I'm on fasting vs I have fasting

Some examples from the web:

• See how long they can go on fasting.
• The thoughtless child that has decided on fasting has started a juvenile war?
• And don't forget that I'm fasting for Ramadan, too.
• I'm still fasting because I misread my calendar.
• I'm fasting and praying for our sins.
• I'm fasting because I said mass.
• In fact, I'm fasting.
• I'm fasting too, Father.
• I'm fasting, followed by a prayer vigil in the church.
• Sorry, I've been fasting and I'm edgy.
• You can drink water during the fasting period.
• Food appears to increase pharmacokinetic variability relative to fasting.
• Prolonged fasting before administration should be avoided.
• Co-administration with a high-fat meal did not affect the AUC of atazanavir relative to fasting conditions and the Cmax was within 11% of fasting values.
• And therein fasting hast thou made me gaunt.
• You know, fasting can actually clear your mind.
• I've been fasting all day to save room for Mulligan's.
• Fasting's not healthy for you, Ron.
• Fasting triglycerides should be normal or normalised with appropriate intervention prior to bexarotene therapy.
• Syncope occurred in a fasting adult who had taken doxazosin 16 mg.

Some examples from the web:

• Apparently, I have to do that fasting so for the last ten hours or so I've been eating nothing, just sipping delicious water.
• it's tough enough to deal with cam when I'm at full strength, but I have been fasting just as long as he has, and I do not have the energy to deal with a big, needy brisketcase - brass - basketcase.
• You can drink water during the fasting period.
• Food appears to increase pharmacokinetic variability relative to fasting.
• Prolonged fasting before administration should be avoided.
• Co-administration with a high-fat meal did not affect the AUC of atazanavir relative to fasting conditions and the Cmax was within 11% of fasting values.
• Therefore I have had my breakfast now, and until tomorrow breakfast I am fasting and sharing with your determination.
• And therein fasting hast thou made me gaunt.
• You know, fasting can actually clear your mind.
• And don't forget that I'm fasting for Ramadan, too.
• I've been fasting all day to save room for Mulligan's.
• Fasting's not healthy for you, Ron.
• Fasting triglycerides should be normal or normalised with appropriate intervention prior to bexarotene therapy.
• Syncope occurred in a fasting adult who had taken doxazosin 16 mg.
• Temodal hard capsules should be administered in the fasting state.
• In the fasting state, AUC increased less than in proportion to dose above 200 mg.
• Carbohydrate metabolism Patients with inadequate growth hormone secretion sometimes experience fasting hypoglycaemia that is improved by treatment with somatropin.
• Somatropin increases insulin but fasting blood glucose is commonly unchanged.
• Following the period of fasting the animals should be weighed prior to test substance administration.
• Overnight fasting of the animals prior to blood sampling is recommended (1).