Clinical Context

Most clinicians and certainly most patients have a mental picture of type 2 diabetes (T2D) that includes diabetes, and the authors of the current study noted that approximately 89% of adults with diabetes have overweight or obesity. Yet the prevalence of lean diabetes, defined as T2D in persons with a body mass index (BMI) < 25 kg/m², may be increasing, and lean diabetes has important clinical characteristics distinct from the majority of patients with T2D. A review by George and colleagues, which appeared in the May 15, 2015 issue of the World Journal of Diabetes,^[1] addressed these issues.

Lean diabetes usually is diagnosed around age 40 years, and it is more common among men compared with women. Although the diagnosis of type 1 diabetes should be considered on the presentation of patients with elevated blood glucose levels and BMI < 25 kg/m², islet cell autoantibodies are not encountered in patients with lean diabetes. Still, insulin sensitivity is better in lean diabetes vs T2D, in general, and the pathology of lean diabetes is more dependent on reduced insulin secretion. Although it might seem that lean patients with T2D would be at lower risk for complications of diabetes, this does not appear to be the case.

The current study by Adesoba et al performed an important analysis of diabetes prevalence in the United States, with a focus on lean diabetes.

Study Synopsis and Perspective

The prevalence of diabetes among lean US adults (BMI < 25 kg/m²) significantly increased from 2015 to 2020, whereas diabetes prevalence stayed flat among people with overweight or obesity, showed data from telephone surveys of more than 2.6 million American adults.

The new study results showed that in lean adults, the prevalence of diabetes rose from 4.5% in 2015 to 5.3% in 2020, a nearly 18% relative increase over the 6 years.

In contrast, among overweight and obese American adults, the prevalence of diabetes was 14% in 2015 and 14.3% in 2020, a nonsignificant difference during the 6-year window, reported researchers from the Department of Health Policy and Management at the University of Arkansas for Medical Sciences in Little Rock, Arkansas, in a recent report published in Diabetes Care.^[2]

"We find it interesting that within the time period of our study only lean adults experienced an increase in diabetes prevalence. More studies are needed to elucidate what may be causing this," said Taiwo P. Adesoba, lead researcher on the study, in an interview.

The results suggest a need to better understand the increasing prevalence of diabetes among people with lower BMI and raise the issue of "whether we need to provide more resources to certain populations to ensure that everyone has access to regular diabetes screening," said Clare C. Brown, PhD, senior author of the report, who is also at the University of Arkansas for Medical Sciences.

Although the American Diabetes Association (ADA) now recommends routine serial diabetes screening for all asymptomatic adults starting when people reach the age of 35 years (and starting at a younger age in adults with risk factors including elevated weight),^[3] this standard has only been in place since 2022.

In addition, the US Preventive Services Task Force 2021 recommendations^[4] called for diabetes screening for asymptomatic people aged 35 to 70 years only if they have obesity or are overweight (BMI ≥25 and ≥30 kg/m²).

Despite this, one possible explanation for the observed rise in diabetes prevalence among asymptomatic US adults with normal weight is increased screening of these people.

"Many clinicians follow the ADA screening guidelines. It is possible that the noted increased prevalence of lean diabetes is due, to some degree, to wider adoption of these screening recommendations”, commented Dan V. Mihailescu, MD, interim chief of endocrinology at Cook County Health in Chicago, Illinois, who was not involved with the new report.

The authors of another recent study have also determined that using age, rather than weight, as the primary screening tool for diabetes would be the easiest, and most equitable, approach to capturing the most cases possible, as reported by Medscape Medical News. The researchers, from Northwestern University Feinberg School of Medicine, Chicago, Illinois, also call for screening from age 35 years upwards for all US adults.

"All major racial and ethnic minority group develop diabetes at lower weights than White adults, and it's most pronounced for Asian Americans," said the lead author of that report, Matthew J. O'Brien, MD.

Mihailescu, too, supports the concept of more liberal screening.

"Broader routine screening for diabetes has very little risk but could identify people with disease who may not present with typical risk factors. I hope that more primary care practitioners adopt the ADA screening guideline" and initiate screening in all adults once they reach 35 years old regardless of their BMI, he said.

The study by Adesoba and colleagues used data collected by the Behavioral Risk Factor Surveillance System,^[5] a program run by the Centers for Disease Control and Prevention, using telephone interviews in 2015 to 2020 with a total of 2,630,463 adult US residents.

Respondents self-reported being diagnosed with diabetes. The authors acknowledged the data limitation of not being able to distinguish between type 1 diabetes and T2D but maintained that "type 1 diabetes is unlikely to be the sole cause" of the increasing US prevalence of lean diabetes."

They based this inference on the generally low prevalence of type 1 diabetes among all adults with diabetes -- a prevalence rate they estimated to be about 6% -- and the increasing prevalence of diabetes they found during the 6 years studied among lean adults who were at least 45 years old.

Mihailescu said the lack of more detailed information on diabetes type is a limitation.

"Some of the cases reported as lean diabetes could have been latent autoimmune diabetes of adults (LADA)," he noted in an interview, adding that some studies have reported that 5% to 10% of adults initially diagnosed with T2D actually have LADA.

The upshot is that the numbers reported by Adesoba and colleagues "might represent a significant over-estimation of the actual prevalence of lean diabetes," Mihailescu said.

The study was also limited by its reliance on self-reports of weight and height, he added.

Additional analyses in the report showed that among the 791,445 people with lean diabetes, the adults who were at least 45 years old had a much higher diabetes prevalence: 9.9% in 2020 compared with younger adults, who had a prevalence of just 1.3% in 2020.

Still, the growth in prevalence from 2015 to 2020 seemed unaffected by age, with virtually identical odds ratios for prevalence in 2020 compared with 2015, which was 1.19 in persons aged 45 years or older and 1.2 in younger adults.

A further subgroup analysis showed that people who self-identified as Black had the highest diabetes prevalence by race or ethnicity in every year included in the study, reaching a peak of 9.2% in 2020, with an OR of 1.44 compared with 2015.

Survey participants who identified as Hispanic had prevalence rates that rose from 5.5% in 2015 to 7.2% in 2020, with an OR of 1.32. Among White survey participants, the prevalence rate in 2020 was 4.4%, a significant OR of 1.15 compared with 2015.

Diabetes prevalence also rose much more in women, who had a diabetes prevalence of 5.3% in 2020, an OR of 1.45 compared with 2015, which brought the prevalence rate in women much closer to the rate in men, which was 5.9% in 2020. Among men, the prevalence rate in 2020 did not significantly change from the rate in 2015 of 5.5%.

"We are still learning about lean diabetes, and we need to know more about the genetic and environmental mechanisms that influence insulin secretion, beta-cell mass and survival, and insulin resistance," noted Mihailescu. "Lean diabetes remains an understudied topic, and much more research is needed to better understand it."

The study received no funding. Adesoba, Brown, and Mihailescu have reported no relevant financial relationships.

Implications for the healthcare team

• Lean diabetes usually is diagnosed around age 40 years, and it is more common among men compared with women. Islet cell autoantibodies are not encountered in patients with lean diabetes. Still, insulin sensitivity is better in lean diabetes vs T2D, in general, and the pathology of lean diabetes is more dependent on reduced insulin secretion. Although it might seem that lean patients with T2D would be at lower risk for complications of diabetes, this does not appear to be the case.
• The current study by Adesoba et al found a moderate increase in the prevalence of diabetes among US adults from 2015 to 2020. The increase in lean diabetes specifically was more profound (~ 18%), and lean diabetes was particularly more common among Black and Hispanic adults along with women.
• The healthcare team should consider screening adults with a body mass index BMI < 25 kg/m² for diabetes, especially if they have risk factors such as a family history of diabetes.

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