But evidently we could stand to make a lot more of at least a couple of them. Beginning in the 1970s, epidemiologists started to notice that Eskimo and other groups of people who ate a lot of cold-water fish tended to have low levels of heart disease and stroke. Oil from such fish is packed with two unusually long omega-3s, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).
The epidemiological evidence was strong enough that it led to a whole series of clinical studies and randomized control trials with fish oil, says nutritionist Penny M. Kris-Etherton of Pennsylvania State University. By 2002 the results were positive enough for the American Heart Association panel on which Kris-Etherton sat to issue a statement recommending increased fish consumption for the general public and daily consumption or supplements of fish oil for coronary heart disease patients. Since then, Kris-Etherton says, the evidence has just grown stronger for a cardioprotective effect from marine-derived omega-3 fatty acids.
Stronger, yes, though not necessarily less complicated. In a 2006 review of 842 scientific papers on omega-3 fatty acids and cardiovascular disease, a research team based at the TuftsNew England Medical Center in Boston concluded that only EPA and DHA seemed beneficial--ALA, their plant-produced precursor, was not. And while the studies showed clear evidence that fish oil helped to prevent heart attacks and cardiac deaths, especially among patients who had already suffered one heart attack, the effects on stroke were all over the map. For people who have pacemakers, too, there is a mixed bag of evidence, Kris-Etherton says. One study shows a benefit, one shows an adverse effect and one shows no benefit. It is a common issue with nutrition studies, she notes--given the vast diversity of human research subjects, variations in the concentration or mixture of supplements, and often uncontrolled factors such as baseline diets or preexisting illnesses, it's not unusual to see different studies canceling each other out.
Understanding exactly how DHA and EPA work would help, but the molecular pathways underlying the fatty acids' heart-protective activity are still unknown. They seem to lower blood levels of triacylglycerol (often called triglyceride), keep cholesterol from gumming up arterial walls, and help to control unwanted blood clotting and inflammation, among other risk factors. Given that fish oil has now been linked to improvements in everything from asthma and rheumatoid arthritis to type 2 diabetes and neurological diseases, there is almost certainly more than one molecular mechanism in play and almost certainly a bright future for omega-3 fatty acids on the supplement shelf.
Science Sours on Favorites
The outlook is not quite so rosy for all the early candidates for nutraceutical stardom, however. In many ways, lycopene was a food manufacturer's dream compound. Grocery profit margins are notoriously slim, and adding nutraceuticals to staple foods has been prohibitive: consumers who will pay 20 for a bottle of fish oil pills balk at shelling out an additional dollar for a loaf of bread supercharged with omega-3 fatty acids. But lycopene, a deep-red plant pigment and powerful antioxidant, not only shows up in plants such as tomatoes for free, its bioavailability is actually increased by the boiling, squeezing and other rigors of food processing.
Early epidemiological studies suggested that men who ate diets rich in tomato products enjoyed lower than average rates of prostate cancer, and lycopene was identified as the likely reason. The ironic result is that while ketchup may not be the school lunch vegetable President Ronald Reagan once claimed it to be, for a while even a foil packet of the stuff had a legitimate shot at being declared a dietary supplement.
Ulrike Peters isn't happy that she had a hand in placing ketchup back in the condiment aisle. A nutrition and genetics epidemiologist at the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle, she had high hopes for lycopene's cancer-fighting ability.