Can You Reduce Your Cancer Risk Through Nutrition?
What is the Evidence?
Karen Duvall, MD, MPH, UCLA Assistant Professor in the Department of Family Medicine and Director of the Preventive Medicine Residency Program, David Geffen School of Medicine at UCLA
This is a summary of a lecture that was presented on June 13, 2006.
The American Cancer Society notes that one half of all cancers are related to diet and lifestyle choices. If this is true, then how does one promote health and wellness? What controllable factors have a scientific basis for reducing the risk of developing disease? Further, lifestyle choices are part of a very complex ecosystem in which each person’s individual genes are at the center. Choices in diet and nutrition may greatly influence how an individual’s genes are ultimately expressed. In order to answer these questions, the scientific community employs what has been termed “evidence-based medicine.” Evidence-based medicine is a way to assure some level of scientific credibility to results and includes studies being peer-reviewed, emphasis on randomized control trials and the accumulation of data across several well-designed studies coming to similar conclusions. However, the average consumer of nutrition information has access to a great deal of information through the internet, so it is important to understand how to evaluate that information and to try to determine whether it really is evidence-based. One way that consumers can help to protect themselves is by visiting sites from credible institutions, such as the American Cancer Society, the National Cancer Institute and some of the major universities such as Harvard and Berkeley that write health and wellness letters.
Inflammation and Obesity
Inflammation is being studied as a core component of many chronic disease states and one of the key components is a class of compounds called cytokines. Cytokines increase oxidative damage to DNA by production of free radicals, which lead to increased circulating hormones that promote the growth of cancer cells. These are pro-inflammatory hormones.
The physiological state that may link cancer and inflammation is obesity. Abdominal obesity results in increased cytokine secretion which leads to increased cell oxidation and the production of the pro-inflammatory hormones mentioned above. The fat cell is an amazing unit. It not only secretes cytokines, but converts adrenal hormones into estrogen via aromatase as well. It also stores energy in the form of calories so a person will not starve should there be famine or low food resources. These qualities are advantageous to people who go through periods of starvation followed by feasting such as primitive man; however, this is no longer applicable in modern life. Instead, nutrition is abundant in many places of the modern world, such as the United States. Although there are no longer extended periods of famine, our genes still continue to function in that same way.
In 2003, the New England Journal published a study by the lead author, Calle, entitled, “Overweight, Obesity, and Mortality from Cancer in a Prospectively Studied Cohort of U.S. Adults.” The study began in 1982 and 900,000 people were followed for 16 years. There were 57,000 cancer deaths during the study. The researchers looked at different groups of people and used their BMI, their Body Mass Index, to judge obesity while taking into account height and weight. A BMI over 40 is considered “morbidly obese,” a BMI of 20-40 is obese, and a BMI of 25-30 is overweight. A healthy BMI is under 25. You can easily calculate your BMI by visiting the Center for Disease Control web site.
The researchers found that the heaviest men and women, those with BMI’s greater than 40, had a 52% and 62%, respectively, greater risk of dying compared to people with normal weight. The proportion of cancer deaths attributed to obesity in people younger than 50 was 14% for men and 20% for women, or approximately one in five. The authors estimated that 90,000 deaths from cancer could be prevented every year in the United States if all adults could maintain a BMI less than 25.
Walter Willet, one of the lead researchers in a study that has become known as “The Nurse’s Study,” recently did a review which noted that, after smoking, weight/obesity was found to be the most avoidable cause of cancer in populations with Western patterns of cancer incidence. One of the conclusions was that among non-smoking people, avoidance of being overweight was the most important cancer prevention strategy. While physical activity is extremely important, it cannot alone reduce the risk of cancer and increases in cancer mortality were seen in populations who were as little as 10-20 pounds overweight.
Dietary Fats
There are many different kinds of dietary fats and some are better for you than others. Monounsaturated oils and fats, such as olive oil and canola oil, are preferred over Omega 6 fatty acids, which are less healthy because they promote the formation of the pro-inflammatory cytokines.. Omega 3 fatty acids are also considered beneficial because they are believed to reduce the formation of inflammatory cytokines. Omega 3 fatty acids include alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docasahexaenoic acid (DHA). In ancient man, there was a ratio of 2:1 of Omega 6 fatty acids to Omega 3 fatty acids. The ratio now is about 20:1. The Institute of Medicine in 2002 set recommended guidelines for the intake of Omega 3 and 6 fatty acids which include 1-2 gm per day of Omega 3 fatty acids and 12 grams per day of omega 6 fatty acids. Although we anticipate you may reduce your risk of cancer by adopting these recommendations, studies suggest an even greater benefit for the prevention of cardiovascular disease and diabetes.
The best sources of Omega 3 fatty acids are flaxseed, fish oils, green leafy vegetables, walnuts and soy. Corn fed beef is lower in omega 3 fatty acids than grass fed beef and should be avoided if grass fed beef is available. Cold water fish (a serving size is approximately 3 ounces) such as wild Alaskan salmon, sockeye (red) salmon, Alaskan black cod and sardines are also sources of Omega 3 fatty acids. Consumption of larger fish such as swordfish, king mackerel, tuna and tilefish should be limited due to a high concentration of heavy metals and organic toxins stored in the flesh. The American Heart Association recommends that people eat 2-3 servings of fish per week.
Fish oil supplements are another source of Omega 3 fatty acids. Some of the brands include Nordic Naturals, Spectrum, Weil Omega 3 complex, and Metagenics. Fish oil supplements can be consumed at a dose of 1g-2g per day and possibly even greater if certain medical conditions exist. Remember that these supplements have an anticoagulation effect and so it is important to communicate with your physicians if you are taking any supplements.
Vegetable oils―such as corn oil, safflower oil and cottonseed oil―are Omega 6 fatty acids that should be limited as much as possible. Margarine should also be limited as well. Many of these are hidden in prepared foods, so it’s very important that consumers carefully read the nutritional labels to find out what is in the food they are buying.
There has been some controversy surrounding the benefits of low fat diets. One of the largest studies ever conducted was presented in the Journal of the American Medical Association in 2006. Over 48,000 women were enrolled in the Women’s Health Initiative Dietary Modification Trial between 1993 and 1998. These women were between the ages of 50 and 79 and were followed for an average of 8 years. In this study, 40% were randomly assigned to a diet with 20% of the calories coming from fat with five servings of fruits and vegetables and 6 servings of grains per day. The other 60% followed their usual diet. After six years, the intervention group averaged 29% calories from fat compared to 37% in the comparison group. Both groups started at 35-38% calories from fat. Results: the women who were on the low fat plan had a 9% lower risk of breast cancer and the risk reduction was even greater for the women who had the greatest decrease in fat intake and most closely adhered to the regimen over the course of the study. The patients in the low fat group, who developed breast cancer, had fewer tumors that were hormone-negative tumors.
This study has some problems. The intervention group only cut total fat, not calories. Most women were overweight and lost only a few pounds on average. There was not a lot of difference between the two groups with regard to fat intake, and this may have masked the benefit of low-fat diets. Also, since the study was designed 15 years ago, it did not differentiate between “good” and “bad” fat. However, fat is not the most important aspect of a healthy diet which needs complex carbohydrates, low saturated and trans fats, high amounts of Omega 3 fatty acids and a balance between animal and vegetable protein sources. Lifestyle issues are also equally important, although controlling calories and weight may be the most important. Studies designed with the information available today may lead to different conclusions.
Dietary components
There are a variety of other dietary components that need to be considered when constructing a healthy diet, such as fruits and vegetables, alcohol intake, protein and supplements.
On any given day 50% of the population does not eat a single piece of fruit. Eighty percent of Americans do not eat five servings of fruits and vegetables, which is the minimum recommended by the NCI. Approximately 1/3 of Americans get 47% of their calories from junk foods. Fruits and vegetables provide essential vitamins and minerals while decreasing calorie density. Seven servings per day of fruits and vegetables average 475 calories, provide fiber which is filling, and begins to approach the amount needed for cancer prevention. Fruits and vegetables also provide over 25,000 different phytochemicals that have multiple beneficial effects.. Since different phytochemicals can have synergistic effects, it is important to eat a diverse range of fruits and vegetables. Some of the important power foods and families of foods include fruits and vegetables with a variety of colors, especially berries, tomatoes, squashes, peppers pomegranate, kiwi, apple, cruciferous vegetables in the cabbage family, soy, spices such as rosemary, parsley, and cinnamon, white and green tea which have polyphenols, mushrooms, and extra-virgin olive oil.
Epidemiological and clinical studies link alcohol intake with an increased risk for breast cancer and suggest that alcohol may have more adverse effects for women than men. Alcohol increases estrogen levels and plasma concentrations of selenium and vitamin E, important anti-oxidants, are decreased in people who are alcoholics. It is recommended that alcohol intake for women be limited to 3-4 alcoholic beverages (5 ounces of wine) per week on average. Men may be able to have more servings per week, but alcohol intake should be limited for everyone. Red wine and beer may confer some benefits; however, if not consumed in moderation, the risks may outweigh the benefits. Physiological response to alcohol is highly variable across individuals and there is no way to predict any one individual response. It should also be noted that alcohol is high in calories and is an appetite stimulant.
Protein is an important part of the diet and it is recommended that 25-30% of calories come from protein. Vegetable sources such as soy, legumes (beans and lentils) seeds and nuts are the best sources. Animal sources tend to have more toxins since they are higher up the food chain and they have more saturated fat. An outstanding source of protein is whey protein which can be used in shakes.
The majority of evidence related to soy food indicates that it is safe when consumed as part of a balanced diet rich in fruits, vegetables and whole grains. Soy is an excellent source of non-animal protein.
Vitamin D is not only important for bone health, but also possibly for cancer prevention. Although there is some debate over dose, recent research suggests vitamin D is an important chemopreventive agent in the diet. A total dietary intake of approximately 800 IU per day is recommended. Remember, certain foods are fortified with Vitamin D and most multivitamins contain 400IU.
Other supplements might include a good multi-vitamin, folic acid, (400 micrograms), selenium (100-200 micrograms), Vitamin C (1 gram), and Vitamin E 200-400 IU.
Summary
To ensure greater wellness, work on getting a well balanced diet that includes adequate high-quality protein, complex carbohydrates, fruits and vegetables. Try to eat your nutrients first and then supplement as needed, taking into consideration which nutrients are more difficult to get adequate supplies through foods.
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