I did keto for a few months a long time ago (2010/2011). This was early in my career and long coding and debug sessions were a normal part of my day-to-day.

There was zero impact to my work focus, positive or negative, from cutting nearly all carbohydrates out for several months.

I am curious were you heard or learned that "sugar is really important for focus". Just a vibe, perhaps?

Been coding while fasting on keto and it's absolutely amazing. Fasting is hard socially, being ketogenic puts a bit more stress on my kidneys, but for me (adhd) it's amazing.

remember your brain can run on ketones which provides a more stable energy than glucose spikes. the brain is metabolically flexible, can run on glucose, ketones or lactate

That's addiction. You'll need time to get out of it.

Cutting off sugar will help you have more focus, not just during coding but the whole day. However, if you were on high amount of sugar before, at initial stage, your body will scream.

For me, it takes a few weeks to get settled in. After that, I don't miss sugar at all. Can focus just fine.

If anything focus gets better without sugar and excessive carbs for me - but those work well for outdoors or workouty days I find.

I have never heard of anyone using sugar to "focus," if you want to focus take amphetamines or cocaine.

I don't code, but I do know that not eating sugar significantly improves my focus no matter what I'm doing.

Why are you cutting out sugar, unless you mean reduce. But you shouldn't stop eating sugar, its required, just not in excessive amounts.

If you're addicted to cocaine, then cocaine is really important for focus. Same for sugar. If sugar is really important for focus for you, then you're likely heading for diabetes type 2.