[codedinosaur]

About 3 years ago, I undertook a water fast that lasted about 17 days. It does take a lot of mental preparation. Nutrition wise, I ate only fruits for about a week before the fast. The first few days were very hard, but then I simply did not feel hunger at all. I intended to continue the fast for 30 days. But from about the 4th day onwards my mouth started having an awful odour and my tongue had a thick white coating that was the source. Into the third week, I simply couldn't bear that smell anymore and gave up. for getting back to regular food, I did the same thing and had only juices and fruits for about 3-4 days.

Now, I'm not an expert, but I read while preparing for the water fast that your body has nutrients it needs to survive for a few weeks. I didn't take any supplements during that time. Unfortunately, at that time i didn't have the means to measure and quantify what changed after the fast. I do remember being in a great mood for a few days after the fast. I don't know how much it benefited me, but it was an interesting exercise

[xarope]

That odour is probably the ketones coming into play when the body starts using fat for energy, instead of carbs or protein. And yes, it's a well known fact.

[dualogy]

For 3 weeks straight would be unusual though and not explain the commonly occurring tongue coating.

[AstralStorm]

Sounds more like lack of immunity and candidosis.

[chongli]

You still have to brush your teeth when fasting. Scrape all that plaque biofilm off your tongue. Plaque bacteria feed on all sorts of nutrients in your mouth and in your saliva, not just food residue.

[codedinosaur]

It is not like I didn't brush my teeth. But the layer on the tongue was about 1mm thick, maybe more, and no amount of brushing it would remove it. It would only make my tongue hurt after a while, so i went back to regular brushing. Ketones may be the answer as the other reply explains, but one thing is for sure, having that foul smell in my tongue and nose at the same time 24 hours a day for 2 weeks is no party.

[baccheion]

Of course the fast means little if you went back to your usual diet. The key is to have it rejuvenate/regenerate/heal your system, then to break it, but by transitioning to a better/cleaner diet (blended (Vitamix'd) vegetables, lean meats, nuts, and cold-pressed organic oils, for example).

Also, you can add in intermittent fasting (eating within the same 8-hour window each day) and mild caloric restriction (calculate your actual daily caloric requirement (more involved than it may seem), then eat 80% of that).

Then there are the supplements and nootropics. After a water fast is the perfect time to take on the habit of supplementing (in addition to continuing to consume mainly blended vegetables) with things like Acetyl L-Carnitine (and other free-form amino acids), CoQ10 (if you're over 30), Astaxanthin, Ashitaba, Vitamin D & K, Magnesium, (Opti)Zinc, etc. Also, there are nootropics like Cerebrolysin (one month every quarter), NSI-189 (also one month every quarter-- maybe after Cerebrolysin), and (N-Acetyl) Semax (Amidate) + N-Acetyl Selank (also one month every quarter-- or two months if you can't source NSI-189). There's also fasoracetam + coluracetam, Tianeptine Sulfate (mainly if you struggle with depression or anxiety), and many other things.

https://news.ycombinator.com/item?id=12386378

https://www.reddit.com/r/Nootropics/comments/4z4t1q/top_5_an...

You can also look into Oil Pulling (unless you have many fillings).