Use 'malnourished' to emphasize serious health issues due to inadequate food. The doctor said he's malnourished; his diet lacks essential nutrients.
Pro Tip 2/3
Not Just Hunger
'Malnourished' means poor diet quality, not just lack of food quantity. Even though she eats enough, she is malnourished because her food isn't nutritious.
Pro Tip 3/3
Beyond Poverty
Malnourishment can result from various issues, not just poverty. Due to his illness, he became malnourished as he couldn't absorb nutrients properly.