04 Feb 2019 Guest Blog: Obesity and cancer – what do we know?
Maxine Lenza is World Cancer Research Fund’s (WCRF) Press and Communications Officer. She gained a BSc (Hons) in Biology from the University of Exeter, and she has an MSc in Science, Technology and Society where her thesis looked at public narratives surrounding universal healthcare. To mark this year’s World Cancer Day (Monday 4th February), Maxine discusses what we know about the relationship between overweight and obesity and cancer.
In 2016, an estimated 1.9 billion adults and over 340 million children and adolescents (aged 5-19 years old) around the world were overweight or obese. The increase in the proportion of adults categorised as obese has been observed both in low- and middle-income countries, as well as in high-income countries. This trend in weight is widely considered to be one of the most pressing public health concerns of this century.
New technologies have encouraged people to increase the time they spend engaging in sedentary behaviours, such as sitting in cars, watching television, and using computers or mobile phones. A shift to ‘Western type’ diets (characterised by a high amount of sugar, meat and fat) has also been linked to the increase in levels of overweight and obesity, and is a feature of the ‘nutrition transition’ that accompanies economic development.
WCRF analyses global research on how body fatness and weight gain affect the risk of developing cancer. This evidence is judged by a panel of independent experts who draw conclusions about the strength of the evidence. Being overweight or obese is a cause of 12 different types of cancer:
- Breast (postmenopause)
- Mouth, pharynx and larynx
- Prostate (advanced)
- Stomach (cardia)
After not smoking, being a healthy weight is the most important way you can protect yourself against cancer.
Our recent report on energy balance and body fatness explored what factors can increase or decrease the risk of weight gain, overweight and obesity. Screen time (time spent being sedentary such as watching television or using a computer) was identified as having a convincing link to excess weight gain in children.
Weight: a balancing act
Our weight is a balancing act between the energy we put in (calories from foods and drinks) and the energy we use (for normal bodily functions and what you burn during exercise). If you eat or drink more than your body needs, you will put on weight. The reverse is also true: if you regularly use more energy than you take in, you will lose weight.
How can obesity cause cancer?
Our research shows that there are several reasons for the link between body weight and cancer. For example, we know that fat cells release hormones such as oestrogen. Excess oestrogen can increase the risk of some cancers, like breast and womb cancer, and promote their growth. Storing too much fat can also cause insulin resistance (where insulin becomes less effective at controlling blood sugar levels), which encourages the body to produce growth hormones. High levels of these hormones can promote the growth of cancer cells.
Body fat also stimulates an inflammatory response. Inflammation can promote the growth of cancer by encouraging cancer cells to divide. This inflammatory response may underpin the wide variety of different cancers that have been linked to obesity.
Tips to help you stay a healthy weight
- Reshape your plate! Feel fuller on fewer calories by swapping high-calorie processed foods such as biscuits, crisps and fast foods like pizza, chips and burgers, for fibre-rich wholegrains, vegetables, pulses and fruit.
- Keep an eye on portion sizes. Opting for smaller serving sizes makes it easier to know how much you’re eating.
- Read food labels. Food labels include lots of useful information to help us make healthier choices. Use the front-of-pack traffic light label to see, at a glance, if a food is high, medium or low in fat, sugar and salt.
- Be more active. Cutting down on screen time and keeping active can help you to maintain a healthy weight.