I started keto very early on during the acute stage of my illness (approx 4 weeks after infection), before I had a diagnosis. My reason for starting was after researching my symptoms (brain fog, insomnia, anxiety, depression, etc.) I kept reading about
inflammation. So my next round of research - "how to reduce inflammation?" - kept pointing towards the role of carbohydrate (particulary those which have a high GI) induced spikes in blood sugar levels contributing to inflammation, particularly in people who are already experiencing high levels of inflammation.
I experimented by doing a 24hr fast and had my best day since getting sick. So then I started introducing a low-carb diet again and my symptoms did return, but they weren't as severe. I did intermittent fasting a few days per week, too. This was with acute untreated (and undiagnosed) Lyme. But the difference was being completely house bound before switching diets to then being able to take short walks to the local park, supermarket, etc. It felt like a game changer at the time - doctors were telling me I was fine and I knew I wasn't, and this was a repeatable technique that resulted in an improvement in my symptoms. I actually suspected a food allergy at this point due to only having the diet improvements to go by.
Once I tested positive for Lyme (approx 8 weeks after infection) I found a LLMD and he suggested that I stayed on the keto diet for the same reasons I already outlined.
I've not been strictly keto for the past month or so - I feel close to remission so wanted to test the waters again, so to speak, and have had no setbacks with adding healthy carbs back to my diet. But I am refocusing now on mould/MCAS/candida I'll switch back to keto for a while again I think.
For those looking to start it, beware the 'keto flu' during the first week or so. It's explained well here: https://www.healthline.com/nutrition/keto-flu-symptoms#get-rid
I managed to avoid it (and twice in the past, too, when I was carb depleting before marathons) simply by:
a) drinking LOTS of water
b) taking lots of salts and electrolytes