It has been estimated that 30 to 40 percent of all cancers can be prevented by lifestyle and dietary measures alone. Obesity, nutrient sparse foods such as concentrated sugars and refined flour products that contribute to impaired glucose metabolism (which leads to diabetes), low fiber intake, consumption of red meat, and imbalance of omega 3 and omega 6 fats all contribute to excess cancer risk. Intake of flax seed, especially its lignan fraction, and abundant portions of fruits and vegetables will lower cancer risk. Allium and cruciferous vegetables are especially beneficial, with broccoli sprouts being the densest source of sulforophane. Protective elements in a cancer prevention diet include selenium, folic acid, vitamin B-12, vitamin D, chlorophyll, and antioxidants such as the carotenoids (α-carotene, β-carotene, lycopene, lutein, cryptoxanthin). Ascorbic acid has limited benefits orally, but could be very beneficial intravenously. Supplementary use of oral digestive enzymes and probiotics also has merit as anticancer dietary measures.

When a diet is compiled according to the guidelines discussed here, it is likely that there would be at least a 60 to 70 percent decrease in breast, colorectal, and prostate cancers, and even a 40 to 50 percent decrease in lung cancer, along with similar reductions in cancers at other sites. Such a diet would be conducive to preventing cancer and would favor recovery from cancer as well.        

The field of investigation of the role of nutrition in the cancer process is very broad. It is becoming clearer as research continues that nutrition plays a major role in cancer. It has been estimated by the American Institute for Cancer Research and the World Cancer Research Fund that 30–40 percent of all cancers can be prevented by appropriate diets, physical activity, and maintenance of appropriate body weight [1]. It is likely to be higher than this for some individual cancers.

Most of the research on nutrition and cancer has been reductionist; that is, a particular food or a nutrient has been studied in relation to its impact on tumor formation/regression or some other end point of cancer at a particular site in the body. These studies are very helpful in seeing the details of the mechanisms of disease. However, they do not help give an overall picture of how to prevent cancer on a dietary level. Even less, they tell little of how to eat when a person already has a cancer and would like to eat a diet that is favorable to their recovery.

This review will focus on dietary factors which have been shown to contribute to increased risk of cancer, and then on those additional protective dietary factors which reduce cancer risk. Finally, some whole-diet studies will be mentioned which give a more complete picture of how these individual factors work together to reduce cancer risk.        

Eating too much food is one of the main risk factors for cancer. This can be shown two ways: (1) by the additional risks of malignancies caused by obesity, and (2) by the protective effect of eating less food.

Obesity has reached epidemic proportions in the United States. Sixty-four percent of the adult population is overweight or obese [2]. About 1 in 50 are now severely obese (with high Body Mass Index -- BMI > 40 kg/m2) [3]. Mokdad et al [4] found that poor diet and physical inactivity was the second leading cause of death (400,000 per year in the USA), and would likely overtake tobacco as the leading cause of death.

It was estimated in a recent study, from a prospective cancer prevention cohort, that overweight and obesity accounted for 14 percent of all cancer deaths in men and 20 percent of those in women [5]. Significant positive associations were found between obesity and higher death rates for the following cancers: esophagus, colon and rectum, liver, gallbladder, pancreas, kidney, stomach (in men), prostate, breast, uterus, cervix, and ovary [5]. The authors estimated that over 90,000 cancer deaths per year could be avoided if the adult population all maintained a normal weight (BMI < 25.0) [5]. Clearly, obesity is a major risk factor for cancer.

On the other side, careful menu planning brings about an approach entitled CRON-Calorie Restriction with Optimal Nutrition. The basic idea is to eat a reduced amount of food (about 70–80 percent of the amount required to maintain "normal" body weight) while still consuming all of the necessary amounts of vitamins, minerals, and other necessary nutrients. The only restriction is the total amount of energy (calories) that is consumed. While being difficult to practice, this approach has a lot of scientific merit for being able to extend average lifespans of many species of animals including rats, mice, fish, and possibly primates (currently being tested). Along with this lifespan extension is a reduction in chronic diseases that are common to mankind, reviewed in Hursting et al [6]. A recent meta-analysis of 14 experimental studies found that energy restriction resulted in a 55% reduction in spontaneous tumors in laboratory mice [7]. Calorie restriction inhibited induced mammary tumors in mice [8] and suppressed implanted tumor growth and prolonged survival in energy restricted mice [9]. Among Swedish women who had been hospitalized for anorexia nervosa (definitely lower caloric intake, but not adequate nutrition) prior to age 40, there was a 23% lower incidence of breast cancer for nulliparous women and a 76% lower incidence for parous women [10]. So, too many calories is definitely counter-productive, and slightly less than normal is very advantageous.

Refined sugar is a high energy, low nutrient food – junk food. "Unrefined" sugar (honey, evaporated cane juice, etc) is also very concentrated and is likely to contribute to the same problems as refined sugar. Refined wheat flour products are lacking the wheat germ and bran, so they have 78 percent less fiber, an average of 74 percent less of the B vitamins and vitamin E, and 69 percent less of the minerals (USDA Food database, data not shown). Concentrated sugars and refined flour products make up a large portion of the carbohydrate intake in the average American diet.

One way to measure the impact of these foods on the body is through the glycemic index (GI). GI is an indication of the blood sugar response of the body to a standardized amount of carbohydrate in a food. The glycemic load (GL) takes into account the amount of food eaten. An international table of the GI and GL of a wide variety of foods has been published [11].

Case-control studies and prospective population studies have tested the hypothesis that there is an association between a diet with a high GL and cancer. The case control studies have found consistent increased risk of a high GL with gastric [12], upper aero digestive tract [13], endometrial [14], ovarian [15], colon or colorectal cancers [16,17]. In multiple studies, diabetes has been linked with increased risk of colorectal cancer [34-37], endometrial cancer [38], and pancreatic cancer [35,39]. It is clear that severe dysregulation of glucose metabolism is a risk factor for cancer. Foods which contribute to hyperinsulinemia, such as refined sugar, foods containing refined sugar, and refined flour products should be avoided and eliminated from a cancer protective diet.

Unrefined plant foods typically have an abundance of fiber. Dairy products, eggs, and meat all contain no fiber. Refined grain products also have most of the dietary fiber removed from them. So, a diet high in animal products and refined grains (a typical diet in the USA) is low in fiber. Slattery et al [40] found an inverse correlation between vegetable, fruit and whole grain intake plant food intake and rectal cancer, while refined grains were associated with increased risk of rectal cancer. A threshold of about 5 daily servings of vegetables was needed to reduce cancer risk, and the effect was stronger among older subjects [40].

Red meat has been implicated in colon and rectal cancer. A Medline search in February 2003 uncovered 26 reports of human studies investigating the link between diet and colon or colorectal cancer. Of the 26 reports, 21 of them reported a significant positive relationship between red meat and colon or colorectal cancer [17,41-64]. Meat and the heterocyclic amines formed in cooking have been correlated to breast cancer in a case-control study in Uruguay as well [66].

Omega 3 fats (alpha-linolenic acid, EPA, DHA) have been shown in animal studies to protect from cancer, while Omega 6 fats (linoleic acid, arachidonic acid) have been found to be cancer promoting fats. Now there have been several studies that have tested this hypothesis in relation to breast cancer. Except for the study by London et al [67], all of these studies found an association between a higher ratio of N-3 to N-6 fats and reduced risk of breast cancer. Flax seed oil and DHA (from an algae source) both can be used to increase the intake of N-3 fat, with DHA being a more efficient, sure source.

Flax seed is an excellent source of dietary fiber, omega 3 fat (as alpha-linolenic acid), and lignans, and is a more potent source of phytoestrogens than soy products.

Ground flax seeds have been studied for their effect on cancer. In one study, the flax seed, its lignan fraction, or the oil were added to the diet of mice who had previously been administered a chemical carcinogen to induce cancer. All three treatments reduced the established tumor load. In another study, the flax lignan SDG was fed to mice starting one week after treatment with a known carcinogen. The number of tumors per rat was reduced by 46% compared to the control group [71]. Flax or its lignan (SDG) were tested to see if they would prevent melanoma metastasis. The flax or lignan fraction were fed to mice two weeks before and after injection of melanoma cells. The flax treatment (at 2.5, 5, or 10% of diet intake) resulted in a 32, 54, and 63 percent reduction in the number of tumors, compared to the control [72]. The SDG also reduced the tumor number, from a median of 62 in the control group to 38, 36, and 29 tumors per mouse in the SDG groups, respectively [73]. More recently, Thompson's research group studied mice injected with human breast cancer cells. After the injection the mice were fed a basal diet (lab mouse chow) for 8 weeks while the tumors grew. Then one group continued the basal diet and another was fed a 10% flax seed diet. The flax seed reduced the tumor growth rate and reduced metastasis by 45% [74].

Other researchers have tested flax seed and prostate cancer. In an animal model using mice, Lin et al [77] found that a diet supplemented with 5% flax inhibited the growth and development of prostate cancer. A pilot study of 25 men who were scheduled for prostatectomy surgery were instructed to eat a low-fat diet (20% or less of energy intake) and take 30 grams of ground flaxseed per day. During the follow-up (of an average of 34 days), there were significant changes in serum cholesterol, total testosterone, and the free androgen index [78].

In summary, flax seed and its lignan were able to reduce tumor growth (both in number and size of tumors), prevent metastasis, and even cause increased differentiation of mouse mammary tissue in suckling mice (making the offspring less susceptible to carcinogenesis even when not consuming any flax products). In addition, ground flax seed may be a very beneficial food for men battling prostate cancer.

One of the most important messages of modern nutrition research is that a diet rich in fruits and vegetables protects against cancer; in fact, this same diet protects against almost all other diseases, too, including cardiovascular disease and diabetes. There are many mechanisms by which fruits and vegetables are protective, and an enormous body of research supports the recommendation for people to eat more fruits and vegetables.

Block et al [80] reviewed about 200 studies of cancer and fruit and vegetable intake. A statistically significant protective effect of fruits and vegetables was found in 128 of 156 studies that gave relative risks. For most cancers, people in the lower quartile (1/4 of the population) who ate the least amount of fruits and vegetables had about twice the risk of cancer compared to those who in the upper quartile who ate the most fruits and vegetables. Even in lung cancer, after accounting for smoking, increasing fruits and vegetables causes an estimated reduction of an additional 20 to 33 percent [1].

Steinmetz and Potter reviewed the relationship between fruits, vegetables, and cancer in 206 human epidemiologic studies and 22 animal studies [81]. They found "the evidence for a protective effect of greater vegetable and fruit consumption is consistent for cancers of the stomach, esophagus, lung, oral cavity and pharynx, endometrium, pancreas, and colon." Vegetables, particularly raw vegetables, were found to be protective; 85% of the studies that queried raw vegetable consumption found a protective effect. Allium vegetables, carrots, green vegetables, cruciferous vegetables, and tomatoes also had a fairly consistent protective effect [81]. Allium vegetables (garlic, onion, leeks, and scallions) are particularly potent and have separately been found to be protective for stomach and colorectal cancers [82,83] and prostate cancer [84].

There are many substances that are protective in fruits and vegetables, so that the entire effect is not very likely to be due to any single nutrient or phytochemical. Steinmetz and Potter list possible protective elements, including allium compounds, isoflavones, protease inhibitors, phytosterols, inositol hexaphosphate, vitamin C, lutein, folic acid, beta carotene (and other carotenoids), lycopene, selenium, vitamin E, flavonoids, and dietary fiber [81].

A joint report by the World Cancer Research Fund and the American Institute for Cancer Research found convincing evidence that a high fruit and vegetable diet would reduce cancers of the mouth and pharynx, esophagus, lung, stomach, and colon and rectum; evidence of probable risk reduction was found for cancers of the larynx, pancreas, breast, and bladder [1].

Cruciferous vegetables (broccoli, cauliflower, cabbage, Brussels sprouts) contain sulforophane, which has anti-cancer properties. A case-control study in China found that intake of cruciferous vegetables, measured by urinary secretion of isothiocyanates, was inversely related to the risk of breast cancer; the quartile with the highest intake only had 50% of the risk of the lowest intake group [89]. In the Nurses' Health Study a high intake of cruciferous vegetables (5 or more servings/week vs less than two servings/week) was associated with a 33% lower risk of non-Hodgkin's lymphoma [90]. In the Health Professionals Follow-up Study bladder cancer was only weakly associated with low intake of fruits and vegetables, but high intake (5 or more servings/week vs 1 or less servings/wk) of cruciferous vegetables was associated with a statistically significant 51% decrease in bladder cancer [91].

Also, prostate cancer risk was found to be reduced by cruciferous vegetable consumption in a population-based case-control study carried out in western Washington state. Three or more servings per week, compared to less than one serving of cruciferous vegetables per week, resulted in a statistically significant 41% decrease in prostate cancer risk [92]. Similar protective effects of cruciferous vegetables were seen in a multi-ethnic case-control study [93]. A prospective study in Shanghai, China found that men with detectable amounts of isothiocyanates in their urine (metabolic products that come from cruciferous vegetables) had a 35% decreased risk of lung cancer. Among men that had one or two genetic polymorphisms that caused them to eliminate these isothiocyanates slower, there was a 64% or 72% decreased risk of lung cancer, respectively [94].

Broccoli sprouts have a very high concentration of sulforophane since this compound originates in the seed and is not made in the plant as it grows [95,96]. One sprout contains all of the sulforophane that is present in a full-grown broccoli plant. So, if sulforophane is especially cancer-protective, it would seem reasonable to include some broccoli sprouts in an anti-cancer diet.

Selenium is a mineral with anti-cancer properties. Many studies in the last several years have shown that selenium is a potent protective nutrient for some forms of cancer. The Arizona Cancer Center posted a selenium fact sheet listing the major functions of selenium in the body [97]:

1. Selenium is present in the active site of many enzymes which catalyze oxidation-reduction reactions; these reactions may encourage cancerous cells to undergo apoptosis (death). 2. Selenium is a component of the antioxidant enzyme glutathione peroxidase; 3. Selenium improved the immune system’s ability to respond to infections; 4. Selenium causes the formation of natural killer cells; 5. P450 enzymes in the liver may be induced by selenium, leading to detoxification of some carcinogenic molecules; 6. Selenium inhibits prostaglandins that cause inflammation; 7. Selenium enhances male fertility by increased sperm motility; 8. Selenium can decrease the rate of tumor growth.

A serendipitous randomized, double-blind, controlled trial of a 200 μg/day selenium supplement in the southeastern region of the USA (where soil selenium levels are low) found that the primary endpoints of skin cancer were not improved by the selenium supplement, but that other cancer incidence rates were decreased by selenium [98,99]. There was a significant reduction in total cancer incidence (105 vs 137 cases, P = 0.03), prostate cancer (22 vs 42 cases, P = 0.005), a marginally significant reduction in colorectal cancer incidence (9 vs 19 cases, P = 0.057), and a reduction in cancer mortality, all cancer sites (40 vs 66 deaths, P = 0.008) (selenium versus control group cases reported, respectively) [98]. The selenium supplement was most effective in ex-smokers and for those who began the study with the lowest levels of serum selenium. Several prospective studies have also examined the role of selenium in cancer prevention, particularly for prostate cancer.

Overall, it appears that poor selenium levels, especially for men, are a cancer risk. If a person has low selenium levels and other antioxidant defenses are also low, the cancer risk is increased even further. Women do not appear to be as sensitive to selenium, as breast cancer has not been found to be influenced by selenium status in several studies [100-104], although both men and women were found to be protected by higher levels of selenium from colon cancer [100] and lung cancer [105,106]. Good vegetarian sources of selenium are whole grains and legumes grown in selenium-rich soil in the western United States, brazil nuts (by far the most dense source of selenium), nutritional yeast, brewers yeast, and sunflower seeds.

All green plants contain chlorophyll, the light-collecting molecule. Chlorophyll and its derivatives are very effective at binding polycyclic aromatic hydrocarbons (carcinogens largely from incomplete combustion of fuels), heterocyclic amines (generated when grilling foods), aflatoxin (a toxin from molds in foods which causes liver cancer), and other hydrophobic molecules. The chlorophyll-carcinogen complex is much harder for the body to absorb, so most of it is swept out as waste. The chemoprotective effect of chlorophyll and its derivatives has been tested in laboratory cell cultures and animals [107,108]. There is much compelling evidence for the anti-carcinogenic effects of chlorophyll. For example, a 55% reduction in aflatoxin-DNA compounds were found in the group that took 100 mg of chlorophyllin three times a day [109].

Vitamin B-12 has not been proven to be an anti-cancer agent, but there is some evidence indicating that it could be beneficial. The form of administered vitamin B-12 may be important.

Laboratory evidence for the effects of vitamin B12 was seen in a study with vitamin B-12 deficient rats. Choi et al [116] found that the colonic DNA of the B-12 deficient rats had undergone changes that could increase risk of carcinogenesis. In two studies, a relation between lower vitamin B12 status (but not deficiency) and statistically significant higher risk of breast cancer was found [117,118]. So, there is evidence from lab studies, prospective cohort studies, and mechanistic studies showing that vitamin B-12 is an important nutrient for genetic stability, DNA repair, carcinogenesis, and cancer therapy.

Folic acid (folate) is the dark green leafy vegetable vitamin. Many studies have found a significant reduction in colon, rectal, and breast cancer with higher intakes of folic acid and their related nutrients (vitamin B-6 and B-12). Alcohol is an antagonist of folate, so drinking alcoholic beverages greatly magnifies the cancer risk of a low-folate diet. Cravo et al [124] used 5 mg of folic acid a day in a study of 20 patients with colonic adenoma polyps, and found that the folic acid could reverse DNA hypomethylation (that is, enhance cancer suppression) in 7 of 12 patients who had only one polyp.

The cancer risk associated with low folate intake is probably higher for colon cancer than for breast cancer. Most of the breast cancer studies only found a protective effect of folate among women who consumed alcohol. However, among women residents of Shanghai who consumed no alcohol, no vitamin supplements and ate unprocessed, unfortified foods, there was a 29% decreased risk of breast cancer among those with the highest intake of folate [125]. So, there may be a true protective effect that is masked in the Western populations by so many other risk factors. Two studies showed that the risk of cancer due to family history can be modified by high folate intake, so a prudent anti-cancer diet would be high in dark green leafy vegetables. The mean intake of folic acid on the Hallelujah Diet was 594 μg/day for men and 487 μg/day for women [88].

Vitamin D is produced primarily from the exposure of the skin to sunshine. Even casual exposure of the face, hands, and arms in the summer generates a large amount of vitamin D. In fact, simulated sunshine, equivalent to standing on a sunny beach until a slight pinkness of the skin was detected, was equivalent to a 20,000 IU oral dose of vitamin D2 [126]. (Note that the RDA is 400 IU for most adults.) It has been estimated that 1,000 IU per day is the minimal amount needed to maintain adequate levels of vitamin D in the absence of sunshine [126], and that up to 4,000 IU per day can be safely used with additional benefit [127].

The concentration of the active hormonal form of vitamin D is tightly regulated in the blood by the kidneys. This active hormonal form of vitamin D has the potent anti-cancer properties. It has been discovered that various types of normal and cancerous tissues, including prostate cells [128], colon tissue [129], breast, ovarian and cervical tissue [130], pancreatic tissue [131] and a lung cancer cell line [132] all have the ability to convert the major circulating form of vitamin D, 25(OH)D, into the active hormonal form, 1,25(OH)2D. So, there is a local mechanism in many tissues of the body for converting the form of vitamin D in the body that is elevated by sunshine exposure into a hormone that has anticancer activity.

Indeed, 25(OH)D has been shown to inhibit growth of colonic epithelial cells [133], primary prostatic epithelial cells [134], and pancreatic cells [131]. So, the laboratory work is confirming what had been seen some time ago in ecological studies of populations and sunshine exposure.

The mortality rates for colon, breast, and ovary cancer in the USA show a marked north-south gradient [135]. In ecological studies of populations and sunlight exposure (no individual data), sunlight has been found to have a protective effect for prostate cancer [136], ovarian cancer [137], and breast cancer [138]. Recently Grant found that sunlight was also protective for bladder, endometrial, renal cancer, multiple myeloma, and Non-Hodgkins lymphoma in Europe [139] and bladder, esophageal, kidney, lung, pancreatic, rectal, stomach, and corpus uteri cancer in the USA [140].

There is a large body of literature indicating that dietary carotenoids are cancer preventative. Alpha-carotene has been found to be a stronger protective agent than its well-known isomer beta-carotene. Studies tend to agree that overall intake of carotenoids is more protective than a high intake of a single carotenoid. So, a variety of fruits and vegetables is still a better anti-cancer strategy than just using a single vegetable high in a specific carotenoid.

The richest source of alpha-carotene is carrots and carrot juice, with pumpkins and winter squash as a second dense source. There is approximately one μg of alpha-carotene for every two μg of beta-carotene in carrots.

Of the various carotenoids, lycopene has been found to be very protective, particularly for prostate cancer. The major dietary source of lycopene is tomatoes, with the lycopene in cooked tomatoes being more bioavailable than that in raw tomatoes. Several prospective cohort studies have found associations between high intake of lycopene and reduced incidence of prostate cancer, though not all studies have produced consistent results [144,145].

In the Health Professionals Follow-up Study there was a 21% decrease in prostate cancer risk, comparing the highest quintile of lycopene intake with the lowest quintile. Combined intake of tomatoes, tomato sauce, tomato juice, and pizza (which accounted for 82% of the lycopene intake) were associated with a 35% lower risk of prostate cancer. Furthermore, lycopene was even more protective for advanced stages of prostate cancer, with a 53% decrease in risk [146].

In addition, another study with 450 cases and controls found an inverse relation between plasma lycopene and prostate cancer risk among older subjects (over 65 years of age) without a family history of prostate cancer [148]. Among younger men, high plasma beta-carotene was associated with a statistically significant 64% decrease in prostate cancer risk. So, the results for lycopene have been found for dietary intakes as well as plasma levels.

In a placebo-controlled study of aspirin and beta-carotene, there was a 60% reduction in advanced prostate cancer risk for those subjects in the placebo group with the highest plasma lycopene levels, compared to the lowest quintile. The beta-carotene also had a protective effect, especially for those men with low lycopene levels [149].

In addition to these observational studies, two clinical trials have been conducted to supplement lycopene for a short period before radical prostatectomy. In one study, 30 mg/day of lycopene were given to 15 men in the intervention group while 11 men in the control group were instructed to follow National Cancer Institute recommendations to consume at least 5 servings of fruits and vegetables daily. Results showed that the lycopene slowed the growth of prostate cancer. Subjects that took the lycopene for 3 weeks had smaller tumors [150]. In another study before radical prostatectomy surgery, 32 men were given a tomato sauce based pasta dish every day, which supplied 30 mg of lycopene per day. After 3 weeks, serum and prostate lycopene levels increased 2-fold and 2.9-fold, respectively. PSA levels (prostate-specific antigens in the blood that warn of higher cancer risk) decreased 17%, as seen also by Kucuk et al [150]. Oxidative DNA damage was 21% lower in subjects' leukocytes and 28% lower in prostate tissue, compared to non-study controls.

Vitamin C, or ascorbic acid, has been studied in relation to health and is the most common supplement taken in the USA. Low blood levels of ascorbic acid are detrimental to health and vitamin C is correlated with overall good health and cancer prevention [153].

Use of vitamin C for cancer therapy was popularized by Linus Pauling. At high concentrations, ascorbate is preferentially toxic to cancer cells. There is some evidence that large doses of vitamin C, either in multiple divided oral doses or intravenously, have beneficial effects in cancer therapy [154-156].

While vitamin C is quite possibly an effective substance, the amounts required for these therapeutic effects are obviously beyond dietary intakes. However, intravenous ascorbate may be a very beneficial adjuvant therapy for cancer with no negative side effects when administered properly.

There are many more substances that have some benefit for cancer therapy. Most of these substances are found in foods, but their effective doses for therapy are much higher than the normal concentration in the food. For example, grape seed extract contains proanthocyanidin, which shows anticarcinogenic properties (reviewed by Cos et al [157]). Also, green tea contains ingredients that might be of benefit.

The bacteria that reside in the intestinal tract generally have a symbiotic relationship with their host. Beneficial bacteria produce natural antibiotics to keep pathogenic bugs in check and produce some B vitamins in the small intestine where they can be utilized. Beneficial bacteria help with food digestion by providing extra enzymes, such as lactase, in the small intestine. Beneficial bacteria help strengthen the immune system right in the gut, where much of the interaction between the outside world and the body goes on, and can help prevent food allergies.

These good bacteria also help prevent cancer at various stages of development. Lactobacillus species and Eubacterium aerofaciens, both producers of lactic acid, were associated with lower risk of colon cancer, while Bacteroides and Bifidobacterium species were associated with higher risk of colon cancer [160].

There is a solid theoretical basis for why probiotics should help prevent cancer (especially of the colon), and even reverse cancer. Probiotics produce short chain fatty acids in the colon, which acidify the environment. Lower colon pH is associated with lower incidence of colon cancer. Probiotic bacteria reduce the level of procarcinogenic enzymes such as beta-glucuronidase, nitroreductase, and azoreductase [161].

L. casei was used in two trials of patients with superficial bladder cancer. In the first trial, the probiotic group had a 50% disease free time of 350 days, compared to 195 days for the control group [162]. The second trial also showed that the probiotics worked better than the placebo, except for multiple recurring tumors [163].

Except for the two studies noted above, most of the research of probiotics and cancer has been done in animals. Studies have looked at markers of tumor growth or at animals with chemically induced tumors. Studies in rats have shown that probiotics can inhibit the formation of aberrant crypt foci, thought to be a pre-cancerous lesion in the colon. Rats fed Raftilose, a mixture of inulin and oligofructose, or Raftilose with Lactobacilli rhamnosus (LGG) and Bifidobacterium lactis (Bb12) had a significantly lower number of tumors compared to the control group [165]. A probiotic mixture, without any prebiotic, given to rats fed azoxymethane reduced colon tumors compared to the control (50% vs 90%), and also reduced the number of tumors per tumor-bearing rat [166].

The research on probiotics and disease is still an emerging field. There is a high degree of variation of health benefits between different strains of bacteria. As new methods for selecting and screening probiotics become available, the field will advance more rapidly.

Many people diagnosed with cancer have digestion or intestinal tract disorders as well. Impaired digestion will greatly hinder a nutritional approach to treating cancer. If the nutrients cannot be released from the food and taken up by the body, then the excellent food provided by healthy diets will go to waste. Digestive enzyme supplements are used to ensure proper and adequate digestion of food. Even raw foods, which contain many digestive enzymes to assist in their digestion, will be more thoroughly digested with less of the body's own resources with the use of digestive enzymes. So, the enzymes taken with meals do not have a direct effect upon a tumor, but assist the body in getting all of the nutrition out of the food for healing and restoring the body to normal function.

Enzymes, especially proteases, can have direct anti-tumor activity. Wald et al [170] reported on the anti-metastatic effect of enzyme supplements. Mice inoculated with the Lewis lung carcinoma were treated with a proteolytic enzyme supplement. The primary tumor was cut out, so that the metastatic spread of the cancer could be measured. After surgical removal of the primary tumor (day 0), 90% of the control mice died by day 18 due to metastasized tumors. In the first group, which received the enzyme supplement from the time of the tumor-removal surgery, 30% of the mice had died from metastasized cancer by day 25. In the second group, which received the enzymes from 6 days prior to removal of the primary tumor, only 10% showed the metastatic process by day 15. In the third group, which received the enzyme treatment since the initial inoculation of the Lewis lung carcinoma, no metastatic spread of the tumor was discernible. 100-day survival rates for the control, first, second, and third groups were 0, 60%, 90%, and 100%.

In a similar experiment, an enzyme mixture of papain, trypsin, and chymotrypsin was given to mice inoculated with melanoma cells. Survival time was prolonged in the test group (38 days in the enzyme group compared to 24 days in the control mice) and 3 of the 10 enzyme-supplemented mice were cured. Again, a strong anti-metastatic effect of the proteolytic enzymes was seen [171].

Further evidence of the efficacy of oral enzyme supplementation is available from Europe. Two different studies demonstrated that two different oral proteolytic enzyme supplements could reduce high levels of transforming growth factor-β, which may be a factor in some cancers [172,173]. In another study, an oral enzyme supplement was tested on multiple myeloma; control group survival was 47 months, compared to 83 months (a 3 year gain) for patients who took the oral enzymes for more than 6 months [174].

Enzyme supplements have also been shown to reduce side effects of cancer therapy. In a large study in Germany, women undergoing conventional cancer therapy were put into a control group or a group that received an oral enzyme supplement. Disease and therapy related symptoms were all reduced, except tumor pain, by the enzyme supplement. Also, survival was longer with less recurrence and less metastases in the enzyme group [178].

It is clear that there are some circumstances that will be helped by enzyme supplementation, with very little danger of negative side effects. At the least, enzymes will improve digestion and lessen the digestive burden on the body, leaving more reserves for disease eradication. However, as the research indicates, the effect may be much greater than that, with the potential for direct anti-tumor activity.

A diet-based cancer therapy, the Gerson Therapy, was used to treat melanoma cancer. The five-year survival rates from their therapy compared very favorably to conventional therapy reported in the medical literature, especially for more advanced stages of melanoma [179].

8,984 women were followed for an average of 9.5 years, with 207 incident cases of breast cancer during that time. Their diets were analyzed by patterns – salad vegetables (raw vegetables and olive oil), Western (potatoes, red meat, eggs and butter), canteen (pasta and tomato sauce), and prudent (cooked vegetables, pulses, and fish). Only the salad vegetable diet pattern was associated with a significantly lower risk of breast cancer, about 35% lower. For women of normal weight (BMI under 25) the salad vegetable pattern was even more protective, about a 61% decreased risk of breast cancer [180]. The overall dietary pattern does make a very significant difference.

In US-based studies the "prudent" diet has been shown to be protective for colon cancer, while the "Western" diet has been shown to be detrimental. The "Western" dietary pattern, with its higher intakes of red meat and processed meats, sweets and desserts, French fries, and refined grains, was associated with a 46% increase relative risk of colon cancer in the Nurses' Health Study [45]. Slattery et al [17] found a two-fold increase in relative risk of colon cancer associated with a "Western" dietary pattern, and a 35–40% decrease in relative risk associated with the "prudent" pattern, especially among those diagnosed at an earlier age (less than 67 years old). The "salad vegetable" pattern is still more likely to be protective compared to the prudent dietary pattern, but this pattern did not exist in this study population.

In an analysis of the colon cancer data from the Health Professionals Follow-up Study, Platz et al [56] found that there was a 71% decrease in colon cancer risk when men with none of six established risk factors were compared to men with at least one of these risk factors (obesity, physical inactivity, alcohol consumption, early adulthood cigarette smoking, red meat consumption, and low intake of folic acid from supplements). If all men had the same health profile as these healthier 3% of the study population, colon cancer rates would have been only 29% of what they measured.

What is the result when all of these things are put together? What if all of the factors reviewed here were taken into account and put into practice? The resultant anti-cancer diet would feature the following elements:  

• adequate, but not excessive calories,
• 10 or more servings of vegetables a day, including cruciferous and allium vegetables (vegetable juice could meet part of this goal),
• 4 or more servings of fruits a day,
• high fiber,
• no refined sugar,
• no refined flour,
• low total fat, but containing necessary essential fatty acids (EFAs),
• no red meat,
• a balanced ratio of omega 3 and omega 6 fats, and DHA,
• flax seed as a source of phytoestrogens,
• about 200 μg/day selenium,
• 1,000 μg/day methylcobalamin (B-12),
• high intake of folic acid (from dark green vegetables),
• adequate sunshine to get vitamin D (or a 1,000 IU/day supplement),
• high intake of antioxidants and phytochemicals from fruits and vegetables, including alpha-carotene, beta-carotene, beta-cryptoxanthin, vitamin C (from foods), vitamin E (from foods),
• high intake of chlorophyll,
• beneficial probiotics,
• oral enzymes.

As reviewed above, reductions of 60 percent in breast cancer rates have already been seen in human diet studies, and a 71 percent reduction in colon cancer for men without the known modifiable risk factors. These reductions are without taking into account many of the other factors considered in this review, such as markedly increased fruit and vegetable intake, balanced omega 3 and 6 fats, vitamin D, reduced sugar intake, probiotics, and enzymes – factors which are all likely to have an impact on cancer. Certainly cancer prevention would be possible, and cancer reversal in some cases is quite likely.

This article is based on an article entitled “Nutrition and cancer: A review of the evidence for an anti-cancer diet” by Michael S Donaldson, available on the Nutrition Journal website. Michael Donaldson is a research scientist at the Hallelujah Acres Foundation, a foundation for investigations pertaining to the Hallelujah Diet.

Donaldson referenced over 200 other works in his original article – some of which are cited above. Instead of reprinting the long list of references here, we refer readers to the original article.