Omega-3 fatty acids may not prevent cancer
* 21:00 24 January 2006
* NewScientist.com news service
* Alison Motluk
Omega-3 fatty acids probably do not help prevent any type of cancer, according to a review that evaluated every cited study looking into the question.
“Taking dietary supplements or regularly consuming fish doesn’t appear to reduce the risk of developing cancer,” says Catherine MacLean, of RAND Health in Santa Monica, California, US, who led the study.
Omega-3 fatty acids are a type of polyunsaturated fat, one of four types of fat the body derives from food. Omega-3 comes in three forms – EPA, DHA and ALA – and they appear to do different things. EPA and DHA come from foods like salmon, fresh tuna and a few plants - or from supplements – and have been most associated with health benefits. ALA, on the other hand, which you can get from flax, walnuts, and enriched soy milks, has to be converted into one of the other two within the body to be beneficial.
Previous work suggests EPA can affect the production of cytokines and tumour necrosis factor, both important in cancer. And animal evidence has suggested that omega-3s suppress the incidence, growth rate and proliferation of breast, prostate, colon and pancreatic tumours.
MacLean and her colleagues scoured the literature for studies on omega-3 consumption and cancer incidence. After reviewing 5145 papers, they found 38 that were prospective studies observing how omega-3 consumption affected the risk of cancer over time.
Several studies looked at omega-3 consumption and breast cancer and, while some found favourable associations, others found the opposite.
Similarly, nine studies looked into omega-3s and colorectal cancer, seven investigated prostate cancer, three examined lung cancer and two each looked at lymphoma, ovarian cancer and pancreatic cancer. Again, there were trends found in both directions. A study on skin cancer actually found a small but statistically significant increased risk, though MacLean suspects that it is experimental “noise”.
Colleen Doyle, at the American Cancer Society, is not surprised by the results. “But it’s not changing anything we say about fish,” she says. She points out that red meat and processed meats are known to increase risk of both colon and prostate cancers, so displacing these foods with fish would be advantageous. “As long as it’s not breaded and deep-fried, we still say ‘eat fish’,” she says.
But Bruce Holub, at the University of Guelph, in Canada, cautions against putting “all the omegas and all the cancers into the same pot”. One large study on prostate cancer, for instance, found that while ALA may increase risk, EPA and DHA reduces it. “It’s dangerous to conclude there’s no relationship,” he says.
Journal reference: Journal of the American Medical Association (vol 295, p 403)
Wow, stop the presses! Doctors don't really know that much about diet! Eggs are bad. Eggs are not bad. Salt is deadly. Well, not that deadly. Avoid fat, eat some fat. etc. Call me when they get it figured out. Until then use a mirror.