ORLANDO, Nov. 11 -- Eating fish -- lots of fish -- is better than a vegetarian diet in reducing the level of one heart-imperiling fat in the blood, an international research group reported today at the American Heart Association's 70th Scientific Sessions.
"Our data provide the first evidence that a stable fish diet lowers lipoprotein (a), or Lp (a), levels, a blood fat that increases the risk of heart attack," says Santica M. Marcovina, Ph.D., Sc.D., a research professor of medicine at the University of Washington at Seattle.
Lp (a) consists of a particle called low-density-lipoprotein (LDL), the "bad" cholesterol, attached to a protein called apo (a). Lp (a) increases fat buildup in the artery walls as well as the risk of blood clots, which can block arteries and cause a heart attack or stroke.
An association between high Lp (a) levels and heart disease and stroke was first reported more than 25 years ago. But only recently have researchers begun to understand the important interaction of genes and environment in determining a person's Lp (a) blood level.
To investigate dietary influences on coronary heart disease risk factors, the Seattle team is collaborating with researchers from Italy in the Lugawala study of East African Bantu people. The study was conducted on two Bantu populations from Tanzania who belong to the same ethnic group and have very similar lifestyle and caloric intake.
The major difference between these two homogeneous groups is that one is formed by people who live in a village near a lake and consume a fish-rich diet while the other population is composed of farmers who are mainly vegetarians. An earlier study from the Italian group, published in The Lancet, found that Bantus living on a fish diet had significantly lower Lp (a) than the vegetarian Bantus.
There is a close relationship between the size of apo (a), which is genetically determined, and the level of Lp (a) in plasma. Therefore to rule out that differences in apo (a) size distribution between the inhabitants of the two villages could explain the difference in Lp (a) values, Marcovina focused the evaluation on Bantus of both groups whose apo (a) were of equal size. The researchers found 410 pairs of people who were apo (a) size-matched.
"Within each size group, Lp (a) was consistently lower in those eating the fish diet as compared to the vegetarians," she says. A striking 40 percent median Lp (a) difference was found between groups (15 mg/dl versus 25.0 mg/dl). These results endorse the view that the fish diet is the environmental factor responsible for the lower levels of this atherogenic lipoprotein observed in this study.
The lake-dwelling Bantu people are among the highest fish consumers in the world and eat fish three to four times per day. Freshwater fish account for 23 percent of the lake dweller's diet, which is 70 percent carbohydrates and 7 percent fat. The typical Bantu vegetarian diet contains 82 percent of calories from carbohydrates, usually from maize and rice, with 12 percent from fat and 18 percent from protein.
The report was from the Lugawala study, led by an Italian research group and partially funded by the World Health Organization. It evaluates the impact of eating fish rich in n-3 polyunsaturated fatty acids (PUFA). The results of this study are very important because they indicate that Lp (a) values, which are largely genetically determined, can be significantly modulated by dietary factors. However, Marcovina says, "it should be noted that it is highly unrealistic to recommend in Italy a diet like the one followed by the Bantus.
"Additionally, the content of PUFA varies in different fish types and the effect that we have observed in blacks needs to be evaluated in other ethnic groups," she adds. While fish oil can also be taken as a dietary supplement, no recommendations can be made to the general public at this point in time.
"We need to wait for the results of large, long-term intervention studies to tell us whether and at what dosages diet supplemented with fish oil is effective in lowering Lp (a) and other cardiovascular risk factors," she explains. The American Heart Association does not recommend fish oil, but does recommend a well-rounded diet that includes fish.
Marcovina is the Core Laboratory Director of the Northwest Lipid Research Laboratories, which conducted the study in association with researchers at the University of Milan and the University of Padova in Italy. Her part of the study was supported by a grant from the National, Heart, Lung, and Blood Institute.
Her co-authors include Hal Kennedy, M.S., the University of Washington, Seattle; Gabriele Bittolo-bon, M.D., and Ospedale Civile, M.D., of Venezia, Venezia, Italy; Claudio Galli, M.D., University of Milan; Edoardo Casiglia, M.D., Massimo Puato, M.D., and Paulo Pauleto, M.D., University of Padova.
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