Undernourished means not getting enough food or the right kinds of food to stay healthy and grow properly. When someone is undernourished, their body lacks the nutrients it needs: proteins to build muscles, vitamins to fight off sickness, or simply enough calories to have energy for daily activities.

You might read about undernourished children in parts of the world where food is scarce, but undernourishment isn't always about having too little food. Someone could eat plenty but still be undernourished if they only eat foods without much nutritional value. A person who eats nothing but candy and chips might feel full but still become undernourished because their body isn't getting what it needs.

The effects of being undernourished show up in various ways: children might grow more slowly than they should, people might feel tired all the time, or they might get sick more easily because their bodies can't fight off infections well. Plants and animals can be undernourished too. A garden with poor soil produces undernourished vegetables that look small and pale.

The opposite of undernourished is well-nourished or simply nourished, meaning someone is getting the food and nutrients their body needs to thrive.