We now know that obesity is a risk factor for a whole series of cancers. The association is particularly marked in the case of endometrial cancer, kidney cancer or colorectal cancer. Thus, people suffering from obesity run a risk of developing colorectal cancer increased by about 30% compared to people of normal weight.
What real contribution of obesity to the risk of colorectal cancer?
To assess the extent of possible current bias, the researchers assessed weight data, at the time of diagnosis, but also years before, from 12,000 participants. This analysis reveals:
- the lack of an established relationship between body weight at diagnosis and the risk of colorectal cancer;
- on the other hand, there is a strong correlation between being overweight and the future risk of colorectal cancer;
- this association is strongest 8 to 10 years before diagnosis;
- participants who are very overweight or obese during this 8-10 year period before diagnosis have a 2-fold increased risk of future colorectal cancer;
- finally, a considerable number of participants affected by colorectal cancer involuntarily lost weight before diagnosis;
- unintentional weight loss of 2 pounds or more in the 2 years before diagnosis was up to 7.5 times more common in participants with cancer than in controls.
“During this period, the cancer is already there, but its symptoms are not yet noticeable. Unintentional weight loss could also be an early indication of cancers or other diseases and should be investigated.
In conclusion, taking weight into account only at the time of cancer diagnosis does not identify this link between obesity and increased risk of colorectal cancer, explains the study’s lead author, Dr. Mandic, researcher at DKFZ. However, obesity is indeed a major precursor factor, years before, of future colorectal cancer.
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