Large, careful human clinical trials are expensive and few have been designed to test dietary interventions. Small trials on individual supplements have been done, though. And scientists have learned a lot from studying populations -- chronicling the natural habits of people and seeing what diseases they get and which they don't.
The drug factor
Statin drugs, for example, are known to cut heart disease risk by reducing cholesterol levels -- among other things, these meds fight inflammation.
"We don't know how much of statins' effect are due to their anti-inflammatory effects," Eckel says. But, he adds, a growing number of researchers suspect that this property is important.
Fish oil, rich in anti-inflammatory omega-3 fatty acids and derived from oily fish such as tuna, salmon and mackerel -- is already recommended by the American Heart Assn. to help prevent cardiovascular disease. It has been shown to reduce blood triglyceride levels and slightly lower blood pressure, lowering the risk for heart attacks and strokes.
There is also reason to believe that anti-inflammatory substances would help to ward off cancers. Non-steroidal anti-inflammatory drugs have been shown to prevent tumors with people with inherited colorectal cancer, for example.
And population studies have shown that people who had been taking non-steroidal anti-inflammatory meds for other conditions were less likely to develop Alzheimer's disease.
In trials, such drugs have failed to treat already-developed Alzheimer's, but the studies suggest that it might be possible to prevent the disease by reducing inflammation, says Greg Cole, a professor of medicine and neurology at UCLA and associate director of the UCLA Alzheimer's Disease Research Center.
But it is not safe to take non-steroidal anti-inflammatory drugs for years because of harmful side effects, such as gastrointestinal bleeding. What about anti-inflammatory foods? Several clinical trials, in the U.S. and abroad, have shown that people with mild memory complaints related to aging (not necessarily Alzheimer's disease) showed significant improvement when given the omega-3 fatty acid docosahexaenoic acid, Cole says.
And in an 18-month study released in June sponsored by the National Institutes of Health, treating Alzheimer's disease with docosahexaenoic acid slowed its progression in a subgroup of the study population.
There are other trials with positive results for fish oil in early Alzheimer's cases, but they are not large enough to be definitive, Cole says.
But, he adds, "the real utility is not to slow the progression of someone who's already demented, but it's to treat before dementia happens. We'd like to turn off or keep down [the inflammation] with something that doesn't cause gastrointestinal bleeding or other side effects."
Cole's laboratory is looking at the potential for Alzheimer's prevention by controlling inflammation with omega-3 fatty acids and curcumin. Other food substances -- such as resveratrol in red wine and flavonoids in fruits -- may have anti-inflammatory effects by acting along the same pathway that curcumin does, he says.
Cole suspects that people are more likely to take a supplement or two than to radically change their diets. "Nutritionists, they'll tell you to eat right. It is good, sound advice, but you can't always get people to do it," he says. "The question is, can you find an easier supplement approach that doesn't require a restricted diet?"
Supplements do have their drawbacks. "Many Alzheimer's researchers were prescribing vitamin E [an antioxidant] to all their patients," says Debra Cherry, a clinical psychologist and the executive vice president of the Alzheimer's Assn. of the California Southland. "But some data came out that people had high bleeds and suffered from cardiovascular problems."
Perhaps a complete diet overhaul -- difficult though that may be -- would be a better strategy. The Mediterranean diet, named for the region in which it originated, has many anti-inflammatory features.
It includes fruits, vegetables, nuts, fish, whole grains, alcohol, and healthful fats like olive and canola oil. It has been shown to lower LDL cholesterol and triglyceride levels and reduce the risk of blood clots. Studies have shown that diets high in fish, olive oil and cooked vegetables reduce the symptoms of rheumatoid arthritis. A Mediterranean diet or elements of it seems linked to reduced risk for a number of chronic conditions, including cardiovascular disease, cancer, diabetes and Alzheimer's. (See related story online.)
"If people noticed they're slightly overweight, or if blood pressure is starting to creep up, or if blood sugar [increases], and they went on a Mediterranean-type diet, they might be able to decrease inflammation and stop the progression of disease," says Dr. Wadie Najm, a clinical professor of family medicine and geriatrics at UC Irvine who directs an integrated medicine clinic at UCI that focuses on complementary and alternative medicine.
Many patients visiting his clinic have chronic inflammatory conditions, including autoimmune diseases such as arthritis and gastrointestinal problems such as Crohn's disease. Patients begin a specialized diet and exercise, and make other lifestyle changes to decrease inflammation.
"In three weeks, if [patients] follow the protocol, we see great results in improvement in symptomology and reduction in flare-ups," says Bianca Garilli, a naturopathic doctor at the clinic.
Of course, these dietary and other lifestyle changes might help treat pain conditions through the placebo effect -- a belief in a treatment rather than the treatment itself, says Dr. Roger Chao, an associate professor of medicine at Oregon Health and Science University and director of clinical guidelines development for the American Pain Society.
"You're giving something for people to focus on and do something good for themselves," Chao says.
At the end of the day, there is evidence to suggest that your best bet at curbing inflammation is to eat a healthful diet -- and keep your weight in check -- without specifically thinking about anti-inflammatory foods.
"There is no doubt that if you lose weight, inflammation is dramatically improved," Greenberg says. When a person is overweight or obese, body fat breaks down into fatty acids, which circulate in the blood. These fatty acids promote an immune response in the same way that infection does, increasing inflammation.
It will take time to tease apart the effects of anti-inflammatory diets and supplements. But Cole thinks the effort is well worth it. "The alternative to these kinds of things aimed at prevention is to pay for treatments," he says. "And we can't always afford them."