Diet and Cancer - What’s New?

The incidence of cancer in Asia has risen over the past few decades with deaths from cancers overtaking previous causes of mortality as we race to catch up with Western countries. Cancers of the bowel, breast and lung are now all too common. But there is some good news. Scientists now believe that most cancers are caused by external factors, many of which we can control. That means that, in theory at least, many cancers are preventable. So how do we reduce our risk of cancer?

In December 2007, the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) announced an update of their 1997 recommendations for the prevention of cancer with a healthy diet and exercise. So what has changed since the previous recommendations and just what do the guidelines mean for people on a day-to-day basis?

More emphasis on managing body weight

Interestingly and perhaps not surprisingly, the recommendations are very similar to the previous set of diet and cancer guidelines (WCRF/AICR Report 1997) and consistent with what most health authorities are recommending for a healthy lifestyle and the prevention of diet-related diseases. The main change is that the revised guidelines have a much heavier emphasis on managing body weight. 

Compared to the 1997 recommendations, the changes found in the new guidelines include: 

-          More focus on body weight. The panel found that there was stronger evidence for the link between being overweight or obesity and an increased risk of certain cancers. In fact the first three recommendations of the Report  relate to keeping body weight under control and staying active

-          More focus on physical activity.  The previous report noted a link between colon cancer and physical activity. Further studies in this area have produced convincing evidence that physical activity itself is protective against several types of cancer in addition to playing a key role in the control of body weight.

-          A recommendation to breastfeed for up to 6 months has been included in the 2007 guidelines. Breastfeeding helps control body weight in both mothers and infants and also appears to reduce the risk of breast cancer.

-          A recommendation for cancer survivors (people who are either living with, being treated for or having survived cancer) has been included for the first time. The guideline for this group is to simply follow the recommendations for cancer prevention.

-          A recommendation to get nutrients from a varied diet and not to rely on supplements.

Putting it into practice

Here's what the recommendations actually mean for the average person trying to follow a healthy diet. 

Recommendation 1: Be as lean as possible within the normal range of body weight

 

What it means: Children and adolescents should keep a healthy weight throughout childhood and adults should try to avoid that gradual creeping up of the scales that often goes hand-in-hand with increasing age. The BMI (weight in kg /height in metres squared) for a healthy weight is usually 20 – 25. The WCRF report recommends that people aim for a BMI at the lower end of the normal body weight range, say a BMI of 21-23. 

Recommendation 2: Be physically active as part of everyday life

What it means: Try to be moderately active (this means brisk walking or something similar) for at least 30 minutes a day. Aim to gradually increase the time (up to 60 minutes) or the intensity of exercise and cut back on screen time (TV, computer, and gaming consoles). 

Recommendation 3: Limit consumption of energy-dense foods.

What it means: Energy-dense foods are foods that are high in calories. While any food will cause weight gain if we eat too much of it, these foods offer calories but little in the way of additional nutrients so they should be consumed in moderation. Energy-dense foods include cakes, biscuits, pastries, soft drinks, sweetened drinks, confectionary, fried and fast foods.  

Recommendation 4: Plant foods – fruits, vegetables and grain foods

What it means – Aim for 5 servings of fruits and vegetables every day. The more colourful the better – so aim to include a variety of fruits and vegetables – red, green, purple, yellow, orange.

Choose high fibre cereals and pulses to increase fibre intakes. And avoid grains or nuts that are spoiled or have not been properly stored as they may be infected by toxins from fungus (aflotoxins) which can cause liver cancer. 

Recommendation 5: Animal foods

What it means: The WCRF recommendation is to eat no more than 500g of cooked red meat (beef, lamb, pork or goat) a week and to make sure the meat is lean and trimmed of fat. This translates to about 750g of raw meat and is consistent with the Australian National Dietary Guidelines that recommend 3-4 servings of lean red meat a week. The Report recommends that processed meats (such as ham, bacon, salami, frankfurts) should be avoided or taken only occasionally in small amounts.  

Recommendation 6: Limit alcoholic drinks

What it means: The recommendation is similar to that of most public health authorities – if alcohol is consumed, men should have no more than two standard drinks a day and women should take no more than one drink a day. 

Recommendation 7: Watch your salt intake

What it means: Salt and foods that are preserved using salt (such as pickled vegetables) are thought to be a cause of stomach cancer so it's best to limit the intake of salt and salty foods.  Of particular note for people living in China, the Panel warned against eating Cantonese style salted fish. This fish, which is often given to children, is thought to increase the risk of naso-pharyngeal cancer. 

Recommendation 8: Aim to meet nutritional needs through diet alone

What it means: You don't need supplements if you are taking a healthy diet.  While there are studies suggesting that some supplements may decrease the risk of certain cancers, the evidence is conflicting.  A healthy well-rounded diet is the best remedy for cancer prevention. 

Recommendation 9: Breastfeeding

What it means:  Aim to breastfeed for up to six months. 

Recommendation 10: Cancer survivors

What it means: People who have survived cancer are advised to follow the 9 recommendations given above if possible. The panel noted that there is no evidence to provide any separate recommendations for people who are living with cancer or who have recovered from the condition.