Obese people lose weight following a cancer diagnosis: but is the weight loss intentional?

As I have discussed before, the relationship with cancer and weight is complicated. However, it is not only of interest to find out how weight impacts on cancer development, but also what happens to people’s weight once cancer is diagnosed and how this relates to cancer survival. For example, medication to treat cancer might make people more prone to weight gain. This could be problematic for people who are already overweight or obese before they were diagnosed with cancer, because an unhealthy weight has been linked to a higher chance of a cancer coming back. Alternatively, it is possible that a cancer diagnosis acts as a ‘teachable moment’ which may motivate people to change their lifestyle. This may help to avoid the cancer coming back after treatment.

Our researchers looked in two large studies, one with people from the UK, and one from the US, at how BMI changed over time in people diagnosed with cancer; and those who stayed cancer-free. Importantly, they also looked at how weight change differed according to people’s weight status before diagnosis, as emerging evidence has indicated that weight loss may improve the prognosis for cancer survivors who are overweight or obese at the point of diagnosis.

Over a four-year period, there was no difference in weight change between normal weight cancer survivors and normal weight cancer-free individuals in either the UK or the US. However, obese cancer survivors in the UK lost an average of 1.48kg vs. cancer-free obese individuals who lost an average of 0.25kg; and in the US, obese cancer survivors lost an average of 2.35kg in comparison to cancer-free obese participants who gained an average of 0.53kg. These results indicate that being diagnosed with cancer has little impact on weight in individuals who are a healthy weight, but is associated with significant weight loss among those who are obese.

Given that there was very little weight loss in normal weight cancer survivors vs. those who were obese, these results suggests that obese cancer survivors may have made a conscious effort to lose weight and to keep it off. However, it is also possible that people who were obese were diagnosed with cancer at a later stage (I discussed here why this is often the case), and that their weight loss was due to their cancer being more advanced, or treatment having taken a greater toll on the body. Unfortunately, the researchers had no data on the stage at which cancers were diagnosed, or whether the weight loss they observed was intentional, so we cannot say which of these options is true. It is important to do more research to see how weight loss relates to cancer survival to investigate whether keeping a healthy weight after a cancer diagnosis really has benefits for surviving longer.

Given that, on the whole, treatment for cancer is getting better, more and more people will survive cancer. Therefore, it is really important to find out what can be done for cancer survivors to improve their quality of life and to ensure that they remain cancer-free.

 

Reference:

Jackson SE, Williams K, Steptoe A & Wardle J (2014): The impact of a cancer diagnosis on weight change: findings from prospective, population-based cohorts in the UK and the US, BMC Cancer , 14:926  doi:10.1186/1471-2407-14-926

http://www.biomedcentral.com/1471-2407/14/926/abstract