PART 2

The Laws of Small Numbers 

Or

How To Have Tight Control Without Hypoglycemia

(To review Part One “The Law of Carbohydrate Estimation” go to http://www.diabetesincontrol.com/drbernstein/article1.htm 

PART 2 

The Law of Insulin Dose Absorption 

Think again of traffic. You're driving down the road and your car drifts slightly toward the median. To bring it back into line, you make a slight adjustment of the steering wheel. No problem. But yank the steering wheel, and it could carry you into another lane, or could send you careening off the road. 

When you inject insulin, not all of it eventually reaches your bloodstream. Research has shown that there's a level of uncertainty as to just how much absorption of insulin takes place. The more insulin you use, the greater the level of uncertainty. 

When you inject insulin, you're putting beneath your skin a substance that isn't, according to your immune system's way of seeing things, supposed to be there. So a portion of it will be destroyed as a foreign agent before it can reach the bloodstream. The amount that the body can destroy depends on several factors. First is how big a dose you inject. The bigger the dose, the more inflammation and irritation you cause, and the more of a "red flag" you send up to your immune system. Other factors include how deep you injected it, how fast you injected it, and where you injected it. 

Your injections will naturally vary from one time to the next. Even the most fastidious person will unconsciously alter minor things in the injection process from day to day. So the amount of insulin that gets into your bloodstream is always going to have some variability. The bigger the dose, the bigger the variation. 

A number of years ago, researchers at the University of Minnesota demonstrated that if you inject about 20 units of insulin into your arm, on average, you'll get a 39 percent variation in the amount that makes it into the bloodstream from one day to the next. They found that abdominal injections had only a 29 percent average variation, and so recommended that we use only abdominal injections. On paper that seems fine, but in practice the effects on blood sugar are intolerable. 

Say you do inject 20 units of insulin at one time. Each unit lowers the blood sugar of a typical 150-pound adult by about 40 mg/dl. A 29 percent variability will create a 7-unit discrepancy in your 20-unit injection, which means a 280 mg/dl blood sugar uncertainty (40 mg/dl x 7 units). The result is totally haphazard blood sugars and complete unpredictability, just by virtue of the different amounts of insulin absorption. 

Research and my own experience demonstrate that the smaller your dose of insulin, the less variability you get. For Type I diabetics who are not obese, we'd ideally like to see doses anywhere from H unit to 6 units or at the most 7. Typically, you might take 3–5 units in a shot. At these lower doses, the uncertainty of absorption approaches zero.

I have a very obese patient who requires 27 units of long-acting insulin at bedtime. He's so insulin-resistant that there's no way to keep his blood sugar under control without this massive dose. In order to ameliorate the unpredictability of large doses, he splits his bedtime insulin into four small shots given into four separate sites using the same disposable syringe. As a rule, I recommend that a single insulin injection not exceed 7 units. 

The Law of Insulin Timing 

Again, it's very difficult to use any medication safely unless you can predict the effect it will have. With insulin, this is as true of when you take it as it is of how much you take. If you're a Type I diabetic, fast-acting (regular) insulin can be injected 30–40 minutes prior to a meal tailored to your diet plan to cover the ensuing preventable rise in blood sugar. Regular, fast-acting insulin, despite the name, doesn't act very fast, and cannot come close to approximating the phase I insulin response of a nondiabetic. To a lesser degree this is also true of the new, faster-acting lispro insulin. Still, these are the fastest we have. Small doses of regular start to work in about 40 minutes and finish in about 5 hours; lispro starts to work in about 15 minutes and finishes in 4–5 hours. This is considerably slower than the speed at which fast-acting carbohydrate raises blood sugar. 

If you eat a meal not specifically tailored to our restricted-carbohydrate diet, you'll get a postprandial increase in blood sugar, eventually followed by a decrease as the fast-acting insulin catches up. This means that you'll have high blood sugars after every meal, and you could still fall prey to the long-term complications of diabetes. If you try to prevent the inevitable postprandial blood sugar spike by waiting to eat until after the start-time of your insulin, you may easily make yourself hypoglycemic, which could in turn cause you to overcompensate and overeat—that is, presuming you don't lose consciousness first.

Type II diabetics have a diminished or absent phase I insulin response, and so they face a problem similar to that of Type 1's. They have to wait hours for the phase II insulin to catch up if they eat fast-acting carbohydrate. 

The key to timing insulin injection is to know how carbohydrates and insulin affect your blood sugar and to use that knowledge to minimize the swings. Since you can't approximate phase I insulin response, you have to eat foods that allow you to work within the limits of the insulin you make or inject. (If you think you'll miss out on the great high-carbohydrate, low-fat diet many have been raving about, there is considerable evidence that restricting carbohydrate is healthier not only for diabetics but for everyone. See Protein Power, by Michael and Mary Dan Eades, Bantam Books, 1996, for more details on this point.) 

If you consume only small amounts of slow-acting carbohydrate, you can actually prevent postprandial blood sugar elevation even with injected regular or lispro insulin. In fact, by restricting carbohydrate intake, many Type II diabetics will be able to prevent this rise with their phase II insulin response, and will not need preprandial injected insulin.