60g of carbs from french fries will mean you take insulin for about 40g of carbs now, then for 60g of carbs starting in one hour and divided to the next 2-3 hours.

For normal potatoes, 60g of carbs, you'd take insulin for the 60g right now and that's it.

You see how a combination of fat and carbs is really tricky when you need to keep a good control of your glucose values. There is good help for us T1 diabetics, algorithms such as oref1 with super micro boluses help to control the delay and additional raise of glucose when eating fatty food.

Ketosis is also something I'd never recommend to a T1D. It can lead to very nasty symptoms; cramps and headache. Can't say anything about T2Ds, people reading these should always consult a doctor before making any decisions of their treatment.