As we discussed in my link on Diabetes and Sexual Function, type II diabetes will assault your erectile strength in a hundred different ways. Of course, it does many other nasty things to the male body and accelerates aging in general. So the bottom line is to keep your blood sugar and glucose under control and do everything within your power to avoid diabetes in the first place. This is especially important if you have a family history of diabetes or are of certain ethnicites as well.
What's a fella to do? Fear not: I've got a great list of preventative measures in my link on Metabolic Syndrome Solutions. Insulin resistance, one of the hallmark features of Metabolic Syndrome, is a risk factor in and of itself for diabetes.
In addition, below are the Many Key Ways to Drastically Reduce Your Risk for type II (adult onset) diabetes. In addition, consider the book Reversing Diabetes, an M.D.'s program to dramatically help and sometimes even completely reverse diabetes.
1) NEWS FLASH (Testosterone): Perhaps testosterone's most important effect is the fact that it decreases insulin levels in us males. Anecdotally, I talked to an HRT clinic and the worker commented that every one of their Type II diabetic patients on HRT was able to completely get off of their insulin. A few had to stay on Metformin, but still that is remarkable that they could completely eliminate insulin from their daily regimen. It should be noted that this clinic raises testosterone to through weekly injections into the young male range, i.e. around 1000 ng/dl. Spread the word!
2) Weight. "We found a strong positive association between overall obesity as measured by body mass index (BMI) and risk of diabetes".  The "we" in this sentence are researcher for the journal Diabetes Care and they are merely echoing what a number of other studies have also discovered: waist size, BMI and any other measures of a guy's spare tire or beer gut are strongly correlated with risk of diabetes.
3) Inflammation. Elevated inflammation levels of C-Reactive protein and IL-6 have been associated in multiple studies with the development of diabetes.  Read my link on How to Control Inflammation for tips to keep this you for tips to keep this your body's inflammatory response under control. This is further exemplified by the fact that people with gum disease are twice as likely to develop diabetes. Again, this is probably due to increased inflammatory levels. 
4) Coffee. This may seem too good to be true for many of you, but coffee is very protective against adult onset diabetes. Read more about here in my link on The Many Advantages of Drinking Coffee.
5) Exercise. Being sedentary and not exercising is a huge risk factor for diabetes. In fact, even for those who have already developed poor glucose tolerance, exercise greatly reduces their risk of diabetes. 
6) Green Leafy Vegetables. Scientists are not sure why, but green leafy vegetables reduced the risk of developing diabetes signficantly.  They suspected, however, that it may be a unique combination of antioxidants or phytochemicals in plants such as spinach.  CAUTION: Remember that spinach is one of the dirtier, i.e. pesticide-ridden crops and, therefore, is better bought organic.
7) Vitamin D. Keep your Vitamin D levels up. One recent study showed that 24% of study participants with low Vitamin D levels developed diabetes by ten years afterward, a very high percentage.  Yet another showed that the lowest Vitamin D levels can incur a 47% higher risk of developing prediabetes. 
8) Sitting. Research shows that every two hours per day that you spend sitting increases your risk of diabetes by 7%.  If you have a desk job or watch much TV - watch out!
9) Potassium. Potassium levels are strongly associated with the risk of developing diabetes in middle age.  In fact, there is a dose dependent risk, i.e. the lower the participant's potassium levels, the greater the likelihood of diabetes. Scientists have not verified that adding potassium through diet, which we recommend, or supplements is actually preventative, but it seems very likely to be the case.
10) Cokes and Sodas. Even one 12 oz. non-diet soda can substantially raise your risk of diabetes (by 15%).  Up that to two cokes per day and you increase your risk of diabetes and Metabolic Syndrome by 26% and 20%, respectively. 
11) Leucine / Branched Amino Acids (BCAA's). Leucine is the key amino in Brached Chain Amino Acids that bodybuilders and athletes consume the world over. Leucine has exhibited near miraculous powers in fighting insulin resistance and prediabetes in a number of studies. See my link on Branched Chain Amino Acids for more details.
Of course, a lot of guys in middle age and beyond have pre-diabetes and insulin resistance. With these come increased blood glucose levels and the possibility of slow long term tissue damage. Elevated blood sugar is hard on kidneys, eyes and dozens of other tissues around the body. So how do you protect yourself? Once again, the sulforaphane in brocolli comes to the rescue. This powerful phytochemical turns on genes that in turn pump out enzymes that protect your body from the damage of high blood sugar. 
And what do you do if you already have diabetes? Well, start by dropping any excess weight if you have any. No, it's not "too late" for you. One study showed that losing just 10% of body weight within a year gave participants much better control of their blood sugar. 
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