I guess eating wholegrain toast might be an improvement on a doughnut. It depends on where you are now in terms of your diet.
Working with pre diabetics right now though not a clinician so my usual advice is to go for a change you can make consistently rather than going straight off the deep end - maybe 1 meal at a time.
However I would say that low gi and keto are NOT on the same spectrum; the former involves lots of starch (which turns into glucose whether it is a doughnut or a bowl of porridge) so won't turn your insulin resistance around whereas the latter, or lower carb, is proven to do so.