Prior to the 1950s, little was known about the link between nutrition and infection. Until that time, it was believed that protein deficiency (kwashiorkor), more than total calorie deficiency (marasmus), was the main reason of nutrition problems, because, as known now, severe protein deficiency bore a definite relationship to antibody formation and the development of the immune system in infants, children and adults. To have a simple approach, the focus then was on energy, with the assumption that if a person consumed enough kilocalories of energy, all nutrient needs would be met, and infection would be reduced.
Many early years of research works showed extensive, synergistic, antagonistic, and cyclical interactions between malnutrition and infection. This suggested that a dual attack was necessary. In 1968, the World Health Organization published “Interactions of Nutrition and Infection,” which suggested that the relationship between infection and malnutrition was a synergistic one. In the 1970s, the metabolic consequences of infection and the relationship between malnutrition and cell-mediated immunity were initially elucidated. Consequently, advances between 1970 and 1980 brought improved tools to assess immune function, the complement system, mucosal immunity, and cell-mediated immune responses. Human studies and better animal models led to the recognition that malnutrition is not unique to children.
Malnutrition can make a person much easier to infection, and infection also contributes to malnutrition, which causes a vicious cycle. An inadequate dietary intake leads to weight loss, lowered immunity, mucosal damage, invasion by pathogens, and impaired growth and development in children. A sick person’s nutrition is further aggravated by diarrhea, malabsorption, loss of appetite, diversion of nutrients for the immune response, and urinary nitrogen loss, all of which lead to nutrient losses and further damage to defense mechanisms. These, in turn, cause reduced dietary intake. In addition, fever increases both energy and micronutrient requirements. Malaria and influenza, for example, have mortality rates proportionate to the degree of malnutrition.
In the old days, less intake of food was the major reason to have malnutrition. Now, the imbalanced dietary intake is a form of malnutrition. If one takes too much “empty” calorie without having the other nutrients in proportion, one is to have malnutrition.
How to achieve a right nutrition? A simple way is to have a variety of food at the moderate amount.