Can You Have Type 2 Diabetes Without Being Overweight?

Can you have type 2 diabetes without being overweight?

Yes, and in parts of Africa it is close to the norm. Nearly 40% of African adults with type 2 diabetes are lean, meaning a body mass index under 25. A new analysis of 3,331 adults found that their disease runs on different biology and produces a different set of complications.

Most people picture type 2 diabetes as a disease of excess weight. In wealthy countries that picture mostly holds. In Africa it does not. The researchers, from Amsterdam UMC and the University of Ghana, pulled together individual patient data from two large studies of adults with type 2 diabetes in Ghana, Nigeria and Kenya: the Africa America Diabetes Mellitus study, with 2,790 people, and the Research on Obesity and Diabetes among African Migrants study, with 541. They split everyone at a BMI of 25 and compared what went wrong in each group.

In people carrying extra weight, type 2 diabetes is mainly a resistance problem. The pancreas makes insulin, sometimes plenty of it, but muscle and liver cells stop responding properly. In the lean patients here, the picture was reversed. Their diabetes was marked by lower beta cell function and low insulin levels. Beta cells are the cells in the pancreas that make insulin. So the shortage is in supply, not in the response.

That distinction is not academic. Almost every first-line diabetes tablet used across Africa, metformin and the sulfonylureas, was designed around the insulin resistance version of the disease. Sabrina Esmail, the first author, put the scale of it plainly: “This means that there are an estimated ten million lean patients on the African continent who do not fit the standard picture. For them, the problem is therefore a shortage of insulin, not a reduced response to insulin.”

What the data show

The complication patterns pulled apart in both directions. Lean adults had about 36% more eye damage from diabetes, called retinopathy (pooled prevalence ratio 1.36), and the range of the estimate makes it very likely the true figure sits somewhere between 13% and 63% higher (95% CI 1.13 to 1.63). Stroke was about 41% more common in the lean group (pPR 1.41), though that number is far shakier: the range stretches from almost no difference to nearly double (95% CI 1.01 to 1.99).

The lean group did better on the blood pressure side. They had about 23% less high blood pressure (pPR 0.77), very likely between 15% and 29% less (95% CI 0.71 to 0.85), and their estimated ten-year cardiovascular risk was about 15% lower (pPR 0.85), likely between 3% and 26% lower (95% CI 0.74 to 0.97). Chronic kidney disease was the one complication that showed up equally in both groups.

The researchers then asked what was driving the split. Body fat percentage accounted for most of it, up to 92% of the difference. That points at real differences in the disease process rather than a quirk of who ended up in which group.

Dr. Kumar’s Take

The clinical implication here is uncomfortable. If a lean patient’s problem is that the pancreas cannot make enough insulin, a drug that improves insulin sensitivity has less to work with. Sulfonylureas do push the beta cells to release more insulin, but they push a system that is already running short, which is not the same as fixing it. Ten million people on one continent are being managed with a drug logic built for the opposite physiology, and nobody has run the trial to find out whether that matters.

The retinopathy signal is the one worth sitting with. Eye damage tracks with how long blood sugar has been high and how badly it has been controlled. Finding more of it in the leaner group, the group that looks healthier by every conventional screening cue, fits a pattern where a thin patient’s diabetes gets caught later and treated less aggressively. Body size is doing a lot of work as a diagnostic shortcut, and this data suggests the shortcut fails in both directions.

This also does not stop at the equator: the same mismatch between the guideline and the patient in front of you can happen anywhere.

What this study cannot tell you

This is a snapshot, not a film. The data are cross-sectional, meaning complications and body size were measured at the same moment, so the study cannot prove that being lean caused the retinopathy or that extra weight caused the hypertension. The analysis adjusted for age, sex, education and treatment, which helps, but it cannot fully separate leanness from the things that travel with it, including a longer or worse-controlled disease course. The stroke finding sits right at the edge of statistical meaning and needs confirming. And these were cohorts from Ghana, Nigeria and Kenya, so the numbers describe those populations rather than every lean person with diabetes everywhere.

Practical Takeaways

A normal or low body weight does not rule out type 2 diabetes, so if you have symptoms such as thirst, frequent urination, or unexplained weight loss, ask for blood sugar testing regardless of your BMI.
If you are lean and have type 2 diabetes, ask your doctor about a dilated eye exam on schedule, since retinopathy was about 36% more common in the lean group in this analysis.
Ask whether your treatment plan has ever been reviewed against measures of insulin production rather than assumed to be an insulin resistance problem, particularly if blood sugar stays high on standard tablets.
Do not stop or change metformin or a sulfonylurea on your own based on this study, because it compared complication rates and did not test any alternative treatment.

FAQs

What counts as lean type 2 diabetes?

In this analysis, lean meant a body mass index below 25, and overweight or obese meant 25 or above. BMI is a blunt instrument, and the researchers found that body fat percentage, not BMI itself, explained most of the difference in complications. That is worth knowing, because two people at the same BMI can carry very different amounts of fat, particularly around the organs. A normal BMI with a high body fat percentage is not the same metabolic situation as a normal BMI with normal body fat.

Why would a thin person’s pancreas stop making enough insulin?

The study did not test causes, but the researchers point to early-life factors that can interfere with how the pancreas develops. Malnutrition and low birth weight both fall into that category, and both are far more common in the populations studied here than in wealthy countries. That is a different origin story from the one behind weight-related diabetes, which builds up over years of an insulin resistant state. It also means prevention advice aimed at diet and exercise in adulthood may not reach the root of the lean form.

Does this apply to lean people with diabetes outside Africa?

The direct evidence here comes from cohorts in Ghana, Nigeria and Kenya, so it describes those populations. The broader question is open. Lean type 2 diabetes exists in every population, and it is common across South and East Asia, but whether the same complication split shows up there has not been established by this work. What travels well is the principle: body size is a poor proxy for what is actually failing in a given patient, and treating it as one leaves a large group on drugs matched to somebody else’s biology.

Bottom Line

Type 2 diabetes in lean African adults behaves like a different disease. It runs on low insulin production rather than insulin resistance, it brings about 36% more retinopathy and more stroke, and it brings less hypertension and lower estimated cardiovascular risk. Kidney disease hits both groups equally. Roughly two-fifths of the nearly 24 million Africans with type 2 diabetes are lean, and all of them are being handed the same tablets designed for the other version of the illness. The trials to find out what actually works for them have not been done yet.

Read the full study