For you middle-aged and beyond guys, this page is one of my most imporant and can save both you and your erections. "You don't know the power of the dark side" until you start looking at what fat can do to you. Sure, it can keep you warm in the winter, but it all goes downhill from there.
Visceral fat, i.e. fat in the stomach area that raps around your internal organs, is what is particularly nasty for us guys, because it is the fat that leads to insulin resistance and decreased blood flow. FMD (Flow Mediated Dilation) is the medical term for decreased blood flow from your precious endothelium and researchers have found that even 10 pounds of extra fat is associated with substantially decreased FMD.  That means less blood flow and into your arteries and your penis when you're trying to do your solemn bedroom duty. The title of this study was "Modest Visceral Fat Gain Causes Endothelial Dysfunction in Healthy Humans" and, if you've read this site much, you know that life for any male is dependent on the all-important endothelium.
Visceral fat also leads to insulin resistance and Metabolic Syndrome (and eventually diabetes, heart disease and so on). It is very correlated with the inflammatory marker TNF-alpha and, more directly, with raising FFA (Free Fatty Acid) levels in the liver and blood. It is these elevated FFA's that will lead you to the land of insulin resistance.  Furthermore, animal studies have shown that if you remove visceral fat you actually get rid of insulin resistance. One prominent theory to explain this is that visceral fat may release fatty acids that uniquely trigger changes in liver metabolism.  In other words, this is something that subcutaneous (normal) fat does not do and further proof of this is the fact that, in animals at least, if you remove visceral fat it actually gets rid of insulin resistance. 
However, scientists have discovered that the primary issue is something called 'lipotoxicity'. Basically, what occurs is that first fat begins accumulating in our normal adipose tissue. Once the adipose, or subcutaneous fat, is "full", then the fatty tissue begins "resistant" to any more fat storage and induces insulin resistance. This is when the river changes course and now the fatty acids begin deposting around your organs, such as the liver.  The trigger point for lipotoxicity is different for everyone, but the signs are insulin resistance and belly fat to be sure.
Researchers have also found that, as you gain weight, your adiponectin levels fall and inflammation rises, and this signals the liver to begin to store fat. As the liver stores fat, all of the above occurs, something I discuss in my page on Inflammation and the Liver.
All of this leads to the viscious cycle that so many of us struggle with in middle age, because visceral fat and cortisol are good buddies. Studies show that visceral fat has four times the cortisol receptors that subcutaneous fat has.  Also, remember those cortisone injections that some athletes receive for joint issues? Cortisone is converted in the body to cortisol by an enzyme that is stored in fat tissues. So the fatter you are, the more cortisol, in general, that you will have. Furthermore, visceral fat has been shown to have higher concentrations of this enzyme! Elevated cortisol levels increase appetite and, again, you have yet another make-you-fatter-and-fatter factor working against you. Finally, "Relative to subcutaneous fat, visceral fat deposits are mobilized at a higer rate to produce fatty acids..." 
Here is where the vicious cycle kicks in as well: many studies have shown that stress and cortisol are associated with visceral fat accumulation.  Yes, cortisol increases visceral fat and cortisol decreases testosterone and lowered testosterone leads to muscle loss which will also make you fatter still.
So how do you get off this runaway train? It's not as hard as you think and here are the several key ways to lose that extra visceral fat:
1. Strength and/or Weight Training. This should be number one in your visceral fat fighting strategies. Strength training builds muscle and that has been shown to directly fight visceral fat and insulin resistance. 
2. Testosterone. If you have low testosterone, testosterone therapy can literally melt away a significant amount of visceral fat with no other changes according to a number of studies. I discuss the reasons in my link on Testosterone and Visceral Fat.
3. Aerobic training. A recent metanalysis showed that aerobic exercise decreased visceral fat in a dose-dependent manner (for those w/o metabolic disorders). Another interesting thing: the study found that just exercise with no accompanying weight loss led to decreased visceral fat. In other words, you can slowly lose visceral fat just by exercising even without trying to lose weight. And when weight loss was added, visceral fat melted off rapidly. 
4. Sleep. Watch your sleep. One recent study showed that those getting less than five hours of sleep had significantly accumulated visceral fat deposits. 
5. Medications. A number of pharmaceuticals increase visceral fat, including Paxil (and other antidepressants), lithium, Depo-Provera - tell your woman if she's on it. 
6. Stress. The stress hormone cortisol is a known visceral fat booster. See my link on Stress Management for ways to decrease cortisol and stress.
7. Tart Cherry Juice. In animal studies, tart cherry juice reduced visceral fat.  This is interesting, because Tart Cherry Juice reduced TNF-alpha (and IL-6) levels in this animal study.
8. Alcohol. It is no secret that alcohol increases overall fat levels by virtue of simply adding extra calories. However, what is not as well known is that several studies have shown that alcohol is also associated with visceral fat accumulation.  Yes, "beer belly" is a good name after all.
NOTE: Visceral fat and fasting insulin levels are also associated with decreased growth hormone.  And, of course, decreased growth hormone levels will also pack on the pounds. Researchers have not found that growth hormone therapy particularly impacts visceral obesity. What this may very well mean, then, is that visceral fat affects growth hormone levels in and of itself.
Sure, there are other things like green tea that will give you a boost in losing visceral fat, but the above three itens are your Big Three Gut Busters. As always, the bottom line is about lifestyle. There's no way to melt away that Beer Gut, except to pay the price and do what you need to do in the gym or on the road, track, court and then sleep it off at night. Well, and lay off the beer...
1) J Am Coll Cardiol, 2010; 56:662-666, "Modest Visceral Fat Gain Causes Endothelial Dysfunction in Healthy Humans"
2) Diabetes Metab Rev, 5:83 109, "Biology of regional body fat distribution: relationship to non-insulin-dependent diabetes mellitus"; Lancet, 1963, "The glucose-fatty acid cycle: its role in insulin sensitivity and the metabolic disturbances of diabetes mellitus"
3) Psychosomatic Medicine 62:623-632, 2000, "Stress and body shape: stress-induced cortisol secretion is consistently greater among women with central fat"
4) Obes Res. 1996 May;4(3):245-52, "Mental distress, obesity and body fat distribution in middle-aged men"
5) J Appl Physiol. 1994;77:614 620, "Effects of strength training on total and regional body composition in older men"
6) Int J Obes (Lond), 2007 Dec;31(12):1786-97. Epub 2007 Jul 17, "A dose-response relation between aerobic exercise and visceral fat reduction: systematic review of clinical trials"
8) Ladies Home Journal, "The Over-40 Factor", Dec 10/Jan 11 issue, p. 133.
9) Journal of Medicinal Food, 2009, 12(5):935-42, "Regular tart cherry intake alters abdominal adiposity, adipose gene transcription, and inflammation in obesity-prone rats fed a high fat diet"
10) The Journal of Clinical Endocrinology & Metabolism, Aug 1 2001, 86(8):3845-3852, "Abdominal Visceral Fat and Fasting Insulin Are Important Predictors of 24-Hour GH Release Independent of Age, Gender, and Other Physiological Factors"
11) Diabetes Care, 2002, 25:1631 1636, "Unique Effect of Visceral Fat on Insulin Sensitivity in One Hispanic Children With a Family History of Type 2 Diabetes"
12) Diabetes, Oct 2002, 51(10):2951-2958, "Removal of Visceral Fat Prevents Insulin Resistance and Glucose Intolerance of Aging An Adipokine-Mediated Process?"
13) J Nutr, Aug 1 2003, 133(8):2655-266, "Alcohol Drinking Patterns Differentially Affect Central Adiposity as Measured by Abdominal Height in Women and Men"
14) International Journal of Obesity, 2003, 27:238 246, "Waist circumference in relation to history of amount and type of alcohol: results from the Copenhagen City Heart Study"
15) Expert Rev. Cardiovasc. Ther, 2008, 6(3):343 368, "Pathogenic potential of adipose tissue and metabolic consequences of adipocyte hypertrophy and increased visceral adiposity"