On Insulin Resistance

Jill Weisenberger, MS, RD, CDE

Chances are that when you hear the words insulin resistance you either think of type 2 diabetes or your eyes simply glaze over. However, the topic is far more complicated and thus more interesting than it first seems.

The hormone insulin regulates glucose in the blood, and when some of the body’s cells ignore insulin, blood glucose may rise to diabetic levels. But even with normal blood glucose levels, this resistance to insulin silently causes damage throughout the bodies of people unaware of their condition.

When Too Much Insulin
Wreaks Havoc on the Body

Researchers are beginning to unravel how insulin resistance plays an important role in medical problems such as high blood pressure, elevated triglycerides, dementia, liver disease, increased cancer risk and more.

Insulin 101
After you’ve finished your plate of spaghetti or had your morning bagel and juice, your blood is flooded with glucose, the product of carbohydrate digestion. The pancreas then sends out insulin to help usher excess glucose out of the blood and into the muscle and fat cells where glucose is used for energy or stored for later use. When fat and muscle cells first become resistant to insulin’s action, the pancreas sends out more and more insulin to do the job. Blood glucose levels normalize without any sign that something is awry. These higher-than-normal insulin levels may occur for years before a diagnosis of type 2 diabetes or pre-diabetes.

Too much insulin
Though best known for its role in glucose control, insulin has numerous other jobs and acts on tissues throughout the body. While fat and muscle cells are resistant to insulin’s action and demand additional insulin, other tissues throughout the body retain normal insulin sensitivity or become hypersensitive to insulin stimulation.

The extra insulin required to maintain normal or near-normal blood glucose levels wreaks havoc on these other systems of the body. For example, since the kidneys do not become resistant to insulin, the excess insulin may cause excess retention of salt and uric acid, which may contribute to both high blood pressure and gout.

Insulin acts on the ovary to stimulate testosterone release. Women with polycystic ovary syndrome (PCOS) may have ovaries hypersensitive to insulin, thus too much insulin results in excess testosterone. Thanks to various actions of insulin, elevated levels frequently lead to low HDL (good) cholesterol and high LDL (bad) cholesterol levels as well as increased blood triglyceride concentrations and nonalcoholic liver disease.

There is still more. “High insulin levels affect the brain and appear to increase the risk of dementia,” says Ewan McNay, PhD, an assistant professor of behavioral neuroscience, University at Albany.

“We now know that insulin acts within the brain as a key piece of several systems, including memory and regulation of proteins such as beta-amyloid. When a patient has elevated insulin for too long, insulin signaling is impaired, causing loss of memory and potential build-up of toxic amyloid, which causes Alzheimer’s-like symptoms.”

There are several proposed mechanisms for cognitive dysfunction including one related to insulin-degrading enzyme, adds Harvard professor of medicine, Francine Grodstein, ScD. The enzyme that breaks down insulin also breaks down amyloid beta, a peptide that accumulates in the brain with Alzheimer’s disease. “However, the enzyme preferentially degrades insulin over amyloid beta. This means that if there is a lot of insulin, then the enzyme will largely be focused on degrading the insulin and will not degrade amyloid beta,” which can accumulate in the brain and lead to cognitive impairment, she explains.

Cancer is another concern. According to a September 2010 publication of the American Institute for Cancer Research, high insulin levels are associated with a 200 to 300 percent increase in the risk of colon cancer in men, and a 200 to 400 percent increase in the risk of pancreatic cancer. Cancers of the liver, endometrium, bladder and breast may also be linked to high insulin levels.

Here again the mechanisms are complex. Insulin, for example, stimulates cell proliferation, and many cancer cells have a high number of insulin receptors. Thus cancer and pre-cancerous cells flourish. Excess insulin also leads to excess insulin-like growth factor (IGF-1), another stimulator of cell growth. Finally, IGF-1 inhibits apoptosis, the self-destruction of abnormal or cancerous cells.

Do you have insulin resistance?
There are no common blood tests for insulin resistance. By evaluating your laboratory results and physical exam, you and your physician can surmise the likelihood of this problem. Elevated blood glucose, triglycerides, blood pressure or low HDL-cholesterol are clues, though these conditions may have evolved for other reasons as well. Two dermatological indications are having multiple skin tags and having acanthosis nigricans, a disorder in which velvety, dark markings appear on the skin, especially in the skin folds of the neck, groin, armpits and under the breasts.

Resisting insulin resistance
Lifestyle changes can help control or prevent the problems associated with insulin resistance.

• Lose weight. Though not everyone with insulin resistance is overweight, most are, and losing weight makes the fat and muscle cells more sensitive to insulin. Researchers with the Diabetes Prevention Program (DPP) found that for each 2.2 pounds lost, people at risk of developing type 2 diabetes reduced their risk by 16 percent, suggesting shedding a few pounds improves insulin resistance. The DPP’s goal was for participants to lose seven percent of their starting weight (14 pounds for someone initially weighing 200 pounds).

• Eat right. Focus on wholesome foods and appropriate portions. Enjoy fruits, vegetables, whole grains, low fat or nonfat dairy foods, nuts, seeds, legumes and fish, poultry and lean meats. Wholesome doesn’t mean that you should eat unlimited quantities; eat the amount that helps you reach and maintain a healthy weight. Saturated fats and trans fats may worsen insulin resistance, so replace animal fats and hydrogenated oils with monounsaturated fats like avocado, nuts, nut butters and olive and canola oils.

• Move it and lift it. Both cardiovascular exercise like brisk walking, jogging, biking and swimming and resistance exercise like weight lifting and pilates improve insulin sensitivity. Do both because the combination is better than either alone. Among 251 adults with type 2 diabetes, those who performed 45 minutes of cardiovascular exercise three times a week and 45 minutes of resistance training three times a week showed improved diabetes control compared to the groups doing just one type of exercise three times weekly or no exercise at all, according to a study in September 2007 Annals of Internal Medicine.

• Hit the hay. Researchers at Leiden University Medical Center found that among both healthy individuals and those with type 1 diabetes, a single night of poor sleep decreases insulin sensitivity by about 25 percent. Aim for seven to eight hours of sleep each night.

Jill Weisenberger, MS, RD, CDE is a Registered Dietitian and Certified Diabetes Educator. Her articles have appeared in Diabetic Living, Diabetic Cooking, Environmental Nutrition, My Weight Loss, The Academy of Nutrition and Dietetics website, newsletters for the American Institute for Cancer Research and other national publications. She is the author of “Diabetes Weight Loss – Week by Week: A Safe, Effective Method for Losing Weight and Improving Your Health” (Academy of Nutrition and Dietetics, 2012). For more information, please visit http://www.jillweisenberger.com

The articles written by guest contributors are the sole responsibility of the individual writers in terms of factual accuracy and opinion and do not necessarily reflect the views of the publisher of this blog.

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