In general, be cautious about consuming energy bars that contain high amounts added sources of caffeine, which may cause adverse effects like headaches and anxiousness. Also, be mindful of sugar alcohols like xylitol, mannitol, or sorbitol in energy bars, used to add sweetness without extra calories. Though safe to consume, your body can’t completely break down sugar alcohols which may cause gas, bloating, and diarrhea if you eat too much. It is best to consume energy bars that contain whole, real foods that you personally tolerate well.