The health effects of eggs have been debated for years. They were once feared to increase risk of heart disease by raising cholesterol levels. However, a 30-year study published most recently by the British Medical Journal suggested moderate egg consumption (one a day) was not associated with increased risk of cardiovascular disease, which can lead to heart attack or stroke.
The association between egg consumption and diabetes, meanwhile, remains inconclusive after an observational study linked higher egg consumption with increased risk of diabetes in Chinese adults.
The new research comes from the University of South Australia in partnership with the China Medical University, and Qatar University. The longitudinal study (1991 to 2009) was the first to assess egg consumption in a large sample of Chinese adults.
It found that people who regularly consumed one or more eggs per day (equivalent to 50 grams) increased their risk of diabetes by 60%.
UniSA's Dr Ming Li said the rise of diabetes was a growing concern in China where changes to the traditional Chinese diet are impacting health.
"Diet is a known and modifiable factor that contributes to the onset Type 2 diabetes, so understanding the range of dietary factors that might impact the growing prevalence of the disease is important," Dr Li said.
"Over the past few decades China has undergone a substantial nutritional transition that's seen many people move away from a traditional diet comprising grains and vegetables, to a more processed diet that includes greater amounts of meat, snacks and energy-dense food.
"At the same time, egg consumption has also been steadily increasing; from 1991 to 2009, the number of people eating eggs in China nearly doubled.”
The study comprised 8,545 adults (average age 50 years). Between the years 1991-2009, researchers found that the average daily consumption of eggs increased continuously from 16 grams in 1991-93, to 26 grams in 2000-04, and 31 grams in 2009.
International egg consumption across the same period was 33.65 g/day in Europe; 28.43 g/day in America; 20.56 g/day in Asia; 18.20 g/day in Oceania (including Australia); 5.93 g/day in Africa; and 21.45 g/day in the world.
"While the association between eating eggs and diabetes is often debated, this study has aimed to assess people's long-term egg consumption of eggs and their risk of developing diabetes, as determined by fasting blood glucose.
"What we discovered was that higher long-term egg consumption (greater than 38 grams per day) increased the risk of diabetes among Chinese adults by approximately 25 per cent.
"Furthermore, adults who regularly ate a lot of eggs (over 50 grams, or equivalent to one egg, per day) had an increased risk of diabetes by 60 per cent."
The effect was also more pronounced in women than in men.
Dr Li said that while these results suggest that higher egg consumption is positively associated with the risk of diabetes in Chinese adults, more research was needed to explore causal relationships.
"To beat diabetes, a multi-faceted approach is needed that not only encompasses research, but also a clear set of guidelines to help inform and guide the public. This study is one step towards that long-term goal."
‘Eggs are a good source of protein and can form part of a healthy diet’
The British Nutrition Foundation pointed out that, as an observational study, it did not prove any link between eggs and diabetes.
“The study suggests that an association was found between higher egg consumption and risk of diabetes in Chinese adults, however this observation does not prove that it was the increase in egg consumption over time specifically that was responsible for the increase in diabetes risk in this population,” a BNF spokesperson told this publication.
Other studies that have investigated this potential link have found mixed results, which may be due to other risk factors for diabetes in the populations studied or different dietary patterns seen in people who tend to eat more eggs.
The BNF spokesperson added: “Eggs are a good source of protein, as well as providing many nutrients including vitamin D, folate, iodine and omega 3s. Current UK government advice states that there is no recommended limit on how many eggs people should eat, so eggs can be included as part of a healthy, balanced diet and only need to be limited if recommended to by a GP or dietitian.”
'Misleading and disingenuous'
The British Egg Information Service went further. It complained that the reported conclusions of this study did not accurately represent the research findings and were therefore misleading. Dr Juliet Gray, a registered nutritionist, told us: “It seems clear from the study results, and indeed the authors discuss the observation, that those people with the highest egg consumption had poorer diets, eating eggs alongside 'fast foods' and 'deep fried foods' - as well as having higher BMI, hypertension, blood lipids and therefore, not surprisingly, higher rates of diabetes. It seems disingenuous not to acknowledge this in the abstract.
"In one of the models analysed there is actually an increased risk of diabetes with decreasing egg consumption, but the authors quote selectively from a separate 'sensitivity' analysis based on the group with highest compliance who attended all rounds of measurement between 1991 and 2009.
"Also absent from the abstract was the observation that the results for women were statistically significant but there was no statistical significance between quartile of egg consumption and diabetes risk in men. There is limited discussion of this and the implication is that the conclusions pertain to all adults.”
Wang, Y., Li, M. and Zumin, S. (2020) 'Higher egg consumption associated with increased risk of diabetes in Chinese adults - China Health and Nutrition Survey' in British Journal of Nutrition.