Insulin and Weight Gain: What’s the Link?

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Nora Saul, M.S, R.D., L.D.N., C.D.E.

Nora Saul is a Certified Diabetes Educator and Manager of Nutritional Education at Joslin Diabetes Center

The song says, “love and marriage, go together like a horse and carriage!”

That’s how many people feel about insulin and weight gain; they’re stuck together and “you can’t have one without the other.”

I am a great believer in love, which I think is alive and well, but if you read the statistics on marriage… So maybe insulin and extra pounds aren’t a foregone conclusion.

Not everybody who uses insulin automatically gains weight, and there are millions of people without diabetes whose bodies make insulin everyday who can maintain a healthy weight without even trying.

So, why has insulin gotten such a bad rap—and are there ways to avoid weight gain?

Delaying Insulin Start

One reason people with type 2 diabetes often see the pounds pile on after they begin taking insulin is that they’ve waited too long to start.

For 99 percent of people with type 2 diabetes, taking pills is by far the more comfortable choice than taking injections, and they—and often their physicians—wait until the eleventh hour before making the transition.

If you wait too long to start insulin, your blood glucose will be severely elevated, and the stage is set for the scale to begin an almost magical, unrelenting climb upward, despite any change in your calorie intake. Why?

When the blood glucose is very high, the normal metabolism of carbohydrate and fat is undermined.  Under normal circumstances, the carbohydrate we eat is converted into glucose. Then, the glucose is used by the muscle cells for immediate energy or excess glucose is changed into triglyceride (a form of fat) for later use.

But in poorly controlled diabetes, instead of insulin moving glucose from the blood stream into the muscle, the muscle cells resist the action of insulin, and the glucose is diverted into the urine. In other words, the body wastes its calories in the urine. In addition, the body loses its ability to store fat efficiently, wasting more calories in the process. (This is why people who have poorly controlled diabetes also sometimes experience weight loss.)

Starting insulin corrects many of the abnormal metabolic pathways, and you now can process glucose as you should—excess glucose that was being lost in the urine can now be stored as fat.

Low Blood Glucose

Another reason that some people experience weight gain post insulin therapy is they may now start to have hypoglycemic reactions or low blood sugars.

When this happens, you need to eat in order to bring your blood glucose back into the normal range. Although necessary, treating low blood sugars adds extra calories to your  diet—and if it happens often enough, you’ll start to gain weight, unless you compensate for the added snacks.

Longer Insulin Action

Finally, injected insulin remains in the body longer than the insulin your pancreas makes. Insulin secreted by the pancreas usually peaks within one hour after a meal—and insulin and glucose levels return to premeal levels within two hours.

This isn’t true for injected fast or rapid acting insulin, where the duration of the insulin’s action can often take twice as long. The longer action time means insulin has a greater chance to lower blood glucose and prompt feelings of hunger.

Is the Battle Lost before It’s Begun?

No, first of all the average weight gain from starting insulin is only about six pounds.  In our experience here at Joslin, those patients in very poor control who—as a result—were losing weight prior to insulin therapy tend to gain the most weight.

And there are things you can do to prevent or minimize your chances of gaining weight. Beginning a solid exercise program and starting to follow a lower calorie meal plan at the time you start taking insulin is your best defense. Ask your healthcare provider to recommend an educator who can help you get started.


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One Response to Insulin and Weight Gain: What’s the Link?

  1. Tom Beatson says:

    On Facebook, the opening lines of your post were:
    “Joslin Diabetes Center
    Did you switch to insulin and experience weight gain?”
    No, I switched to insulin and it saved my life, 68 years ago!
    Tom Beatson

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