HI Bamboo I work in Human Resources and can honestly say that for most companies, this will not be an issue regards whether you get the job or not unless the nature of the job is such that your diabetes would affect your ability to do it.
What I advise when managers recruit, is to assess the candidate independently of any health concerns and then if they are appointable, consider any health concerns as a separate matter. As a disability discrimination act illness, the employer has to make any reasonable adjustments to allow you to do the job - only if the adjustment is so great that it would not be reasonable are they justified in not offering
I don't know what your line of work is, but I would be suprised if they are failing to invite you to interview or offer you a job because of your diabetes.But if you are concerned, don't tell them about your health until you get a firm offer. I know you may need to put something in an applicaiton form, but I'd avoid mentioning it at interview unless they do, and when you have a firm offer you will probably have to declare it but by then it will be too late for them to not give you the job offer!
Hope that helps