Bariatric Surgery Significantly Decreases the Prevalence of Type 2 Diabetes Mellitus and Pre-Diabetes Among Morbidly Obese Multiethnic Adults: Long-Term Results

• This study of over 1,600 patients found bariatric surgery normalized blood sugar levels across diabetes, undiagnosed diabetes, and pre-diabetes groups, sustained through 3 years.
• A1c dropped more than 2 percentage points, exceeding what most diabetes medications achieve.
• The cohort was two-thirds Hispanic, reflecting Dr. de la Cruz-Muñoz's South Florida community, filling an evidence gap at the time.
• Pre-diabetic and undiagnosed diabetic patients achieved the greatest weight loss, suggesting earlier intervention benefits.
• This supports the American Diabetes Association's current recommendation of metabolic surgery for type 2 diabetes and obesity.

Why This Study Was Needed

Type 2 diabetes and obesity feed each other, and both fall hardest on Hispanic and other minority communities. By 2010, studies had shown that bariatric surgery could reverse abnormal blood sugar, but nearly all of those patients were non-Hispanic White. Whether the same benefit applied to Hispanic adults, who make up most of South Florida’s population, was largely unknown.

How the Study Was Done

The team reviewed 1,603 adults who had bariatric surgery with Dr. de la Cruz-Muñoz’s program between 2002 and 2010. Two-thirds were Hispanic, 77% were women, and the average age was 45. Patients were grouped by their blood sugar before surgery:

• 377 with diagnosed type 2 diabetes
• 107 with undiagnosed diabetes (fasting glucose of 126 mg/dL or higher, not on treatment)
• 276 with prediabetes (fasting glucose 100–125 mg/dL)
• 843 with normal fasting glucose

Weight, BMI, fasting glucose and hemoglobin A1c were tracked at 6, 12, 24 and 36 months.

What the Study Found

• By one year, and through three years, every group had a normal average fasting glucose.
• Fasting glucose fell 43% in patients with undiagnosed diabetes and 33% in patients with diagnosed diabetes.
• Hemoglobin A1c dropped by 2.30 percentage points in diagnosed diabetes and 2.13 points in undiagnosed diabetes, larger than the effect of most diabetes medications.
• Weight loss was substantial in every group: 47.0 kg in prediabetes, 46.6 kg in undiagnosed diabetes, 43.1 kg with normal glucose and 41.4 kg in diagnosed diabetes.

What This Means for Patients

If you have diabetes or prediabetes, surgery can do more than help you lose weight; it can normalize blood sugar. This study showed that the benefit extends to Hispanic patients, and it highlights a group that is easy to miss: about 1 in 15 patients had diabetes that had never been diagnosed. The benefit comes partly from weight loss and partly from hormonal changes after surgery that improve insulin resistance within days. Learn more in our guide to diabetes remission after surgery.

Since this paper, randomized trials such as the STAMPEDE trial and a 10-year Italian randomized trial confirmed that surgery outperforms medical therapy for type 2 diabetes, and the 2016 Diabetes Surgery Summit joint statement endorsed metabolic surgery as a standard diabetes treatment.

Clinical Pearls

• Bariatric surgery normalized fasting glucose by one year across all glucose categories, sustained to three years.
• A1c reductions of more than 2 points were seen in patients with diabetes.
• Screening before surgery uncovers undiagnosed diabetes in a meaningful share of patients.
• Patients with prediabetes lost the most weight, an argument for treating obesity before diabetes develops.

Strengths and Limitations

This was one of the first large studies of metabolic outcomes in a majority-Hispanic surgical population, with follow-up to three years. It is retrospective and single-program, follow-up became less complete over time, and it reports average glucose values rather than strict diabetes remission definitions used in later trials.

Expert Commentary

When we started this work, most of the diabetes data came from populations that looked nothing like my patients. Two-thirds of the people in this study were Hispanic, and they did just as well. That mattered to the patients sitting in my waiting room, and it mattered to the insurers deciding whether to cover them.

The finding I still emphasize is the prediabetes group. Those patients lost the most weight and never progressed to diabetes. Treating obesity before diabetes arrives is one of the best things we can do.

— Dr. Nestor de la Cruz-Muñoz

Related Research

• Obesity Surgery study on ethnicity and weight loss
• 10- to 18-year follow-up of adolescent patients