Researchers have now discovered how malnutrition kills a person. They've found that that under low food conditions or through consuming foods with low nutritional value, the bacteria in the human intestines turn against the body and cause severe inflammation in the intestines.. This apart from a weakened immune system makes humans especially vulnerable to various diseases.

Researchers found that a key enzyme called the Angiotensin Converting Enzyme 2, or ACE2, that helps control blood pressure, kidney function and lung injury has an additional role in the uptake of amino acids from food. In particular the enzyme helps in the uptake of an amino acid called tryptophan.

The present study describes how malnutrition affects the body and what causes the body to be so weak that it can't defend itself against common pathogens. Researchers say that just increasing level of tryptophan in the body might let the immune system bounce back to life.

"The research shows how the food we eat can directly change the good bacteria in our intestines to bad bacteria and so influence our health," said Thomas Perlot from the University of Kiel, Germany and first author of the study.

When the levels of tryptophan go down, then the immune system can no longer keep a check on the kinds of bacteria that can live in the gut, leading to diarrhea and inflammation.

The researchers used animal models to demonstrate the effect of hunger on the body. They found that just by increasing the level of tryptophan in malnourished mice, they were able reverse some of the inflammation caused by gut bacteria.

"Our results might also explain nutritional effects that have been known for centuries and provide a molecular link between malnutrition and the bacteria living in our intestines. This discovery could be used in the future to treat patients with a simple regulated diet or by taking tryptophan as a food supplement. And there is hardly any risk of side effects from artificially increasing an amino acid found in the normal diet," said Perlot.

Malnutrition kills over a billion people in the world, researchers say. According to World health Organization, one out of every three people in the world is malnourished.

"I hope that our findings have opened a door to a better molecular understanding how malnutrition affects human health. Whether simple tryptophan diets can indeed cure the effects of malnutrition in humans now needs to be carefully tested in clinical trials," said Josef Penninger, director of the Institute of Molecular Biotechnology (IMBA) in Vienna, Austria, the lead author of the study, in a press release. The study was published in the journal Nature.