The Cancer Research
Grapefruit are rich sources of vitamin C and the pink and red varieties contain carotenoids (including lycopene and beta-carotene) and dietary fiber. Dietary fiber can act in several ways to lower cancer risk, including helping with weight control. (Excess body fat increases the risk of eleven different cancers, and dietary fiber can increase the feeling of fullness.)
What Current Evidence Shows: AICR/WCRF Expert Report and its Updates (CUP)
|Grapefruit are fruits that contain dietary fiber. After a systematic review of the global scientific literature, AICR/WCRF weighed the strength of the evidence linking these factors to lower risk for several cancers.|
|Source: Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective and the Continuous Update Project (CUP) reports.|
|Diets high in:||CONVINCINGLY lower risk of the following cancers:|
|Foods containing dietary fiber||Colorectum|
|Diets high in:||PROBABLY lower risk of the following cancers:|
|Fruits||Mouth, Pharynx, Larynx
”Grapefruit's vitamin C and unique phytochemicals offer potential for acting through several paths to reduce cancer risk.”
- Karen Collins, MS, RDN, CDN
Open Areas of Investigation: Laboratory Research
In animal and cell studies, grapefruit powder, limonin and naringenin decrease growth and increase self-destruction of colon, mouth, skin, lung, breast and stomach cancers. Lab studies suggest these compounds act in a variety of ways: They decrease inflammation and increase enzymes that deactivate carcinogens. In lab studies, naringenin inhibits enzymes that activate carcinogens and the aromatase enzyme that stimulates estrogen production.
Vitamin C protects DNA from damage by trapping free radicals and inhibiting formation of carcinogens. It also helps other compounds maintain their antioxidant power. Carotenoids are also antioxidants. They reduce inflammation, improve immune function and decrease cancer cell growth.
Open Areas of Investigation: Human Studies
Evidence shows that diets high in fruits decrease risk of certain cancers (see chart) but most human studies look at overall fruit consumption. Some studies also investigated overall citrus intake, which includes oranges and lemons. Studies show a lower risk of several cancers in people who eat more fruit or citrus fruit, compared with people who eat the least. Research is ongoing as to grapefruit and citrus fruits specifically.
After some lab studies suggested phytochemicals in grapefruit affect estrogen metabolism, researchers investigated a grapefruit-breast cancer connection. One 2007 study linked frequent grapefruit consumption with greater risk of postmenopausal breast cancer. However, two other large population studies did not find any increase in estrogen levels or breast cancer risk linked to grapefruit. (See Frequently Asked Questions for more.)