I was 37 mmol/l when diagnosed. At the time it meant nothing to me, and I didn't really know much about diabetes - just the usual misconceptions. Interestingly, I spent 8 days in hospital and as far as I'm aware no-one monitored my food intake. As I hadn't eaten for 5 days prior to admission (DKA - couldn't even hold water down), once my treatment started I was ravenous, even for hospital food (which was actually rather good, I'm pleased to say!). They took readings and I was nearly always over 20 after a meal - no idea if they were adjusting the insulin doses, although I was on intravenous most of the time, so maybe that works differently. My first HbA1c was 11.8.
Something good about being fed in hospital for those first few days was that I learned that diabetes placed very few limitations on diet - I think only the treacle pudding was off the menu for me!