Scientists have found that a number of flavanol compounds in plants help prevent colon cancers and rectal cancers – collectively called colorectal cancer.
What are flavonoids?
There are six major types of flavonoids. These include isoflavonoids, flavones, anthocyanidins, flavanones, flavanols and flavonols.
Some types of flavonoids – most specifically those in citrus – have been dubbed ‘bioflavonoids’ but the broader term flavonoid has a greater specificity among the various food groups.
Flavonoids have a variety of health benefits. Most flavonoids are free radical scavengers – antioxidants. They reduce inflammation and many have been found to prevent cancers of different types.
Some of the more well-known flavonoids include quercetin – a nutrient found in apples, onions, garlic and other foods; hesperidin and rutin from citrus products; epicatechins from vegetables, green tea, herbs and cocoa; kaempferol from cabbage, brussels sprouts, kale, leeks, grapes and apples; and proanthocyanidins from oats, barley and flax. Other research has found that legumes and beans help prevent cancer. Olives and olive oil are also anticancer.
Diets that contain significant quantities of these constituents are typically diets high in fresh foods – as many flavonoids are heat sensitive. Diets high in fresh foods also have many other benefits, because these foods are nutrient-dense and rich in fiber.
The researchers’ study confirmed this. Their conclusion: “Total dietary flavonoid intake is associated with a significant reduction in the risk of gastric cancer in women.”
According to the World Health Organization, gastric cancers cause some 800,000 deaths globally. Gastric cancers typically start in the walls of the stomach, but tumors often grow in the intestines and esophagus. From there, they can metastasize into the lymph nodes and spread elsewhere. Gastric cancer comes with only a 65% average six-month survival rate.Flavanols in quince halt cancer growth
In a 2018 study from Poland’s Medical University of Lodz, researchers studied human colon cancer cells. In particular, they tested an extract of the Japanese Quince fruit (Chaenomeles japonica). The extract isolated a collection of compounds called flavanols. This flavanol extract contained polyphenols such as procyanidin monomers and oligomers. These are components of the fresh quince fruit as well as other foods, as we’ll discuss below.
The researchers found that the flavanol extract significantly blocked the ability of the cancer cells to continue to expand. After 72 hours, they found the quince extract blocked the genetic expression of proteins by up to 77 percent. It also inhibited the MMP-9 levels in the cells. MMPs are linked to tumor progression. The quince extract also inhibited the production of key enzymes that allow the cancer cells to migrate and expand.
Okay, but do flavanols protect against colon cancer when people eat more foods containing them on a daily basis?
Colorectal cancer research follows 400,000 people
A review of research that included nearly 400,000 people from China’s National Center of Colorectal Surgery has determined that certain phytonutrients, specifically flavanols and other flavonoids, have the ability to significantly reduce the risk of colorectal cancer.
After an extensive review of the evidence, the researchers narrowed the research down to eight studies, which included 390,769 people. These included a range of protocols, including large population studies as well as controlled randomized studies.
The researchers utilized the Cochrane library and the Cochrane protocol for reviews. This process helps quantify the results – often creating more conservatism among the results due to strict result comparisons.
Flavanols protect against cancer
The research found that foods containing flavanols – more technically referred to as flavan-3-ols – resulted in a significant reduction in incidence in colorectal cancer. The greater the flavanol consumption, the greater the association. More specifically, they found that greater consumption of epicatechin – a flavanol – significantly decreases the risk of colorectal cancer.
Flavanols include the category of catechins, which includes epicatechin, gallocatechin and epigallocatechin. Depending upon the molecular classification, they can also include kaempferol. Collectively these and others are also referred to as polyphenols. Plant polyphenols like catechins are found in many fruits and vegetables and vinegar. They are also found in herbal teas and green tea, as well as cocoa (from Theobroma cacao). Significant flavanol content has also been found in apples, onions and some beans.
The research also found that the consumption of procyanidins and phytoestrogens also reduced colorectal cancer incidence. The researchers characterized the association of these as “medium quality,” meaning there was a definite association between the consumption and colon cancer, but not as strong as the polyphenol association.
Two other phytocompounds found to reduce colorectal cancer was genistein and formononetin. These are considered isoflavonoids but also phytoestrogens because they have the ability to bind to the body’s estrogen receptors. This can be significant because as people age – especially women – estrogen availability slows and this can be pro-inflammatory. When phytoestrogens are in the diet, these can help dampen the effects of estrogen reduction as we age.
Good sources of flavanols
The phytoestrogens genistein and formononetin are significantly found in beans, soy, red clover and some whole grains.
The number of plant compounds – phytonutrients – available from a plant-based diet is gigantic. The researchers described more than 5,000 individual flavonoids that have been divided into more than ten different categories. The big six categories include isoflavanoids, flavones, anthocyanidins, flavan-3-ols, flavanols and flavanones.
Flavanones are significant in citrus, while the flavones are in many vegetables and herbs. Anticancer parsley contains flavanols. Tree nuts – found to reduce colon cancer – are also high in flavanols. Legumes also contain flavanols. And several medicinal mushrooms contain anticancer flavanols. In addition, olives and olive oil contain anticancer flavanols.
One of the studies included in the review was from the U.S. National Cancer Institute. The study followed 1,905 people and their diet with an average age of 61. The researchers compared the consumption of 29 different flavonoids together with the incidence of the occurrence of adenomatous polyps – a frequent symptom of colorectal cancer. The research used colonoscopies to determine polyp incidence. This study also showed that switching to a high-fiber diet also significantly reduced polyp incidence and subsequent colorectal cancer.
Furthermore, the study found that colorectal cancer prevention occurred most significantly among those who consumed the higher levels of flavanol foods. In other words, just adding a few veggies to the diet won’t necessarily tip the scale.
Large cancer and nutrition study
In a large study from ten European countries, Italian researchers have found that diets containing higher levels of flavonoids significantly reduce the incidence of gastric cancer.
In this subset of the European Prospective Investigation into Cancer and Nutrition study (EPIC), the researchers from the Catalan Institute of Oncology followed 477,312 people – the majority of whom were women.
The subjects answered extensive diet and lifestyle surveys, and they were followed for ten years. The compositions of their diets were compared to the USDA’s database on food-composition along with the Phenol-Explorer database to determine their flavonoid content.
Those women who had diets with greater amounts of total flavonoid content had nearly 20% lower incidence of gastric cancers than those women with lower flavonoid diets. The inverse association was even greater among intestinal tumors. And specific flavonoid types also had greater association with cancer prevention – anthocyanidins, flavonols, flavones, and flavanols.
REFERENCES:
Owczarek K, Hrabec E, Fichna J, Sosnowska D, Koziołkiewicz M, Szymański J, Lewandowska U. Flavanols from Japanese quince (Chaenomeles japonica) fruit suppress expression of cyclooxygenase-2, metalloproteinase-9, and nuclear factor-kappaB in human colon cancer cells. Acta Biochim Pol. 2017;64(3):567-576. doi: 10.18388/abp.2017_1599.
Jin H, Leng Q, Li C. Dietary flavonoid for preventing colorectal neoplasms. Cochrane Database Syst Rev. 2012 Aug 15;8:CD009350.
Bobe G, Sansbury LB, Albert PS, Cross AJ, Kahle L, Ashby J, Slattery ML, Caan B, Paskett E, Iber F, Kikendall JW, Lance P, Daston C, Marshall JR, Schatzkin A, Lanza E. Dietary flavonoids and colorectal adenoma recurrence in the Polyp Prevention Trial. Cancer Epidemiol Biomarkers Prev. 2008 Jun;17(6):1344-53.
Zamora-Ros R, Agudo A, Luján-Barroso L, Romieu I, Ferrari P, Knaze V, Bueno-de-Mesquita HB, Leenders M, Travis RC, Navarro C, Sánchez-Cantalejo E, Slimani N, Scalbert A, Fedirko V, Hjartåker A, Engeset D, Skeie G, Boeing H, Förster J, Li K, Teucher B, Agnoli C, Tumino R, Mattiello A, Saieva C, Johansson I, Stenling R, Redondo ML, Wallström P, Ericson U, Khaw KT, Mulligan AA, Trichopoulou A, Dilis V, Katsoulis M, Peeters PH, Igali L, Tjønneland A, Halkjær J, Touillaud M, Perquier F, Fagherazzi G, Amiano P, Ardanaz E, Bredsdorff L, Overvad K, Ricceri F, Riboli E, González CA. Dietary flavonoid and lignan intake and gastric adenocarcinoma risk in the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Am J Clin Nutr. 2012 Dec;96(6):1398-408.
Bevan R, Young C, Holmes P, Fortunato L, Slack R, Rushton L; British Occupational Cancer Burden Study Group. Occupational cancer in Britain. Gastrointestinal cancers: liver, oesophagus, pancreas and stomach. Br J Cancer. 2012 Jun 19;107 Suppl 1:S33-40. doi: 10.1038/bjc.2012.116.