There is a lot of conflicting information out there, one thing that research is showing is that diabetes is not caused by ingestion of sugar or by eating too many carbs per se, but by body fat (and yep, many of the studies mention the fat around organs as being one of the causes of type II diabetes). Sugar and simple carbs cause a huge glycemic reaction which in turn leads to your body producing fat rapidly, but it is the fat itself that messes around with the insulin reaction. Eating a high fat diet also contributes to this, the reason that body weight is an indicator for type II diabetes is pretty simple, if you are heavy, odds are your body fat is high, so exercise and losing weight will cause you to lose body fat, which will improve the insulin mechanism. I would be very careful about the demonization of carbs you hear out there, I have heard people advocating diets like atkins for people with type II diabetes or pre diabetes and that is ridiculous. Complex carbs found in green vegetables and the like are very different than simple carbs (white flour, rice, sugar) and they are different than whole grains (whole grains are better than things like white flour and rice, but still have problems if you eat too much of them). The problem with low carb diets is that they often cut out all carbs and emphasize eating protein, and often it is protein that is heavy in fat, or things like nuts and the like and eating a lot of them isn’t good, they are calorie dense (take a look at the calorie levels on many nuts), and they lead to producing body fat, which is from what I have been reading, the big contributor to pre diabetes and diabetes II. From what I can tell, a diet that is based around eating mostly vegetables, with lesser amounts of whole grains, and lean protein (keyword, lean), and healthy oils sparingly, nuts, nut oils and so forth.
In terms of exercise, if he is running he may want to include strength training as well, mix that with the running, it may help.
One of the biggest things is to work with a nutritionist and see what works, everyone is different, and someone might work better with more protein and less things like whole grains, someone else might work better with less protein. On the American Diabetes website they basically say the best diet is what most people should be eating, it pretty much is what I said up above, carbs are not the evil thing, people see low carb and they think atkins (I am not talking here about people with full blown diabetes), or that if you eat something like pasta or bread you are going to get diabetes, that simply isn’t true, but if you eat a lot of pasta and bread and aren’t eating vegetables and some protein, you aren’t going to be healthy, but that would be true in any event;). Nutritionists generally have ideas what to try and ways to find what works best. The other thing is to remember that food is not fuel, and that if you try some ridiculous diet that totally cuts out things you like, like bread or pasta, because of the idea ‘all carbs are evil’, it will be really hard to maintain it. Better to moderate intake and enjoy it once in a while as a treat, then treat something like carbs (or any other food) like a Puritan treats sex, the enemy, it isn’t:).
The other thing is by all means get retested, those tests can fluctuate, and he could get another reading and see the numbers back to normal…