Photo by Bill Branson
New research suggests that body mass index (BMI) is an inadequate method for estimating changes in body fat and obesity in children with acute lymphoblastic leukemia (ALL).
Investigators found a discrepancy between BMI and body composition in this population, and the cause of this appeared to be increases in body fat with simultaneous loss of lean muscle mass during treatment.
The team reported these findings in Leukemia & Lymphoma.
With previous work, the investigators found that obese children diagnosed with high-risk ALL had a 50% greater risk of their disease recurring compared with children who were not obese.
“In my lab, we’ve seen a direct interaction between fat cells and leukemia cells that may help explain this increased risk of disease relapse,” said study author Steven Mittelman, MD, PhD, of Children’s Hospital Los Angeles in California.
“It appears that the fat cells ‘protect’ leukemia cells, making them less susceptible to chemotherapy and making an accurate measure of body fat essential.”
To determine if BMI accurately reflects body fat in ALL, the investigators analyzed 50 patients. They were predominantly Hispanic, between the ages of 10 to 21, and had newly diagnosed high-risk B-precursor ALL or T-cell ALL.
The team measured the percentage of total body fat and lean muscle mass at the time of diagnosis, at the end of induction, and at the end of delayed intensification. They also calculated BMI Z-score—a measure of how a given child’s BMI deviates from a population of children of the same age and sex—at these time points.
The investigators said sarcopenic obesity—gain in body fat percentage with loss of lean muscle mass—was “surprisingly common” during ALL treatment.
And sarcopenic obesity resulted in poor correlation between changes in BMI Z-score and body fat percentage overall (r=-0.05), within the time points (r=0.02), and within patients (r=-0.09, all not significant). BMI Z-score and body fat percentage changed in opposite directions in more than 50% of interval assessments.
“We found that change in BMI did not reflect changes in body fat or obesity,” said Etan Orgel, MD, of Children’s Hospital Los Angeles.
“In some patients, reaching a ‘healthy’ BMI was due solely to loss of muscle even while body fat continued to rise. Based on these results, we believe that evaluation of obesity in patients with leukemia should include direct measures of body composition.”
