Obesity Paradox and Diabetes

By Seema Gupta, MD, MSPH

Primary Care Physician, Charleston, WV

Dr. Gupta reports no financial relationships relevant to this field of study.

SYNOPSIS: In a prospective cohort study of overweight or obese type 2 diabetics, being overweight was associated with a lower mortality risk, but being obese was not. Overweight or obese patients suffered a higher rate of cardiac events.

SOURCE: Costanzo P, et al. The obesity paradox in type 2 diabetes mellitus: Relationship of body mass index to prognosis: A cohort study. Ann Intern Med 2015;162:610-618.

Obesity has reached epidemic proportions in the United States, in both adults and children. It is associated with numerous comorbidities, including type 2 diabetes, hypertension, dyslipidemia, obstructive sleep apnea and sleep-disordered breathing, osteoarthritis, gout, certain cancers, and major cardiovascular diseases (CVD). In fact, more than 80% of cases of type 2 diabetes can be attributed to obesity. The association between obesity and increased risk for CVD such as heart failure, coronary heart disease, sudden cardiac death, and atrial fibrillation is well-established. However, numerous studies have documented that once CVD develops, there seems to be an obesity paradox in which patients with elevated body mass index (BMI) have a better prognosis compared with their lean counterparts.^1,2 The evidence for a similar obesity paradox among patients with diabetes has been less consistent.

To assess the association between body weight and prognosis in patients with type 2 diabetes, Costanzo et al conducted a prospective cohort study of type 2 diabetics attending an outpatient clinic in England. Researchers enrolled 10,568 patients who were followed for a median of 10.6 years. Median age was 63 years, 54% of patients were men, and more than 99% of patients had no known history of CVD. The median baseline BMI was 29.0 kg/m². Data on age, diabetes duration, smoking history, height, weight, and blood pressure were collected. But data on exercise and medications were not. The primary outcome of the analysis was all-cause mortality.

Researchers found that being overweight (BMI, 25-29.9 kg/m²) was associated with a lower mortality risk, whereas obese patients (BMI > 30 kg/m²) had a mortality risk similar to that of normal-weight persons. Patients with low body weight had the worst prognosis. However, overweight or obese patients (BMI > 25 kg/m²) were found to have a higher rate of cardiac events (such as acute coronary syndrome and heart failure) than those of normal weight (BMI, 18.5-24.9 kg/m²).

COMMENTARY

Previously, many studies have attempted to examine the relationship between obesity and mortality in patients with type 2 diabetes, with varying results.^3,4 Although some have reported an increase in mortality in obese patients with type 2 diabetes, others have shown that being overweight or obese was associated with better overall survival rates, and some have even found a lack of association between BMI and mortality. The current study has several strengths, including a large sample size and long follow-up period. Adjustments were also made for other key characteristics, such as smoking, comorbid conditions, and systolic blood pressure.

However, I would not advise my diabetic patients to not lose that extra weight just yet. There may be several alternate explanations for the study findings, including that patients with lower weight may represent a higher mortality risk as they may already be sick from an etiology unrelated to diabetes. Also, neither data related to fitness nor medications were captured or evaluated in the study. Finally, the development and treatment of type 2 diabetes may influence body weight. Therefore, to develop an informed clinical opinion, it is vital to conduct a randomized, controlled trial in which overweight and obese patients with diabetes are randomized to weight-loss and non-weight-loss groups. Only then, over time, can the risk of cardiac events and death be assessed accurately. Until that time, it would be prudent to recommend a healthy lifestyle change for obese diabetic patients, including the goal to achieve weight loss, in addition to pharmacotherapy.

REFERENCES

1. Morse SA, et al. The obesity paradox and cardiovascular disease. Curr Hypertens Rep 2010;12:120-126.
2. De Schutter A, et al. The impact of obesity on risk factors and prevalence and prognosis of coronary heart disease—the obesity paradox. Prog Cardiovasc Dis 2014;56:401-408.
3. Balkau B, et al. Risk factors for early death in non-insulin dependent diabetes and men with known glucose tolerance status. BMJ 1993;307:295-299.
4. Carnethon MR, et al. Association of weight status with mortality in adults with incident diabetes. JAMA 2012;308:581-590.