The hen's egg - is its role in human nutrition changing?

This paper reviews the contribution that eggs can make to the human diet and considers the additional benefits that can be derived from modifying the egg's nutritional profile and in particular the egg's fats and antioxidants. Attempts to modify the egg's fat component have tended to focus on the means by which the cholesterol level in the egg may be reduced or the ratio of n-3 to n-6 polyunsaturated fatty acids (PUFAs) manipulated. The cholesterol content of the egg has been lowered by either reducing the mass of the yolk relative to the egg (i.e. a non-specific reduction) or by using feed additives such as beta-cyclodextrin that have a specific effect on the cholesterol content of the yolk. The ratio of n-3:n-6 PUFAs in the diet is important not only because of their role in energy metabolism and biological membranes but because they affect eicosanoid metabolism, gene expression and intercellular communication. Eggs produced from hens receiving conventional feeds tend to be relatively high in n-6 PUFA but dietary manipulation can be used to either increase the amount of the n-3 PUFAs directly (using fish oil) or indirectly by increasing the levels of the precursor n-3 PUFA by feeding alpha-linolenic acid (ALA) in the form of linseeds, flaxseeds or similar. Of particular interest is the n-3 PUFA docosahexaenoic acid (DHA). The relatively high degree of unsaturation makes this PUFA susceptible to oxidation during storage and cooking but this can be resolved, at least in part, by enriching the egg yolk with antioxidants such as vitamin E. Apart from reducing the rate of PUFA oxidation, enriching the level of antioxidant in the egg can also enhance levels of antioxidants in the consumer. The effect on the consumer of consuming modified and conventional eggs is considered.