Children with obesity diagnosed with cancer face significantly worse health outcomes, including a heightened risk of relapse and death, according to a new Canadian study.

The research, published in the journal Cancer, analyzed data from over 11,000 cancer patients aged 2 to 19, of whom 10.5% were obese at diagnosis. The study examined various cancers, including leukemia, lymphoma, and other tumors, and found that obesity negatively impacted outcomes across the entire cohort.

Increased Risk of Relapse and Mortality

The findings revealed that obese children had a 16% higher risk of cancer relapse and a 29% increased risk of death within five years of diagnosis, even after accounting for factors such as age, sex, and ethnicity.

“Our study highlights the negative impact of obesity among all types of childhood cancers,” said Dr. Thai Hoa Tran, a pediatric hematologist and oncologist at the University Hospital Centre Sainte-Justine in Montreal, Canada, and one of the study’s authors.

Dr. Tran emphasized the need for strategies to address obesity’s impact on cancer outcomes in future clinical trials and highlighted the importance of combating the childhood obesity epidemic to prevent severe health consequences.

Acute Lymphoblastic Leukemia and Brain Tumors Most Affected

The study found the impact of obesity was particularly pronounced in children with acute lymphoblastic leukemia (ALL)—a cancer of the blood and bone marrow—and brain tumors. Researchers suggested that fat tissue may play an active role in tumor progression, metastasis, and resistance to treatment.

Previous research has indicated that adipose (fat) tissue cells can promote tumor development and hinder the effectiveness of therapies. Additionally, the study noted concerns about potential undertreatment and inappropriate dosing of chemotherapy in obese patients, which could further compromise outcomes.

Limitations and Calls for Improved Measures

The researchers acknowledged limitations in their study, including reliance on body mass index (BMI) to define obesity. They pointed out that BMI is an imprecise measure that does not fully capture body composition or nutritional status.

“BMI remains a crude and imperfect measure,” the authors wrote, echoing recent calls from experts to adopt more accurate diagnostic tools for obesity. Critics argue that BMI may lead to overdiagnosis or fail to reflect the nuanced impact of weight on health outcomes.

Implications and Urgency

The findings underscore the urgent need for interventions targeting childhood obesity and call for more precise research to better understand the interplay between obesity and cancer treatment. As childhood obesity rates continue to rise globally, addressing this epidemic could have far-reaching implications for improving survival rates and health outcomes for young cancer patients.

Global health experts have called for a fundamental reevaluation of how obesity is diagnosed, urging a shift from the long-standing reliance on body mass index (BMI) to a more nuanced and individualized approach. The recommendations come from a panel of 56 specialists and patients, who published their findings in The Lancet Diabetes & Endocrinology.

A Complex Condition

Obesity, affecting roughly one in eight people worldwide, is a risk factor for numerous health conditions, including type 2 diabetes, cardiovascular disease, and certain cancers. However, experts argue that it is not always synonymous with ill health. The commission has proposed distinguishing between clinical obesity, a chronic disease marked by organ dysfunction or physical limitations caused by excess fat, and preclinical obesity, where individuals have obesity but maintain normal organ function.

“There are some people who have obesity and manage to live a relatively normal life … and on the other hand, you have [people] who may suffer significant health issues due to obesity alone,” said Dr. Francesco Rubino, the commission’s chair and a professor at King’s College London.

BMI Under Fire

BMI, a measure derived from a person’s weight and height, has been the primary diagnostic tool for obesity since the World Health Organization adopted it in the 1990s. A BMI of 30 or higher classifies an adult as obese. While BMI offers a simple proxy for body fat and related health risks, critics say it is flawed and outdated.

“It’s not just how much fat you have, it’s also where the fat is that’s important,” said Dr. Adam Collins, a nutrition expert at the University of Surrey. He highlighted that BMI does not account for fat distribution or differentiate between fat and muscle mass, leading to potential misclassifications.

Athletes with high muscle mass, for example, may fall into the obese category despite being in excellent health.

A New Framework

The commission has recommended that BMI remain a preliminary screening tool but that an official diagnosis of clinical obesity should involve more comprehensive criteria. These include signs such as obesity-induced breathlessness, heart failure, and joint pain, among others.

Adopting this approach could reduce overdiagnosis and ensure medical care is tailored to an individual’s health needs rather than focusing solely on weight loss. This shift is especially crucial as governments debate how to allocate resources, such as expensive weight-loss drugs like Wegovy and Mounjaro, which are in limited supply.

Changing Perspectives

Beyond medical practice, experts hope the new framework will combat the stigma around obesity and promote better understanding of metabolic health for people of all sizes. “This leads to a change in practice and, maybe even before that, a change in mindsets,” Rubino said.

Though it may take time to implement these changes, advocates believe this step could reshape how obesity is perceived and treated globally.