Why Nutrition Research for Cancer Prevention?

According to the National Cancer Institute, as much as 80 percent of all cancers are due to lifestyle factors that you can change. That means up to 80 percent of all cancers are potentially preventable. Within that 80 percent of potentially preventable cancers, cancer researchers estimated that 35 to 50 are due to foods we consume in our daily diet. That’s an incredible number! No wonder there’s so much research about diet and cancer.

However, before we look at the latest research, we need a basic understanding of why diet plays a role in cancer development.

Cancer begins as a single abnormal cell that begins to multiply out of control. Groups of these rapidly multiplying cells form tumors that invade healthy tissue. Carcinogens from foods, the air, and even substances made in our own bodies promote the development of tumors.

It takes years for a noticeable tumor to develop. During this time, compounds known as inhibitors can keep the tumor cells from growing. Some vitamins and phytochemicals in plant foods are known to be inhibitors. Dietary fat, particularly saturated fat, is known to be a promoter that encourages the tumor cells multiple quickly.

The latest research is pointing to overall eating patterns – not specific nutrients or foods – as the more important way to view diet and cancer prevention. However, everyday scientists are still seeking to understand the beneficial biological processes specific nutrients or foods seem to promote in the fight against cancer.

Cancer is one of the most feared medical diagnoses, and many people who’ve been given this unfortunate news seek out new research and new alternative therapies that may help the fight their tumors. In research, unfortunately, not one study ever provides the last word on the subject.  Brief reports in the daily news often put too much emphasis on new findings - findings that may contradict previous studies.

It is with this disclaimer that this posting is not meant to diagnose or treat cancer and note of caution for you to do further research that I present some recent research on diet, nutrients, and four major cancers (breast, prostate, colorectal and liver). 

Overview: Phytochemicals and Foods linked to cancer prevention

Phytochemical	Foods with the highest content (from highest to lowest)
Glucosinolates (converted to sulforaphane when food is chewed or minimally cooked)	Brussels sprouts Collard greens Kale Watercress Turnip White or red cabbage Broccoli Bok Choy Cauliflower
Sulfur compounds (alliin converted to allicin when food is crushed, allicin converted to diallyl sulfide and diallyl disulfide)	Garlic Onions
Isoflavones (flavonoids)	Soy flour Dry roasted soybeans Edamame Miso Tofu Soy milk Tofu hot dog Soy sauce Chickpeas Soybean oil
Ellagic acid (antioxidant)	Raspberries and blackberries Nuts Pecans Strawberries Cranberries Blueberries Citrus fruits
Proanthcyanidins (polyphenol)	Cinnamon Cocoa powder Red beans Hazelnuts Cranberries Wild blueberries Strawberries Red Delicious Apples (with peel) Grapes Red Wine
Alpha-linolenic acid (plant omega-3)	Fresh Walnuts Ground Flaxseeds Walnut Oil Canola Oil Soybeans Tofu
EPA and DHA (animal omega-3)	Sardines Herring Mackerel Altantic Salmon Rainbow Trout

Cruciferous vegetables are a good source of glucosinolates and their hydrolysis products, including

indoles and isothiocyanates. A high intake of cruciferous vegetables has been associated with a lower

risk of lung and colorectal cancer in some epidemiological studies. Glucosinolate hydrolysis products

alter the metabolism or activity of sex hormones in ways that could inhibit the development of hormone-

sensitive cancers, but evidence of an inverse association between cruciferous vegetable intake and breast

or prostate cancer in humans is limited and inconsistent. Organizations such as the National Cancer

Institute recommend the consumption of 5-9 servings of fruits and vegetables daily, but separate re-

commendation for cruciferous vegetables have not been established.

Isothiocyanates and indoles derived from the hydrolysis of glucosinolates, such as sulforaphane and 

indole-3-carbonol (I3C), have been implicated in a variety of anti-carcinogenic mechanisms, but de-

leterous effects have also been reported in some experimental protocols, including tumor promotion 

over prolonged periods of exposure. (1) Epidemiological studies indicate that human exposure to 

isothiocyanates and indoles through cruciferous vegetable consumption may decrease cancer risk, but 

the protective effects may be influenced by individual genetic variation (polymorphisms) in the 

metabolism and the elimination of isothiocyanates from the body.

Cooking procedures also affect the bioavailability and intake of glucosinolates and their derivatives. Supplementation with I3C or the related dimer 3,3'-diindolylmethane (DIM) alters urinary estrogen metabolite profiles in women, but the effects of I3C and DIM on breast cancer risk are not known. Small preliminary trials in humans suggest that I3C supplementation may be beneficial in treating conditions related to human papilloma virus infection, such as cervical intraepithelial neoplasia and recurrent respiratory papillomatosis, but larger randomized controlled trials are needed.¹

Researchers at the Linus Pauling Institute at Oregon State University have found that sulforaphane – a compound found in cruciferous vegetables such as broccoli, bok choy and brussels sprouts – has strong anti-cancer properties.

Even more promising results have been found in broccoli sprouts. The tiny, thread-like broccoli sprouts sold at stores next to alfalfa sprouts have more than 50 times the amount of sulforaphane than found in mature broccoli.

Emily Ho, a researcher with the Linus Pauling Institute and an assistant professor in the Department of Nutrition and Exercise Sciences at OSU, described these dietary inhibitors for cancer prevention at the conference on “Diet and Optimum Health,” organized by the Linus Pauling Institute.

Ho’s main area of research is on the dietary prevention of prostate cancer. The Asian diet could be a key in this prevention. White males born in the United States have dramatically higher rates of prostate cancer than Asian men. But when Asian men live in the U.S. for five years or more, their rates of prostate cancer rise significantly, Ho says.²

Past studies in Ho’s lab have focused on dietary elements in cancer prevention such as green tea and soy. In her new study, which was published in the Journal of the Society of Experimental Biology and Medicine, Ho and her colleagues at Linus Pauling Institute looked at cruciferous vegetables. While many cruciferous vegetables have sulforaphane, broccoli and broccoli sprouts have the highest amount and thus could be a major player in the prevention of prostate and colon cancer.

Ho said drugs classified as histone deacetylase (HDAC) inhibitors are being looked at as potentially preventing cancer. She said their research shows that these same effects of inhibiting HDAC might be obtained by consumption of cruciferous vegetables. “I would say if you’re at all worried about cancer or at high risk of cancer, especially of prostate or colon cancer, then increasing your dietary intake of broccoli and other vegetables could be a good idea,” Ho said. “It certainly can’t hurt. And drugs can have negative side effects and be difficult to administer.”²

While Ho said the research is not at the point where she can make a specific recommendation on how much broccoli or bok choy to eat, she personally tries to have two servings of cruciferous vegetables a day. In human subjects, just eating some broccoli sprouts on top of a bagel with cream cheese resulted in HDAC inhibition. “The compound in broccoli may be one of the strongest anti-cancer fighters we have,” Ho said.²

1. Higdon JV. Cruciferous vegetables and human cancer risk: epidemiologic evidence and mechanistic basis. 

Pharmacol Res. 2007 Mar;55(3):224-36. Epub 2007 Jan 25.

2. Oregon State University. "Eat Your Broccoli: Study Finds Strong Anti-Cancer Properties In Cruciferous Veggies." ScienceDaily. ScienceDaily, 18 May 2007. www.sciencedaily.com/releases/2007/05/070517100315.htm