ggs are a rich source of cholesterol, and for this reason they have been demonised by proponents of the cholesterol theory of cardiovascular disease. However, evidence does not support a role for eggs in the elevation of plasma cholesterol concentrations (here) and there is no evidence to support a role for eggs in the development of cardiovascular disease. In fact, avoidance of eggs may be counterproductive, because eggs are a good sources of nutrients, including protein. In addition, eggs are useful functional foods because the fatty acid content of the yolk can be modified through changes to the diets of the hens. By increasing the polyunsaturated fatty acid content of the diet of the hens, eggs can be produced that contain high concentrations of omega-3 (n-3) fatty acids. Such eggs may be beneficial, because high intakes of n-3 fatty acids are associated with protection from cardiovascular diseases.
High n-3 eggs may be a useful source of eicosapentanoic acid (EPA, C20:5 (n-3)) and docosahexanoic acid (DHA, C22:6 (n-3)) for vegetarians, who can not rely on fish for their supply of these long-chain fatty acids. A number of studies1 have investigated the influence of diet on the final egg concentrations of fatty acids and generally shown positive results. Feeding hens menhaden fish oil containing EPA and DHA at around 15 to 30 g/kg increased concentrations of n-3 fatty acids in the egg yolks. However, only the hens fed 15 g/kg menhaden oil produced eggs that remained palatable to a panel of tasters. Because polyunsaturated fatty acids are more chemically reactive than saturated fatty acids, it might be expected that the high n-3 eggs are more prone to spoilage. However, comparison of the shelf life of the 15 g/kg menhaden oil eggs with normal control eggs showed that the shelf life of the eggs was comparable.
In another study, hens were fed ground flax seeds in order to increase the concentration of α-linolenic acid (ALA, C18:3 (n-3)) in the yolks of their eggs. At 150 g/kg diet ALA was able to modify the fatty acid content of the yolks. However, the concentration of DHA in the yolks did not increase significantly. When the hens were fed whole flax seeds the ALA content of the egg yolks did not change, suggesting that the whole seeds are not digested, When marine algae were fed to the hens, the DHA levels in the yolks of the eggs increased more when compared to eggs from hens fed menhaden fish oil. Marine algae and menhaden oil are both good sources of DHA, but hens fed marine algae may be more appealing to vegetarians. Interesting, egg yolks do not increase in DHA content after hens consume ALA, suggesting that like humans, hens may not to convert ALA to DHA efficiently.
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