The Correlation between BMI, Fitness, and Mortality in Patients with Diabetes  

Trying to understand the “obesity paradox” in patients with diabetes.  

Patients that have diabetes have an increased risk of cardiovascular disease. When physicians educate patients on diabetes, healthy eating and exercise is the first-line treatment. But there is a phenomenon when it comes to patients with obesity and mortality, called the obesity paradox. Obesity paradox is an observation that in some patients  overweight and/or obesity could have a protective or survival benefit in cardiovascular or peripheral vascular disease. This study tries to evaluate the obesity paradox in patients with diabetes.  

This study had 8,528 patients with diabetes from the Henry Ford Exercise Testing Project (FIT Project) from 1991 to 2009. Patients had to be at least 18 years old and diagnosed with diabetes. Of the 8,528 patients, 85% of the patients had an A1C of ≥ 6.5%, and of patients taking diabetic medication, 11% of the patients had an A1C of 5.7-6.4%, and 4% of the patients had an A1C of < 5.7%. Patients with a BMI < 18.5 kg/m2 or cancer were excluded from this study. The primary outcome of this study was total mortality and was determined by the Social Security Death Index with a follow up in 2013. To assess the patient’s stress levels, patients used a standard methodology through the Bruce protocol treadmill. Patients had their fitness calculated through maximal exercise capacity (METs) by the Quinton treadmill controller. Fitness categorization: patients with low fitness had < 6 METs, with moderate 6-9.9 METs, and high ≥ 10 METs.  

Patients within the highest fitness group were younger, less likely to be a woman, and had a less likely chance of having CVD risk factors. Also, patients within the highest fitness group had the lowest mortality rate. Still, there was little difference in mortality rate between patients with average weight and patients with obesity who achieved ≥ 10 METs. Patients within the <6 METs group had more than double the mortality rate than patients that fell within the 6-9.9 METs group regardless of what the patient’s BMI was. The patients in less fitness level, < 6 METs, had a hazard for total mortality of 0.74 for  patients with obesity compared to patients that were average weight. The regression model showed for every 1 kg/m2 increase in the patient’s BMI there was a 0.96 lower chance of mortality. For every 1 MET increase in the patient’s fitness, there was a 0.76 lower chance of death. This study determined that patients within the higher fitness group had a significantly lower mortality rate. During the study, they were able to find that within each BMI category, patients within the top fitness group had the lowest mortality risk, and patients with higher BMI who were in the lowest fitness group < 6 METs had a significantly lower risk for total mortality. 

Patients with higher fitness were associated with less obesity paradox and had a lower relative risk for mortality. This study showed that it is in line with other studies demonstrating the obesity paradox. A limitation that comes with this is study is they did not have each patient’s maximal lifetime BMI or change in BMI; it was proposed that it could play a part in the obesity paradox. Another limitation of the study was they did not have information on the duration of diabetes, and patients with obesity had an average of A1C of 0.3% higher than patients that were average weight. Some strengths of this study were men and women were nearly equal, there was a large proportion of African Americans, and a long follow up period. Patients should still be advised to improve fitness and lose weight, but these results show that patients should focus on their improved fitness rather than weight loss to reduce mortality. More studies need to be done to determine more factors determining the reasons behind the obesity paradox.   

Practice Pearls: 

• A higher fitness level is associated with less obesity paradox and lower mortality rate regardless of BMI.
• Patients should be advised to improve overall fitness to reduce mortality. 
• Patients with obesity had a 30% lower mortality rate compared to patients that were average weight. 

Whelton, Seamus P, et al. “Association of BMI, Fitness, and Mortality in Patients With Diabetes: Evaluating the Obesity Paradox in the Henry Ford Exercise Testing Project (FIT Project) Cohort.” Diabetes Care, U.S. National Library of Medicine, Mar. 2020 

Karlena Pope, PharmD Candidate, South College School of Pharmacy

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