Poor diet and cancer risk

Can unhealthy eating give you cancer?

What you eat can have a big impact on your risk of developing cancer. One of the biggest risk factors for cancer is being overweight or obese. Eating food that is high in fat or sugar can make you gain weight, and there is strong evidence that being overweight or obese increases the risk of 11 cancers.

However, diets that are high in plant foods – such as fruit, vegetables, wholegrains and pulses – can help you stay a healthy weight, and may also protect against certain cancers.

Our recommendation is to avoid high-calorie food and drink – find out how

Our recommendation is to enjoy more grains, veg, fruit and beans – find out how 

Find out more about other aspects of diet including:


There is no strong evidence to directly link sugar to cancer risk. However, foods that are high in added sugar tend be high in calories without being nutritious or filling. Eating high-calorie foods or drinking sugary drinks too often or in large quantities can lead to weight gain, and there is strong evidence that being overweight or obese increases the risk of 11 cancers

Maintaining a healthy weight through eating a healthy diet and keeping active, coupled with not smoking, are the most effective ways to reduce your cancer risk.  

How much high-calorie food do we eat?

The table below shows examples of high-calories foods commonly eaten in the UK, and how much men and women are eating each day, on average.  

  Amount consumed in grams (g) per day in the UK
  Men, by age Women, by age
  4–10 11–18 19–64 65+ 4–10 11–18 19–64 65+
Biscuits (one chocolate digestive = 18g) 18 17 12 15 16 16 14 12
Buns, cakes, pastries and pies (one slice of Victoria sponge = 60g) 21 18 20 32 22 17 16 25
Puddings (one portion of crumble = 170g) 15 14 13 24 15 10 9 24
Ice cream (one scoop of ice cream = 60g) 12 8 5 8 13 9 5 7
Chips, fried and roast potatoes (one small portion of chips = 100g) 39 58 47 41 35 50 35 22
Savoury snacks (one small bag of crisps = 30g) 11 14 9 3 10 12 6 2
Sugary sweets (one fruit pastille = 3g) 8 8 2 1 9 6 2 1
Chocolate bars (one square of milk chocolate = 7g) 9 13 10 4 9 11 7 5
Sugary soft drinks (one can of fizzy drink = 340g) 139 310 160 54 117 210 112 53

Figures from 2008–12

Fibre, fruit and vegetables

Research shows that vegetables and fruit probably reduce your risk of cancers, including mouth and throat, and lung cancer. Diets rich in fibre have been shown to reduce the risk of bowel cancer. Eating lots of wholegrains, vegetables, fruit and pulses can help you stay a healthy weight, which is an important way to reduce your cancer risk.

Unfortunately, in the UK, many people do not eat enough fruit or vegetables, or fibre. The recommended intake of fibre for adults in the UK is 30g a day. On average, adults in the UK eat about 18g of fibre a day.

How many portions of vegetables and fruit do we eat?

Age group Average fruit and vegetable portions consumed per day % of people achieving 5 A DAY
11–18 2.9 9
19–65 4.1 30
65 and over 4.6 41

Figures from 2008–12. One portion is equivalent to 80g.

Approximately how many cases of cancer could be prevented in the UK each year if everyone ate enough vegetables, fruit and fibre?

Type of cancer Amount of cases preventable through eating non-starchy vegetables
  % Number
Mouth, pharynx and larynx 34 3,600
Type of cancer Amount of cases preventable through eating fruit
  % Number
Mouth, pharynx and larynx 17 1,800
Lung 33 15,000
Type of cancer Amount of cases preventable through eating foods containing fibre
  % Number
Bowel 12 5,100

Information on sugar comes from the International Agency for Research on Cancer. Statistics on high calorie foods and sugary drinks come from the National Diet and Nutrition Survey headline results from years 1–4 (combined) of the rolling programme 2008–9 – 2011–12. Information on food portion sizes comes from the Ministry of Agriculture, Fisheries and Food’s Food Portion Sizes, second edition. Find out more about preventability estimates or, for more detailed information, download appendix A of our policy report
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