Genetic tendency
Certain inherited genes raise the risk of type 1. Having a close relative with type 1 increases the chance, but most people who develop it have no family history.
Diabetes is caused by a problem with insulin — the hormone that moves sugar from the blood into the body's cells. But why insulin stops working differs by type: type 1 is an autoimmune condition you can't prevent, while type 2 develops from a mix of genetics and lifestyle. This medically reviewed guide explains the real causes of diabetes and the risk factors behind each type.
All diabetes comes down to one problem: too much sugar (glucose) in the blood because insulin isn't doing its job. Insulin is the hormone that lets sugar move from the blood into your cells for energy. When the body can't make enough insulin, or can't use it properly, sugar builds up in the blood instead of fuelling the body — and that is diabetes.
To understand what causes diabetes, it helps to picture how blood sugar normally works. Almost everything you eat that contains carbohydrate — rice, roti, fruit, sugar — is broken down into glucose, which travels in your blood. Glucose is fuel, but it can only get into your cells with help.
That help is insulin, made by the pancreas. Think of insulin as a key that unlocks your cells so glucose can enter. When this system works, blood sugar stays in a healthy range. Diabetes develops when the key system breaks down — and there are two main ways that happens.
Carbohydrates in food are broken down into glucose, which enters the bloodstream and raises blood sugar.
The pancreas releases insulin — the "key" that unlocks cells so glucose can move out of the blood and into them.
Glucose enters the cells for energy, and blood sugar falls back to a healthy level.
If the cells that produce insulin are destroyed, there's no "key" at all. This is what happens in type 1 diabetes (causes below).
The key is there, but the locks stop responding (insulin resistance), so glucose stays in the blood. This is what happens in type 2 diabetes (causes below).
Each type has very different causes. Let's start with what causes type 1 diabetes — the one most people misunderstand.
Type 1 diabetes is caused by an autoimmune reaction — the body's own immune system mistakenly attacks and destroys the cells in the pancreas that make insulin. The exact trigger isn't fully known, but it involves a genetic tendency combined with an environmental trigger. Importantly, type 1 diabetes is not caused by diet, sugar, or lifestyle, and it cannot be prevented.
In type 1 diabetes, the immune system — which normally fights infections — turns on the body's own insulin-making beta cells and destroys them. With these cells gone, the body can make little or no insulin, so glucose can't enter the cells and builds up in the blood. This usually develops in childhood or young adulthood, though it can appear at any age — and is one of the main types of diabetes.
Researchers believe two things have to come together: an inherited tendency, and something in the environment that "switches on" the immune attack. It is no one's fault — and nothing a parent or person did caused it.
Certain inherited genes raise the risk of type 1. Having a close relative with type 1 increases the chance, but most people who develop it have no family history.
Something — possibly a common virus — is thought to trigger the immune attack in those with the genetic tendency. The exact trigger is still being researched.
The immune system produces antibodies that destroy the insulin-making beta cells in the pancreas — the direct cause of type 1 diabetes.
Clearing up a common myth: type 1 diabetes is not caused by eating too much sugar, being overweight, or any lifestyle choice. It can't be prevented and isn't anyone's fault. This is what sets it apart from type 2 — which we look at next.
Type 2 diabetes has very different causes — a mix of genetics and lifestyle. Next: what causes type 2 diabetes.
Type 2 diabetes is caused by insulin resistance — the body still makes insulin, but the cells stop responding to it properly, so blood sugar rises. It develops from a combination of genetics and lifestyle factors like excess weight, inactivity and a carb-heavy diet. It usually builds slowly over years, often passing through a prediabetes stage first.
Unlike type 1, the body in type 2 diabetes still produces insulin — at least at first. The problem is that the cells become resistant to it, like a key that no longer turns the lock easily. The pancreas works harder to compensate, but over time it can't keep up, and blood sugar climbs.
This is why type 2 develops gradually and often silently. Many people pass through prediabetes — a reversible warning stage — before reaching type 2. The causes are a mix of factors you can't change and ones you can.
Genes load the gun — but lifestyle often pulls the trigger.
These are the causes treatment and prevention focus on.
The key driver is insulin resistance. Excess fat — particularly around the abdomen and liver — makes cells less responsive to insulin. This is why weight, diet and activity matter so much in type 2, and why losing even a little weight can improve blood sugar significantly.
Several things raise the chance of developing type 2. Next, we list the main diabetes risk factors — and which ones you can act on.
Diabetes risk factors are the things that raise your chance of developing type 2 diabetes. Some can't be changed — like age, genetics and ethnicity — while many can, such as weight, diet, activity and smoking. The more risk factors you have, the higher your risk, but acting on the modifiable ones can lower it significantly.
These risk factors mostly apply to type 2 diabetes, which is by far the most common type. Having one or more doesn't mean you'll definitely develop diabetes — but it's a good reason to get checked and act early, especially since the most powerful risk factors are ones you can influence.
If several risk factors sound familiar, a quick check is worth it — prediabetes and early type 2 often have no symptoms. Our free assessment gives you a personal risk estimate in about 2 minutes.
If you have these risk factors, catching things early matters — many people first pass through prediabetes, which is often reversible. Next: why diabetes risk is higher in India.
Indians develop type 2 diabetes earlier and at lower body weights than many other populations. This is largely due to the "thin-fat" pattern — carrying more fat around the abdomen even at a normal weight — combined with genetics, and rapid shifts toward refined-carb diets and less active lifestyles. It's why India is often called the diabetes capital of the world.
If you're in India, the usual risk factors carry extra weight — quite literally. Indians tend to develop type 2 diabetes about a decade earlier than Western populations, and at a lower BMI, which means you don't have to look overweight to be at risk. Understanding why helps explain the country's rising numbers — and what to watch for.
Many Indians carry more body fat — especially around the abdomen and organs — even at a normal weight. This visceral fat drives insulin resistance, the main cause of type 2 diabetes.
South Asians have a stronger inherited tendency toward insulin resistance and diabetes, which is why family history is such a common thread.
More white rice, refined flour (maida), sugar and fried, processed foods — and larger portions — push blood sugar up. Traditional balanced meals have given way to carb-heavy ones.
Desk jobs, longer commutes and urban living mean less daily movement than a generation ago — reducing how well the body uses blood sugar.
What this means for you: get checked earlier — from your 30s, or sooner with a family history — and don't rely on weight alone as a sign. The good news is the same Indian foods can work for you with small changes. Our Indian diabetes diet guide shows simple swaps that lower the sugar load while keeping meals familiar.
A lot of myths surround what causes diabetes — especially around sugar. Next, we separate myths from facts.
Many beliefs about what causes diabetes are wrong — and some can be harmful. Eating sugar alone doesn't directly cause diabetes, thin people can get it too, and type 1 has nothing to do with lifestyle. Knowing the facts helps you focus on the causes that actually matter, without fear or blame.
Diabetes is one of the most misunderstood conditions, and myths about its causes can lead to unnecessary worry — or false reassurance. Here are the most common ones, set straight.
"Eating too much sugar causes diabetes."
Sugar alone doesn't directly cause diabetes. However, a diet high in sugar and refined carbs can lead to weight gain, which raises the risk of type 2. Sugar matters — but as part of the bigger picture of weight and lifestyle, not as a single cause.
"Only overweight people get diabetes."
Thin people can develop type 2 diabetes too — especially in India, where the "thin-fat" pattern means risk can be high even at a normal weight. Weight is one factor, not the whole story.
"Type 1 diabetes is caused by a bad diet."
Type 1 is an autoimmune condition, not a lifestyle disease. It isn't caused by diet, sugar or anything a person did, and it can't be prevented. It's important not to blame those who have it.
"If no one in my family has diabetes, I won't get it."
Family history raises risk, but many people with type 2 have none. Lifestyle, age and ethnicity all play a part — so everyone benefits from healthy habits and timely checks.
The bottom line: for type 2, the causes that matter most are weight, diet, activity and genetics working together — not sugar by itself. Eating well still helps a lot. See our Indian diabetes diet guide for realistic, balanced eating.
Still have questions about what causes diabetes? The FAQ below answers the most common ones.
Clear, evidence-based answers to common questions about the causes of diabetes.
Diabetes is caused by a problem with insulin, the hormone that moves sugar from the blood into the body's cells. In type 1, the immune system destroys the cells that make insulin. In type 2, the body becomes resistant to insulin and eventually can't make enough. The result in both is high blood sugar.
People get diabetes for different reasons depending on the type. Type 1 results from an autoimmune reaction combined with genetic and environmental factors, and can't be prevented. Type 2 develops from a mix of genetics and lifestyle factors such as excess weight, inactivity and diet. Having risk factors raises the chance but doesn't guarantee diabetes.
Eating sugar does not directly cause diabetes. However, a diet high in sugar and refined carbohydrates can lead to weight gain, which raises the risk of type 2 diabetes. Sugar is part of the bigger picture of weight and lifestyle, not a single cause — and it has no role in causing type 1 diabetes.
The main cause of type 2 diabetes is insulin resistance — the body's cells stop responding properly to insulin, so blood sugar rises. This is driven by a combination of genetics and lifestyle factors, especially excess weight around the abdomen, inactivity and a carb-heavy diet. Learn more on our type 2 diabetes guide.
Both. Type 2 diabetes usually results from genetics and lifestyle working together — you may inherit a tendency, but weight, diet and activity strongly influence whether it develops. Type 1 is mainly genetic and autoimmune, and is not caused by lifestyle.
Yes. While family history raises risk, many people who develop type 2 diabetes have no family history. Lifestyle, age, ethnicity and weight all contribute. This is why everyone benefits from healthy habits and regular checks, regardless of family history.
Indians develop type 2 diabetes earlier and at lower body weights than many populations, largely due to the "thin-fat" pattern of carrying more abdominal fat even at a normal weight, a stronger genetic predisposition, and shifts toward refined-carb diets and less active lifestyles.
Type 1 diabetes cannot currently be prevented. Type 2 diabetes can often be delayed or prevented by managing the modifiable causes — maintaining a healthy weight, staying active, and eating a balanced diet — especially for those with risk factors or prediabetes.
Descriptions of causes and risk factors are general and based on the authorities above. They are not a diagnosis. Confirm against the latest published guidance before publishing.
This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. If you're concerned about your risk of diabetes, please consult a qualified doctor. Read our full Medical Disclaimer and Editorial Policy.