Frequent strenuous exercise has been shown to reduce significantly the Ukelihood of heartattack, stroke, andblockage of blood vessels by lowering serum fibrinogen levels.
Long-term strenuous exercise low ers resting heart rate and blood pressure, further reducing the risk of heart attacks and stroke.
Weight-bearing, resistance, and impact exercise slow the loss of bone mineral associated with aging.
Ever hear the slogan "Use it or lose it"?
In a very real sense, if we don't use our bones, we lose them.
Although exercise does make weight control easier, it does not di rectly , atleast not as muchas wemaywish, "burn fat." Unless you work out at very strenuous levels for several hours each day, exercise isn't going to have a significant direct effect upon your body fat.
The effects of exercise are broader andmore indirect.
Oneof the great ben efits is that many people find that when they exercise, they have less desire to overeat.
The reasons for this are probably related to the re lease in the brain of neurotransmitters suchas endorphins. (As noted in the previous chapter, endorphins are "endogenous opiates" manu factured in the brain.
They can elevate mood, reduce pain, and reduce carbohydrate craving.
Brain levels of endorphins are reduced in poorly controUed diabetes.*) It might be said that in the samewaythat obe sity leads to further obesity, fitness leads to further fitness.
Even though your fat won't "melt away," exercise, particularly if you're atype 2 diabetic, isstill of value in aweight-reduction program because muscle buUding reduces insulin resistance.
Insulin resistance, remember, is linked to your ratio of abdominal fat to lean body mass.The higher your ratio ofabdominal fatto muscle mass, the more insulin-resistant you're likely to be.As you increase your musclemass, your insuUn needswiU be reduced , and having less insulin present in your bloodstream wUl reduce the amount of fat you pack away.
If you remember my old friend Howie from Chapter 12, his insulin re sistance dropped dramatically when he lost 100 pounds and radicaUy changed his ratio of abdominal fat to lean body mass.
Long-term, regular, strenuous exercise also reduces insulin resis tance independently of its effect upon muscle mass.
This makes you more sensitive to your own and injected insulin.
As a result, your in-
Plasma endorphin levels can be measured by most commercial laboratories. If you are curious about your level, just askyour physician to order plasmabeta en dorphin prior to starting an exercise program or a regimen of naltrexone and again a fewweeksor months later.
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sulin graduaUy becomes more effective at lowering blood sugar.
If you inject insulin, your dosage requirements wiU drop, and the fat- buUding effects of large amounts of insulin wiU likewise drop.
In my experience, daUy strenuousexercise wiU, overtime,bring about a steady, increased level of insuUn sensitivity.
This effect continues for about two weeksafter stopping an exercise program.
Awareness of this is es peciaUy important for those of us who inject insulin and must in crease our doses after two weeks without our usual exercise.
If you go out of town for only a week and cannot exercise, your increased in sulin sensitivity wiU probablynot suffer.
Although increased muscle bulk also increases insulin sensitivity, independently of the aboveeffect, this isverygradual and may require many months of bodybuUding beforeits separate blood sugar effects become noticeable.
HOW DOES EXERCISE DIRECTLY AFFECT BLOOD SUGAR?
Exercise does affectblood sugar,and for that reason it can make your efforts at blood sugar control sUghtly more difficult if you're taking in sulin or sulfonylurea blood sugar-lowering medications.* The bene fits, however, are so great that if you're a type 2 diabetic, you'd be fooUsh not to get involved in an exercise program.
For years, guidelines for the treatment of diabetes haverepeated the half-truth that exercise always lowers blood sugar levels.
In reaUty, physical exertion can indeed lowerblood sugar via increased number and mobilization of glucosetransporters in muscle ceUs.
Certain con ditions, however, must be present: exertion must be adequately pro longed, serum insulin levels must be adequate, blood sugar must not be too high, and for most of us, exercise should not be performed within 3 hours of arising in the morning (seepage 216).
Moderate to strenuous exercise such as swimming,running, weight Ufting, or tennis , as opposed to more casual exercise, such as walk ing , causes an immediate release of "stress," or counterregulatory, hormones (epinephrine, Cortisol, et cetera).
These signal the Uver and
As I will explain in Chapter 15,1 recommend against the use of sulfonylureas and similar medications.
UsingExercise to Enhance Insulin Sensitivity 215
muscles to return glucose to the bloodstream by converting stored glycogeninto glucose.The nondiabetic response to the additional glu cose is to release smaU amounts of stored insulin to keep blood sugars from rising.
Blood sugartherefore wUl not increase.
If a type 2 diabetic without phase I insulin responsewereto exercise for a few minutes, his blood sugar might increase for a whUe, but eventuaUy it would return to normal, thanks to phase II insulin response.
Thus, brief strenuous exercise can raise blood sugar, whileprolonged exercise can lower it.
For this reason, Dr.
EUiot P.
Joslin told a group of us (in 1947): "Don't run a block for a bus, run a mUe." When insulin is nearly absent in the blood, the glucose released in response to stress hormones cannot readUy enter muscle and Uver cells.
As a result, blood sugar continues to rise, and the muscles must rely upon stored fat for energy.
On the other hand, suppose that you have injected just enough long-acting insulin within the previous 12 hours to keep your blood sugar on target without exercise, and then you run a few mUes.
You wiU have a higher serum insuUn level than needed, because exercise facUitates the action of the insulin already present.Blood sugarmay thereforedrop too low.The same effect may occur if you are using sulfonylureas, a class of oral hypoglycemic agents.
Furthermore, if you haveinjectedinsulin into tissue that over- Ues the muscle being exercised, or perhaps into the muscle itself, the rate of release of insulin into the bloodstream may be so great as to cause serious hypoglycemia.
Nondiabetics and type 2s not on insulin or sulfonylureas can automaticaUy turn down their insuUn in response to exercise.
It may be unwise for you to exercise if your blood sugar exceeds about 170 mg/dl.
This number varies with the individual and the medications taken.
This is because elevated blood sugars wiU tend to rise even further with exercise.
This effect wiU be less dramatic if you're making a lot of insulin, and is most dramatic for a type 1 dia betic who doesn't take extra insulin to prevent the blood sugar eleva tion.
I have one type 1 patient who keeps her blood sugars essentiaUy normal.She stUl makesalittle insulinand dislikes insulin injectionsso much that she works out every dayafterlunch to save herself a shot to cover the lunch.
In her case, the exercise plus the smaU amount of in sulin she stiU makes together work very weU.
One greatbenefit of regular, strenuous exercise in type 2 diabetes, as mentioned earlier, is that it can bring about a long-term reduction of insulin resistance, by increasing muscle mass.
Long-term muscle de-
216 Treatment
velopment, therefore, can faciUtate blood sugar control and weight loss. It also reduces the rate of beta ceUburnout, because the increased ratio of muscle mass to abdominal fat reduces insulin resistance and thus reduces the demand for insulin production.
THE DAWN PHENOMENON AND EXERCISE
Several of my type 1 patients must take additional fast-acting insulin when they exercise in the morning, but not when they exercise in the afternoon. This is a dramatic exampleof how the dawn phenomenon reduces even injected serum insulin levels. In the afternoon their blood sugardrops with exercise, but in the morning it actuaUy goesup if they do not first inject some rapid-acting insuUn.
RESTRICTIONS ON EXERCISE
Despite the benefits that exercise can have, an exercise program that isn't sensibly put togethercan have disastrous results.
Even if you think you're perfectiyfit, your physicianshould be consulted before you pro ceed.
Keep in mind that there are certain physical conditions that may restrict the type and intensity of exercise you should attempt.
Yourcur rent age, your cardiac and muscle fitness, the number of years you've had diabetes,the average level of your blood sugars,whether or not , and how much , you'reoverweight, and what sort of diabetic compli cations you havedeveloped: aU thesemust be considered to determine what kind of exercise you should undertake,and at what intensity.
Before You Start FoUowing are severaldifferent aspectsof your health you should con sider and discusswith your physicianbefore embarking upon an exer cise program.
Heart. Everyone over the age of forty, and diabetics over the age of thirty, should be tested for significant coronary artery disease before beginning a new exercise program. At the veryleast,an exercisingelec trocardiogram, stress echocardiogram (my preference), or stress thal lium scan is usuaUy advised. An abnormal test may not necessarUy
Using Exercise to Enhance Insulin Sensitivity 217
rule out exercise, but it may suggest restraint or close supervision whUe exercising. Again, seek your doctor's advice before starting any new exercise program.
High blood pressure. Although long-term exercise helps to lower resting blood pressure, your blood pressure can risewhUe you are ex ercising. If you're subject to wide pressure swings, there maybe risk of stroke and retinal hemorrhages during strenuous exercise. Again, first contact your physician.
Eyes.
Before beginning anyexercise program, you should have your eyes checked by a physician, ophthalmologist, or,ideaUy, a retinologist experienced in evaluating diabetic retinal disease (retinopathy).
Cer tain typesof retinopathy are characterized by the presence of neovas cularization, or very fragUe newbloodvessels growing from the retina into the vitreous gel that overUes it.
If you strain too much, assume a head-down position, or landhardon yourfeet, these canrupture and hemorrhage, causing blindness.
If yourphysician or ophthalmologist identifies such vessels, you'U probablybe warned to avoidexercises re quiringexertion of strong forces (e.g., weight Ufting, chinning, push ups, sit-ups) and sudden changes of motion (e.g., running, jumping, falling, diving).
Bicycling and surface swimming are usuaUy accept able alternatives, but first check withyourphysician.
Fainting. A form of nerve damage caUed vascular autonomic neu ropathy (caused by chronically high blood sugars) can lead to light headedness and even fainting during certain types of exertion (see page 341), such as weight Ufting and sit-ups. Such activities should therefore be embarked upon graduaUy and only after instruction by your physician.
If you take blood sugar-lowering medications. If you take in sulin or oral hypoglycemic agents, it is wise to make sure your blood sugars are stabilized before you begin a strenuous exercise program. As previously noted, exercise can have significant effects upon blood sugars and introduce another variable that can confuse anyone re viewing your blood sugar data. It's much easier to readjust your diet and/or medications to accommodate physical activity after blood sug ars are under control.
218 Treatment