The nutritional properties and health benefits of e ggs

.

Opinions on the role of eggs in the diet have changed several times over the past few decades. From 1957 the Egg Marketing Board successfu lly marketed eggs, proposing that an egg for breakfast was a good source of protein and “the best way to start the day” (Guter and Low, 2008). By the 1960 s, egg consumption peaked to nearly 5 eggs per person per week (National Food Surv ey, 2001). However, attention was then drawn to the cholesterol content of eggs, with research studies suggesting that cholesterol-rich foods may elevate blood cholesterol and, hence, increase the risk of coronary heart disease (CHD) (Kannel et al., 1969). More recently, experts have acknowledged that such conclusions a re unfounded because previous studies on eggs had not adequately controlled for potential confounders, e.g. saturated fat intake or smoking (Kritchevsky & Krit chevsky, 2000; McNamara, 2000). A recent review reported that public health b odies, such as the Food Standards Agency (FSA) and British Heart Foundation, n o longer recommend limits for egg consumption (Gray and Griffin, 2009). Instead, the emphasis for heart health is placed on controlling levels of saturated fat. Past concerns have also related to food safety. Eggs sale s declined by 60% overnight in December 1988 when Junior Health minister , Edwina Currie, announced that “most of Britain’s egg production was affected with salmonella” (MAFF, 1993). Since then, the Lion Quality Code of Practice has signif icantly reduced the number of Salmonella enteritiditis cases in the UK (Lion Quality Code of Practice, 2007). Indeed, in a cross-section of 28,518 eggs from UK stores, n o salmonella was found (FSA, 2004). Consumers who avoid eggs in the belief that this will r educe serum cholesterol may exacerbate other health problems. In an analysis of cost- benefit, Schmier et al. (2009) found that eliminating eggs from the diet app eared to increase the risk of age- related macular degeneration (ARMD), leading to high er healthcare costs. Egg yolk contains specific antioxidant nutrients that support eye function. Thus, the overall health benefits of foods must be considered when formul ating dietary advice. The present review aims to investigate associations between eg g/egg nutrient consumption and health outcomes. Evidence on eggs/egg nut rients was collated 4 from both published literature and a secondary analysi s of the National Diet and Nutrition Survey (NDNS; Henderson et al., 2002). Nutritional benefits Eggs can make a significant contribution to a healthy d iet. A medium-sized egg provides 78 kcals, yet contains 6.5g protein. The fat con tent is 5.8g, of which 2.3g is monounsaturated fat (Table 1). Eggs contain a variety of important vitamins, minerals and trace elements (Song et al., 2000). According to the European Commission (EC) Nutrition & Health Claims regulation ( European Parliament and Council, 2007) a ‘source’ claim can be made for foodstu ffs that meet at least 15% of the Recommended Daily Amount (RDA) per 100g, while a ‘rich in’ claim applies when nutrient levels exceed 30% RDA. To that end, the average egg is high in protein, ‘a source’ of vitamin A, folate, choline, ph osphorus and selenium, and ‘rich in’ vitamin D, riboflavin, vitamin B12, biotin and iodine. The lipid matrix within the egg yolk is believed to enhance the bioavailability of nut rients, such as lutein and zeaxanthin (Heron and Fernandez, 2004). Table 2 compares the nutrient density of eggs with othe r protein sources. Although eggs are a rich source of cholesterol (391mg/100g) they are relatively low in energy and high in vitamin A, folate, biotin and iodine com pared with other protein foods (Table 2). Eggs provide the richest mix of essential am ino acids (Layman & Rodriguez, 2009) which is important for children, adol escents and young adults since protein is required to sustain growth and build muscle (Rodriguez, 2005). For older adults, high-quality protein may prevent the degener ation of skeletal muscle (sarcopenia) (Thalacker-Mercer et al., 2007) and protect against some of the health risks associated with ageing (Morais et al., 2006). For those consuming milk-free diets, eggs are an important high-quality protein sour ce (Symons et al., 2007). Research has shown that regular consumption of eggs is associ ated with a better diet quality. An analysis of data from the American Na tional Health and Examination Survey (NHANES III) found that egg consumers had highe r intakes of all nutrients (except vitamin B 6 and dietary fibre) compared with those who did not e at eggs. Interestingly, cholesterol levels were lower amongst fre quent egg consumers (Song et al., 2000) Secondary analysis of egg consumption among British adults in the NDNS Seven-day weighed dietary records from the NDNS (for methods, see Henderson et al., 2002) were analysed to explore associations between eg g consumption and markers of diet quality and health. Approximately 30% of British adults consumed no eggs in the week of survey, while consumers ate an avera ge of 2-3 eggs per week (women) or 3-4 eggs per week (men). The contribution of eggs to total daily intakes of energy and nutrients was correspondingly modest over all, (approximately 2% of energy, 3% of protein, 3% saturated fatty acids, 5% of monounsaturated fatty acids). However, for high consumers (3+eggs per week), eggs were a substantial source of vitamin D, vitamin B12, biotin, and iodine. To examine these associations further, egg consumption w as stratified into 3 levels: none, less than 3 eggs per week.