) of at least 25 kg/m2 were randomized to a healthy weight-loss diet either high or low in eggs.
The diet emphasized replacing saturated fats (such as butter) with monounsaturated and polyunsaturated fats (such as avocado and olive oil).
Patients were a mean age of 60 years and had a mean BMI of 34 kg/m.2 About three quarters had type 2 diabetes and 54% were women.
Their mean baseline HDL-cholesterol (the primary outcome) was 1.3 mmol/L (approximately 50 mg/dL) and more than half (58%) were taking a cholesterol-lowering medication.
For the 3-month run-in, patients were instructed to maintain their weight. Those in the high-egg group were instructed to eat 2 eggs/day for breakfast, whereas the low-egg group were instructed to eat less than 2 eggs/week and match the protein intake of the high-egg group by consuming 10-g lean animal protein (meat, chicken, or fish) or other protein-rich alternatives, such as legumes and reduced-fat dairy products (also consumed at breakfast).
Eggs could be boiled or poached, but could also be fried if a polyunsaturated cooking oil, such as olive oil, was used.
Participants were provided with eggs or grocery vouchers and were encouraged to increase their steps to 10,000/day.
After the run-in, participants entered a 3-month active weight-loss phase, during which they met with a dietician once a month. They then entered a 6-month follow-up phase and were advised to continue eating the same number of eggs.
Participants were compliant with their egg intake: at 6 and 12 months, those in the high-egg group reported consuming a mean 12.2 and 10.5 eggs/week, respectively, and those in the low-egg group consumed 1.0 and 1.1 eggs/week, respectively.
Patients in both groups lost approximately 2 kg at the end of the 3-month active weight-loss phase and another 1 kg during the next 6 months.
From 3 to 12 months, participants in both groups had similar changes in lipids (HDL-cholesterol, LDL-cholesterol, total cholesterol, and apolipoprotein B), inflammatory markers (C-reactive protein, interleukin-6, and soluble E selectin), oxidative stress markers (F2-isoprostanes), and glycemic markers (glucose, HbA1c, adiponectin, and 1,5-anhydroglucitol).
Egg Industry Propaganda?
"This focus on fasting lipid levels and blood markers is a classic red herring — one of the pillars of the egg industry propaganda," says Spence.
Instead, what is important is that "eggs increase the risk of diabetes, and in people with diabetes they increase the risk of heart attacks," he maintains, noting that egg yolks are one of the most concentrated sources of cholesterol.
As part of his argument, he cites a Greek study in which an egg a day was associated with a five-fold increase in coronary risk in patients with diabetes (J Intern Med. 2006;259:583-591).
Spence adds that it's much harder to show the harm from eggs in the US diet as "only 0.1% of Americans eat a healthy diet."
Virtanen says it is "true that higher egg intake has been associated with a higher diabetes risk in general populations and with higher CVD risk in people with diabetes in some epidemiological studies," as Fuller and colleagues describe in their article.
But in a dose–response meta-analysis of prospective cohort studies that he coauthored (Br J Nutr. 2016;115:2212-2218), "the higher risk of diabetes is seen mainly in the epidemiological studies in the United States, and not in other countries," Virtanen pointed out.
In the United States, higher egg intake is associated with more smoking, less physical activity, and higher intake of processed red meat, which may partly explain the results, he added.
And in the prospective, population-based Kuopio Ischaemic Heart Disease Risk Factor (KIHD) study (Am J Clin Nutr. 2015;101:1088-1096), of which Virtanen was lead author, a higher egg intake was associated with a lower risk of new-onset diabetes in middle-aged and older men in Finland.
"While eggs themselves are high in dietary cholesterol — and people with type 2 diabetes tend to have higher levels of the 'bad' low-density lipoprotein (LDL) cholesterol — this [current] study supports existing research that shows consumption of eggs has little effect on the levels of cholesterol in the blood of the people eating them," Fuller explained in a statement by the University of Sydney.
Biochemical Chain From Egg Yolks Leads to Hardening of Arteries
Spence explained the biochemical process that he believes contributes to the adverse effects of eggs in patients with diabetes.
Eggs yolks are rich in phosphatidylcholine, which is converted by intestinal bacteria to trimethylamine, which is then oxidized in the liver to trimethylamine N-oxide (TMAO), "and TMAO is bad for the arteries," he asserts.
"TMAO is also produced from carnitine in meat (four times as much as in chicken), so egg yolks and red meat have a double whammy. They should not be consumed by people at risk of heart attack or stroke — which includes people with diabetes."
Although Virtanen agrees that "phosphatidylcholine in eggs is one of the major sources of TMAO production in the body," he stresses "there is a large variability in TMAO formation after egg intake between people, so some studies have observed an increase in TMAO after increased egg intake and some studies have not."
"It would have been interesting to see the effects on TMAO concentrations in the DIABEGG study," he notes.
Spence maintains that "eating egg yolks is not okay" for people with diabetes or prediabetes. "I recommend to my patients that they use egg whites, or what is more enjoyable, egg white-based substitutes," he told Medscape Medical News.
Fuller: "Eating Eggs as Part of a Healthy Diet Is OK"
However, Fuller counters that "despite differing advice around safe levels of egg consumption for people with prediabetes and type 2 diabetes, our research indicates people do not need to hold back from eating eggs if this is part of a healthy diet."
Moreover, "eggs are a source of protein and micronutrients that could support a range of health and dietary factors including helping to regulate the intake of fat and carbohydrate, eye and heart health, healthy blood vessels, and healthy pregnancies," he concludes.
The study was funded by the Australian Egg Corporation, which had no role in the study or manuscript. Fuller has received research grants for other clinical trials from Sanofi-Aventis, Novo Nordisk, Allergan, Roche, MSD, and GlaxoSmithKline. Disclosures for the other authors are listed in the article. Virtanen and Spence have reported no relevant financial relationships.
Am J Clin Nutr. Published online May 7, 2018. Abstract