Insufficiently fed or nourished:a horse that is underfed is likely to be dull and lethargic...
Some of the dogs are poorly fed or underfed, perhaps because after spending a lot of money to buy them, their owners do not want to spend any more to get them proper food.
Whilst not as stark as rumours suggest it is in the countryside, children in the capital do look quite thin and underfed.
The food was sparse and the children were underfed.