Anti-Cancer Effects of Green Vegetables

Nutrition scientists have shown over and over that people who eat more natural plant foods – vegetables, fruits, legumes – are less likely to be diagnosed with cancer. But are all vegetables equally protective?

 If we wanted to design an anti-cancer diet, we would want to know which foods have the most powerful anti-cancer effects. 

Then, we could eat plenty of these foods each day, flooding our bodies with the protective substances contained within them.

Cruciferous Vegetables May Have
The Most Powerful Anti-Cancer Properties

This family of vegetables includes green vegetables like kale, cabbage, collards, and broccoli, plus some others like cauliflower and turnips (see the full list at the bottom of this post). They are named for their flowers, having four equally spaced petals in the shape of a cross, from the Latin word “crucifer” meaning “cross-bearer.”

All vegetables contain protective micronutrients and phytochemicals, but cruciferous vegetables have a unique chemical composition: They have sulfur-containing compounds which are responsible for their pungent or bitter flavors. When cell walls are broken by blending or chopping, a chemical reaction occurs that converts these sulfur-containing compounds to isothiocyanates (ITCs) – compounds with proven anti-cancer activities.

Over 120 ITCs have been identified, and the various ITCs have different mechanisms of action. Because different ITCs can work in different locations in the cell and on different molecules, they can have combined additive effects, working synergistically to remove carcinogens and kill cancer cells. Some ITCs have anti-inflammatory, antioxidant, or even immunologic effects. Some ITCs can inhibit angiogenesis, the process by which a tumor establishes a blood supply.

Some ITCs detoxify and/or remove carcinogenic compounds; the combined consumption of broccoli and Brussels sprouts (rich sources of the ITC sulforaphane) increases the excretion of certain dietary carcinogens. (1) Some ITCs inhibit cancer cell growth or induce cancer cell death: Cruciferous vegetable juice, containing a variety of ITCs, has been shown to induce apoptosis, or programmed cell death, in breast cancer cells. (2)

Some ITCs can prevent carcinogens from binding to DNA and initiating cancerous changes in the cell. Sulforaphane activates enzymes that protect cells from DNA damage by carcinogens. (3) But if DNA does indeed become damaged, the growth of the damaged cell can be stopped to allow for DNA repair, or the cell can be programmed for cell death. These processes can control this damage. Several ITCs, including sulforaphane, indole-3-carbinol (I3C), and diindolmethane (DIM) stop growth or induce death in cultured cancer cells. (3) Sulforaphane blocks tumor formation and induces programmed cell death in colon cancer cells. (4) Allyl isothiocyanate (AITC), present in several cruciferous vegetables, inhibits proliferation and induces cell death in bladder cancer cells. (5)

Indole-3-carbinol and its metabolite DIM may be especially protective against hormone-sensitive cancers; they help the body transform estrogen and other hormones into forms that are more easily excreted from the body. (6-7)

These observations in cell culture and animal studies have been confirmed by epidemiological studies drawing connections between cruciferous vegetable intake and cancer incidence. Inverse associations between cruciferous vegetable intake and breast, lung, prostate, and colorectal cancers have been reported. Similar associations exist for total vegetable intake, but cruciferous vegetables are far more potent:

• Cruciferous vegetables are twice as powerful as other plant foods. In population studies, a 20% increase in plant food intake generally corresponds to a 20% decrease in cancer rates, but a 20% increase in cruciferous vegetable intake corresponds to a 40% decrease in cancer rates. (8)

• 28 servings of vegetables per week decreased prostate cancer risk by 33%, but just 3 servings of cruciferous vegetables per week decreased prostate cancer risk by 41%. (9)

• 1 or more servings of cabbage per week reduces risk of pancreatic cancer by 38%. (10)

How can we maximize the ITC benefit of our cruciferous vegetables?
Methods of preparation and cooking can affect the availability of ITCs to be digested and absorbed. Chopping, chewing, blending, or juicing allows for production of ITCs. Some ITC benefit may be lost with boiling or steaming, so we get the maximum benefit from eating cruciferous vegetables raw; however, some production of ITC in cooked cruciferous vegetables may occur in the gut once the vegetables have been ingested.

Cruciferous vegetables are not only the most powerful anti-cancer foods in existence, they are also the most nutrient-dense of all vegetables. Although the National Cancer Institute recommends 5-9 servings of fruits and vegetables per day for cancer prevention, they have not yet established specific recommendations for cruciferous vegetables. I recommend 6 fresh fruits and 8 total servings of vegetables per day, including 2 servings of cruciferous vegetables, one raw and one cooked. Consuming a large variety of these ITC-rich cruciferous vegetables within an overall nutrient-dense diet can provide us with a profound level of protection against cancer.

List of cruciferous vegetables
Arugula, bok choy, broccoli, broccoli rabe, broccolini, Brussels sprouts, cabbage, cauliflower, collards, horseradish, kale, kohlrabi, mache, mustard greens, radish, red cabbage, rutabaga, turnips, turnip greens, watercress.

Recipe for “Braised Bok Choy”
Serves: 2
Ingredients:
8 baby bok choy or 3 regular bok choy
1 teaspoon Bragg Liquid Aminos or low sodium soy sauce
2 cups coarsely chopped shiitake mushrooms
2 large cloves garlic, chopped (optional)
1 tablespoon unhulled sesame seeds, lightly toasted*
*Lightly toast sesame seeds in a pan over medium heat for 3 minutes, shaking pan frequently.

Instructions:
1. Cover bottom of large skillet with ½ inch water. Add bok choy (cut baby bok choy in half lengthwise or cut regular bok choy into chunks).

2. Drizzle with liquid aminos. Cover and cook on high heat until bok choy is tender, about 6 minutes.

3. Remove bok choy; add mushrooms and garlic to the liquid in the pan.

4. Simmer liquid until reduced to a glaze. Pour over bok choy. Top with toasted sesame seeds.

For an extensive collection of green vegetable recipes like these, visit Dr. Fuhrman’s website and check out his most recent book, Eat for Health.

References

1. Walters DG, Young PJ, Agus C, Knize MG, Boobis AR, Gooderham NJ, et al. Cruciferous vegetable consumption alters the metabolism of the dietary carcinogen 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) in humans. Carcinogenesis 2004; 25: 1659–69.

2. Brandi G et al. Mechanisms of action and antiproliferative properties of Brassica oleracea juice in human breast cancer cell lines. J Nutr 2005; 135(6): 1503-9

3. Higdon JV et al. Cruciferous Vegetables and Human Cancer Risk: Epidemiologic
Evidence and Mechanistic Basis. Pharmacol Res. 2007 March; 55(3): 224–236

4. Gamet-Payrastre I et al. Sulforaphane, a naturally occurring isothiocyanate induces cell cycle arrest and apoptosis in HT29 human colon cancer cells. Cancer Res 2000; 60: 1426-1433