Not all diseases are caused nutrient deficiencies, but they often do come with one.

A deficiency of vitamin D, for example, is found most cases of illness, from cancer to upper-respiratory tract infections to sepsis and osteoporosis.

Recently, researchers at the renowned Salk institute for Biological Studies have identified that a simple amino acid called methionine, one which we all get from our diets mostly through animal-sourced foods, plays a key role in ameliorating the risk of death from infections.

Ambitiously, the Salk team were investigating what's known as "disease trajectory" which describes the process from which an infection is contracted, or injury sustained, to the point at which the patient recovers or dies. Salk scientist Janelle Ayres, PhD, has spent decades researching why some patients go down the former track and others the latter.