WebMD explains that the primary symptom of malnutrition is sudden and unexpected weight loss. Individuals do not have to be severely underweight to be malnourished. Instead, they only have to have taken in too few calories to sustain healthy bodily functions to be considered malnourished. However, the majority of people who are malnourished are categorized as underweight by the BMI index.
According to WebMD, other symptoms of malnutrition include a lack of energy, a depressed immune system that has trouble fighting off infection and healing cuts, irritability, depression, and a lack of concentration or other cognitive functions. Since malnutrition can be caused by a lack of food as well as difficulty absorbing nutrients from food, persistent diarrhea, vomiting or other gastrointestinal problems may also be symptoms. If left untreated, malnutrition may become acute. The symptoms of this final stage include heart palpitations, organ failure and death.
Young children are particularly susceptible to malnutrition. In addition to the above symptoms, children suffering from malnutrition may show delayed growth and a failure to hit developmental milestones, according to WebMD. Their hair, skin, fingernails and teeth may also unexpectedly change color. They may also exhibit swollen stomachs as the muscles of the abdomen begin to break down and lose shape.