Even with a healthy diet, defects in immune system function from birth could contribute to a malnourished state throughout life, a new study suggests.
Researchers speculate that targeting immune pathways could be a new approach to reduce the poor health and mortality caused by under- and over-nutrition.
"That traditional image of malnutrition that we're unfortunately so familiar with - of someone wasting away - that's just the external picture," said Claire Bourke, a postdoctoral research assistant at Queen Mary University of London.
"Those height and weight defects that we see are the tip of the iceberg - there are a whole range of pro-inflammatory conditions, impaired gut function, weakened responses to new infections, and a resulting high metabolic burden underlying them," said Bourke.
The most common form of under-nutrition globally is stunting - where children fail to achieve their full height potential.
Despite looking healthy, children in developing countries who are stunted in height may also have stunted immune development, making them more vulnerable to death by common infections, researchers said.
How malnutrition and immune function are related is actually still poorly understood; however, there is wide acceptance that malnutrition comes with a range of immune problems.
These include reduced numbers of white blood cells, skin and gut membranes that are easier for pathogens to break through, and malfunctioning lymph nodes.
What is also emerging is that the relationship between malnutrition and immune dysfunction may be a bit "chicken and egg," with both causing and being the consequence of the other, researchers said.
Immune dysfunction results when people consume too few calories because of lack of food or have an excess of fat and sugar in their diet.
That dysfunction is recorded in the DNA through epigenetic marks, so that if malnourished people have offspring, their children inherit an altered immune system (even after multiple generations).
This altered immune system may then cause malnutrition even if children have an adequate diet.
"It's been thought for a long time that the immune system is driving pathology, but new experimental tools have made it possible to separate out the effects of the immune system from those of the diet alone," said Bourke.
The research was published in the journal Trends in Immunology.
