The Cancer Research
Carrots’ cancer-fighting potential comes from being a non-starchy vegetable as well as a source of carotenoids and other phytochemicals. Beta-carotene is the carotenoid that has received the most attention, but research into carrot’s other compounds, and carrots as a whole food, is underway.
Interpreting the data
After a systematic review of the global scientific literature, AICR/WCRF analyzed how vegetables and their nutrients affect the risk of developing cancer.
“Convincing” or “probable” evidence means there is strong research showing a causal relationship to cancer—either decreasing or increasing the risk. The research must include quality human studies that meet specific criteria and biological explanations for the findings.
A convincing or probable judgement is strong enough to justify recommendations.
- There is probable evidence that non-starchy vegetables and fruit combined DECREASE the risk of:
- Aerodigestive cancers overall (such as mouth, pharynx and larynx; esophageal; lung; stomach and colorectal cancers)
“Limited suggestive” evidence means results are generally consistent in overall conclusions, but it’s rarely strong enough to justify recommendations to reduce risk of cancer.
- Limited evidence suggests that foods containing carotenoids may DECREASE the risk of:
- Lung and estrogen receptor-negative (ER-) breast cancers
- Limited evidence suggests that foods containing beta-carotene may DECREASE the risk of:
- Lung cancer
- Limited evidence suggests that non-starchy vegetables may DECREASE the risk of:
- Estrogen receptor-negative (ER-) breast cancer
- Limited evidence suggests that non-starchy vegetables and fruits combined may DECREASE the risk of:
- Bladder cancer
Ongoing Areas of Investigation
Carotenoids act as antioxidants themselves and stimulate the body’s own antioxidant defenses, decreasing free radical damage to DNA that can lead to cancer. Very high levels in cell studies, however, can have an opposite effect, promoting damage from oxidation.
- Beta-carotene and alpha-carotene promote cell-to-cell communication that helps control cell growth. These carotenoids also increase carcinogen-metabolizing enzymes and stimulate self-destruction of abnormal cells. The body uses beta-carotene and alpha-carotene to form vitamin A, which helps protect against cancer through the immune system and expression of genes that regulate cell growth.
- Phenolic acids increase cells’ antioxidant and anti-inflammatory defenses against damage that could lead to cancer in cell and animal studies. Emerging evidence in animal studies suggests they may also improve glucose metabolism and decrease insulin resistance, and alter the gut microbiota (microbes living in the colon), creating an environment in the body less likely to support cancer.
- Polyacetylenes (such as fulcarinol in carrots) decrease cancer cell growth and increase cancer cell death in cell and animal studies.
People who eat more vegetables and fruits have a lower risk of a wide range of cancers. This probably reflects combined protection from many different nutrients and compounds they contain.
In population studies, higher blood levels of total carotenoids and of beta-carotene are linked with a lower risk of overall cancer. Blood levels may more accurately reflect the consumption of carotenoid-rich foods than diet questionnaires, and they include differences in how much is absorbed from food. However, it may be that the lower cancer risk is seen because blood levels of these compounds are recognized as signals of greater overall vegetable and fruit consumption.
- Lung cancer: Population studies link higher dietary and blood levels of beta-carotene or total carotenoids with a lower risk of lung cancer. Larger studies now show protection less clearly than earlier studies, and the AICR/WCRF Third Expert Report categorizes this link as Limited Suggestive. Additional research is needed.
- Breast cancer: Some population studies also link higher blood levels of carotenoids (including beta-carotene and alpha-carotene) in the diet or blood to lower risk of breast cancer, mainly for estrogen receptor-negative (ER-) forms. The AICR/WCRF Third Expert Report categorized this link as Limited Suggestive. It is possible that an effect of carotenoids on ER-positive (ER+) tumors is simply masked by the hormonal influences that dominate risk of ER+ breast cancer. Additional research is needed.
These research findings do not support the idea of “the more, the better”. Beta-carotene in high-dose supplements increases lung cancer risk when taken by people who smoke or used to smoke tobacco, according to evidence rated convincing in the AICR/WCRF Third Expert Report. The big picture of overall research on prostate cancer shows higher dietary, supplement and blood levels of beta-carotene unlikely to have any substantial effect, according to the AICR/WCRF Third Expert Report.
Tips for Selection and Preparation
- Choose smooth, firm carrots. Some carrots may have cracks as a result of growing or storage conditions. Make sure to wash all your carrots thoroughly and cut out the damaged areas.
- Green tops, if attached, should be feathery and not wilted.
- Deeper orange color indicates higher beta-carotene content. Carrots of other colors have higher levels of other compounds. For example, purple and black carrots contain polyphenols called anthocyanins, red carrots contain lycopene and yellow carrots contain lutein (another carotenoid).
- Cooking brings out their natural sweetness and heat does not destroy their alpha- and beta-carotene.
- For better absorption of these carotenoids, chop, grate, purée or heat the carrots and eat with a small amount of fat, whether added to carrots or from other foods.
- Stir grated or matchstick-cut carrots into muffin batter, spaghetti sauce and soups.
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