Obesity and Type 2 Diabetes: Why the Conditions Are Closely Linked

• Explains the actual mechanism step by step, rather than repeating that the two conditions are "linked".
• Answers the question people really have: why some people with obesity never develop diabetes and others do.
• Sets out what a UK trial found about remission, including how the chance rises with the amount of weight lost.
• Covers the part rarely explained: why the relationship runs in both directions, and why some diabetes treatments make weight harder to lose.

Obesity is one of the strongest modifiable risk factors for type 2 diabetes. The relationship is not simply about body weight. It is also about where the body stores excess fat and what happens when its usual fat-storage capacity is exceeded.

Fat tissue is designed to store energy. When its ability to store excess energy safely is overwhelmed, more fat can accumulate in organs such as the liver, muscle and pancreas. This can contribute to insulin resistance and, over time, impair the pancreas's ability to produce enough insulin to keep blood glucose under control.

People living with obesity have a substantially higher risk of developing type 2 diabetes, but obesity does not inevitably lead to diabetes. Individual differences in fat distribution, genetics and metabolic health help explain why some people develop diabetes while others do not.

Key things to know

• Obesity causes type 2 diabetes mainly through fat accumulating in the liver, muscle and pancreas, which is called ectopic fat.
• The result is insulin resistance, meaning the body's cells respond less well to insulin, followed over time by the pancreas losing its ability to compensate.
• Not everyone living with obesity develops type 2 diabetes, and not everyone with type 2 diabetes is living with obesity.
• Each person appears to have their own threshold for how much fat they can store safely, which is why the same BMI produces different outcomes in different people.
• Where fat sits matters more than total weight. Fat around the abdomen and organs carries more risk than fat elsewhere.
• Type 2 diabetes can go into remission. A UK primary care trial found remission in 46 per cent of participants at 12 months in the treated group, and the chance rose sharply with the amount of weight lost.
• Remission is not the same as cure. Blood glucose can rise again if weight returns.
• Diagnosis is by blood test. An HbA1c of 48 mmol/mol or above is consistent with type 2 diabetes.

How does obesity cause type 2 diabetes?

Obesity causes type 2 diabetes through obesity and insulin resistance: excess body fat and excess body weight can overwhelm the body’s safe fat-storage capacity, push fat into organs not designed to store it, and drive metabolic dysfunction that makes tissues less responsive to insulin and can eventually damage the cells that produce it.

What is insulin resistance?

Insulin is a hormone released by the pancreas after you eat. Its job is to tell cells in the muscles, liver and fat tissue to take glucose out of the blood and use or store it.

Insulin resistance means those cells respond less well to that instruction. The pancreas notices that blood glucose is staying high, so it produces more insulin to force the message through. For years this works, and blood glucose stays normal while insulin levels quietly climb. In obesity, chronic inflammation can disrupt the insulin signaling pathway, reduce insulin sensitivity, and impair insulin signaling in skeletal muscle, which lowers glucose uptake. Nothing is felt during this stage.

What is ectopic fat?

Ectopic fat is fat stored outside the usual fat-storage tissue, including in the liver, skeletal muscle and pancreas. The term simply means fat stored in an unusual location.

This is an important part of the link between excess body fat and diabetes. When adipose tissue can no longer safely store additional energy, excess fat can accumulate elsewhere and interfere with normal metabolic function. Fat accumulation in the liver and pancreas appears particularly important in the development and progression of type 2 diabetes, while fat accumulation in skeletal muscle is closely linked with insulin resistance.

The chain of events, in order

Energy intake exceeds what the body uses, over a sustained period.

Fat is stored in adipose tissue, until adipose tissue production and storage signals are no longer coping well.

Surplus fat begins to accumulate in the liver, muscle and pancreas.

Liver and muscle become resistant to insulin, so glucose transport into tissues is reduced and insulin can no longer suppress hepatic glucose production.The liver also contributes through hepatic gluconeogenesis and increased hepatic glucose production, while the pancreas compensates by producing more insulin, and blood glucose stays normal.

Fat accumulating in the pancreas begins to impair pancreatic β cell function, and insulin secretion starts to deteriorate.Compensation fails. Blood glucose starts to rise, first after meals and then persistently.HbA1c crosses the diagnostic threshold and type 2 diabetes is diagnosed.These changes can develop for years without causing noticeable symptoms

Why do some people develop it and others do not?

Because the amount of fat a person can store safely varies enormously between individuals. This is often described as a personal fat threshold, and it explains something that otherwise looks arbitrary.

What is the personal fat threshold?

The idea is that each person has their own limit for how much fat their fat tissue can hold before the surplus starts going into their liver and pancreas. That limit is not the same for everyone.

One person may have a large safe storage capacity, carry a great deal of weight, and never develop type 2 diabetes. Another may have a much smaller capacity, be only modestly above a healthy weight, and cross their own threshold at a BMI of 27. Both are behaving normally. Their storage capacity simply differs.

This matters practically for two reasons. It explains why someone can be diagnosed at a weight that seems low compared with friends who are heavier and unaffected. And it explains why losing a relatively modest amount of weight can have a disproportionate effect: the goal is to get back below your own threshold, not to reach a particular number.

Why are BMI thresholds lower for some family backgrounds?

BMI does not carry exactly the same health implications across all populations. In the UK, NICE recommends lower BMI thresholds for people from South Asian, Chinese, other Asian, Middle Eastern, Black African and African-Caribbean backgrounds because cardiometabolic risk can occur at a lower BMI.

For these groups, a BMI of 23 to 27.4 kg/m² is classified as overweight and a BMI of 27.5 kg/m² or above as obesity for practical assessment purposes.

Central adiposity is also important. Measuring waist size alongside BMI can give a better indication of whether excess fat is concentrated around the abdomen. NHS guidance recommends aiming for a waist circumference of less than half your height.

Does where fat sits matter more than how much there is?

Yes. Visceral fat accumulation and central obesity are more strongly associated with insulin resistance than fat carried on the hips and thighs. By contrast, body fat stored in safer depots is generally less strongly linked with metabolic risk. This is why waist measurement adds information that weight alone does not.

The practical check used in UK guidance is waist to height ratio, with the target that your waist should be less than half your height. It is a better guide to the fat that drives this process than the number on the scales.

The relationship runs in both directions

Obesity drives type 2 diabetes, but once diabetes is established it can make weight harder to lose. This loop is rarely explained, and not knowing about it leads people to blame themselves for something with a physiological cause.

Why does weight loss become harder?

Weight management can become more difficult after diabetes develops because of changes in appetite, metabolism and physical activity, as well as the effects of some diabetes medicines. Insulin and sulfonylureas, for example, are commonly associated with weight gain.

Do diabetes treatments affect weight?

Some do, in both directions, and this is worth understanding before a review appointment.

For some people with severe obesity, metabolic or bariatric surgery can produce substantial and sustained weight loss and can also lead to type 2 diabetes remission.

This creates a genuine tension in treatment. A medicine that controls blood glucose well may make weight harder to manage, and weight is itself driving the condition. It is a legitimate thing to raise with your prescriber, and there may be options.

Never stop or change a prescribed diabetes medicine on your own because of its effect on weight. Stopping treatment abruptly can cause blood glucose to rise dangerously.

How the conditions are diagnosed

Type 2 diabetes is diagnosed by blood test, not by symptoms. The usual test is HbA1c, which reflects average blood glucose and plasma glucose control over roughly the previous two to three months.

In someone without symptoms, a result of 48 mmol/mol or above is normally confirmed with a second test on a separate day. HbA1c is also not reliable in every situation, including pregnancy, in children, in suspected type 1 diabetes, and in conditions affecting red blood cells, where a different test is used instead.

The middle band matters more than its informal name suggests. A result of 42 to 47 mmol/mol indicates non-diabetic hyperglycaemia and a higher risk of developing type 2 diabetes. It is an important point at which lifestyle and weight-management interventions can help reduce that risk.

Can type 2 diabetes go into remission?

Yes, for some people, and the evidence for this is stronger than most people realise. Remission means blood glucose returning to a non-diabetic level and staying there without diabetes medication.

What did the DiRECT trial find?

DiRECT was a UK primary care trial involving 306 adults with type 2 diabetes. Participants were aged 20 to 65, had been diagnosed within the previous six years, had a BMI of 27 to 45 kg/m² and were not taking insulin. The intervention group received a structured, clinically supervised weight-management programme, while the comparison group received usual care.

At 12 months, 46% of participants in the intervention group were in remission, compared with 4% in the comparison group. Average weight loss in the intervention group was about 10 kg. At 24 months, 36% of the intervention group remained in remission, compared with 3% of the comparison group.

Remission was defined as an HbA1c below 48 mmol/mol (6.5%) after withdrawal of diabetes medication.

How much weight loss does remission take?

The trial's most useful finding is that the chance of remission rose steeply with the amount of weight lost, rather than being all or nothing.

Two things follow. First, there is no cliff edge: every increment of weight loss improves the odds. Second, the largest gains came in the middle of that range, which is a more achievable target than many people assume when they hear the word remission.

Is remission the same as a cure?

No, and this distinction is important. Remission means the condition is not currently active. It does not mean the underlying tendency has gone.

If weight returns, blood glucose commonly rises again. Sustained weight loss is more likely when ongoing diet and activity habits are maintained. Regular physical activity should aim for 150 minutes per week. Dietary changes, including reducing refined carbohydrates and increasing fibre, can support glycemic control and significantly reduce the risk of type 2 diabetes. People in remission continue to need regular monitoring, including HbA1c checks and the usual screening for eye and foot complications, because the risk has been reduced rather than removed.

Who is most likely to achieve remission?

Remission was more likely among people with a shorter duration of diabetes and fewer diabetes medicines, but the strongest predictor in the analysis was the amount of weight lost.

This is an argument for acting early rather than a reason for anyone else to give up. Weight loss improves blood glucose control and cardiovascular risk factors even without formal remission.

An important safety point about the trial

The programme used in DiRECT began with a total diet replacement phase, delivered under clinical supervision, with diabetes and blood pressure medicines withdrawn in a planned way at the start. It is not something to attempt independently.

Continuing some diabetes medicines while eating far less can cause blood glucose to fall dangerously low. Anyone considering an intensive weight loss approach while taking diabetes medication needs their treatment reviewed by a clinician first.

What this means for treatment

Weight management is an important part of type 2 diabetes care, particularly when excess weight is contributing to insulin resistance and metabolic risk.

Where do weight management medicines fit?

Some medicines are licensed for both type 2 diabetes and weight management, though usually under separate product licences with different criteria. Others are licensed for one or the other. You can learn more about the different weight-loss treatments, but which, if any, is appropriate depends on your full clinical picture rather than on the diagnosis alone

The broad licensed criteria for weight management treatment are a BMI of 30 or above, or 27 to 29.9 alongside a weight related health condition, and type 2 diabetes counts as such a condition. Meeting a threshold is a starting point, not an outcome. Treatment suitability depends on an individual clinical assessment, and your prescriber will determine the appropriate treatment.

If you take diabetes medication already, tell any prescriber assessing you for weight management treatment. Adding one without adjusting the other is how problems arise.

What safety issues should I know about?

The MHRA has issued safety advice relevant to this group of medicines. In January 2026 it strengthened warnings about severe acute pancreatitis with GLP-1 and dual GLP-1/GIP receptor agonists, advising urgent medical attention for severe, persistent abdominal pain that may spread to the back.

The MHRA has also warned about diabetic ketoacidosis where insulin was rapidly reduced or stopped when one of these medicines was started. Any change to insulin is a clinical decision, never a self-directed one.

When to seek help urgently

Contact a healthcare professional the same day, or seek emergency care, if you experience:

• Very high blood glucose with vomiting, abdominal pain, deep or rapid breathing, or a fruity smell on the breath.
• Symptoms of very low blood glucose that do not improve after treating them: shaking, sweating, confusion, difficulty concentrating or unusual behaviour.
• Severe, persistent abdominal pain that spreads to the back, with or without nausea and vomiting.
• Sudden loss of vision, or eyesight worsening rapidly.
• A foot wound, ulcer or infection that is not healing.

Medical Disclaimer

This article is for general information and does not replace personalised medical advice. It cannot diagnose type 2 diabetes, obesity or any other condition. Prescription only medicines should be used only under the supervision of an appropriately qualified prescriber, following a clinical assessment, and results vary between individuals. Do not stop, reduce or change a prescribed medicine, particularly insulin or any other diabetes treatment, without discussing it with your prescriber first. Follow the patient information leaflet supplied with your medicine, and if you miss a dose, follow that leaflet and never take extra to make up for it. Report suspected side effects through the MHRA Yellow Card scheme, and seek urgent medical attention for severe or rapidly worsening symptoms.