Diabetes develops through several distinct pathways depending on the type. In some cases, the immune system destroys the cells that produce insulin. In others, the body gradually loses its ability to use insulin effectively, often driven by weight gain, inactivity, and genetics. Some forms appear only during pregnancy, and rarer types are caused by a single gene mutation passed down through families. Here’s how each type develops and what increases the risk.
Type 1: The Immune System Attacks Insulin-Producing Cells
Type 1 diabetes is an autoimmune disease. The immune system’s T-cells, which normally fight infections, mistakenly identify the insulin-producing beta cells in the pancreas as threats. Immune cells travel to the pancreas, multiply there, and progressively destroy those beta cells. Once enough are gone, the body can no longer produce meaningful amounts of insulin, and blood sugar rises uncontrollably.
This process requires a genetic predisposition, but genes alone aren’t enough. The steady rise in type 1 diabetes rates across the globe over the past 60 years points to environmental triggers. Viral infections, changes in gut bacteria, and early dietary exposures have all been linked to the onset of the autoimmune attack. The leading theory is that an environmental event sets off the immune response in people whose genes make them vulnerable. Type 1 accounts for roughly 5 to 10 percent of all diabetes cases and most often appears in children and young adults, though it can develop at any age.
Type 2: Insulin Resistance That Overwhelms the Pancreas
Type 2 diabetes develops in two stages. First, cells in your muscles, liver, and fat tissue become resistant to insulin, meaning they stop responding to it normally. Your pancreas compensates by producing more and more insulin to keep blood sugar in check. For a while, this works. But eventually the beta cells can’t keep up with the demand, insulin production falls short, and blood sugar starts climbing. That progression from insulin resistance to full diabetes can take years.
Excess body fat, especially around the abdomen, is the most common driver of insulin resistance. Fat tissue in the belly triggers low-grade inflammation throughout the body, including in the pancreas, liver, and muscles. This inflammation interferes with insulin signaling at a cellular level, making it harder for glucose to enter cells. Women with a waist measurement over 35 inches and men over 40 inches face notably higher risk. A BMI of 30 or above (the threshold for obesity) raises risk substantially, though people in the overweight range (BMI 25 to 29.9) are also at increased risk.
Mitochondrial dysfunction, where cells struggle to convert fuel into energy efficiently, also plays a role in developing insulin resistance. This helps explain why physical inactivity is such a strong risk factor: regular movement improves how well your cells’ energy systems function and how sensitively they respond to insulin.
How Genetics Shape Your Risk
Family history is one of the strongest predictors of type 2 diabetes. If your mother has diabetes, your risk roughly doubles. If your father has it, the increase is nearly as large (about 1.8 times the average risk). If both parents have diabetes, the risk jumps to about 3.4 times normal. Having a sibling with diabetes raises risk by a factor of nearly three, and for twins the risk is almost six times higher.
These numbers reflect shared genetics and, to some degree, shared environments and habits. But even in studies that account for lifestyle, the genetic component remains powerful. For type 1 diabetes, specific immune system genes are the primary inherited factor. For type 2, dozens of genes influence how your body produces insulin, stores fat, and manages inflammation.
Sugary Drinks and Dietary Patterns
What you eat and drink matters, and liquid sugar stands out as a particularly well-documented risk factor. People who drink one to two sugary beverages a day have a 26 percent greater risk of developing type 2 diabetes compared to those who rarely drink them. A large study tracking over 192,000 people for more than two decades found that increasing sugary beverage intake by just four ounces per day over a four-year period was associated with a 16 percent higher risk of diabetes in the following four years. That includes not just soda but fruit punch and even 100 percent fruit juice.
The mechanism is straightforward: liquid sugar floods the bloodstream with glucose faster than the body can handle, forcing the pancreas to release large bursts of insulin repeatedly. Over time, this pattern wears down insulin sensitivity. Diets high in refined carbohydrates and low in fiber produce a similar effect, though sugary drinks are the most concentrated and easily overconsumable source.
Ethnicity and Age Disparities
Diabetes does not affect all populations equally. CDC data from 2021 to 2023 shows striking differences in diagnosed diabetes rates among U.S. adults: 15.7 percent of American Indian or Alaska Native adults have been diagnosed, compared to 12.2 percent of Black adults, 11.8 percent of Hispanic adults, 9.7 percent of Asian adults, and 7.1 percent of white adults. New diagnosis rates tell a similar story, with Black and Hispanic adults developing diabetes at nearly twice the rate of white adults each year.
These disparities reflect a combination of genetic susceptibility, differences in access to healthcare and healthy food, and the cumulative effects of socioeconomic inequality. Age also matters: the risk of type 2 diabetes climbs with every decade of life, partly because insulin sensitivity naturally decreases with aging and partly because the effects of lifestyle accumulate over time.
Gestational Diabetes During Pregnancy
Some women develop diabetes for the first time during pregnancy, typically between weeks 20 and 24. The placenta produces hormones, including estrogen, cortisol, and human placental lactogen, that partially block insulin’s action. All pregnant women experience some degree of this insulin resistance. But in women whose pancreas can’t ramp up insulin production enough to overcome it, blood sugar rises into the diabetic range.
Risk factors include being overweight or obese before pregnancy, having a family history of diabetes, being over age 25, having previously delivered a baby weighing more than nine pounds, and having prediabetes. Gestational diabetes usually resolves after delivery, but it signals that your body’s insulin system is vulnerable. Women who have had it carry a significantly elevated risk of developing type 2 diabetes later in life.
Rarer Genetic Forms: MODY
Maturity-onset diabetes of the young, or MODY, accounts for a small percentage of all diabetes cases but is important to recognize because it’s caused by a single gene mutation and runs in families with an autosomal dominant pattern. That means if one parent carries the mutation, each child has a 50 percent chance of inheriting it.
Different gene mutations cause different forms of MODY. Some mutations affect proteins that control how beta cells develop and function, leading to reduced insulin production. Others affect a glucose-sensing protein in the pancreas. Normally, this protein detects rising blood sugar and triggers insulin release. When mutated, it fails to sense the rise, so the pancreas doesn’t respond appropriately. MODY is often misdiagnosed as type 1 or type 2 diabetes, but it behaves differently and often requires different treatment. It typically appears before age 25 in people who aren’t overweight, which can be a clue that something other than the common types is at play.