An injector sitting on a scale denting it. The display is cracked and has an up arrow on it.

Does Insulin Cause Weight Gain? Not Exactly

One reason people with type 2 diabetes avoid insulin treatment is because they have heard that insulin causes weight gain. In a quick internet search, I’m seeing phrases like “insulin and weight gain go hand-in-hand” or “weight gain is a side effect of insulin.” In one place this description was provided “Insulin causes weight gain when the cells absorb too much glucose and the body converts this into fat.1 All of these statements are wrong!! It’s like saying hammers cause smashed thumbs. Here’s the real story.

How insulin functions in our bodies

Insulin – whether it’s “natural” as produced by your pancreas or injected (inhaled) as a “medication” – gets glucose out of your bloodstream and into your cells, where it’s needed for fuel. As a treatment for diabetes, it is the most efficient tool available for lowering blood glucose levelsand providing energy to all of your cellular activities. If insulin is not moving glucose into your cells, you are slowly excreting excess blood glucose in urine as your body seeks to establish a more normal blood glucose level.

Why might people with diabetes need insulin therapy?

If you have type 2 diabetes this is the “struggle.” Cells become less sensitive to insulin – some medications (metformin) help increase cell sensitivity to insulin. Your ability to produce enough insulin lags – some medications stimulate your pancreas to release more insulin. Other medications work to manage how efficiently or how quickly glucose from food (or stored glucose in your liver) gets into the bloodstream. Newer drugs increase glucose excretion in urine. Insulin therapy is straightforward.

The story behind insulin and weight gain

In simple terms, insulin therapy increases your efficiency. The excess glucose that’s been circulating in your bloodstream, keeping blood sugar levels high as your kidneys work to excrete more, is instead taken into your cells more efficiently. And, so are all of the glucose calories – 4 calories per gram of glucose – that you’ve been flushing down the toilet. Your increased efficiency means you are retaining more calories from the food you consume. The statement “insulin causes weight gain when the cells absorb too much glucose and the body converts this to fat” is both misleading and backward. We want our metabolism to be more normal – we want our cells absorbing glucose in a more normal way to keep blood glucose levels in a more normal zone. This statement should read "too much glucose causes weight gain when our body efficiently absorbs glucose into cells and converts excess glucose to fat."

We have control over weight gain

Yes, weight gain is often associated with insulin therapy. But to call insulin a “cause” or to call weight gain a “side effect” or “going hand-in-hand” implies that we have no ability to counteract this possible outcome by adjusting our diet or by using “excess” glucose by exercising more. Of course, we can counteract this possible outcome.

Smashed thumbs are associated with hammer use, but we can take steps to avoid smashing our thumb when using a hammer. Weight gain is associated with insulin use, but we can take steps to avoid gaining weight when using insulin. End of story.

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