News · Heart & Metabolic
A third of people with 'preclinical' obesity crossed into the clinical kind within five years
A Lancet commission split obesity into two conditions: one that is only a body measurement, one that has started causing harm. Nobody had counted how often people move between them. In 92,396 US adults, 26% did in under three years.
- 319,815 US adults in the All of Us dataset, classified under the new Lancet Commission definition.
- At baseline: 28.9% had preclinical obesity and 40.0% had clinical obesity.
- Of 92,396 with preclinical obesity, 24,057 (26.0%) transitioned over a median 2.9 years.
- Cumulative incidence of transition: 12.7% at 1 year, 25.7% at 3 years, 34.3% at 5 years.
- Older age, higher HbA1c, higher BMI and waist ratios, and poorer self-rated health predicted transition.
For most of the last forty years, obesity has been one thing with one number attached to it. Cross a body mass index of 30 and you had it.
Last year a Lancet commission argued that this was wrong in both directions, and split the condition in two. Obesity is a disease that means having too much body fat, and it is different from being overweight, but the commission went further: excess fat that is not yet doing any damage is a different situation from excess fat that is.
Writing in the International Journal of Obesity, researchers pointed out the obvious gap. The frequency and determinants of progression from preclinical to clinical obesity have never been studied.
They studied it. Of the 92,396 individuals with preclinical obesity, 24,057 transitioned to clinical obesity over a median follow-up of 2.9 years.
What the two categories mean
Preclinical obesity is a body, measured. Clinical obesity is a body plus a consequence.
The commission redefined obesity by considering both anthropometric and direct measures of adiposity, in addition to body mass index, and distinguishing preclinical from clinical obesity based on physical function and related conditions. Somebody with a large waist and no metabolic problem, no joint limitation and no organ dysfunction is in the first group. When one of those appears, they move to the second.
The point of the split is that the two states call for different responses. Treating a measurement is a different proposition from treating an illness, and the commission’s argument was that the field had been doing the first while claiming to do the second.
Why the definition needed two measurements
BMI on its own is a blunt instrument, and the new definition does not rely on it.
Obesity was defined as meeting at least two of four criteria: a BMI of 30 or above, a large waist circumference, a raised waist-to-hip ratio, or a waist-to-height ratio above 0.50. A BMI of 40 or higher qualified on its own.
Requiring two of four is what removes the muscular person misclassified by BMI alone and captures the person whose weight looks acceptable but whose fat sits around the organs. Body Mass Index measures how much you weigh compared to how tall you are, and it has never been able to tell where the weight is.
The number, and how to read it
The headline figure is the transition rate, and it is worth being precise about what it counts.
The cumulative incidence at 1, 3, and 5 years was 12.7%, 25.7%, and 34.3%. That is not a measure of how many people got fatter. It is a measure of how many acquired a condition or limitation that moved them across the definitional line, which usually means a new diagnosis of something like diabetes, sleep apnea or joint disease.
Roughly a third crossed over within five years. Two thirds did not, and the study does not follow them long enough to say whether they eventually would.
What the predictors do and do not tell you
Older age, elevated HbA1c, higher BMI, higher waist ratios, insurance coverage, and poorer self-reported overall health were strongly and independently associated with a greater likelihood of transition.
Most of that list is what you would expect: the people closest to the line crossed it soonest. A creeping long-term blood sugar reading is the clearest early warning in the group, which is unsurprising given that a diabetes diagnosis is one of the commonest routes across.
Insurance coverage is the item that does not belong with the others, and it is not a biological finding. You cannot be recorded as having developed a related condition unless somebody diagnoses it, and diagnosis requires access. That is a reminder that the transition being measured is partly a transition in what the health system noticed.
The limits worth holding onto
This is a cohort study of a research volunteer population, and All of Us participants are not a random sample of Americans.
The median follow-up is 2.9 years, which is short for a condition that develops over decades, and the categories being counted were defined retrospectively from records that were never collected with this framework in mind. Self-reported physical function is doing part of the classification work.
The study also cannot say anything about intervention. It observes who crossed over; nobody was treated to prevent it.
Why this matters more than a definitional argument
Reclassifying a disease sounds like a committee exercise until you notice what it decides.
If preclinical obesity is a risk state rather than a disease, then treating it with drugs that cost thousands a year is prevention, and prevention has to justify itself differently from treatment. If a quarter of that group develops the clinical form inside three years, the calculation changes.
That is what this analysis supplies: the rate that the argument was missing. As we age, our minds and bodies change, and having a healthy lifestyle can help you deal with those changes. The commission’s framework is an attempt to say which of those changes has already become a disease, and this is the first count of how quickly people move from one side of that line to the other.
People also ask
What did the study find?
Among 319,815 participants, 28.9% had preclinical obesity and 40.0% had clinical obesity at baseline. Of the 92,396 individuals with preclinical obesity, 24,057 (26.0%) transitioned to clinical obesity over a median follow-up of 2.9 years. The cumulative incidence at 1, 3, and 5 years was 12.7%, 25.7%, and 34.3%.
What is preclinical obesity?
Excess body fat confirmed by more than one measurement, but without any of the organ dysfunction or limitation of daily activities that the commission uses to define the clinical form. In plain terms: the body composition is there, the harm has not arrived yet.
Why did the definition change?
Because BMI alone misclassifies people in both directions, and because calling everyone above a threshold 'diseased' does not match what happens to them. The commission proposed treating obesity as a disease only when it is doing measurable damage.
How was obesity identified here?
By meeting at least two of four criteria: a BMI of 30 or more, a large waist circumference, a raised waist-to-hip ratio, or a waist-to-height ratio above 0.50. Or a BMI of 40 or more on its own.
What predicted crossing over?
Older age, elevated HbA1c, higher BMI, higher waist ratios, insurance coverage, and poorer self-reported overall health. Insurance coverage in that list is a detection effect: you cannot be diagnosed with a related condition if nobody is looking.
Is transition inevitable?
No, and that is the useful half. Roughly two thirds of the preclinical group had not crossed over by the end of follow-up. The study measured how often it happens, not that it must.
What does this mean for treatment?
The commission proposed different treatment considerations for the two states, and this supplies the missing number for how urgent the preclinical one is. Whether treating people earlier changes the trajectory is a separate question no cohort study can answer. This is general information rather than medical advice.