It all comes down to nutrition and getting active. I'm not sure if he/she drinks soda, but that is the first thing I would cut out of their diet, whether it's regular or diet. Completely cut out all artificial sugar and refuel their sugar craving with natural sugars like fruit. Beware of grapes, as they have too much sugar. I would also go easy on the bananas. To increase activity try going out for 15-30 minute walks around the block. Try some of these simple tips and you will see a noticeable difference in their energy level too.