Nutrition and Cancer

Most people think changing their diet would make them healthier, and they are right. Nutrition affects health in a profound way, and unhealthy eating habits are a big risk factor in many diseases.

Excess weight (overweight or obesity) is increasingly recognized as an important risk factor for some cancers. Since two thirds of Americans are overweight or obese, overeating is a major contributor to cancer occurrence in the US, even more so than cigarette smoking.

Last week, a new study in the prestigious Lancet, showed further evidence that increased BMI is associated with increased risk of common and less common malignancies (The Lancet, Volume 371, Issue 9612, 16 February 2008-22 February 2008, Pages 569-578). The researchers found that in men, a 5kg/m2 increase in BMI raised the risk of esophageal adenocarcinoma by 52%, thyroid cancer by 33%, and colon and kidney cancers each by 24%.

In women, a BMI increase of 5kg/m2 increased the risk of endometrial (59%), gallbladder (59%), esophageal adenocarcinoma (51%) and kidney (34%) cancers.

They also noted weaker but significant positive associations between increased BMI and rectal cancer and malignant melanoma in men; postmenopausal breast, pancreatic, thyroid, and colon cancers in women; and leukemia, multiple myeloma, and non-Hodgkin's lymphoma in both sexes.

This study is a meta-analysis combining findings of 141 carefully selected previous studies, and looking at over 282,137 cases of cancer.

It offers further support to the link between obesity and cancer, but does not supply a clear mechanism for how extra weight causes the disease.

Evidence has been accumulating about the relationship between lifestyle, nutrition and cancer prevention, and that led to collaboration between the World Cancer Research Fund and the American Institute for Cancer Research. Their second expert report was published recently, and was a huge undertaking, involving over 100 scientists from 30 different countries. WCRF/AICR commissioned and funded the report, but the content has been driven by an independent panel of 21 world renowned scientists. Over 5 years the group systematically collected and reviewed all the relevant global scientific literature on the subject. They then evaluated the evidence and produced consensus recommendations for reducing the risk of developing cancer and promotion of general good health and well-being. This report is the largest study of its kind, and its conclusions are as definitive as the available evidence allows.

The full report is very long and can be downloaded (free) at http://www.dietandcancerreport.org. Chapter 12 of the report features eight general recommendations for cancer prevention:

“1: Body Fatness: Be as Lean as Possible Within the Normal Range of Body Weight.” As discussed in the Lancet article, maintaining a healthy weight throughout life may be one of the most important ways to protect against cancer, and being overweight or obese increases the risk of some cancers.

“2: Physical Activity: Be Physically Active as Part of Everyday Life.”

“3: Foods and Drinks That Promote Weight Gain: Limit the Consumption of Energy-Dense Foods and Avoid Sugary Drinks.” Sugary drinks were targeted specifically in the report: “Such beverages appear to exert little influence on total daily self-selected energy intakes and their habitual consumption can lead to rapid and sustained weight gain even in the face of restricted solid food intake”. Another recommendation under this heading is “Consume 'fast foods' sparingly, if at all.”

“4: Plant Foods: Eat Mostly Foods of Plant Origin.” Diets that are protective against cancer are characterized by large intakes of foods of plant origin and, indeed, several cancers are responsive to increased intakes of plant-based foods.

“5: Animal Foods: Limit the Intake of Red Meat and Avoid Processed Meat.”

“6: Alcoholic Drinks: Limit Alcoholic Drinks.” (Men-to 2/day, women to 1/day).

“7: Preservation, Processing, Preparation: Limit Consumption of Salt and Avoid Moldy Cereal Grains and Pulses (Legumes).” Salt and salt-preserved foods are probably a cause of stomach cancer, and foods contaminated with aflatoxins are a cause of liver cancer. Although salt is necessary for human health, typical levels of consumption are vastly excessive.

“8: Dietary Supplements: Aim to Meet Nutritional Needs Through Diet Alone.” Dietary supplements are not recommended for cancer prevention. According to the report the greatest danger associated with the use of dietary supplements is the possibility that consumption of supplements is serving as an alternate to good nutrition, and supplements are taken as “magic bullets” to compensate for cancer-friendly dietary and lifestyle practices.

Changing dietary habits may not be easy, but the gathered evidence makes me hopeful. By taking steps to improve our diet a lot of diseases can be prevented.

Dr. Ayala