Shedding fat and staying fit: omega-3 myth
Aren't there some relatively "good" - or at least harmless - fats? Judging from recent reports, you'd think that the omega-3 fatty acids, a type of polyunsaturated fat found in cold-water seafood and in canola and soybean oils, are beneficial to your health. In fact, these fats have been so highly touted of late that some of us may be tempted to go a little too far with them. But remember that all fats are a highly concentrated source of calories and your body does best with very sparing amounts - amounts optimally provided by foods as they naturally exist. Fish oil (and olive oil) is no exception: Overdosing does you no good and in fact may do you harm.
Research with such populations as the Greenland Eskimos suggests that the oils present in cold-water fish tend to lower serum triglycerides (blood fats) and discourage blood clotting. On the other hand, fish oil does not effectively lower your LDL, or "bad," cholesterol; in fact, several studies have actually shown that fish-oil supplements will increase LDL cholesterol.
If you like seafood or wish to enjoy the likely benefits of a reasonable amount of omega-3 fatty acids, substitute cold-water fish for red meat and poultry more often - but don't exceed our recommendation of 3 1/2 ounces of fish, lean poultry, or lean red meat a day based on the scientifically unfounded belief that "more is better."
Fish containing the highest amounts of omega-3 include mackerel, trout, salmon, some species of tuna, halibut, and herring (in general, the colder the water, the less saturated and more polyunsaturated the fish oil will be). But eating too much of these - more than Ç5 ounces a day - puts excessive animal protein in your diet and exposes you to its many consequences, including an increased demand on the kidneys, elevated uric-acid levels, mineral loss, and possible heightened risk of thinning bones. (There is also an increasing concern about commercially caught near-shore fish, many of which have been found to be contaminated with a variety of potentially toxic or carcinogenic pollutants. While the risk of eating these particular fish remains to be determined, it would obviously be related to the amount of them that you ate.)
It's important to understand that neither cold-water fish nor their omega-3 oils have any LDL-cholesterol-lowering abilities per se; in fact, their cholesterol contents are similar to those in meat. But since the ratio of fatty acids in fish is more favorable than in other sources of animal protein, making a change in your diet could help. If you normally eat meat, which contains saturated fats, substituting an equal amount of fish for the meat might cause the cholesterol output of your liver to fall slightly, and thus could lower your blood cholesterol from what it would be if you ate the meat instead of the fish. On the other hand, it's important to realize that because fish does contain both saturated fatty acids and cholesterol, the more fish you eat, the higher your serum cholesterol level will go. (In terms of cholesterol, though, as you'll learn, substituting beans for fish will lower your serum cholesterol level much more than will substituting fish for chicken or beef.)
What about fish-oil supplements? We've heard a lot about them lately, too. Not surprisingly, food sources of fish oils are best. Highly touted fish-oil supplements are calorically dense and in large amounts may also partially inhibit normal blood clotting. In addition, they may be subject to internal "rancidity reactions" that can generate within the body an excess of free radicals, the destructive molecular particles that can damage healthy cell membranes. And when given to non-insulin-dependent diabetics, fish-oil supplements have been found to raise blood sugar and increase the need for insulin.
The only safe assumption we can make right now is that if you want to prevent heart disease, fish can be your first animal-protein choice - not only because of the likely omega-3 benefits, but because it has fewer saturated fatty acids than even chicken or the leanest beef. But if you have a very high cholesterol level, remember that the more fish you eat, the more you'll raise your LDL cholesterol level - whereas making beans your primary choice in the high-protein group will lower your serum cholesterol level even further than if you choose fish instead of lean poultry or lean meat.