Thanks for the blog link, Victor.
First, congratulations are in order.
Second... I've probably spent a good 10 percent of my time in my new job dissecting health care data on people (hundreds of thousands) with all forms of diabetes. Yours is Type II (not stage two, by the way).
Type I is sometimes called juvenile onset diabetes. It usually is an autoimmune condition where the body attacks its own insulin-producing cells (islets of Langerhans) in the pancreas. This type of diabetes always results in a need for insulin.
Type II is sometimes called adult onset. It comes with age and/or obesity. You probably had a touch of both. It's not a case of the body losing its ability to produce insulin, but rather the body's biochemistry becoming resistant to the action of insulin. As you've noted, you can improve your status dramatically just by losing weight and by exercising. Since this generally comes on when people are older and/or in terrible shape, that's easier said than done. But you're the martial artist, and so have the discipline it takes to deal with the condition head on.
By all means see your doctor regularly. By now you know there are a series of tests (both physical exam and lab) that you need to do to make sure you're managing your condition properly. Failure to do so can result in all kinds of bad things. Poorly controlled diabetes affects virtually every organ in the body.
Anyhow... congratulations for the weight loss, and your renewed interest in eating right and walking.
If you can... You might try weight lifting. You don't need to go crazy; just do "enough" weight and ideally stick with the classic, freeweight exercises in the body of your routine. Increasing muscle mass will rev your basal metabolic rate, and that makes everything else you do easier. It also won't hurt your karate. Try working with a trainer, and emphasize to him that you're training as a means to an end (martial arts) so don't want to waste a bunch of time on machines that won't transfer to physical movement like martial arts. A good trainer should be able to get you started right and keep you from hurting yourself.
Or you could do what I did and go buy a bunch of books. Only later did I have the good fortune to run into some really good strength coaches.
Meanwhile... I'm impressed that you put yourself out there, Victor. You are one of a few. It's a shame we can't see the video. (Hint, hint!!!