Can someone faint by not eating properly?

Syncope: Fewer than 1% of people with syncope turn out to have metabolic causes. Metabolic causes of syncope include hypoxia (reduced oxygen in the blood, which is never seen unless some severe and obvious lung or heart disease is present); hyperventilation, which occurs in severe anxiety reactions or panic attacks; and severe hypoglycemia (low blood sugar), which should be suspected in diabetics.