I've heard that I should avoid drinking grapefruit juice or eating the fruit if I'm on medication. True?
Grapefruit can interfere with the activity of some medicines, both prescription and non-prescription. Phytochemicals in grapefruit decrease the enzymes that break down several prescription drugs, raising drug levels in the body and increasing the chances of side effects from it. This can be dangerous, so check with your healthcare provider about eating grapefruit or drinking grapefruit juice if you take any prescription medicines.
The Food and Drug Administration has more information on medicines that may not mix with grapefruit.
Is it true that women should avoid grapefruit because of a possible link to breast cancer?
A 2009 population study (Spencer et al., Cancer Causes Control) did not find any link between grapefruit consumption and breast cancer risk or estrogen levels. The study included about 114,000 women. A 2007 population study (Monroe et al. Br J Cancer) with about 50,000 women, had found an association with breast cancer risk but the researchers emphasized that more studies were needed to confirm their finding.
Grapefruit is a good source of vitamin C and several antioxidant phytochemicals. One of them, naringenin, has been shown to inhibit growth of breast cancer and other cancer cells in laboratory studies. So for now, unless a woman's doctor tells her otherwise or if she is taking medications that necessitate avoidance of grapefruit, she can reasonably include grapefruit as one fruit among the recommended wide variety of healthy fruits.
Does drinking grapefruit juice help promote weight loss?
Claims that grapefruit or grapefruit juice can somehow burn body fat are not true. Even the one study widely circulated on the Internet, in which people consuming grapefruit or grapefruit juice before each meal lost more weight than people who ate no grapefruit, does not prove that the grapefruit was responsible.
Grapefruit juice, like grapefruit, is an excellent source of vitamin C and antioxidants, so if drinking a small glass of it before a meal helps you get used to smaller portions of food at your meals, that's great. But keep in mind that it's not a fat-burner and not to be consumed in endless amounts. The 96 calories per cup will add up if you overdo. And, of course, make sure you are working on ways you can continue long-term to keep calorie consumption in balance with what you burn up in activity.