How Does Insulin Resistance Affect Your Brain Health?

Written by Carolyn Williams, PhD, RD

Alzheimer’s disease and type 2 diabetes are two of the most common chronic diseases¹ in the United States, conditions that on the surface appear to have little overlap or relationship. But if you look a little deeper, you’ll find that research suggests there’s a substantial amount of overlap between the two, and the connection is the role that insulin resistance plays in the development and progression of both.

What is Insulin Resistance?

When it works as designed, insulin is easy to take for granted because of how seamlessly it keeps blood glucose in check.  Glucose, which serves as the main energy source for cells, is released into the bloodstream when carbohydrates are broken down. This influx of glucose into the bloodstream causes blood glucose (also referred to as blood sugar) levels to rise. Sensing this increase, the pancreas secretes insulin into the bloodstream. Circulating insulin then helps glucose enter cells. In doing this, cells get energy, and blood sugar levels return to within the normal range as glucose is removed from the bloodstream.

Assisting cells in their uptake of glucose is one of insulin’s primary roles, and it’s one that is essential for survival since most cells in the body can’t do this without insulin. Consequently, issues arise when insulin can’t fulfill these job duties. This usually occurs for one of two reasons:  1.)  the pancreas stops making insulin (the scenario that occurs in type 1 diabetes²) or 2.) the body’s cells become insulin resistant (the scenario that occurs in type 2 diabetes³).

Insulin resistance⁴ develops slowly and quietly, largely influenced by lifestyle habits, and it’s a condition where cells progressively become less sensitive and responsive to insulin. This decrease in sensitivity reduces glucose uptake, which leaves cells struggling to meet energy needs, and it also means that blood glucose levels don’t decline like they should. The pancreas compensates by secreting additional insulin which is effective temporarily in pulling levels back to within normal levels. However, the pancreas can’t keep up with these extra insulin requirements for too long, so individuals will slowly exhibit elevated fasting blood glucose levels (measures used as diagnostic criteria for prediabetes and type 2 diabetes). These elevated levels also contribute to issues like inflammation and weight gain.

Insulin Resistance in the Brain^5,6

The role that insulin plays in the brain is slightly different. This is due to the fact that most neurons are not dependent on insulin for glucose uptake, something that caused the idea of brain insulin resistance to be overlooked by researchers for years. In fact, it wasn’t until about two decades ago that researchers looked closely at the potential impact that insulin resistance has on brain health. This was spurred by epidemiological data that pointed to a significantly higher prevalence of cognitive decline and dementia in individuals with type 2 diabetes. To give you an example of the significance, a 2013 meta-analysis suggested that type 2 diabetes is associated with a 60% increase in risk for dementia and a 56% increased risk for Alzheimer’s disease when compared to healthy individuals without diabetes.⁷

Even though neurons aren’t dependent on insulin like other cells, we now know that insulin plays key signaling and regulatory roles that influence brain metabolism, neurotransmitter turnover, and protein regulation. Research also suggests that the brain can develop its’ own form of insulin resistance where receptors become less sensitive to circulating insulin. This form leads to impaired signaling, an accumulation of neurotoxins, and an increase in oxidative stress that can impact cognition, memory, and mood. Because of this, brain insulin resistance is considered a key factor in risk and progression of cognitive decline and dementias, as well as degenerative brain conditions such as Alzheimer’s and Parkinson’s diseases. In cases of Alzheimer’s disease, the decreased sensitivity of insulin receptors on neurons is believed to contribute to impaired clearance of beta-amyloid plaques and increased formation of proteins that form tangles. Some researchers now even go as far as referring to Alzheimer’s as “type 3 diabetes” because of how strong the evidence is linking insulin resistance to the disease’s progression and cognitive decline.⁸

Who’s at Risk for Insulin Resistance?

Insulin resistance starts well before an individual meets the diagnostic criteria for prediabetes (a fasting blood glucose of 100 mg/dl to 125 mg/dl) or type 2 diabetes (a fasting blood glucose of 126 mg/dl or higher), so it’s important that individuals take an active approach to support blood glucose management early, even before fasting glucose levels become elevated.⁹ According to the CDC, top factors¹⁰ that increase one’s risk for developing insulin resistance include the following:

• Age: Individuals 45 years or older.
• Race and ethnicity: African Americans, Hispanic Americans, American Indians, Pacific Islanders, and some Asian Americans.
• Family history: Individuals with an immediate family member (parent or sibling) with type 2 diabetes.
• Body weight: Individuals who are overweight or obese (BMI ³0).
• Activity: Individuals who are sedentary or who get less than three days of physical activity each week.
• Medical history: Women who have polycystic ovarian syndrome, as well as those who have had gestational diabetes.

Taking Action to Reduce and Prevent Insulin Resistance

Incorporating lifestyle habits that prevent and minimize insulin resistance are key in risk reduction for dementia and most degenerative brain conditions. Individuals shouldn’t wait for elevated glucose levels, but rather take action in early to middle adulthood for maximum risk reduction. If you’re getting a later start, you can still reap significant benefits that minimize risk and progression. Here are 4 top diet and lifestyle tips.

1. Keep Tabs on Overall Carbohydrate Intake^11,12

Diabetes guidelines don’t specify an ideal macronutrient breakdown for prevention due to needs being highly individualized. However, growing research suggests that following a low to moderately-low carbohydrate diet is effective for both individuals looking to control and improve type 2 diabetes and individuals hoping to prevent type 2 diabetes and insulin resistance. While most find that a diet that derives 30 to 50% of calories from carbohydrate is adequate to meet daily needs, this should be individualized for specific needs and conditions.

2. Choose Carbohydrate Foods Wisely^12–14

When it comes to the insulin and glucose response they trigger, carbohydrates are not created equal, and your best bets are complex, whole or minimally processed food sources. The fiber and complex molecular structure that carbohydrates foods like beans and vegetables contain helps to slow the influx of glucose into the bloodstream. If you want to take this a step further, then opt for foods that have a low to moderate glycemic index, since carbohydrates’ impact on glucose and insulin varies even among whole grains, fruits, and vegetables. Everyone should limit added sugars, even people with no signs of insulin resistance. Added sugars trigger sudden glucose spikes, followed by drops, and these fluctuations can make one more prone to insulin resistance down the road. They’re also full of non-nutritive calories, which can contribute to excess weight, one of the risk factors for insulin resistance.

3. Follow a Mediterranean Approach to Eating^11,12,14

Center meals around the Mediterranean or MIND diets, rich in vegetables, legumes, whole grains, seafood, fruit, healthy oils, nuts, and seeds. Then, fill in the gaps with low-fat dairy and lean animal proteins. This approach to meal planning is recommended for the prevention and management of insulin resistance and type 2 diabetes, but it’s also associated with a reduce risk for dementia and decline in brain health. These foods contain key nutrients needed for brain health while supporting healthy glucose-insulin management in the body. They also contain antioxidants and bioactive compounds, which are important for minimizing oxidative stress and inflammation. 

4. Take Action Beyond Diet

It’s easy to see the connection between food choices and overall diet when it comes to preventing and managing insulin resistance and diabetes, but there are other lifestyle aspects equally as important. These other aspects include maintaining or striving towards a healthy body weight, staying active, getting adequate and restful sleep, and finding techniques to effectively manage stress. Each of these has a direct impact on one’s risk for insulin resistance and, thus, brain health.

For more information on insulin resistance and diabetes, the CDC has a helpful resource here.⁴ 

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Written by Carolyn Williams, PhD, RD

Carolyn is an author, registered dietitian, and James Beard Award-winning food and health journalist. NeuroReserve is delighted to partner with Carolyn to develop brain healthy recipes for Brain Table. Carolyn is the founder of Meals That Heal, an online platform providing numerous new recipes, evidence-backed resources, and time-saving tricks to make getting dinner on the table quicker and easier. She is also the author of Meals That Heal cookbook that includes over 100+ quick and tasty recipes to cool inflammation, balance gut health, and detox the body.  She is a contributing editor for Eating Well, Cooking Light, Allrecipes and eMeals and has been featured in many other publications.  Carolyn is a busy mom of two who knows the necessity of having quick, healthy meal ideas. Carolyn’s philosophy on food is that eating and living well isn’t about perfection. It’s about doing the best you can with the resources you have.

References

1. National Center for Chronic Disease Prevention and Health Promotion (NCCDPHP ). Health and Economic Costs of Chronic Diseases. 6 (2021). Available at: https://www.cdc.gov/chronicdisease/about/costs/index.htm.
2. Centers for Disease Control and Prevention (CDC). What Is Type 1 Diabetes? 5 (2021). Available at: https://www.cdc.gov/diabetes/basics/what-is-type-1-diabetes.html.
3. Centers for Disease Control and Prevention (CDC). Type 2 Diabetes. 6 (2019). Available at: https://www.cdc.gov/diabetes/basics/type2.html.
4. Centers for Disease Control and Prevention (CDC). Insulin Resistance and Diabetes. 5 (2019). Available at: https://www.cdc.gov/diabetes/basics/insulin-resistance.html.
5. Diabetes and brain health. Lancet Diabetes Endocrinol. Diabetes Endocrinol. (2020).
6. Arnold, S. E. et al. Brain insulin resistance in type 2 diabetes and Alzheimer disease: concepts and conundrums. Nat Rev Neurol 14, 168–181 (2018).
7. Gudala, K., Bansal, D., Schifano, F. & Bhansali, A. Diabetes mellitus and risk of dementia : A meta-analysis of prospective observational studies. J. Diabetes Investig. 4, (2013).
8. Nguyen, T. T., Thanh, Q., Ta, H., Kim, T. & Nguyen, O. Type 3 Diabetes and Its Role Implications in Alzheimer ’ s Disease. Int. J. Mol. Sci. Rev. 1–16 (2020).
9. American Diabetese Association. Understaning A1C. 2021 (2021). Available at: https://www.diabetes.org/a1c/diagnosis.
10. Centers for Disease Control and Prevention (CDC). Prediabetes - Your Chance to Prevent Type 2 Diabetes. 5 (2020). Available at: https://www.cdc.gov/diabetes/basics/prediabetes.html.
11. Care, D. Prevention or Delay of Type 2 Diabetes : Standards of Medical Care in Diabetes - 2021. 44, 34–39 (2021).
12. Ley, S., Hamdy, O., Mohan, V. & Hu, F. B. Prevention and Management of Type 2 Diabetes: Dietary Components and Nutritional Strategies Sylvia. Lancet 383, 1999–2007 (2014).
13. Juanola-falgarona, M., Salas-salvad, J., Herna, P., Balanza, R. & Guasch-ferre, M. Effect of the glycemic index of the diet on weight loss , modulation of satiety , inflammation , and other metabolic risk factors : a randomized. 27–35 (2014). doi:10.3945/ajcn.113.081216.Despite
14. Kellar, D. & Craft, S. Brain insulin resistance in Alzheimer’s disease and related disorders: mechanisms and therapeutic approaches. Lancet Neurol. 19, 758–766 (2020).