Type 2 diabetes is as close to a disease of choice as you're likely to find: provided that you adopt a sensible lifestyle of good diet and exercise then you are never going to suffer the condition, barring extremely bad luck in your genes. Similarly, if you are headed down the path towards diabetes, you can turn back by changing the way you live your life. Here's evidence that the turn can be made quite late if made aggressively enough: "An extreme eight-week diet of 600 calories a day can reverse Type 2 diabetes in people newly diagnosed with the disease .... the low-calorie diet reduced fat levels in the pancreas and liver, which helped insulin production return to normal. Seven out of 11 people studied were free of diabetes three months later. ... More research is needed to see whether the reversal is permanent, say experts. ... The 11 participants in the study were all diagnosed with Type 2 diabetes within the previous four years. They cut their food intake drastically for two months, eating only liquid diet drinks and non-starchy vegetables. ... After one week of the diet, researchers found that the pre-breakfast blood sugar levels of all participants had returned to normal. MRI scans of their pancreases also revealed that the fat levels in the organ had decreased from around 8% - an elevated level - to a more normal 6%. Three months after the end of the diet, when participants had returned to eating normally and received advice on healthy eating and portion size, most no longer suffered from the condition. ... This diet was only used to test the hypothesis that if people lose substantial weight they will lose their diabetes. Although this study involved people diagnosed with diabetes within the last four years, there is potential for people with longer-standing diabetes to turn things around too."

Link: http://www.bbc.co.uk/news/health-13887909