Several substances produced by animals and fungi have been investigated for immune-modulating effects. Fish oils are the most studied. As a source of n-3 fatty acids, fish oil consumption by humans has been shown to influence the synthesis of inflammatory signaling molecules like prostaglan-dins, leukotrienes, and cytokines. In addition to direct effects on prostanoid synthesis, n-3 fats have also been shown to directly alter the intracel-lular availability of free calcium ions, the function of ion channels, and the activity of protein kinases. Generally administered as nutraceuticals rather than as functional foods, fish oil supplements have demonstrated anti-inflammatory and immune sup-pressive effects in human adults. A high intake of the n-3 fatty acids eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acid (DHA) from seafood or fish oil supplements has also been associated with prevention of several types of cancer, myocardial infarction, ventricular arrhythmias, migraine headaches, and premature births, and with improved control of type 2 diabetes mellitus, inflammatory bowel disease, rheumatoid arthritis, cystic fibrosis, multiple sclerosis, bipolar disorder, and schizophrenia. 20:5n-3 but not 22:6n-3 is effective for schizophrenia and depression; 22:6n-3 but not 20:5n-3 improves control of blood sugar in diabetics. The benefits of fish oil supplements have prompted efforts at increasing the n-3 fatty acid content of common foods by adding fish oil or flax oil extracts. Consumption of these has been associated with decreased levels of some inflammatory biomarkers, including thromboxane B2, pros-taglandin E2, and interleukin 1-beta.
Feeding flax seed meal or fish meal to hens enriches the n-3 fatty acid content of the yolks of the eggs they lay. Consumption of these eggs increases the n-3 fatty acid content of plasma and cellular phospholipids and produces an improved blood lipid profile when compared with consumption of standard eggs. Egg yolk is not only a source of fatty acids, but also of carotenoids and immuno-globulins. The xanthophyll carotenoids zeaxanthin and its stereoisomer lutein are readily absorbed from egg yolk. Their consumption is associated with a decreased incidence of macular degeneration and cataract. Immunizing hens to specific pathogens and extracting the antibodies present in their egg yolks yields a functional food that has been shown to prevent enteric bacterial or viral infection in experimental animals.
Bovine colostrum, the milk produced by cows during the first few days postpartum, has a long history of use as a functional food. Compared to mature milk, colostrum contains higher amounts of immunoglobulins, growth factors, cytokines, and various antimicrobial and immune-regulating factors. Consumption of bovine colostrum has been shown to reduce the incidence of diarrheal disease in infants and the symptoms of respiratory infection in adults. Specific hyperimmune bovine colostrums, produced by immunizing cows to pathogenic organisms like Cryptosporidium par-vum, Helicobacter pylori, rotavirus, and Shigella spp., may prevent or treat infection by these organisms.
Human studies have also shown that consumption of bovine colostrum can improve anaerobic athletic performance and prevent the enteropathy induced by use of nonsteroidal anti-inflammatory drugs.
Mushrooms play a major role in traditional Chinese medicine and as components of contemporary Chinese health foods. Many Basidiomycetes mushrooms contain biologically active polysacchar-ides in fruiting bodies, cultured mycelium, or culture broth. Most belong to the group of beta-glucans that have both beta-(1^3) and beta-(1^6) linkages. Although they stimulate macrophages and natural killer cells, the anticancer effect of mushroom polysaccharide extracts appears to be mediated by thymus-derived lymphocytes. In experimental animals, mushroom polysaccharides prevent oncogen-esis, show direct antitumor activity against various cancers, and prevent tumor metastasis. Clinical trials in humans have shown improvement in clinical outcome when chemotherapy was combined with the use of commercial mushroom polysaccharides like lentinan (from Lentinus edodes or shiitake), krestin (from Coriolus versicolor), or schizophyllan (from Schizophyllum commune). Mushroom extracts may fulfill their potential more as medicines than as functional foods.
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