Diet, Exercise and Cancer Risk

In November 2007, the results of an expert panel reviewing the scientific evidence linking diet and other lifestyle factors to the development of various types of cancer was published. This distinguished panel of experts was put together by the American Institute of Cancer Research and the World Cancer Research Fund to review more than 7,000 published studies. The final report is on line at dietandcancerreport.org and is 537 pages. The report contains no real surprises but does provide a useful summary of the strength of the research linking various dietary and lifestyle factors to the development of all the most common types of cancer.

The panel’s recommendations included:

• Limiting the consumption of salt, alcohol and red and processed meats

• Consuming mostly minimally processed foods of plant origin

• Being as lean as possible within the normal range.

• To avoid excess body fat, the panel recommended people be active daily and avoid sugar-rich drinks and calorie-dense foods, which promote excessive energy intake and weight gain over time.

Research in numerous animal species has consistently shown the most powerful dietary measure for dramatically reducing the risk of most cancers is a reduction in energy intake.

Research in studies with people show that weight gain increases the amount of growth factors, anabolic hormones, and inflammatory substances while reducing the levels of sex-hormone binding proteins (SHBP). All of these risk factors are associated with an increased risk of numerous cancers in people.1

Growing data suggests that one of the most potent promoters of cell growth and cancer development is insulin-like growth factor-1 (IGF-1). Weight gain, increased calorie intake, and increased protein intake increase IGF-1 levels in short-term studies.

It is difficult to do long-term studies in people because long-term compliance with diet and exercise recommendations is generally not good.

To get around this problem researchers examined 3 groups of people. The control group followed a typical modern diet and were moderately overweight (mean BMI = 26.70). By contrast, the two other groups of subjects were thin by modern standards either because they were following a low calorie/low protein diet high in fiber or because they were long-term endurance runners (BMI = 21.3 and 21.1, respectively).

Compared to the control subjects both the endurance runners and those consuming a low protein and low calorie diet had levels of numerous plasma components associated with a reduced risk of cancer and longevity in animals.

However, while the IGF-1 levels were somewhat lower in the endurance runners than the control group, IGF-1 levels were not nearly as low in the runners as they were in those following the low calorie, low protein and higher fiber diet.2

Bottom Line:

There is no doubt that remaining thin, regular exercise and a healthful, low-calorie diet all help prevent numerous types of cancer in people. Increasing research in animals and people suggests that a low calorie dense diet consisting mostly of minimally processed plant foods is best for reducing calorie intake. Fewer calories appears to be the single most important way to cut the risk of cancer and increase longevity.

By James J. Kenney, Ph.D., RD, FACN

References

1. Nat Rev Cancer 2004;4:579-91

2. Am J Clin Nutr 2006;84:1456-62