The present invention relates to a process for producing an egg yolk with a very high content of antisecretory factor (AF) proteins, in particular with a very high content of AF protein fragment consisting essentially of the amino acid sequence as shown in SEQ.ID.NO.1 (AF-16) and/or in SEQ.ID.NO.2 (AF-8), said process comprising for at least 4weeks feeding a poultry, such as a hen, an AF-16 inducing pelleted feed for poultry comprising at least 0.14% free tryptophan, such as 1-2 g tryptophan/kg feed,and thereafter harvesting egg from said poultry, separating egg yolk from egg white, and alternatively spray-drying, grinding, leaching, extracting, evaporating, membrane filtrating, and/or or freeze-drying said egg yolk. The present invention further relates to said egg yolk with a very high content of antisecretory factor (AF) proteins, produced according to the herein described process, and to their use for the preparation of functional food products and pharmaceutical products for the treatment and prophylaxis of abnormal physiological conditions caused e.g. by exceptionally high levels of body fluid discharge. The invention also relates to food products and pharmaceutical products so prepared.