The Cancer Research
Is grapefruit a fat-burner? Many people associate grapefruit with dieting to lose weight. But research suggests any weight loss help that grapefruit provides is not necessarily different than what you get from any other food that provides low calories in a satisfying portion. Regardless, grapefruit has plenty to offer beyond any connection to weight management due to the cancer-protective potential of its nutrients and phytocompounds.
If you enjoy grapefruit or grapefruit juice and take any medications, talk with your pharmacist or health care provider. Grapefruit and its juice can cause too much or too little of certain medications to reach cells in the body, either increasing the risk of side effects or reducing the medication’s effectiveness. Your health care provider may be able to switch your prescription to something unaffected by grapefruit, or advise you on the best time to eat it in relation to when you take medication.
Interpreting the data
After a systematic review of the global scientific literature, AICR/WCRF analyzed how fruits and their nutrients affect the risk of developing cancer.
There is probable evidence that non-starchy vegetables and fruit combined DECREASE the risk of:
- Cancers of the aerodigestive tract (mouth, pharynx, nasopharynx, larynx, esophagus, lung, stomach and colorectal cancers)
Limited evidence suggests that fruits may DECREASE the risk of:
- Lung cancer (in people who smoke or used to smoke tobacco) and squamous cell esophageal cancer
Limited evidence suggests that citrus fruits may DECREASE the risk of:
- Stomach cancer (cardia type only)
Limited evidence suggests that non-starchy vegetables and fruit combined may DECREASE the risk of:
- Bladder cancer
Limited evidence suggests that foods containing vitamin C may DECREASE the risk of:
- Lung cancer (in people who smoke) and colon cancer
Limited evidence suggests that foods containing beta-carotene may DECREASE the risk of:
- Lung cancer
Limited evidence suggests that foods containing carotenoids may DECREASE the risk of:
- Lung and estrogen receptor-negative (ER-) breast cancers.
- Evidence categorized as “probable” 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 probable judgement is strong enough to justify recommendations.
- Evidence categorized as “limited suggestive” means results are generally consistent in overall conclusions, but it’s rarely strong enough to justify recommendations to reduce risk of cancer.
Ongoing Areas of Investigation
- Laboratory Research
Grapefruit contains a variety of nutrients and phytocompounds that show potential to protect against cancer in laboratory studies.
Vitamin C is a powerful antioxidant. In lab studies, it protects cells’ DNA by trapping free radicals, and it helps renew the antioxidant ability of Vitamin E. In cell studies, vitamin C also inhibits formation of carcinogens and supports the immune system.
Flavanones (such as grapefruit’s naringenin) influence gene expression and cell signaling in ways that increase antioxidant, anti-inflammatory and carcinogen-deactivating enzymes in cell and animal studies. They inhibit cancer cells’ growth and ability to spread, and activate signaling that leads to self-destruction of abnormal cells. In these laboratory studies, flavanones dial down expression of oncogenes (genes that have potential to cause increased cell growth that can lead to cancer) and increase expression of tumor suppressor genes.
Coumarins (especially a type called furanocoumarins) are a type of polyphenol present in grapefruit pulp, juice and peel. In cell and animal studies, they show antioxidant and anti-inflammatory effects. They also decrease the growth and reproduction of several types of cancer cells, such as breast and skin cancer and leukemia.
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 promotes 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.
- Lycopene and compounds that form as it is metabolized serve as antioxidants in cell studies. Lycopene also helps renew the ability of vitamins E and C to serve as antioxidants, and it activates the body’s antioxidant defenses. In cell studies, lycopene decreases cell growth and reproduction, increases self-destruction of abnormal cells and influences androgen hormones that can drive development of prostate cancer.
Terpenes function as antioxidants in cell studies. They also decrease growth and reproduction of isolated cancer cells.15 These terpenes, mainly limonene, lie in grapefruit’s essential oils, which are found in tiny sacs in the flavedo (the outer colored portion of the peel). It’s possible that cold-pressed juice from juice extractors would provide some amount of these terpene compounds, but it’s not clear how the amount would compare to amounts effective in laboratory studies, and eating the fruit (without the peel) would not provide these compounds.
- Human Studies
Human studies related to grapefruit and cancer risk compare groups of people who consume relatively high and low amounts of total fruit, citrus fruit or grapefruit specifically.
People who eat more fruits have lower risk of a wide range of cancers. This probably reflects combined protection from many different nutrients and compounds they contain.
Citrus fruit: Limited evidence ties citrus fruit specifically to lower risk of stomach cancer, according to the AICR/WCRF Third Expert Report. Analysis for the report also links citrus fruit consumption and lower risk of lung cancer, but relatively large variation in results of different studies (heterogeneity) means that further research is needed.
Vitamin C: Population studies comparing people with higher and lower levels of vitamin C in their diets, and especially levels circulating in their blood, link higher amounts with lower overall risk of cancer. This effect is greater when comparing people with very low levels to moderately increased levels than comparing people with moderate to much higher levels. Higher levels of vitamin C from foods are linked with lower risk of lung cancer among people who smoke tobacco, although not in those who used to smoke or who have never smoked. People with more vitamin C in their diet are also associated with less likely to develop colon cancer. That’s even after adjusting for other risk factors for colon cancer, such as alcohol, red meat and tobacco. Evidence for both lung and colon cancer is rated as Limited Suggestive in the AICR/WCRF Third Expert Report, and more research is needed.
Carotenoids: In population studies, higher blood levels of total carotenoids and of beta-carotene are linked with lower risk of overall cancer. Blood levels may more accurately reflect 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 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.7 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 is unlikely to have any substantial effect, according to the AICR/WCRF Third Expert Report.
- Questions We Hear
Grapefruit and breast cancer: An early study raised concerns of a possible link to breast cancer, but later studies did not support that conclusion. One observational population study linked frequent grapefruit consumption with greater risk of postmenopausal breast cancer. Since grapefruit consumption can affect enzymes that metabolize certain medications, it’s possible that levels of estrogens, which are metabolized by the same enzymes, could be affected. However, evidence overall does not support this conclusion or a relationship to breast cancer risk.
Two other large population studies did not find any increase in estrogen levels or breast cancer risk linked to grapefruit. Even when looking specifically at particular groups of women or types of breast cancer, there was still no link in these studies. And a decade later, no additional studies have shown evidence of increased or decreased risk of breast cancer related to grapefruit.
- AICR-Supported Studies
- Tips for Storage and Preparation
- For grapefruit at its juiciest, store at room temperature up to a week. Or store it two to three weeks in the refrigerator. Return to room temperature before serving for best flavor.
- Rinse grapefruit before you cut into it, even if you aren’t eating the peel. Otherwise bacteria on the outside can get transferred from the knife to the portions you will eat.
- To eat grapefruit by scooping out sections, cut the grapefruit in half and cut around each section with a sharp knife or serrated grapefruit knife.
- Sprinkle a grapefruit half with a touch of brown sugar and broil just until bubbly.
- You can also peel a grapefruit like an orange. Peel it with your hands or a knife, and pull apart each section by hand. In doing this, you get more fiber because you eat the membrane surrounding each section too.
- These grapefruit sections add a delicious tang to green salads. Add avocado slices, too, for a classic combination.
- Make salsa out of diced grapefruit, chopped bell peppers and cilantro.
- Fujioka, K., et al., The effects of grapefruit on weight and insulin resistance: relationship to the metabolic syndrome. Journal of medicinal food, 2006. 9(1): p. 49-54.
- Silver, H.J., M.S. Dietrich, and K.D. Niswender, Effects of grapefruit, grapefruit juice and water preloads on energy balance, weight loss, body composition, and cardiometabolic risk in free-living obese adults. Nutrition & metabolism, 2011. 8(1): p. 8.
- U.S. Department of Agriculture, A.R.S., Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2. 2010.
- Wolfe, K.L., et al., Cellular antioxidant activity of common fruits. Journal of agricultural and food chemistry, 2008. 56(18): p. 8418-26.
- Vanamala, J., et al., Suppression of colon carcinogenesis by bioactive compounds in grapefruit. Carcinogenesis, 2006. 27(6): p. 1257-65.
- Roy, A. and S. Saraf, Limonoids: overview of significant bioactive triterpenes distributed in plants kingdom. Biological & pharmaceutical bulletin, 2006. 29(2): p. 191-201.
- Chidambara Murthy, K.N., et al., Citrus limonin and its glucoside inhibit colon adenocarcinoma cell proliferation through apoptosis. Journal of agricultural and food chemistry, 2011. 59(6): p. 2314-23.
- Miller, E.G., et al., Inhibition of oral carcinogenesis by citrus flavonoids. Nutrition and cancer, 2008. 60(1): p. 69-74.
- Leonardi, T., et al., Apigenin and naringenin suppress colon carcinogenesis through the aberrant crypt stage in azoxymethane-treated rats. Experimental biology and medicine, 2010. 235(6): p. 710-7.
- Moon, Y.J., X. Wang, and M.E. Morris, Dietary flavonoids: effects on xenobiotic and carcinogen metabolism. Toxicology in vitro : an international journal published in association with BIBRA, 2006. 20(2): p. 187-210.
- World Cancer Research Fund / American Institute for Cancer Research, Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective, 2007: Washington, DC. p. 82-113.
- Monroe, K.R., et al., Prospective study of grapefruit intake and risk of breast cancer in postmenopausal women: the Multiethnic Cohort Study. British journal of cancer, 2007. 97(3): p. 440-5.
- Spencer, E.A., et al., Prospective study of the association between grapefruit intake and risk of breast cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC). Cancer causes & control : CCC, 2009. 20(6): p. 803-9.
- Kim, E.H., et al., A prospective study of grapefruit and grapefruit juice intake and breast cancer risk. British journal of cancer, 2008. 98(1): p. 240-1.