Officially it's a threshold thing. For instance one of the ideas about the airdrops is one meal a day will sustain people but that doesn't mean it's good for general health. The early effects show up in the young and aspects such as breast milk. It can also effect development problems in the young. That one can be fixed if the right stuff is available at the right time.IPC definition is more than 2 per 10,000 people per day.
Taken too far and we have seen the results in various media reports in places such as Africa. Again mostly the young. The UN view is totally avoid things getting to this stage, They have specific name for the stage where thing start getting like that. We have heard them even from the US. So even they press for more aid getting in. A secondary effect is the need for a balanced diet. Poor diets have all sorts of secondary effects on general health as does too little food.