Chicken leukemia virus, bovine leukemia virus in our food chain and chlamydia pneumonia in common bird flu infections were found to be related to common cancers. Growth-promoting hormones which are used in intensive livestock breeding strengthen this connection. The time without symptoms is 50% - 70% of the total growth time of a tumor. The human body refreshes itself constantly by food and in a few years all the cells and tissues are completely renewed. With age, the choice of animal or vegetable protein in the diet is very important for our defense to chronic diseases and cancer. The consumption of animal fats and proteins has increased sharply since the last century. Cardiovascular disease, obesity and uncontrolled growth of derailed cells are the consequence thereof. Fresh fruits and vegetables are eaten too little. Complete plant food contains more phytonutrients and dietary fibers to protect us. Medical science has (rightly or wrongly) fully focused on curing diseases and patients with medicines. It is too late to wait for the development of vaccines, against oncogenic retroviruses as chicken and bovine leukemia virus in our food (To date this has not succeeded).