04 December 2012
Type 2 diabetes
Recruitment site location(s) (State)
New South Wales, Victoria
Anticipated date of first participant enrolment
05 January 2013
Ethics application status
T2DM is the fastest growing chronic illness in Australia, with over 3.2 million people estimated to have diabetes and pre-diabetes, and a further 275 individuals being diagnosed with diabetes every day. As diabetes is the 6th leading cause of death in Australia, interventions to manage this condition and its complications should be a priority for Australian society.
Despite many theoretical advantages of eggs in T2DM, there is a general paucity of good quality prospective data on the effects of high egg consumption in this group. There has only been one short duration clinical investigation in people with T2DM (Pearce KL, Clifton PM, Noakes M. Egg consumption as part of an energy-restricted high –protein diet improves blood lipid and blood glucose profiles in individuals with type 2 diabetes. Br J Nutr, 2011, 105: 584-592). After 12 weeks, participants with T2DM on a high cholesterol, reduced energy diet (2 eggs/day) lost the same amount of weight and had similar improvements in lipids, blood pressure and glycaemic control as those on an isoenergetic low cholesterol diet. The major limitations of this study were its short duration (12 weeks), the null finding in the primary outcome for which the study was powered (10% difference in the change in LDL-C between groups), and participants being prescribed a reduced energy diet which could be a confounding factor.
Eggs contain a number of important nutrients that may reduce the risk of cardiovascular disease including folate, long chain omega 3 fatty acids, and arginine (a precursor for nitric oxide). They have also been shown to improve HDL-C (Pearce KL, Clifton PM, Noakes M. Egg consumption as part of an energy-restricted high–protein diet improves blood lipid and blood glucose profiles in individuals with type 2 diabetes. Br J Nutr, 2011, 105: 584-592; Mutungi G, Ratliff, J, Puglisi, M et al. Dietary cholesterol from eggs increases plasma HDL cholesterol in overweight men consuming a carbohydrate-restricted diet. J Nutr 2008; 138: 272-276). Improvements in HDL-C are known to reduce cardiovascular risk (Barter P, Gotto AM, LaRosa JC et al. HDL cholesterol, very low levels of LDL cholesterol, and cardiovascular events, N Engl J Med 2007; 357: 1301-1310). Eggs are a nutrient-dense food, yet are not high in energy. Despite being rich in cholesterol, the amount of total fat and saturated fat in eggs is not high and the fat in eggs is predominantly unsaturated (44% monounsaturated; 11% polyunsaturated).
In addition to potential beneficial effects of eggs on circulating lipid levels, higher protein eating patterns may have benefits for weight loss by inducing increased satiety and enhancing metabolic rate and lipid metabolism. Thus eggs are unlikely to be detrimental to people with T2DM and may be beneficial. Despite this, there is a negative perception toward egg consumption in people with diabetes. This notion largely results from world-wide press releases that have followed the publication of a number of epidemiological studies indicating that a high egg consumption, though not associated with adverse cardiovascular outcomes in the general population, may be associated with worse outcomes in people with T2DM (Hu FB, Stampfer MJ, Rimm EB et al. A prospective study of egg consumption and risk of cardiovascular disease in men and women, JAMA 1999; 281: 1387-94; Djousse L & Gaziano JM. Egg consumption in relation to cardiovascular disease and mortality: the Physicians’ Health Study. Am J Clin Nutr 2008; 87: 964-9). While epidemiological studies may provide insight into possible associations, they do not show causal relationships and findings are often affected by many confounding, and often hidden, factors. For example, at the time that these studies were being conducted, a public health campaign was advising people to limit their cholesterol intake, including their consumption of eggs. Therefore, individuals that were consuming > 7 eggs per week at this time may have been less likely to follow healthy dietary and lifestyle advice in general. It would be impossible to control for these factors from the available data. Furthermore the theoretical increase in cardiac risk from the cholesterol contained in eggs is likely to be minimal when compared to other cardiovascular risk factors including saturated fat intake, lack of physical activity, smoking, hypertension and obesity.
To address the limitations of previously conducted research, this prospective, randomised controlled study will include both an active intervention (initial 3 month weight maintenance period followed by a 3 month weight loss period) and follow-up period (6 months) to determine the potential health benefits of a high egg diet in pre-diabetes and those with T2DM. Both groups will be stratified during the randomisation process according to medication usage. The palatability and acceptability of both the diets will be examined throughout the 12 month study.