Weight, obesity and cancer

What’s the science behind weight and cancer?

Having too much body fat can raise the levels of certain hormones and cause inflammation in the body. This can increase the risk of cancer cells developing.

While living with overweight or obesity doesn’t mean you will get cancer, it does increase your risk, compared with if you were a healthy weight.

That’s why as part of our Cancer Prevention Recommendations, we recommend that people be a healthy weight.

What is a healthy weight?

To check if you are a healthy weight and whether you are at a higher health risk, you can:

1. Calculate your <link>Body Mass Index (BMI)</link> – it’s a simple way to check if you are a healthy weight for your height. Use our online BMI calculator: wcrf-uk.org/bmi-calculator
2. <link>Measure around your waist</link> – this can help you determine if you have too much fat around your waist and whether you are at a higher health risk.

Keeping a healthy weight

Your body weight can be influenced by many different factors, such as your genetics, whether you are taking certain medications, your environment and your lifestyle. These may make it harder for some people to lose weight.

However, what you can control is what and how much you eat and drink, and how much physical activity you do. These are important factors that can help keep you healthy, beyond maintaining a healthy weight.  

We have strong scientific evidence that the following can help you maintain a healthy weight:

• Keeping physically active, like brisk walking. Aim for at least 20-30 minutes a day.
• Eating high-fibre foods such as fruit, vegetables, wholegrains (like brown rice), pulses (like chickpeas and lentils), nuts and seeds.
• Eating a ‘Mediterranean-type’ diet, which typically includes high-fibre foods, olive oil, and moderate amounts of fish, poultry and dairy, and small amounts of red meat.

To incorporate these into your daily life, consider setting small, achievable goals, like adding an extra serving of vegetables to your meals or taking a walk during your lunch breaks. 

 Equally, we have strong evidence that the following can increase the risk of weight gain: 

• Too much screen time, like watching TV. Try to limit screen time and take breaks every 30 minutes to move around.
• Regularly drinking sugary drinks, like cola. Choose sugar-free alternatives and have water as your go-to drink.
• Regularly eating ‘fast food’, like fried chicken and chips. Try cooking more homemade meals using a variety of plant-based foods and lean meats.
• Eating a ‘Western-type’ diet, which typically includes a high amount of red meat and processed food high in fat, sugar and salt.

By making one change at a time, you can support your health now and in the future. Download our Weight Matters guide – it’s full of information and practical tips to lose and maintain a healthy weight.

Healthy weight loss tips

1. Avoid ‘fad’ dietsA ‘fad’ diet typically involves eating very little food or only certain types of food. They usually promise quick weight loss but lack strong scientific evidence. When you go back to eating normally, the weight you have lost often comes back quickly, and you might gain even more weight. Instead, it’s best to eat a healthy, balanced diet that includes food you can enjoy and that can be maintained in the long-term.
2. Reshape your plateFill three-quarters of your plate with fruit, vegetables, wholegrains and pulses. The remaining quarter should be for protein sources like plant-based protein (like tofu), eggs, low-fat dairy, skinless poultry or fish. Try to reduce the amount of ‘fast’ food and processed food and drinks that are high in fat, sugar and salt in your everyday diet.
3. Read food labelsFood labels include useful information to help us make healthier choices. Use the front-of-pack traffic light label (if it has one) to see if a food is high, medium or low in fat, saturated fat, sugar and salt. You can also use food labels to compare calorie content between similar products, and see how many servings are in a pack.
4. Get familiar with portion sizesEven if you are making healthier choices, eating and drinking too much can lead to weight gain if you are consuming more calories than your body needs. That’s why it’s important to know what a healthy portion size looks like for different foods.< Download our What is a Healthy Portion size poster > 
5. Be more activeKeeping physically active can help you to maintain a healthy weight by burning calories. Aim for 20-30 minutes a day and reduce how much time you spend sitting down.< Find out more about keeping active in our Physical Activity Factsheet or Living and Active guide > 

Further research

• World Cancer Research Fund International (2018). Obesity, weight gain and cancer risk. Available from: https://www.wcrf.org/diet-activity-and-cancer/risk-factors/obesity-weight-gain-and-cancer/
• World Cancer Research Fund (2018). Diet, nutrition and physical activity: Energy balance and body fatness. Available from: https://www.wcrf.org/wp-content/uploads/2021/02/Energy-Balance-and-Body-Fatness.pdf