There’s lots of info on the Diabetes UK website about diet, including recipes etc. if your GP is dismissive, I’d ask to see a different one, or a diabetes specialist nurse. As others have said, there can be serious consequences with untreated diabetes and the impact on his internal organs may not show up until later. Yes, cholesterol levels are important too, and its Often suggested that people with diabetes have lower levels. Many are prescribed Statins to achieve this, but that’s a whole other subject!