Mechanisms by which obesity leads to type 2 diabetes: Insulin resistance and scientific weight loss

1. Insulin Resistance
The vast majority of obese individuals have varying degrees of insulin resistance. Insulin resistance forces pancreatic islet cells to secrete more insulin to maintain blood sugar levels close to normal.

Over time, pancreatic β-cell function declines, and insufficient insulin secretion to counteract insulin resistance leads to a gradual increase in blood sugar levels. Hyperglycemia further exacerbates insulin resistance and simultaneously reduces the sensitivity of β-cells to glucose stimulation, resulting in decreased insulin secretion and significant hyperglycemia.

Insulin, besides lowering blood sugar, also inhibits lipolysis. Therefore, in a state of insulin resistance, insulin's anti-lipolysis effect is weakened, allowing large amounts of fat to be broken down and released into the bloodstream. The rate of fat breakdown varies in different parts of the body. Peripheral subcutaneous fat is the slowest, followed by abdominal subcutaneous fat, with visceral fat being the fastest. Therefore, patients with abdominal obesity are more prone to type 2 diabetes. Free fatty acids, a product of lipolysis, have the following functions:

First, once free fatty acids enter the liver, their oxidation increases while glucose oxidation decreases. This downregulates hepatic insulin receptors, reducing insulin binding and leading to hepatic insulin resistance.

Second, excessive free fatty acids compete with glucose for entry into skeletal muscle cells for metabolism, increasing free fatty acid oxidation in muscles and reducing glucose utilization, resulting in peripheral tissue insulin resistance.

Third, high concentrations of free fatty acids have lipotoxic effects on pancreatic β-cells, affecting their secretory function, exacerbating β-cell dysfunction, and promoting the development of diabetes.

In summary, insulin resistance leads to increased insulin secretion and lipolysis, thereby damaging pancreatic β-cell function. β-cell dysfunction further elevates blood glucose, which in turn exacerbates insulin resistance and β-cell damage. This creates a vicious cycle, leading to persistent hyperglycemia and type 2 diabetes.

Studies have found that weight loss helps control blood glucose in patients with non-insulin-dependent diabetes mellitus. As body weight decreases, the percentage of glycated hemoglobin decreases accordingly, and lipid composition also improves significantly, alleviating dyslipidemia in obese patients.

2. Gene Involvement
Obesity is a polygenic disease, and abnormalities in many genes are related to the formation of obesity. These gene abnormalities are also closely related to diabetes.

(1) The Trp64Arg gene in the β₃ adrenergic receptor is closely related to obesity, insulin resistance, and the early onset of type 2 diabetes. Drug experiments show that β-adrenergic agonists have anti-obesity and glucose tolerance-improving effects.

(2) Obesity gene: The protein product Leptin of the 0b gene can not only regulate the appetite center in the hypothalamus but also directly inhibit glucose-mediated β-cell insulin secretion, affecting glucose metabolism. Hyperleptinemia is also associated with insulin resistance.

(3) Tumor necrosis factor-α (TNF-α) is overexpressed in the mRNA and protein of patients with type 2 diabetes, which may be related to obesity and insulin resistance.