Weight Changes and BMI Shape Colon Cancer Survival

The study examined 5,521 adults aged 30 or older who had been diagnosed with colorectal cancer. They were recruited from over 20 hospitals in southwest Germany. Follow‑up data went until September 2018, and the analysis was done in 2025‑2026.

People were split into four weight groups based on their body mass index at the time of diagnosis. Underweight was below 18.5, normal was 18.5‑24.9, overweight was 25‑29.9, and obesity was 30 or higher. The data showed that those in the overweight group lived a bit longer than the normal‑weight group, with a hazard ratio of about 0.89. No clear link was found for the obesity group.

The researchers also measured how much weight each person had lost in the years before the cancer was found. Losing more than ten percent of body weight before diagnosis was tied to a higher risk of death, with a hazard ratio around 1.55. This meant that substantial weight loss before diagnosis made survival worse.

When the analysis took both the BMI at diagnosis and the earlier weight loss into account, the survival differences for the overweight and obesity groups disappeared. In other words, the apparent benefit of higher BMI seemed to be driven by the weight loss that often preceded the cancer diagnosis.