No need to worry about ketones unless your BG is high - very high.
Two different things, ketosis and ketoacidosis. The second one is the one that we must avoid at all costs. That can get going after someone hasn't had enough insulin in their system (injected or their own) over a long period so BG has been high, often very high, for a long time. Then the body starts eating itself. Muscle tissue is broken down to produce ketones (which are really an alternative energy source to glucose, as I understand it - correction welcomed if that's wrong) for energy for the body to run on, but that process needs some insulin too so it goes awry, and the net result is the blood becomes more and more acidic. Which would kill in the end if left unchecked.
Ketoacidosis is often called DKA (for diabetic ketoacidosis).
But ketosis in the context of low-carb food intake is a benign ketone phenomenon. The thinking is that when you restrict carbs below a certain point that varies person to person, because glucose is in short supply, your body will switch to the alternative energy supply system that uses ketones. These are mainly made from fat - often from fat you eat, rather than fat in flobby bits.
The argument is that ketosis was more common in pre-modern times because diet was different. Hence ketogenic diets are more or less the same as paleo diets - carnivore stuff, eggs, lots of veg or green veg. No grain or starchy roots.
Ketogenic diets are quite controversial. Some people think they're harmful. That's a matter for individuals to research and think about for themselves. This thread is among keto enthusiasts.
I found ketones very confusing at diagnosis and in fact was seriously misled by a doctor who said I'd get DKA if I didn't take large doses of insulin immediately. I worried myself sick for days. Hope this helps.
