Why is orally taking insulin useless without applying nanotechnology?

• Because having insulin pass by the esophagus would cause damages to the tissues in it
• Because gastric juices can destroy insulin making it useless for oral intake of insulin Correct
• Because having insulin taken orally would increase the acidity of the stomach therefore having a side effect of stomach ache
• Because insulin would be considered foreign by the body that's why its directly injected in the blood stream