I can jump in here. I lost 16kg on a ketogenic diet.

My gut is a lot happier as evidenced by more regular and better (firm, soft, not runny) bowel movements.

There is a definite smell (breath) associated with ketosis. It varies by person but it is often noticeable.

I asked my wife to track it as it's very hard to notice it yourself and she says that my system produces a slightly metallic smell the isn't objectively bad, just different to normal.

I have Muslim friends and during Ramadaan there is a noticeable smell which is subjectively bad from some of them.

A friend who works as a nurse in a very low income area says that she can detect someone who isn't eating normally by the smell - very important to spot if that person is also pregnant.

It's a long way of saying: yes there is a smell, it varies by person.

During Ramadan Muslims are not allowed to drink water, right? That probably means their mouth is very dry during the fasting time meaning there's more than usual amount of odor-causing bacteria in their mouth.

I'd pick better health before better breath! Keto is amazing, I'm never hungry - you not only live longer, because it's less harmful, but you save so much time and energy having to think about food and eating it! I eat 1-2 times a day, ideally, I want to eat once a day and I can, but for social reasons, I eat twice most of the time. Eating once at night has a name - Warrior Diet [0].

[0]: https://en.wikipedia.org/wiki/Warrior_diet

This might be an effect of too much protein in a diet. If you are controlling for carbs, then the solution is to replace protein with more fat.

Keto diet makes your body produce ketones for energy, so you get the acetone breath - or something like that