Dr Amanda Cross, Reader in Cancer Epidemiology, Imperial College London

The big fat cancer question


Dr Amanda Cross
Reader in Cancer Epidemiology, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London
Member of the Population Health work stream of the NIHR Cancer and Nutrition Collaboration

Date: 07 March 2019

Someone in the UK is diagnosed with cancer every two minutes, and the number of new cases each year is increasing. Although survival has improved in the UK, cancer causes one in four deaths and has overtaken cardiovascular disease as the leading cause of death.

Similarly, the prevalence of obesity around the world has increased dramatically over the past five decades. It is estimated that nearly two billion adults and over 340 million children and adolescents are now overweight or obese. In the UK, almost two thirds of the adult population are overweight or obese.

The link between obesity and cancer risk has been widely studied in observational epidemiologic studies. In this approach, various measures of body size are generally either self-reported by study participants or measured on one occasion at recruitment.

These studies allow large numbers of people to be investigated, which enables analyses across a range of variables such as gender, age, country etc. However, the analyses are often based on the assumption that these physical measures don’t change throughout the course of the study.

It is these studies that have shown that body size is associated with the development of at least 13 different cancers, including some of the most common cancers, such as bowel and breast cancer.

However, there is very little evidence on whether weight loss in overweight and obese individuals reduces cancer risk. To address this question, and others - such as the interplay between diet quality, caloric intake and physical activity - we need evidence from randomised controlled trials.

Although the evidence that obesity increases cancer risk is convincing, little is known about the effect of being overweight or obese on prognosis after a cancer diagnosis. Cancer patients desperately want to know what they can do to increase their chances of disease-free long-term survival. Currently, we do not have good quality, evidence-based data to support specific advice for clinicians to give to these patients.

There is an urgent need to conduct robust evidence-based research to enable us to reduce risks of both primary cancer and recurrent disease in people who are overweight or obese. Research can also help reduce the impact of comorbidities and treatment side effects, ultimately improving overall quality of life for patients.

Randomised controlled trials have successfully shown that weight loss can prevent and control diabetes, but undertaking similar trials for cancer prevention is notoriously challenging. Some of the difficulties include the study size and length requirements, because cancer is a heterogeneous and often slow growing disease. Other problems include uncertainties about the life stage for preventative interventions to be implemented and the correct “dose” for the intervention, as well as assessing adherence and determining an appropriate and feasible endpoint.

The development of such randomised controlled trials requires a multidisciplinary team, including epidemiologists, clinicians, behavioural change experts, nutritionists and patients, to ensure that interventions are feasible, acceptable, and likely to produce the biological benefits that are needed to improve cancer outcomes.

To meet this need, the NIHR launched the NIHR Cancer and Nutrition Collaboration. This collaboration provides a coordinated framework to support research and networks in the fields of cancer and nutrition, bringing together interested parties from all over the country. It encourages a national collaborative effort in this area, to better inform the research needs and identify opportunities for collaborative working.

Within the collaboration, the Population Health work stream focuses on diet and nutrition, alcohol, physical activity and obesity in the primary, secondary and tertiary prevention of cancer. The scope of work includes research into biological mechanisms, understanding behaviour change, and the impact of lifestyle exposures on markers of cancer risk and cancer development. The research encompasses basic science, epidemiology, modelling, and intervention studies.

Several of the members of the Population Health work stream will be discussing and debating some of the issues described above at the European Congress on Obesity in Dundee on April 27th 2019. Come and join us at the Action on Weight Management in Cancer satellite meeting to find out about research needs in this area and meet potential collaborators.

Elucidating the mechanisms underlying the association between obesity and cancer will enable clear recommendations to be devised for clinicians, the general public and for the growing number of cancer survivors. Our NIHR-funded collaboration is bringing together the expertise to make this happen.

To find out more about the NIHR Cancer and Nutrition Collaboration, visit our website at:

The views and opinions expressed in this blog are those of the authors and do not necessarily reflect those of the NIHR, NHS or the Department of Health and Social Care.
  • Summary:
    People who are obese are more likely to develop cancer, but little is known on whether weight loss reduces this risk or whether obesity in cancer survivors leads to a poorer prognosis. Dr Amanda Cross outlines the pitfalls in conducting research in this area and how the NIHR is helping.
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  • Author:

    Dr Amanda Cross
    Reader in Cancer Epidemiology, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London
    Member of the Population Health work stream of the NIHR Cancer and Nutrition Collaboration

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