Metabolic Syndrome is a curse on modern society and a risk factor for cardiovascular disease, erectile dysfunction and many other chronic diseases. It is extraordinarily common and probably around 50 million Americans have the condition. We'll discuss just exactly what it is, but, before I go on, I want to start by saying that below I will give a "miracle solution" for the Metabolic Sydrome. This solution had an 83% success rate, which means it completely reversed the Metabolic Syndrome in about 5 out of 6 of the males in the study! Not bad, eh?
Living in a developed country ain't as easy as it sounds. Our lives of comparitive luxury lead us (unless we are careful) to a loss of blood sugar and insulin control in middle age and beyond. Of course, this manifests itself eventually in the full blown plague of type II diabetes. But long before diabetes sets in, prediabetes will rear its ugly head. Similar to the way that prehypertension is now considered a huge warning sign before full-fledged hypertension, prediabetes was found to be a potent medical condition in and of itself.
Prediabetes is actually insulin resistance, an ugly condition where insulin receptors and processing lose their sensitivity. This allows blood sugar levels to build up and eventually damage accumulates to the beta cells of the pancreas and diabetes results. One curious thing about prediabetes is the fact that it is usually accompanied by a suite of symptoms including high blood pressure, stomach/visceral fat, low HDL, and high triglycerides (and elevated glucose).
And even though it sounds somewhat benign because it is termed prediabetes, implying it's not yet a problem, Metabolic Syndrome has been tied to an increased risk of cardiovascular death and all-cause mortality.  As mentioned above, it also been linked to erection issues, a fact I cover in my link on Metabolic Syndrome and Erectile Dysfunction.
But what does Metabolic Syndrome have to do with low testosterone? Low testosterone raises insulin levels very significantly and I go into detail about this fact in my link on Testosterone and Insulin. And this is the reason that it directly worsens Metabolic Syndrome. For example, one study of middle-aged men found that those in the lowest fourth of total testosterone were 1.9-2.5X as likely to develop Metabolic Syndrome over the next 11 years. The threshold for the quartile of total testosterone was 450 ng/dl (15.6 nmol/l).  450 ng/dl would be considered reasonable testosterone by most doctors and yet this study indicates that many men may be getting into trouble near this threshold.
I often have men writing into The Peak Testosterone Forum in the 400's who just don't feel well. This is undoubtedly one of the primary reasons: they are beginning to lose insulin sensitivity. Some good tests for men to monitor are a post-prandial blood glucose, A1C, and fasting blood glucose.
So we know that Metabolic Syndrome is nasty and can be accelerated by low testosterone. But is there a solution for men who have already developed the condition?
Yes! One study showed that 83% of men who ate a supervised diet, exercised and went on testosterone therapy completely reversed their Metabolic Syndrome.  By simply engaging in various natural and quasi-natural solutions: exercise, diet and adding Bioidentical Testosterone back to more youthful levels, a man can (generally) undo this nasty condition.
Think of how difficult it is is to treat and reverse cancer. Or consider how many chronic diseases cannot be reversed at all, such as Parkinson's and Alzheimer's. But, fortunately, with Metabolic Syndrome, the great majority of men can actually escape this death trap. And that is good news!
NOTE: See also my link on Testosterone and Diabetes, where I discuss a similar anecdotal story on the reversal of diabetes. And how does testosterone work its magic on Metabolic Syndrome and insulin resistance? One review lists a number of reasons: 
1. "Influencing the commitment of pluripotent stem cells" [in muscle, i.e. accelerating muscle growth].
2. Insulin sensitivity of muscle cells is increased by augmenting mitochondrial capacity
3. Insulin sensitivity of muscle cells is increased by "fostering expression of oxidative phosphorylation genes"
4. Protectig pancreatic Î² cells" [which produce insulin]
5 "Influence of inflammatory cytokines" (See this page on Testosterone and Inflammation for more information.)
It would be remarkable if a drug or supplement did any one of these five things, but having one thing doing all five?? Well, no wonder testosterone can usually produce downright spectacular results for men with Metabolic Sydrome (or adult onset diabetes)!
1) Circulation, 2004, 110:1245-1250, "Impact of the Metabolic Syndrome on Mortality From Coronary Heart Disease, Cardiovascular Disease, and All Causes in United States Adults"
2) JAMA, 2002, 288(21):2709-2716, "The Metabolic Syndrome and Total and Cardiovascular Disease Mortality in Middle-aged Men"
3) Diabetes Care. May 2004 v27 i5 p1036(6), "Testosterone and sex hormone-binding globulin predict the metabolic syndrome and diabetes in middle-aged men"
4) Journal of Andrology, November/December 2009, 30(6), "Fifty-twoâ€“Week Treatment With Diet and Exercise Plus Transdermal Testosterone Reverses the Metabolic Syndrome and Improves Glycemic Control in Men With Newly Diagnosed Type 2 Diabetes and Subnormal Plasma Testosterone"
5) Nature Reviews Endocrinology, December 2009, 5:673-681, "Testosterone deficiency, insulin resistance and the metabolic syndrome"
6) The Journal of Urology, Sep 2005, "HYPOGONADISM AND METABOLIC SYNDROME: IMPLICATIONS FOR TESTOSTERONE THERAPY"