Explain one medical reason why balanced diet may vary

One medical reason is diabetes and those who need food or else they faint. Diabetes need a balanced diet in SUGAR, and just like me, there are people, (I don't know what the sickness is called), who need a lot of food to eat and water to drink or else they start to get dizzy and fainnt. So that's why balanced diets vary.  

Use trash cans hope this helps