Patterns of Obesity Development Before the Diagnosis of Type 2 Diabetes: The Whitehall II Cohort Study
Vistisen D, Witte DR, Tabák AG, et al
PLOS Medicine. 2014;11:e1001602
Stable Overweight vs Persistent Obesity: Does It Matter?
Without question, obesity is a major risk factor for type 2 diabetes, but 2 recent studies challenge what we thought we knew about body weight, changes in weight, and risk for diabetes and its complications.
Using Whitehall II Cohort Study data, Vistisen and colleagues applied latent class trajectory analysis to 6705 participants who were free of diabetes at baseline. Latent class trajectory analysis is a statistical method that groups distinct classes of individuals on some common risk factor over time. In this study, the risk factor of interest was body mass index (BMI) as measured during up to 9 follow-up examination phases.
The analysis identified 3 distinct BMI classes. The "stable overweight" group was characterized by an average BMI that increased over time, but started and remained in the overweight range (25-29.9 kg/m2) during the entire observation period. The "progressive weight gainers" group had an average BMI in the overweight range more than 15 years before diagnosis and an early large weight gain with stable BMI in the obese range until 4-5 years before diagnosis, followed by an increase of BMI into morbid obesity. The third, "persistently obese" group was characterized by BMI in the obese range more than 15 years before diagnosis of diabetes, and with persistent obesity until the time of diagnosis.
During a median follow-up of 14 years, 645 individuals developed diabetes, but of those, 94% (n = 604) were in the stable overweight group, 2% (n = 15) were in the progressive weight gain group, and 4% (n = 26) were in the persistently obese group. The 6060 participants who remained free of diabetes were characterized by a mean BMI just below 25 kg/m2 that rose gradually over the follow-up period.
Measures of the underlying causes of diabetes did little to explain these results. Whereas insulin resistance rose sharply near the time of diabetes diagnosis for progressive weight gainers and beta cell function appeared to decline for the persistently obese group, changes in both these measures were small for those in the stable overweight group. Meanwhile, fasting glucose and 2-hour glucose increased considerably and similarly for all groups except those who remained diabetes-free.
It is critical to note that the study does not provide any information on risk within the above groups, or the relative risk between groups. For example, whereas as only 4% of those who developed diabetes were in the persistently obese group, these 26 individuals could comprise a very large proportion of all persistently obese people, whereas the 94% in the stable overweight group could represent a relatively small proportion of all stable overweight individuals. Nevertheless, the findings are clear that the vast majority of people diagnosed with diabetes were overweight but not obese, and did not experience a period of rapid weight gain.
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