A review of research that included nearly 400,000 people from China's National Center of Colorectal Surgery has determined that a dietary regimen that includes certain phytonutrients, specifically flavonoids and flavanols, have the ability to significantly reduce the incidence 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.
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.
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 isoflavonoids, flavones, anthocyanidins, flavan-3-ols, flavonols (note the "o" instead of a second "a"), and flavanones.
The flavanones are significant in citrus, while the flavones are in many vegetables and herbs.
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 flavonol foods. In other words, just adding a few veggies to the diet won't necessarily tip the scale.
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