Indoor Cycling and Insulin Resistance

By Joan Kent

ICI/PRO readers know that exercise can reduce the risk of heart disease, type 2 diabetes, hypertension, cholesterol problems, cancer, and more. Underlying those diseases is insulin resistance. Exercise reduces health risks by making skeletal muscle more sensitive to insulin, effectively reducing the resistance.

Insulin is a hormone that”™s produced by the pancreas and allows glucose to enter cells for metabolism. It has several other functions, as well.

Under certain circumstances, someone might become insulin resistant, and the cells no longer respond to insulin”™s cues. To get the job done, the body”™s first line of defense is to produce more insulin. This may work, and can continue to work until the production of insulin no longer outpaces the degree of resistance. (That”™s an extremely oversimplified description of the onset of type 2 diabetes.)

Along the way, the high levels of insulin are likely to cause a variety of health issues. So it”™s not insulin resistance per se that causes disease, but the extra insulin that”™s released to compensate. This is associated with Series 2 prostaglandins and inflammation, a topic covered in a previous post (An Important Key to Health).

What we typically learn about insulin resistance (IR) is that it”™s a result of overweight. That”™s a true enough statement, but not the whole picture. For example, IR can be caused by genetic factors. Over 40 genetic mutations can result in someone”™s being born with insulin resistance or with a predisposition to it.

IR can also be the result of lifestyle factors. Lack of exercise is one obvious cause, along with diet. A high-fat diet can cause resistance to insulin through a specific mechanism, a high-carb diet through a different mechanism, and a high-fructose diet through yet another.

Insulin resistance isn”™t always a result of overweight/obesity. It can also be a cause. Cells differ in their sensitivity to insulin. The primary site of IR is skeletal muscle. How does insulin-resistant skeletal muscle behave? It doesn”™t allow glucose to enter the cell. The glucose ends up being transported to fat cells.

Another important site is the liver. How does an insulin-resistant liver behave? It doesn”™t respond to the feedback loop that tells it to stop releasing glucose, so glucose levels remain high.

An interesting connection with depression exists, as well.

You recall from 7th grade biology that amino acids are “the building blocks of protein.” One of insulin”™s functions is to transport amino acids to skeletal muscle, where they can be used for a variety of functions. Those functions include immune support, formation of hormones and enzymes, insulin receptor site turnover, pH and fluid balances, wound healing, tissue growth and repair, blood protein formation, energy use, and more.

The most important function is the formation of specific brain chemicals from specific amino acids. One amino acid, tryptophan, is the precursor of serotonin. The brain chemical serotonin has become commonly known, due to the anti-depressant medications that have been on the market for years.

Insulin resistance interferes with the transport of tryptophan to the brain and can therefore contribute to depression.

To the degree that indoor cycling can help reduce the incidence of insulin resistance, it can therefore help reduce the incidence of depression. This isn”™t as far-fetched as it sounds. In the research for my dissertation, participants completed tests for depression and anxiety, both before and after they had gone through the 8-week study. Consistently, the participants who were exercising regularly had lower scores for depression and anxiety.

It”™s kinda cool to realize that what we love to do helps our riders reduce their risk for health problems — along with their risk for mood issues.

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