Insulin sensitivity and insulin resistance have lately become buzzwords in the news, social media, and even dinner table conversations. With the ability to keep an eye on glucose control better than ever with the plethora of direct to consumer continuous glucose monitors, these topics have made their way from the exam room and into popular culture. We also know insulin resistance is an important risk factor for a whole host of chronic conditions, including heart disease.. But what exactly is insulin resistance, the invisible culprit that can eventually result in type 2 diabetes? And what can we do about it? 

What is insulin resistance? 

Every time we eat, our bodies break down what we consume into building block components—protein, fat, and carbohydrates. Carbs get further broken down into sugar, which goes into the blood, also known as blood sugar, or glucose. Our bodies are smart, and they’ve got a built-in regulation system to make sure that not too much, not too little, but the right amount of glucose stays in the blood. How do our bodies regulate this amount of sugar that stays circulating in the blood? With a hormone called insulin. It’s when insulin can’t effectively perform this glucose regulation job that type 2 diabetes develops. 

The pancreas is the organ responsible for releasing insulin into the bloodstream. When insulin is released, it helps glucose enter into cells, particularly muscle, for energy. Over time though, muscle cells - due to excess cellular fat buildup - can stop responding properly to insulin, and they become insulin resistant. Insulin resistance occurs when the pancreas has to pump out more and more insulin in order to maintain glucose homeostasis Eventually it just can’t pump out enough to do so, resulting in insufficient transport of glucose into the muscle cell, hyperglycemia, and eventually type 2 diabetes. 

How is insulin resistance diagnosed?

Insulin resistance is the first step on the path of prediabetes and type 2 diabetes. As your cells become increasingly resistant to insulin, the sugar in your blood creeps up. Prediabetes means the sugar levels aren’t yet high enough for a diabetes diagnosis, but without lifestyle modifications, you’re likely headed that way. 

The first sign of insulin resistance is an elevated fasting insulin level, followed by an elevated fasting glucose. An oral glucose tolerance test can also be used. More typically, the diagnosis of prediabetes and diabetes is made with a hemoglobin A1C - a HgbA1c over 5.7 is diagnostic of prediabetes. Type 2 diabetes is diagnosed when the HgbA1c is over 6.5.

Why is insulin resistance bad? 

Insulin resistance is not only central to the pathogenesis of diabetes, it’s also associated with several other conditions, namely Alzheimer’s, cancer, fatty liver disease, and of course, heart disease. If diabetes develops, the potential complications are numerous including heart attack, stroke, nerve damage, eye disease, and kidney disease. 

Insulin resistance, and the intermediaries on the road to it, high blood sugar and high blood insulin levels, are associated with an increased risk of cardiovascular disease. Individuals with type 2 diabetes are more than twice as likely to have coronary artery disease, and cardiovascular disease is the top cause of death in those with diabetes.  A recent study that tracked more than 28,000 women’s cardiovascular risk factors for a median time period of 21 years found that diabetes and insulin resistance appeared to be the strongest risk factors for coronary heart disease.

Diabetes type 2 and insulin resistance are also independent risk factors for a type of heart failure called diabetic cardiomyopathy. Disruptions in insulin signaling cause cardiac muscle cells (cardiomyocytes) to increase fatty acid uptake and contribute to cardiac remodeling and cardiomyocyte death. Basically, this means that healthy heart muscle, normally agile and dynamic so that it can effectively supply blood to the entire body with its strong contractions and expansions, gets replaced by stiff, fibrotic tissue. This remodeling ultimately limits the amount of blood the heart is able to pump with each beat, a metric known as the ejection fraction and ultimately heart failure.

How can I prevent or treat insulin resistance? 

The good news is that insulin resistance is very treatable and even reversible! The mainstays of reversing insulin resistance are lifestyle changes, which include:

1. Exercise - Maintaining cardiorespiratory fitness (CRF)- basically a measure of how “in shape” you are -  is one of the best things you can do. Glucose uptake into muscle cells is independent of insulin, and so it can be very powerful way to improve glucose levels. Studies have shown that exercise can improve insulin sensitivity. Sustained improvement in CRF also proved one of the biggest differentiators in a 2020 analysis of a >5,000 participant trial assessing lifestyle modification impact on cardiovascular disease progression in people with Type 2 diabetes. Aim for at least 150 minutes per week of moderate to vigorous aerobic activity (with 2 days of strength/resistance sprinkled in during the week as well if possible). Read more about how to think about the best exercise program for optimal cardiovascular prevention here

2. Diet -  Diets high in whole, unprocessed plant foods such as whole grains, beans, veggies, fruits, nuts, and seeds have been well studied to reverse and prevent insulin resistance and type 2 diabetes. A plant predominant Mediterranean diet has been found to yield significant improvement in glucose control as well as a 29% cardiovascular disease reduction over 4.8 years among a cohort of people with Type 2 diabetes. In addition to focusing on whole plant foods, this diet also aims to limit processed carbohydrates, refined sugar, and sugar-sweetened drinks. 

Weight loss if above ideal body weight, adequate sleep, and controlling stress are also very important to improve glucose control.

The skinny on insulin resistance 

Insulin resistance is an insidious process beginning the road to Type 2 diabetes that often flies under our screening radar. It’s not at all uncommon that as a cardiologist, I’m the first one to pick this up - all too often, we’re not realizing there’s a problem until someone develops type 2 diabetes, which means there has been decades of smoldering insulin resistance. Given it is one of the top causes of cardiovascular disease, it’s crucial to screen for it more aggressively and then target it. Lifestyle modifications, focusing on diet, exercise, stress, weight loss, and sleep are key.