It definitely is true. I know a few diabetics who no longer take [synthetic] insulin and reversed their diabetes. Also they had blood work done to see which vitamins and minerals they were deficient in and started to supplement with a good pharmaceutical grade supplements.
Many diabetics are deficient in trace minerals--especially chromium and vanadium. Chromium and Vanadium shown to help metabolize glucose and regulate blood sugar levels.
Sources:
https://level4now.com/image/data/Cl...um-Support-For-Healthy-Glucose-Metabolism.pdf
http://curezone.com/foods/trace_minerals.asp
http://www.ncbi.nlm.nih.gov/pubmed/3575229
http://www.umm.edu/altmed/articles/chromium-000294.htm
http://www.ncbi.nlm.nih.gov/pubmed/9550454
Even if people didn't go as in depth as you have and just thought a out what they ate and got some basic exercise, this type 2 diabetes would be a thing of the past. Why aren't doctors focusing more on nutrition and exercise? I know, I know...follow the money.