Fasting insulin levles are, in my opinion, one of the most important numbers that you need to know and evaluate regularly. Fasting insulin isn't as sexy as testosterone, but it can sure affect your sex life! (Actually, as we will discuss below, testosterone powerfully impacts insulin levels and this is one of the primary reasons that low testosterone is potentially so dangerous for hypogonadal men.) One study looked at the relationship between erectile dysfunction and insulin resistance/levels and found the following: 
a) Metabolic Syndrome, a.k.a prediabetes, was present in 43% of the participants compared to 24% in a control group.
b) About three fourths of the erectile dysfunction patients had insulin resistance compared to only a fourth in the general population.
c) Metabolic syndrome (P = 0.01), IR (P = 0.01), and fasting blood sugar (FBS) >110 mg/dL (P = 0.01) correlated positively and moderately with increasing severity of ED by SHIM score
So you don't just want to monitor testosterone for bedroom performance but insulin as well. In fact, I always say that you have two big enemies that create 90% of all health issues (and probably erectile dysfunction) for men in urban societies: Insulin Resistance and Inflammation. These Two I's wreak havoc in virtually every tissue of your body from the brain to the penis if allowed to go out of control. And guess what? Fasting insulin is currently the measurement of choice used by physicians for determining insulin resistance.
What exactly is insulin resistance? The condition occurs when insulin does not push glucose into your cells at the normal rate, creating a toxic environment where both blood glucose and insulin levels rise. Insulin resistance is the hallmark feature of Metabolic Syndrome, or prediabetes, and it is a HUGE risk factor many kill-you-slowly diseases such as heart disease and erectile dysfunction. If you are a middle-aged or senior male in a Western society, you very likely have the beginnings of insulin resistance, whether you know it or not.
So what are safe fasting insulin levels and how can you bring them down? Well, first of all, your lab results will probably have a huge range associated with it. My physical a few months ago showed a range of 2-25 mIU/l (or uIU/ml). Physicians generally regard you to have an actual medical condition, insulin resistance and/or hyperinsulemia, in the 10-12 range.
However, I recommend that you try to get your fasting insulin well below 12 or even 10 mIU/l. (My doctor, for example, recommended getting it below 5, which, interestingly enough, is the level that some health indigenous populations have.) The reason is that researchers have found that blood glucose/insulin issues cause major health issues:
a) Post-Meal Blood Sugar Spikes. The refined carbohydrates in many of our meals spike glucose levels which actually kills a few of our pancreatic beta cells. Over the decades these cells dwindle in number and you have prediabetes and diabetes setting in. (Your beta cells actually produce insulin, so as they die off, you're in trouble.) Of course, I urge you to a) stay away from refined carbohydrates and sugars and b) buy an inexpensive blood glucose monitoring kit. This article by LEF covers simple testing that you can do after a meal.
b) Small, Dense LDL Particles. As insulin resistance sets in, many men begin to produce smaller LDL particles and these smaller particles accelerate arterial/vascular damage and injury to your all-important endothelium. As your endothelium as injured with the passing years, your nitric oxide levels fall and erectile dysfunction sets in. Many studies have verified that LDL particle size, fasting insulin and various inflammation factors are tightly related to heart disease. 
c) Cognitive Decline and Dementia. Almost everyone knows about the cardiovascular issues associated with insulin resistance. However, many men to do not know that as the decades roll by insulin resistance injures the delicate tissues in the brain as well. 
So how you control your fasting insulin levels? It will probably not surprise you to find that all the key things I push on this site as a natural lifestyle greatly help control and reduce fasting insulin levels. Below we have a list of some of thse key factors and the studies to go along with them:
Also, it should be noted that one study looked at men and women with lower or medium cholesterol levels (less than about 210), yet with many signs of Metabolic Syndrome. It found that insulin levels appeared to be independent risk factor for heart disease even when things like non-smoking, blood pressure, exercise levels and blood gluose were taken into account. In fact, it conferred about twice the risk of heart disease.  So never ignore the signs of insulin resistance and discuss with your doctor.
So how can you control fasting insulin levels? Below are 15 Ways to Control Your Insulin Levels based on the research.
CAUTION: If you are diabetic or on medications, be doubly sure to talk with your doctor before making any changes as low or high blood sugar is potentially very serious.
1. Weight. Get those high school abs back. Your woman will love it and it will drop your insulin levels significantly. Yes, those extra pounds around your gut have been found to be very correlated to fasting insulin levels.  And many studies have verified that losing weight helps you drop your fasting insulin levels accordingly.
2. Exercise. When it comes to lower insulin levels and decreasing insulin resistance, exercise is king. As we all know, physicians are reluctant to prescribe natural lifestyle solutions generally speaking. However, very often now, physicians will immediately tell type II diabetics to start an exercise program. The reason is simple: moving the body just as surely moves the blood sugar. One interesting study on children found that fitness levels were actually a better predictor of fasting insulin levels than the degree of being overweight. 
Many studies have shown the power of exercise over insulin levels. But one research summary pointed out that one of the surprising reasons that exercise is so effective is that it converts fast twitch glycolytic IIb fibres to fast twitch oxidative IIa fibres and increases the capillary density of muscle tissue.  Yeah, muscle is much more important than just simple appearance: it helps you inside and out.
Early research did not show improved insulin sensitivity with low intensity workouts. However, more up-to-date research using the latest technology did show virtually any type of exercise improved insulin sensitivity, which makes sense considering that the vast majority of human history is based upon simple walking. 
3. Testosterone. Low testosterone is associated with both diabetes and Metabolic Sydrome.  And the reason is not well-know to many men. However, in my book Low Testosterone by the Numbers, I document how testosterone has a very significant effect on insulin levels and men with low testosterone will very likely see their insulin levels and insulin resistance rise accordingly. This is one of the many reasons that low testosterone is correlated with increased cardiovascular mortality, arterial plaque, diabetes and Metabolic Syndrome. For more information, see my link on Testosterone and Insulin.
4. Coffee. Counterintuitvely, coffee can be a big help with managing blood glucose and insulin levels due to a phytochemical that is naturally occurring in the coffee bean (chlorogenic acid). Supplement manufacturers have actually begun creating "green coffee bean extracts" for just this reason. You can read more about it in my link on The Benefits of Coffee Consumption, where I document how regular coffee consuption can reduce your risk for cardiovacular disease and diabetes.
5. High Fat Diets. When researchers want to induce insulin resistance in laboratory animals, how do they do it? Do they give them some kind of special drug? No, it's much simpler than that: they simply feed them a high fat diet.  And, yes, you too can drive yourself into insulin resistance, just like a lab rat, if you eat enough fat in your meal. Whole food, plant-based, high fiber diets are excellent choices to avoid insulin resistance. NOTE: Fish oil can offer some protection against the insulin promoting effects of high fat diets. 
6. Low Fat Diets: Triglycerides are very correlated with insulin resistance and some studies have even suggested using triglycerides along with fasting insulin as an excellent way to diagnose insulin resistance in the general populatiion. It is a myth that a Low Fat Diet will push triglycerides and fasting insulin to unsafe levels. For example, I eat a predominantly Low Fat Diet and my triglycerides were 80 at my last checkup! This is about half of the threshold usually given as a warning for patients. Furthermore, Dr. Barnard has actually used a Low Fat Diet to reverse diabetes quite successfully in his practice and you can read about it in his book. Of course, the key is that a Low Fat Diet must be comprised of whole foods. Cheating with sugars and refined carbohydrates ann calling those Low Fat could get you into trouble. It may also be smart to avoid wheat as you'll see in my link on Review on Wheat Belly. But doing a true Low Fat Diet has been shown to actually increase LDL particle size, which is what you want. 
7. Mediterranean Diet. Several studies have shown that a Mediterranean Diet can help with insulin resistance and other features of the Metabolic Syndrome. For more information, see this link on The Many Benefits of a Mediterranean Diet.
8. Sleep. Yes, exercise is critical to control insulin sensitivity, but NOT moving is just as critical. That's right - your pillow time has a dramatic effect on your insulin levels. In fact, one study on diabetics showed that those who slept 7-8 hours had almost half the insulin levels of those who slept 5-6 hours!  That's an incredible reduction. Many studies have looked the nasty effects of sleep apnea upon insulin sensitivity as well. One study actually found that sleep apnea was an independent risk factor for loss of insulin sensitivity.  (See my links on Sleep and Testosterone, Apnea and Erectile Dysfunction and Apnea and Testosterone for more information.)
NOTE: Does having hyperinsulinemia (clinically high insulin levels) or elevated fasting insulin levels in young adulthood matter later in life? You bet! According to a recent study, it did not matter what ethnicity or gender you were: everyone was significantly more likely to develop hypertension 20 years later.
9. Stress. Sleep is actually a stressor and lack of sleep usually increase cortisol levels. And, in fact, any stressor will do the same. The problem is that increasing cortisol increases Visceral Fat, which begins to affect the liver. I discuss the Visceral Fat/cortisol/liver connection in my link on Insulin Resistance and the Liver.
10. Fiber. A number of studies have verified that fiber has a positive effect on insulin levels and insulin sensitivity.  Of course, it's best to get this from vegetables, fruits and whole grains (excluding wheat and soy in my opinion). And, as expected, fiber consumption is tied to a lower risk of Type II diabetes as well. 
11. Alcohol. Some study work has shown that moderate alcohol consumption leads to lower insulin levels.  This is likely one of the many reasons that (moderate) alcohol consumption is associated with reduced cardiovascular risks. However, there are defiites downsides to alcohol, including slighly elevated estrogen and increased risk for GI cancers. See my links on Beer and Testosterone and The Pros and Cons of Alcohol for some additional information.
12. Dark Chocolate. Chocoholics might say it is too good to be true, but there is study out there showing that dark chocolate and dark cholocate alone improved insulin sensitivity. 
13. ALA (Alpha Lipoic Acid). This supplement improves insulin sensitivity in muscle tissue.  It works in diabetics as well  Of course, discuss with your doctor as it can change medication requirements. Also, it should be taken several time during the day since it has a relatively short half life in the body.
14. Fructose. Actually, there is another way (besides high fat diets) that researchers use to induce insulin resistance: high fructose diets.  If you have enough fructose, greater than about 25-50 grams/ day, you can increase your insulin resistance and many other nasty things that can affect your fasting insulin levels. For more information, see these Fructose Summary Links.
15. Probiotics. Perhaps the most counterintuitve way to improve insulin responsiveness is shoving good bacteria in your gut. Well, it's true, yet another reason to take probiotics is for their insulin-improving characteristics. 
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