Besides adjusting to physical stressors, our species has had to cope with the vicissitudes of life on the food chain: finding food while avoiding being eaten. Finding sufficient food continues to be, at least in certain circumstances, a serious problem for many human populations. Predation by lions, tigers, bears and other carnivorous mammals is much less of an issue for our species in recent millennia, but we still face the challenge of being the preferred food for a large variety of microbial organisms. Thus this chapter will explore in general terms how humans adapt to the biological stresses caused by malnutrition and infectious disease. As will become evident, these two stresses are interrelated.