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United States Department of Agriculture

Agricultural Research Service

Nutrition, Obesity and Colon Cancer Risk
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By Huawei Zeng

What is obesity? People who are obese have an abnormally high and unhealthy proportion of body fat. Currently, the most common formula to measure obesity is based on weight and height, which is referred to as body mass index (BMI). BMI is the ratio of weight (in kilograms) to height (in meters) squared.

According to the guidelines established by the National Institutes of Health (NIH), adults age 20 and older can be placed into one of four categories based on their BMI: (1) underweight (<18.5); (2) healthy (18.5 to 24.9); (3) overweight (25.0 to 29.9); (4) obese (>30.0).

Obesity results from an imbalance between energy expenditure and energy intake, and scientists have suggested that a sedentary lifestyle (lack of physical activity) and over consumption of high calorie food are the main causes of obesity.

Colon cancer is the third-leading cancer in the United States. About 149,000 people have been diagnosed with colon cancer and 50,000 die from the disease annually, according to estimates from the American Cancer Society. The average rate of colon cancer amongst males in countries defined by the World Health Organization as "less developed" is about 20% of that in the industrialized west.

Migrants moving from regions of low incidence to developed countries tend to reach the same colon cancer risk as that of the new host population within one generation. This observation suggests that diets and life style, rather than genetic variations, play key roles in the etiology of colon cancer.  

There is evidence for adverse effects of overweight and obesity and protective effects of high physical activity against colon cancer. In particular, several studies suggested that abdominal obesity was more strongly related to increased colon cancer risk than was overall obesity. In addition, the association between obesity and colon cancer was [suggested to be? stronger in men and weaker in women. However, the mechanism underlying this linkage is poorly understood. It is speculated that obesity may alter the metabolism of certain hormones fat-derived factors.

According to the American Cancer Society, a significant reduction in the incidence of obesity-related cancers can be achieved if we can reduce the obesity epidemic in the future. Thus, the effect of diet and nutrition status on obesity-related cancer risk has been a major focus of our research. There is a growing body of evidence showing that colon cancer is largely a preventable disease, and dietary modification can reduce the incidence of colon cancer. Recent studies have shown that increased intakes of vegetables and fruits resulted in body weight reduction. Similar to their anticancer effects, phytochemicals from vegetables and fruits are known to have anti-obesity and lipid-lowering effects.

There are several outstanding dietary agents that may have both anti-cancer and anti-obesity effects. For example, garlic and other allium vegetables have long been thought to have beneficial effects in human history. Sulfur compounds in these allium vegetables are believed to have beneficial effects in a number of human diseases including cancer, obesity, and Type 2 diabetes. Selenium enriched garlic has been also well documented to have very strong chemopreventive potential.  Second, green tea has powerful antioxidant properties because of its polyphenols. These polyphenols present in green tea have health benefit against cancer, obesity and cardiovascular diseases. Third, soy beans have been consumed for a long time in Asian countries. Soybeans contain high-quality proteins and high isoflavone content. In addition, soybeans contain minerals, fiber, ascorbic acid, phytic acid, phytosterols and saponins.

It has been demonstrated that soy isoflavone improve the insulin sensitivity by reducing inflammation and visceral fat deposition, and can lower plasma cholesterol. Several recent studies have shown that the consumption of soy food is associated with the reduction of the body fat content in obesity, and a decrease in colon, breast and breast cancer risk.

Lastly, fish oil has been given much attention.  Fish oil is rich in omega-3 polyunsaturated fatty acids.  It has been demonstrated that fish oils can reduce inflammation, cancer risk, and have anti-obesity effects. There are many other foods that contain antioxidants, which help detoxify or neutralize free radicals. Selenium, zinc, copper, manganese, folic acid, vitamins A, C, E and B-6 are key antioxidants.

Consumption of antioxidants is thought to provide protection against obesity and cancer. Thus, it is a healthy choice to consume a varied diet with fruits, vegetables, and whole grains along with increasing your physical activity (regular exercise).


Last Modified: 12/17/2009