What causes a person that is malnourished to have what seems like a bloated abdomen?
You are right, the abdomens of the severely malnourished do appear bloated. Specifically, this is due to a protein deficiency called PEM: protein energy malnutrition, two common protein deficiency diseases are Marasmus and Kwashiorkor. These diseases are most commonly seen in Third World locations whose citizens are protein deficient because of the available food supply.
Dietary protein intake plays a large role in intra- and extracellular fluid balance. Protein deficient people have fluid shifts due to osmotic pressures in the cells. For example, people with an albumin (plasma protein) deficiency will have areas of edema in the feet or ankles (pedal edema) or in the sacral or periorbital regions. Please note that many other conditions also result in edema, protein deficiencies are not the sole cause.
It is confusing to many people to see pictures of starving people with what look like swollen or bloated bellies, so it is a common question. But one of the first symptoms of malnutrition or starvation is a bloated belly or abdomen.
One of the causes can be the stomach filling with gas provoked by the production of acid and other hunger responses.
But the most common cause is actually brought about by a protein deficiency in the diet that causes the body to begin to metabolize protein in the body, muscles, bones, etc. Once that is gone, there is capillary leakage into the stomach and abdominal area producing the distended belly.