Up to 80% of the body's immune system is localized in the gastrointestinal tract. This offer unique opportunities to modulate the immune response and prevent disease by eating right. Among the substances regarded as having positive effects are many thousand antioxidants, not only traditional vitamins but numerous flavonoids, carotenoids and similar plant-and vegetable produced antioxidants. Also health-promoting bacteria (probiotics) and numerous plant and vegetable fibres (prebiotics) are increasingly documented to have strong health-promoting influence. The intestine harbours about 300, 000 genes, to be compared to the about 60, 000 in the rest of the body. This is an indication of the enormous chemical activity going on in the intestine. One can anticipate that there are several times more enzymes active in the intestine than in the rest of the body. These enzymes release 100, 000 or more of substances, which are absorbed and hereby serving as health-promotors in the body. Among these are antioxidants, but also amino acids, polyamines, short chain and other long chain fatty acids, various carbohydrates etc. In addition do the microbial cells produce signal molecules, called bacteriokines, with which the microbes communicate both with the mucosal cells and the immune system. The world of fermentation products, often referred to as synbiotics are poorly investigated and understood. It is a priority task for this new millennium to explore and understand the production of synbiotics and their role both for human and animal health, well-being, performance and long life.