What Is Insulin Resistance?
The concept of “insulin sensitivity” was introduced by scientists as early as 1936, Jeng said. Glucose is the primary energy source for every cell in the body, and insulin functions as a key that unlocks the cell membrane, allowing glucose to enter. When cells become less responsive to insulin, this process is disrupted, leading to a condition known as insulin resistance.In the early stages of insulin resistance, blood sugar levels typically remain within the normal range as the body compensates by producing more insulin to regulate blood glucose. However, the pancreatic beta cells responsible for insulin production can become overworked and gradually lose functionality. Over time, this dysfunction may lead to the development of Type 2 diabetes, as these cells can no longer produce enough insulin to meet the body’s needs.
Diseases Linked to Insulin Resistance
An earlier study found that people with elevated insulin resistance are at a higher risk of developing various diseases over time, including cardiovascular disease, obesity, nonalcoholic fatty liver disease, Alzheimer’s disease, certain types of cancer, chronic kidney disease, and polycystic ovary syndrome.
Insulin not only regulates blood sugar metabolism but also plays a crucial role in fat metabolism, Jeng said. In the early stages of insulin resistance, high insulin levels cause fat to “relocate,” moving from fat cells around the body to the liver, which increases the risk of fatty liver disease. The liver subsequently converts this fat into large amounts of very low-density lipoprotein (VLDL), potentially harming vascular health.
Alzheimer’s Disease: The Brain’s Diabetes
Insulin resistance has implications beyond metabolic health; it can alter the brain’s glucose metabolism and is strongly linked to Alzheimer’s disease, Jeng said. A study published in Diabetes Care in August used a chart to illustrate differences in brain aging among patients with varying degrees of diabetes.
By comparing brain images across various age groups using data from the UK Biobank, the researchers found that even patients with mild insulin resistance, such as those in the prediabetic stage, had brains that appeared nearly half a year older than those in the control group. Furthermore, more severe forms of diabetes correlated with increased brain age; patients with hemoglobin A1C levels above 8 percent had a brain age gap that was about 4.2 years greater than their chronological age.
Symptoms of Insulin Resistance
Although insulin resistance is quite common, Jeng said many people are unaware that it might affect them. Symptoms that may indicate insulin resistance include:- Persistent thirst
- Frequent urination
- Intense hunger and difficulty tolerating hunger
- Intense cravings for sweets after meals, often accompanied by a tendency to keep eating even after satisfying the craving
- Fatigue and drowsiness after meals
- Dark, velvety patches of skin (acanthosis nigricans)
A Simple Method for Assessment
The hyperinsulinemic-euglycemic clamp, a physiological test, is regarded as the “gold standard” for testing insulin sensitivity. However, it is both time-consuming and expensive. In clinical practice, the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) is more commonly used, as it only requires measurements of fasting insulin and fasting glucose levels. This test can be completed with a single blood draw, but its cost is higher than standard blood tests, limiting its widespread use, Jeng said.The TyG index is calculated using the formula:
TyG index = Ln [(fasting triglycerides (milligrams per deciliter) × fasting glucose (milligrams per deciliter)) / 2]
Ideal values: <4.55 (strict criteria) or <4.78 (relaxed criteria)
According to this formula, the product of glucose and triglycerides, both in milligrams per deciliter (mg/dL), should not exceed 14,200, with a stricter recommendation of keeping it below 9,000.
The TyG index is approximately 80 percent accurate in evaluating insulin resistance, Jeng noted. In other words, if the product of blood glucose and blood lipid levels exceeds 14,200, there is an 80 percent likelihood of having insulin resistance. Conversely, if the product falls below 14,200, there is an 80 percent likelihood of not having it.
Reversing Insulin Resistance Through Exercise
When detected early, insulin resistance can often be reversed through lifestyle changes, including eating a balanced diet, quitting smoking and alcohol, exercising regularly, and getting enough sleep.Exercise is essential for both preventing and reversing insulin resistance, as it promotes glucose uptake by muscle cells, thereby lowering blood sugar levels, Jeng said.
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