Jacinta Bryce (nee Orr), APD, Nutrition Consultant

[email protected]

A new study published by Costanzo et al. in the Annals of Internal Medicine (Ann. Intern. Med. 2015; 162: 610-618) has taken a fresh look at the ‘obesity paradox’ and the relationship with type 2 diabetes. A growing body of research shows that, paradoxically,overweight or obese patients may survive longer with established cardiovascular disease (CVD) than those of normal weight. However the evidence remains unclear whether obesity also provides such a survival advantage for people with type 2 diabetes.

Costanzo et al. followed over 10,500,adults with type 2 diabetes without CVD at baseline. Data on age, diabetes duration, smoking history, height, weight and blood pressure were collected at the initial visit. Thereafter investigators collected information on CVD events and all-cause mortalityacross 8 to 13 years (median 10.6 years). The cohort consisted of 54% men, with a median age of 63 years (interquartile range, 55 – 71) and a median baseline of BMI, 29 kg/m2. Patients were from a single outpatient diabetes service in the United Kingdom, and were classified as either underweight, normal weight, overweight or obese.

The take out findings were that obese and overweight patients (BMI > 25 kg/m2) with type 2 diabetes were more likely to develop cardiac events, like acute coronary syndrome (ACS) and heart failure (HF), and be hospitalised, compared to normal weight patients (BMI, 18.5 to 24.9 kg/m2). However being overweight (BMI,25-29.9 kg/m2) was associated with a significantly lower mortality risk and also the best survival rate. On the other hand obese patients (BMI, 30 kg/m2) had a mortality risk similar to that of normal weight persons. The lower mortality risk linked with overweight or obesity seemed to develop around 60 years of age. As you would expect, underweight patients (BMI< 18.5 kg/m2) had the worst prognosis, i.e. the highest mortality risk and the CVD events.

Strengths of this study included:

          the large numbers of patient and cardiovascular events

          the long term follow up

          exclusion of underweight patients from the normal weight group

          use of primary data that was collected for this study viaa specifically designed electronic database

          conducting the study in a single centre to achieve consistent data definitions

          the authors correcting for potential comorbid conditions, like cancer, chronic kidney disease and lung disease

          adjusting for cardiovascular risk factors, like smoking history and systolic blood pressure.

Limitations of this study included: not collecting information on patient fitness levels, medications (including cholesterol or diabetic medications), cholesterol levels, alcohol consumption or the actual cause of death. Another weakness appears to be that Costanzo et al. used results from prevalent cases of type 2 diabetes (which were already diagnosed or developed beforebeing identified for the study). The authors also list many baseline characteristic differences between the BMI categories – which may have introduced selection bias.

In conclusion, an obesity paradox was observed in this cohort with type 2 diabetes, however further research is needed into possible mechanisms involved. The authors suggest several possible explanations, such as type 2 diabetes induced by metabolic stress, which may be fundamentally different to diabetes without the presence of obesity. They conclude that randomised controlled trials are needed to investigate weight loss, prognosis and mortality risk.

Reference: Costanzo 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, and corresponding Summary for Patients