Links between cancer and weight, nutrition and physical activity

The links between body composition, nutrition, physical activity and cancer risk are complex. These risk factors are interrelated, and may act synergistically. Each risk factor also has an independent effect on cancer risk. It is difficult to separate these combined effects of body mass, nutrition, and physical activity. For example, physical inactivity may increase cancer risk through its contribution to overweight and obesity, but it can also affect cancer risk directly, even in people who are not overweight.

Table 1 presents a summary of evidence of the link between overweight and obesity, physical activity, nutrition, and specific cancer types. Please note the terms ‘convincing’ and ‘probable’ relate to the strength of the evidence and not the size of effect.

Table 1. Summary of evidence of the link between overweight and obesity, physical activity, nutrition, and cancer

_{Source: World Cancer Research Fund International 2018, except where indicated}

Overweight and obesity

The World Cancer Research Fund’s Continuous Update Project report concluded that there is strong evidence that adult body fatness increases the risk of 12 types of cancer and the International Agency for Research on Cancer (IARC) has shown there is sufficient evidence that high body mass increases the risk of 13 types of cancer.

A recent study has shown that in Australia in 2010, 3.4% (3,917 cases) of all cancers diagnosed were attributable to overweight/obesity. This included 1,101 colon cancers, 971 female post-menopausal breast cancers and 595 endometrial cancers.

Diet

There is growing evidence that shows specific foods and nutrients can either increase or decrease cancer risk. Eating patterns based on the Australian Dietary Guidelines that protect against weight gain, overweight and obesity protect against cancers associated with excess body weight.

Dietary advice for reducing cancer risk is consistent with recommendations for promoting good health, including preventing cardiovascular disease and type 2 diabetes. The Australian Dietary Guidelines recommend eating patterns consistent with preventing cancer – this includes consuming a diet based on vegetables, legumes and fruit, grains and cereals (preferably wholegrain), limiting red meat, avoiding processed meats and avoiding energy-dense, nutrient-poor foods such as fast food and sugar-sweetened beverages.

Specific foods and nutrients

Both IARC and WCRF conduct evidence reviews of factors associated with cancer. IARC’s Monographs programme identifies environmental factors that can increase the risk of cancer including physical, chemical, biological and lifestyle agents. WCRF’s Continuous Update Project programme analyses global research on diet, weight, physical activity and cancer risk. The key findings from IARC and WCRF in relation to specific foods and nutrients are summarised below.

Dietary fibre

Dietary fibre occurs naturally in foods such as wholegrain cereals, fruit, vegetables, seeds, nuts and legumes and is highest when these foods are minimally processed. Consumption of these foods is associated with a lower risk of a range of diseases including obesity, type 2 diabetes and cardiovascular disease, and may also prevent some cancers.

WCRF found there is strong evidence that dietary fibre probably decreases the risk of bowel cancer. In Australia in 2010, 18% (2,609 cases) of bowel cancers diagnosed were attributable to inadequate levels of dietary fibre.

For further information see Information sheet: Foods from plant sources and cancer.

Wholegrains

WCRF found that wholegrains are probably protective against bowel cancer.

For further information see Information sheet: Foods from plant sources and cancer.

Fruit and vegetables

In 2018, WCRF concluded that fruit and non-starchy vegetables are probably protective against aerodigestive cancers (mouth, larynx, pharynx, nasopharynx, oesophagus, lung, stomach and bowel). In Australia, 1,555 (1.4% of all) and 311 (0.3% of all) cancers in 2010 were attributable to inadequate intakes of fruit and non-starchy vegetables, respectively.

In 2003, IARC found that a high intake of vegetables probably reduces the risk of oesophageal and bowel cancer, while a high intake of fruit probably reduces the risk of oesophageal and stomach cancers. Likewise, IARC found evidence that higher vegetable intake possibly reduces cancer of the mouth, pharynx, larynx, kidney, stomach, lung and ovary and higher fruit intake possibly reduces cancers of the mouth, pharynx, larynx, kidney, bowel and bladder. In 2004, IARC reviewed the evidence relating to cruciferous vegetables, isothiocyanates and indoles and found a protective effect on cancer risk based on limited evidence.

For further information see Information sheet: Foods from plant sources and cancer.

Red and processed meat

IARC systematically reviewed all available evidence on red and processed meat in 2015 and classified these agents based on carcinogenicity

• red meat as a Group 2A carcinogen (probably carcinogenic to humans) and processed meat as a Group 1 carcinogen (carcinogenic to humans).

WCRF found that there is strong evidence that consuming processed meats (including bacon and ham) increases the risk of bowel cancer and that this risk increases with increased consumption. There is strong evidence that consuming red meat increases the risk of bowel cancer.

An estimated 2,614 cases (18%) of bowel cancer occurring in Australians in 2010 were attributable to red and processed meat consumption (16% of colon cancers; 23% of rectal cancers). It was estimated that if all Australian adults had consumed ≤65 g/day (cooked weight) of red and processed meat, then the incidence of bowel cancer would have been 5.4% (798 cancers) lower.

For further information see Information sheet: Meat and cancer.

Dairy products

WCRF found evidence to suggest that dairy products probably decrease the risk of bowel cancer; however, no advice is currently available on consumption levels specifically for cancer prevention. Calcium supplements also probably decrease the risk of bowel cancer.

For further information see Information sheet: Dairy foods and cancer.

Salt-preserved foods

WCRF found that evidence indicates that salt-preserved foods are probably associated with an increased risk of stomach cancer. These foods include pickled vegetables and salted or dried fish. Cantonese-style salted fish probably increases the risk of nasopharynx cancer.

Processed foods high in fat, starches or sugars and sugary drinks

WCRF found strong evidence that diets containing higher amounts of processed foods (foods high in fat, starches or sugars) are causes of overweight and obesity by increasing excess energy intake relative to expenditure. There is convincing evidence that consumption of sugar sweetened drinks is a cause of weight gain, overweight and obesity in both children and adults, especially when consumed frequently or in large portions. Increased body fatness increases the risk of obesity-related cancers.

Breastfeeding

WCRF found strong evidence to suggest that breastfeeding reduces the risk of breast cancer. There is evidence that breastfeeding probably protects children from excess weight, overweight, and obesity.

Physical activity

Physical activity is important for good health and wellbeing, and can help to prevent some cancers and a range of chronic diseases including heart disease. A pooled analysis of 1.44 million adults across Europe and US found physical activity was associated with decreased the risk of 13 types of cancer: oesophageal, liver, lung, kidney, stomach (gastric cardia), endometrial, myeloid leukaemia, myeloma, bowel, head and neck, bladder, and breast. Emerging evidence suggests that sedentary behaviour (sitting time) may also contribute to cancer risk.

In Australia in 2010, an estimated 1,814 cases of colon, post-menopausal breast and endometrial cancer were attributable to insufficient levels of physical activity: 707 colon; 971 post-menopausal breast; and 136 endometrial cancers. If those exercising below the recommended level had increased their activity by 30 minutes/week, it is estimated that 314 fewer cancers would have occurred in 2010.

In 2018, physical inactivity was responsible for 2.5% of the total disease burden in Australia, and contributed to 16% of the uterine cancer burden, 12% of the bowel cancer burden, and 3.2% of the breast cancer burden.

It is important to note that physical activity confers a protective effect over and above the risk reduction derived via weight management; thus, physical activity is beneficial for all individuals, regardless of their body composition. There is evidence of a dose-response relation between increasing levels of physical activity and decreasing cancer risk. For general health, current Australian guidelines recommend accumulating 150-300 minutes of moderate intensity physical activity or 75 to 150 minutes of vigorous intensity physical activity each week. However, to prevent cancer and unhealthy weight gain people should aim for 300 minutes of moderate intensity physical activity or 150 minutes of vigorous intensity physical activity each week.

Sedentary behaviour

Sedentary behaviour (sitting time) is defined by low energy expenditure and a sitting or lying posture during waking hours and is a risk factor that is additional to insufficient physical activity. Recent evidence suggests that sedentary behaviour may contribute to an increased risk of breast, bowel, endometrial and lung cancer. There is insufficient evidence to make recommendations relating to specific limits on daily sedentary time. Current Australian guidelines recommend minimising the amount of time spent in prolonged sitting, and breaking up long periods of sitting as often as possible.